Angiosperms anatomy calicut University

1. INTRODUCTION TO
THE ORIGIN OF VASCULAR PLANTS

2. Timeline of plant evolution
• There are four key stages in the timeline of plant evolution.
These are:
• The evolution of ancestral streptophyte algae and the first
land-dwelling plants.
• The development of vascular systems.
• The emergence of seeds and pollen.
• The rise of flowering plants.

3. • Pre-Cambrian Era (4000-541 Million Years Ago) - Plants first
appeared on land approximately 700 million years ago.
• Cambrian Period (541-485 Million Years Ago) -
Due to Extremely high levels of carbon dioxide in the atmosphere,
Earth's temperature would have been approximately 120
degrees during the Cambrian Period.
Most plant life consisted of small, soft, marine plants, such as green
algae. As terrestrial plants evolved, they cooled the climate and
provided oxygen to pave the way for life to flourish on land

4. • Ordovician Period (485-443 Million Years Ago) - Because the
earliest land plants were non-vascular, they did not have any
way to conduct water. Therefore, terrestrial plants of this period
lived primarily in wet environments.
• Silurian Period (443-419 Million Years Ago) - The first vascular
plants evolved during this period.
• Devonian Period (419-358 Million Years Ago) - The first
recognizable soils developed during this time. Plants
developed sexual organs for reproduction, stems with vascular
tissue, woody tissue for structure, and stomates for respiration.
Ecosystems, dominated by plants, included forests of large trees,
and many plants reproduced by bearing seeds.

5. • Carboniferous Period (358-298 Million Years Ago) - Plants
continued to develop differentiated structures. Seed plants
developed and colonized habitats where spore-producing plants
could not flourish. These were gymnosperms.
• Permian Period (299-251 Million Years Ago) - The climate dried,
leading to the evolution of advanced conifers. Cycads and
ginkgos appeared. Widespread forestation appeared in some
regions.

6. • Triassic Period (251-201 Million Years Ago) - Seed-bearing plants
dominated over all others. Gymnosperms, such as cycads, ginkgos,
and conifers, were the most prevalent plants of this period.
• Jurassic Period (201.3-145 Million Years Ago) - The climate became
wetter, leading to development of large jungles where conifers
dominated the landscape. Flowering plants appeared during this
period, but they played only a minor role among other plants.
• Cretaceous Period (145-66 Million Years Ago) - Angiosperms, plants
in which male or female reproductive organs are housed in a flower,
proliferated and became the dominant plants. Modern-day trees
appeared. Conifers continued to be important trees in colder
regions. Ancestors of modern-day ferns evolved during the late
Cretaceous period.

7. • Tertiary Period (66-1.8 Million Years Ago) - Grasses evolved during
this period leading to the development of vast savanna
ecosystems. The proliferation of grasses provided food for large,
grazing mammals and protection for small animals such as
rodents. Conifers dominated in colder climates, while
angiosperms dominated in tropical climates.
• Quaternary Period (1.8 Million Years Ago - Present Day) - As the
climate cooled, large forests died off, leaving open grasslands. This
happened around 30 million years ago, and grasses flourished due to
their ability to adapt to dry, arid conditions. Humans first appeared
during the Quaternary period of the Cenozoic era.

11. VASCULAR TISSUES IN
ANGIOSPERMS

12. XYLEM

13. • Xylem tissue consists of
a variety of specialized,
water-conducting cells
known as tracheary
elements.
• Plays an essential
'supporting' role
providing strength to
tissues and organs, to
maintain plant
architecture and
resistance to bending
Derived from the
Ancient Greek word
xylon meaning
wood

15. Origin
From meristematic cells called
procambium and cambium.
These meristems contain
pluripotent stem cells - maintain
stem cell population -'stem cell
niche'

19. Dynamic nature of vascular
cambium When the organizer cells
differentiate into a xylem vessel, a
new organizer is formed in adjacent
cambial stem cell. Stem cells and
their xylem-side daughters
dynamically gain organizer-cell gene
expression as they mature towards
xylem identity.

20. Ray in xylem
Phloem parenchyma
Xylem parenchyma
vessels
Immature vessel
Immediate derivative of cambium
Cambium
Young sieve element
Sieve tube

21. Immature sieve cells
Cambium
Immature trachieds or vessels
Mature vessels
Xylem ray
Phloem ray

23. Primary xylem - divided
into two types according
to their period of
formation and internal
structure - protoxylem
and metaxylem.
Secondary xylem -
formed during the
secondary growth from
the vascular cambium of
the lateral meristem

25. Endarch Centrifugal) , Exarch (Centripetal), Mesarch

26. Vessel elements
▪ Shorter-building blocks of vessels.
▪ Connected together into long tubes
called vessels
▪ Originate from vascular cambium.
▪ The cell wall becomes strongly
lignified.
▪ Side walls of a vessel element
have pits.
▪

28. ▪ Only in vessel elements - openings at both ends - connect individual
vessel elements to form a continuous tubular vessel.
▪ Simple perforation (a simple opening)
▪ Scalariform perforation (several elongated openings in a ladder-like
design).
▪ Reticulate perforation plate (a net-like pattern, with many openings).
▪ Foraminate perforation plate (several round openings
Perforation plates

30. Vessel elements- Thickening patterns

32. Annular
thickenings
Spiral thickenings
ANNULAR VESSELS SPIRAL VESSELS

33. SCALARIFORM VESSELS RETICULATE VESSELS PITTED VESSELS
Scalariform
thickenings
Reticulate
thickenings
Pitted
thickenings
1-porate end walls
Multi-porate endwall

35. Cavitation occurs in xylem of
vascular plants when the tension
of water within the xylem
becomes so high that dissolved air
within water expands to fill either
the vessels or the tracheids.
The blocking of a xylem vessel or
tracheid by an air bubble or cavity
is called as embolism

36. Vessel elements- Evolutionary significance
The presence of vessels in xylem - one of the key innovations that led
to the success of the flowering plants.
It was once thought that vessel elements were an evolutionary
innovation of flowering plants, but their absence from some
basal angiosperms and their presence in some members of the
Gnetales suggest that this hypothesis must be re-examined
Vessel elements in Gnetales may not be homologous with those of
angiosperms.
Vessel elements that originated in a precursor to the angiosperms may
have been subsequently lost in some basal lineages (e.g.
Amborellaceae), described by Arthur Cronquist as "primitively
vesselless".

37. Cronquist considered the vessels of Gnetum to be convergent
(distantly related organisms independently evolve similar traits to adapt
to similar necessities) with those of angiosperms.
Vessel-like cells have also been found in the xylem
of Equisetum (horsetails), Selaginella (spike-mosses), Pteridium
aquilinum (bracken fern), Marsilea and Regnelidium (aquatic
ferns), and the enigmatic fossil group Gigantopteridales.
It is generally agreed that the vessels evolved independently.
It is possible that vessels may have appeared more than once
among the angiosperms as well.

38. • The longer the wood vessels, the
more primitive they are.
• Pit areas with round pits are looked
upon as primitive.
• Oblique perforation plate is
primitive, Horizontal is advanced.
• Scalariform perforations are more
advanced
• Complete opening is the final stage
in the development from tracheids
to wood vessels.

39. Tracheid
First named after the German botanist Carl Gustav Sanio in 1863,
from the German Tracheide.
The main functions - transport water and inorganic salts, and to
provide structural support for trees.
Less specialized than the vessel members.
Dead tubular spindle shaped cells with tapering ends
Do not have a protoplast.
There are often pits on the cell walls of tracheids, which allows for
water flow between cells.

40. Capillary storage—water is stored mainly in the lumen of dead fibers
and tracheids.
Can hold water against the force of gravity due to high surface area
to volume ratio.
Cell walls are composed of a thin primary wall layer and a thick
secondary wall.
The individual tracheids adhere to one another by a thin middle
lamella and this together with the two adjacent primary walls are
often referred to as the compound middle lamella.
Tracheids, being unicellular, were restricted to less than 6 mm in
length.
Tracheids are tiny conductive elements linked to one another by
bordered pits and openings in the secondary cell wall.

41. The tracheid functions not only in transport, but also in mechanical
support.
Although the unicellular tracheid type of conduit is ancestral, the
intertracheid pitting in conifers is derived because it has a torus-
margo pit membrane.

42. Trachieds- Evolutionary significance
Tracheids were the main conductive cells found in early vascular plants.
Only type of water-conducting cells in most gymnosperms and seedless vascular
plants
Tracheids are also the main conductive cells in the primary xylem of ferns.
In the first 140-150 million years of vascular plant evolution, tracheids were the only
type of conductive cells found in fossils of plant xylem tissues.
Ancestral tracheids did not contribute significantly to structural support, as can be
seen in extant ferns.

43. The fossil record shows three different types of tracheid cells found in early
plants, which were classified as S-type, G-type and P-type.
S & G - lignified and had pores to facilitate the transportation of water between
cells.
P-type tracheid cells had pits similar to extant plant tracheids.
Later, more complex pits appeared, such as bordered pits on many tracheids,
which allowed plants to transport water between cells while reducing the risk of
cavitation and embolisms in the xylem.
Tracheid length and diameter also increased, with tracheid diameter increasing
to an average length of 80 μm by the end of the Devonian period.
Tracheids then evolved into the vessel elements and structural fibers that make
up angiosperm wood. Angiosperm wood exploits the efficiency of specialization

44. Trachieds Vessels
In all vascular plants In angiosperms
Imperforated Perforated
Thin cell wall Thick cell wall
Lateral connection End to end connection
Polygonal , length 1 mm,
tapering end walls
Circular, length 10 mm,
transverse or diagonal end
walls
Inefficient conduction Very efficient conduction
Narrow lumen
Less large pits
Wide lumen
Large small pits

45. Comprised of parenchyma cells.
It is the only living tissue amongst the elements of the xylem.
Xylem parenchyma is composed of thin cellulosic cell walls, large
vacuoles, prominent nucleus, and protoplasts.
Cells in the parenchyma of the xylem are primarily responsible for
the storage of carbohydrates, lipids, tannins etc. and water
conduction.
Circular transportation of water through the ray parenchymatous
cell.
Outgrowth called tyloses helps to combat vascular tissue damage
during infection or drought.
Xylem parenchyma

46. Non-living sclerenchyma cells.
Because of their elasticity and tensile strength, they are an important
component of the xylem.
They protect and provide mechanical support to the xylem's major
water-carrying tissues.
Water is transported through xylem fibers.
Xylary fibers - Libriform fibers and fiber tracheids.
Another type of xylary fiber, present in tension wood, is the gelatinous
or mucilaginous fibers.
Xylary fibers constitute an integral part of the xylem and develop from
the same meristematic tissues as do the other xylem components.
Xylem fibres

47. LIBRIFORM FIBRES
COMPARISON OF
DIFFERENT
XYLEM ELEMENTS

48. PHLOEM

49. Components of Phloem
Phloem is the living tissue in vascular plants that transports the
photosynthates, in particular the sugar sucrose.
This transport process is called translocation.
In trees, the phloem is the innermost layer of the bark, hence the
name, derived from the Ancient Greek word ‘phloiós’, meaning ‘bark’.
The term was introduced by Carl Nägeli in 1858

50. Components of Phloem

51. Sieve elements
First discovered by the forest
botanist Theodor Hartig in 1837.
Major conducting cells in phloem.
Containing sieve areas on their walls.
Pores on sieve areas allow the movement of
photosynthetic material and other organic
molecules.
Structurally, they are elongated and parallel
to the organ or tissue that they are located in.
Sieve elements
Sieve tube
member
Sieve cell
shorter and wider
with greater area
for nutrient
transport
longer and
narrower with
smaller area for
nutrient
transport
found in
Angiosperms
found in
Gymnosperms
associated with
companion cells
flanked with
albuminous
cells

52. Sieve tube member
The main functions -transport necessary molecules with the help of
companion cells
Living cells (which do not contain a nucleus).
Associated with companion cells- sieve element-companion cell complex.
This allows for supply and signaling between distant organs within the
plant body.
Do not have ribosomes or a nucleus and thus need companion cells to
help them.
Sieve tube members and companion cells are connected
through plasmodesmata.

53. Sieve tube member
Very long and have horizontal end walls
containing sieve plates.
Structurally, the walls of sieve tubes tend to be
dispersed with plasmodesmata grouped
together and it is these areas of the tube walls
and plasmodesmata that develop into sieve
plates over time.
Sieve plates contain sieve pores which can
regulate the size of the openings in the plates
with changes in the surroundings of the
plants.

54. Sieve tube wall
Sieve Plate
Sieve pore
Sieve area
SIEVE TUBE
Sieve tube member
Nucleus
Companion cell
Sieve Plate
Sieve tubes and Companion cells

55. Middle lamella
Plasmodesmata
Callose deposit
Plasmodesmata (Pd)
Co-axial membranous channels
that cross walls of adjacent
plant cells, linking the
cytoplasm, plasma membranes
and endoplasmic reticulum (ER)
of cells and allowing direct
cytoplasmic cell-to-cell
communication of both small
molecules and macromolecules
(proteins and RNA

56. Callose deposit
Callose plugs
Callose is a plant polysaccharide that can
occur in sieve tubes.
It is not a constitutional component of the
plant's cell wall but is related to the plant's
defense mechanism.
It is produced to act as a temporary cell wall
in response to stress or damage.
Callose is present in the sieve plate at a
basal level under normal growth conditions.
When plants are subject to stress, it
accumulates rapidly and drastically,
plugging the sieve pores

57. Companion cells
Specialized form of parenchyma cell.
Provide sieve tube members with proteins necessary for signaling
and ATP in order to help them transfer molecules between different
parts of the plant.
It is the companion cells that helps transport carbohydrates from
outside the cells into the sieve tube elements.
The companion cells also allow bidirectional flow.
All of the cellular functions of a sieve-tube element are carried out by
the (much smaller) companion cell.

58. Companion cells
The dense cytoplasm of a companion cell is connected to the sieve-tube element
by plasmodesmata.
The common sidewall shared by a sieve tube element and a companion cell has
large numbers of plasmodesmata.
There are three types of companion cells.
1.Ordinary companion cells, which have smooth walls and few or no
plasmodesmatal connections to cells other than the sieve tube.
2.Transfer cells, which have much-folded walls that are adjacent to non-sieve
cells, allowing for larger areas of transfer. They are specialized in scavenging
solutes from those in the cell walls that are actively pumped requiring energy.
3.Intermediary cells, which possess many vacuoles and plasmodesmata and
synthesize raffinose family oligosaccharides

59. Transfer cells
Cells with secondary wall ingrowths.
Parenchyma cells, called transfer cells and border
parenchyma cells, are located near the finest
branches and terminations of sieve tubes in leaf
veinlets, where they also function in the
transport of foods.
The transfer cells differ from the ordinary
companion cells in having plasma membrane
infoldings, which increase the surface area that
permit larger areas of transfer. Companion cells
are present only in angiosperms.

60. Plant transfer cells can be subdivided into two
categories, flangelike and reticulate types, based on
the morphology of cell walls.
Transfer cells (TCs) play key roles in optimizing
such nutrient transport processes in plants.
The resulting increase in plasma membrane surface
area enables increased densities of membrane
transporters to optimize nutrient transport across
apoplasmic/symplasmic boundaries at sites where
TCs form

61. Transfer cells (TCs) are ubiquitous throughout the plant kingdom.
Their unique ingrowth wall labyrinths, supporting a plasma membrane
enriched in transporter proteins, provides these cells with an enhanced
membrane transport capacity for resources.
In certain plant species, TCs have been shown to function to facilitate phloem
loading and/or unloading at cellular sites of intense resource exchange
between symplasmic/apoplasmic compartments.
Within the phloem, the key cellular locations of TCs are leaf minor veins of
collection phloem and stem nodes of transport phloem.
With the evolutionary advancement of vascularization, TCs are found located
in close proximity to sieve and xylem elements throughout the vascular
highway

62. Collection Phloem
confined to the minor vein network in leaves including cotyledons of
germinating seed.
Transport Phloem
located in the major vein network of leaves and extends through petioles to
the vascular systems of stems, rhizomes and roots.
Release Phloem The main task of the release phloem in the sinks is
to unload assimilates from the SECCCs into growing or storage cells. The
decreasing volume ratios between the companion cells and the sieve
elements along the phloem stretch

63. Phloem parenchyma
Other parenchyma cells within the phloem are generally
undifferentiated and used for food storage.
Phloem parenchyma is absent in most of the monocots.
living cells.
Elongated tapering cylindrical cells with dense cytoplasm and nucleus.
Store food as well as other materials like resins, tannins, latex,
mucilage etc.

64. Phloem fibres
Although its primary function is transport of sugars, phloem may also
contain cells that have a mechanical support function.
These are sclerenchyma cells which generally fall into two
categories: fibres and sclereids.
Both cell types have a secondary cell wall and are dead at maturity.
The secondary cell wall increases their rigidity and tensile strength,
especially because they contain lignin.
Fibres: Bast fibres are the long, narrow supportive cells that
provide tension strength without limiting flexibility.
Sclereids: Irregularly shaped cells that add compression strength,
also serve as anti-herbivory structures.

65. Phloem fibre

66. Phloem fibre
Illustration of fiber elongation.
First phase of
coordinated
growth
More advanced
step
of coordinated
growth
Beginning of the
intrusive growth
with fibers having
‘knees’ on both ends
more advanced phase
of the intrusive growth,
with fibers becoming
a much longer structure
than the neighboring
cells and showing tapered
ends

68. Origin of Phloem
Phloem originates and grows outwards from meristematic cells in
the vascular cambium.
Phloem is produced in phases.
Primary phloem is laid down by the apical meristem and develops
from the procambium.
Secondary phloem is laid down by the vascular cambium to the
inside of the established layer(s) of phloem.

69. Origin of Phloem
In some eudicot families (Apocynaceae, Convolvulaceae, Cucurbitaceae, Solanaceae, Myrtaceae,
Asteraceae, Thymelaeaceae), phloem also develops on the inner side of the vascular
cambium; in this case, a distinction between external and internal or
intraxylary phloem is made.
Internal phloem is mostly primary, and begins differentiation later than the
external phloem and protoxylem, though it is not without exceptions.
In some other families (Amaranthaceae, Nyctaginaceae, Salvadoraceae), the cambium also
periodically forms inward strands or layers of phloem, embedded in the
xylem: Such phloem strands are called included or interxylary phloem

70. Development and differentiation of sieve tube members
Sieve tube members (and associated companion cells) were
evolutionarily modified from sieve cells and are found only in
flowering plants.
Sieve tube members differ from the ancestral sieve cells in that the
pores at the end walls are differentiated, being much larger than
those on the side walls.

71. Development of Sieve tubes
The differentiation of an idealized sieve
element: Cells are initially indistinguishable
from their neighbors, yet the pattern of the
future pores is already determined by apical
and basal plasmodesmata.
During further differentiation, callose is
deposited around terminal plasmodesmata and
lateral sieve areas are formed, while nuclear
breakdown and cytoplasmic clearing begin.
Once selective autolysis is completed, residual
organelles remain tethered to the lateral
plasma membrane. Sieve pores are opened,
and sieve elements stretch with the growing
surrounding tissues.

72. Sieve pore formation
The progression of the sieve pore formation: A plasmodesma with the protruding ER
desmotubule is gradually transformed. Callose is deposited as cones around the
plasmodesma, creating a callose plug, while cellulose of the primary cell wall is
simultaneously degraded. Just until pore opening, callose maintains the cell wall
integrity. Pore opening begins from the center of the structure and degrades the callose
plug, including the remaining middle lamella, while autolysis removes the desmotubule.
The size of the final pore is determined by the original extent of the callose plug. CC:
companion cell; PPC: phloem parenchyma cells; PPP: phloem pole pericycle; SPl: sieve plate; LSA: lateral sieve area;
PD: plasmodesma; ER: ER desmotubule; PCW: primary cell wall with middle lamella; CA: callose; PM: plasma
membrane; and SPo: sieve pore.

73. CAMBIUM

74. Layer of actively dividing cells between xylem (wood) and
phloem (bast).
Responsible for the secondary growth of stems and roots-
provide necessary cells for increasing the width of the plant.
Its main purpose is to encourage the growth of plants by
providing non-specialized stem cells.
The cambium present in the vascular bundle between the
conducting tissue xylem and phloem is called a fascicular
cambium (intrafascicular cambium) as it is found within the
vascular bundle.
The cambium present between two vascular bundles is called an
interfascicular cambium

75. STORIED & NON STORIED CAMBIUM
Fusiform initial
Ray initial

76. Storied

77. Phloem developed from cambium - nonstoried

78. Xylem developed from cambium
storied non storied

79. Plerome is the type of meristematic tissue that gives rise to the vascular tissue. Therefore
the tissue is also called as procambium.
Procambium -concerned with primary xylem & primary phloem
Cambium proper -continuous cylinder of meristematic cells -new vascular tissues
(secondary xylem & phloem) in mature stems and roots.
Procambium/cambium contains pluripotent stem cells and provides a microenvironment
that maintains the stem cell population.
Because vascular plants continue to form new tissues and organs throughout their life
cycle, the formation and maintenance of stem cells are crucial for plant growth and
development.
Primary Thickening Meristem (PTM) is only found in monocots. Procambium is abundant
in the derivative cells of the PTM. These are the primary vascular bundles of the stem.
These plants have many veins in their leaves and this is reflected in the number of
vascular bundles in the stem.

81. Residual meristem
A residual meristem is a type of meristem that remains active in mature
plant tissues, allowing for continued growth and repair throughout the
life of the plant.
It is a transitional tissue in which the forefront of the advancing
procambial strands develop.
Residual meristems, however, are found in older or mature parts of the
plant that have already undergone primary growth.
These meristems can be found in various plant tissues, such as the
cambium and cork cambium, which are responsible for secondary growth
in woody plants

82. In the event of formation of wound, the cambium rapidly forms a soft parenchyma
tissues, callus or wound tissue, on or below the damaged surface.
In the injured portion, phellogen produces wound cork. Soon after the injury, the
preexisting cells of the phellogen form a fresh layer of suberized cells just below the
injured parts, thus the dead tissue is sloughed off by this suberized layer.
In subsequent stages a new layer of phellogen develops which produces phellum and
phelloderm in a usual manner. The new layers of the cork formed seal the wound.
Thus, the cork, which is resistant to the infection of bacteria and fungi, protects the
inner tissue.
Wound cork is developed more easily in woody plants as compared to herbaceous
plants.
Moist and warm climate favours the early development of wound cork than cold and
dry climate.
Cambium in wound healing

83. Cambium in budding and grafting
In grafting, as well as budding, the vascular cambium of the scion or bud must be
aligned with the vascular cambium of rootstock.
This vascular cambium initiates callus tissue at the graft and bud unions in
addition to stimulating tissue growth on the basal ends of many vegetative
cuttings before they have rooted.
Successful graft union formation involves a series of steps viz., lining up of
vascular cambium, generation of a wound healing response, callus bridge
formation, followed by vascular cambium formation and subsequent formation of
the secondary xylem and phloem.
For grafted trees compatibility between the rootstock/scion is the most essential
factor.
Formation of vascular connection between the stock and scion during wound
healing is of utmost importance as the wound given to the stock and scion during
grafting causes disruption of the vascular system in plants, hence connecting up
of the vascular system is required to facilitate water uptake as well as to ensure
nutrient transport to the graft junction

84. Stage 1- Parenchymatous tissue
divides to form callus cells.
Stage 2- Xylem vessel
formation.
Stage 3- Formation of vascular
cambium across the graft union
linking the two partners.
Stage 4- Secondary xylem and
phloem dedifferentiate across
the graft union establishing
sufficient vascular continuity
for plant growth.

85. Differentiation

86. Cellular differentiation is the process
in which a cell changes from one cell
type to another.
This Change mainly happens to form
a more specialized type of cell.
It is processes by which distinct cell
types arise from precursor cells and
become different from each other.
Plants have about a dozen basic cell
types.

87. The meaning of the word differentiate, and any of its derivative forms,
depends on the context or application of the term.
The apical meristem has a functional differentiation into a region of
proliferation and a region of histogenesis and organogenesis.
In the former there is no differentiation with respect to histology, but
there may be cytological differentiation among the cells.
In the region of histogenesis and organogenesis there
is histological differentiation (because the primary meristematic
tissues of the three tissue systems can be recognized) and there
is differentiation of plant parts (stem vs. leaves).

88. The late changes in cytological differentiation are referred to as
cell maturation, because a stable condition or endpoint is being
approached.
The implication that a mature cell should not be able to change - is
not a useful concept in the study of plant anatomy.
Much of a mature plant part can consist of parenchyma cells.
These are capable of remarkable changes under the right conditions,
for each parenchyma cell has the potential to reproduce the whole
plant. This potential is not manifested under normal circumstances,
and it is therefore permissible to consider a parenchyma cell as a
mature cell type.
Certainly, there is more than one approach to studying cellular
differentiation. eg. changes in the structural characteristics of cells

89. The concept of a procambium-cambium continuum
The part of the continuum associated with the formation of primary vascular
tissues is subdivided to facilitate interpretation of the consecutive stages of
primary xylem differentiation. Thus, the procambium is subdivided into
procambium, initiating layer, and metacambium, all of which develop
acropetally and in complete continuity.
The procambium is derived from the residual meristem in the form of
acropetally developing strands and traces. The initiating layer is represented
by the first, tangentially separated, periclinal divisions that delineate the
position of the prospective cambium.

90. The metacambium is a later stage during which additional periclinally dividing
cells unite the initiating layer into a tangentially continuous meristem within
a trace bundle.
After establishment of the initiating layer, the procambial trace is completely
phloem dominated.
Protoxylem differentiation begins in an originating center at the base of the
leaf primordium and it progresses basipetally to form the protoxylem pole.
Cells of the initiating layer do not contribute to the formation of either
protoxylem or protophloem.
Those cells of the initiating layer directly opposite the protoxylem pole divide
precociously and later differentiate to metaxylem, thus forming a radial file of
protoxylem-metaxylem elements.
Protoxylem elements of lateral traces are longitudinally continuous with the
protoxylem of their parent traces.

91. Vessel Elements. Vessel elements differentiate from cells of the procambium.
Vessel elements are first differentiated from other procambial cells because they
expand more than their neighbors. Vessel element precursors next begin to
deposit the thickened, lignified parts of their cell walls in either the ringlike,
helical, netlike, or pitted pattern. The pattern can be predicted by the location of
elements of the cytoskeleton within the cytoplasm that help guide wall precursor
to the proper location. When cell wall synthesis is complete,
special enzymes attack the end walls of the cell, forming the perforation
between adjacent elements in a vessel.
Finally, the vessel elements undergo
programmed cell death.
The cell makes protease enzymes and
nuclease enzymes that reduce proteins and
nucleic acids to their simple building blocks.
Surrounding parenchyma cells absorb these
small molecules, leaving an empty vessel

92. Bundle Sheath Cells. In most plants, the cells of the photosynthetic ground tissue
are uniform in size, shape, and chloroplast development. Two types of
photosynthetic parenchyma cells are sharply differentiated in plants that have the
C4 photosynthetic pathway,
These two cell types, the mesophyll and bundle sheath cells, begin differentiation as
similar appearing ground meristem cells.
During leaf expansion, the bundle sheath cells begin to enlarge first. The cell wall
becomes thickened and impermeable to the diffusion of gases. Their plastids
replicate, grow, and become asymmetrically placed within the cell.
In contrast, the mesophyll cells undergo a minimal amount of enlargement and have
thin, permeable cell walls. The number of plastids is low and the plastids remain
small.
During cell differentiation the genes encoding the
enzymes of the C4 biochemical pathway are
expressed exclusively in the mesophyll cells, whereas
the genes encoding the enzymes of the C3 pathway
are expressed only in the bundle sheath cells

93. Cell Differentiation and Development
Cell differentiation is only part of the larger picture of plant development.
As plant organs develop (the process of organogenesis), the precursors of the
tissue systems form in response to positional signals.
Within each tissue system precursor, cell types must be specified in the proper
spatial pattern.
The spacing of trichomes and stomates within the protoderm must be specified
before their precursor cells begin differentiation.
Exchange of signals among neighboring cells is an important aspect of the
processes of spatial patterning and cell differentiation.
In addition, long distance signals are required so that the strands of xylem and
phloem cells within the leaf vascular bundles connect perfectly with those in the
stem.

94. Hormonal Influences
Many aspects of differentiation are controlled by hormones .
The hormone auxin, plays an important role in the differentiation of vessel
elements, both in intact and wounded plants.
Auxin produced by the apical meristem and young leaves above the wound induces
parenchyma cells to regenerate the damaged vascular tissue. Parenchyma cells
undergo transdifferentiation.
Although they already had differentiated as parenchyma cells from ground meristem
precursors, they now repeat the steps that procambial cells take when they
differentiate as vessel elements.
Cells are induced to do this in a chainlike pattern, so that a new continuous strand
of vascular tissue is formed as a detour around the original incision.
Transdifferentiation is blocked when the sources of natural auxin (young leaves and
buds) are removed or when auxin transport inhibitors are applied.
If natural sources of auxin are removed, and artificial sources added,
transdifferentiation of parenchyma cells will occur, regenerating the vascular bundle.

95. Acropetal and Basipetal differentiation in leaves
Leaf growth is characterized by an initial phase of cell proliferation followed by
cell differentiation where growth is driven by the expansion of the differentiating
cells.
The phase of differentiation has a specific pattern in the proximo-distal axis
wherein differentiation begins near the distal tip and proceeds toward the
proximal base.This pattern of growth is known as basipetal growth because the
cells near the base continue to proliferate and cause leaf expansion for the longest
duration.
Basipetal leaf growth is considered universal.
The direction of leaflet initiation on a compound leaf can be basipetal (younger
leaflets are formed near the proximal end while the terminal leaflets are more
mature), acropetal (younger leaflets are formed toward the distal end) or divergent
(younger leaflets are formed at both ends).

96. Leaf growth patterns
(i) Acropetal leaf growth where differentiation begins near the base and
progresses toward the tip (opposite of basipetal growth);
(ii) Even or diffused growth where the cells begin to differentiate
synchronously throughout the lea
(iii) Bidirectional growth where differentiation begins from both
extremities and progresses toward the middle of the leaf.
Since all these growth patterns are essentially different forms of polar or
differential growth, we used the law of simple allometry to classify the
growth patterns
positive allometry (basipetal growth)
negative allometry(acropetal growth)
isometry (diffused/even growth)
complex allometry (bidirectional growth)

98. Control of differentiation: Genetic aspects
The polarity of the maturation of individual leaflets is independent of the polarity of
their initiation on a compound leaf, and therefore these two polarities are likely
regulated by different molecular mechanisms.
The expression of the conserved miR396-GROWTH REGULATING FACTOR module,
is responsible for the lamina growth along the proximo-distal axis of simple leaves.
It is linked to the divergent growth polarity of leaves/leaflets.
The polarity of leaflet initiation on compound leaves, on the other hand, is possibly
regulated by genes involved in meristem programs such as KNOTTED1-like
homeobox (KNOX) genes.

101. ANATOMY OF THE NODE

102. Leaf trace
Extension of the vascular system to the leaf
Leaf
Microphyllous and Megaphyllous (Macrophyllous)
Leaf gaps
At the nodal region some portion of vascular elements are diverted from the
vascular cylinder to form the leaf traces. This makes a gap in the vascular cylinder
and this gap is filled with parenchyma tissue. This is called leaf gap.

103. Leaf gap
Filled with parenchyma
Leaf trace
Pith
Secondary xylem cylinder
Secondary phloem
Secondary phloem

105. Leaf gap
Leaf trace
Leaf trace xylem
Leaf trace phloem
Pith
Secondary xylem cylinder
Secondary phloem
UNILACUNAR WITH ONE LEAF TRACE

106. Continuity of vascular cylinder
Leaf gaps do not make a break in the vascular cylinder. Continuity is
maintained below and above the leaf gaps by lateral connections.
Leaves and leaf gaps
If the leaf receives one leaf trace from the vascular cylinder it leaves one
gap in the axial cylinder and such nodal pattern is called unilacunar with
one leaf trace (most common type)

107. Nodes and phyllotaxy
More leaves at node, more leaf traces to each leaf make other types of nodal
conditions.
Bilacunar, trilacunar and multilacunar etc,
Future of leaf gaps
In older stems the parenchyma of the leaf gaps are crushed and filled with
lignified xylem tissues.

108. 1. UNILACUNAR WITH ONE LEAF TRACE
AT THE NODE ABOVE NODE

109. AT THE NODE ABOVE NODE
Leaf trace
Leaf gap
2. UNILACUNAR WITH TWO LEAF TRACE

110. 3. 2- LACUNAR WITH 4 - LEAF TRACES
(TWO LEAVES AT NODE)
AT THE NODE ABOVE NODE
Leaf trace
Leaf gap

111. 4. TRILACUNAR WITH 3 LEAF TRACES
AT THE NODE ABOVE NODE
Leaf trace
Leaf gap
Three Leaf traces united to one

112. Three Leaf traces united to one
Three Leaf traces
TRILACUNAR
WITH 3 LEAF TRACES

113. 5. MULTI LACUNAR
WITH MANY LEAF TRACES
AT THE NODE ABOVE NODE

114. PHYLOGENY OF LEAF
TRACES
Multilacunar with
many leaf traces
3-lacunar with
3 leaf traces
1-lacunar with
1 leaf traces
1-lacunar with
2 leaf traces

116. Branch trace
Leaf traces
Leaf gap
Branch gap
Secondary phloem
Secondary xylem cylinder
Pith

117. Types of bundles
The nodal vascular system is complicated by the divergence of some vascular tissue into
the leaves and the branches.
The vascular cylinders are generally continuous at the internode and their continuity is
interrupted at the nodal region due to emergence of bundles that terminate either at the
leaf bases, axilliary buds or stipules, etc.
(i) Leaf trace bundle : The single vascular bundle that connects the leaf base with the
main vascular cylinders of stem is designated as leaf trace bundle. In a leaf there may
be several leaf trace bundles that collectively are termed as leaf traces.
(ii) Cauline bundle : The vascular bundles that entirely form the vascular system of stems
is known as cauline bundles. Sometimes these bundles anastomose with each other
and extend from stem to leaf as leaf traces.
(i) Common bundle : The vascular bundles, which run unbranched through a few
successive nodes and internode and ultimately terminate as leaf traces are called
common bundles.

118. Types of Nodal Anatomy Sinnott (1914)
(i) Unilacunar type : Only one gap associated with a leaf trace bundle. -when the vascular
trace or traces of each leaf produce a single gap. -characteristics of many families such
as Annonaceae, Lauraceae, Resedaceae, Ericaceae, Apocynaceae, Solanaceae and
Verbenaceae. One, two, three or many traces are associated with a unilacunar node and
then the nodes are known as Unilacunar one trace, Unilacunar two trace, Unilacunar
three trace and Unilacunar multitrace respectively.
(ii) Trilacunar type : three gaps ( one median and two lateral gaps) each being associated
with three traces of each leaf. Eg; Winteraceae, Polygonaceae and in Centrospermae
and Amentiferae.
(iii) Multilacunar type : More than three gaps and traces in a leaf, and each gap is
associated with each leaf. Multilacunar node occurs in Degeneriaceae, Araliaceae,
Chenopodiaceae and in some other taxa where leaf bases are sheathing.

119. According to Sinnott (1914)
Trilacunar node is most primitive among dicotyledons.
During evolution unilacunar and multilacunar types are derived from it by reduction
and amplification in the number gaps and traces.
The various phylogenetic changes are involved in deletions, fusions and additions of
traces.

120. Evolution of nodal vasculature as envisaged by Sinnott (1914).
Trilacunar
three trace
node
Multilacunar
multitrace
node
Unilacunar
one trace
node.

121. The arrangement of leaves at a node may be opposite or whorled and
then the node is termed on the basis of number of gaps.
e.g., unilacunar opposite, unilacunar whorled, etc.
Veronica, unilacunar node
with two, opposite, leaves;
branch trace, two to a branch,
in axil of each leaf.

122. Though unilacunar condition is considered as advanced, later studies
on nodal anatomy by Bailey (1956), Fahn and Bailey (1957) and others
reveal that unilacunar conditions is primitive as this type is found in
some primitive groups like pteridophyta, fossil gymnosperms like
Bennettitales and Cordaitales, Ginkgo and Ephedra.
Ozenda (1949), on the basis of his studies of the nodal anatomy of
Magnoliales, considered multilacunar node as primitive.
According to him, three nodal types reported in angiosperms form a
regressive series, multilacunar-trilacunar-unilacunar.

123. Takhtajan: The most accepted concept is that the trilacunar condition is
primitive in dicots and unilacunar and multilacunar have been derived
from it . Several monocots plants with sheathing leaf bases and nodes
with a large number of leaf traces seperately inserted around the stem

124. Marsden and Bailey ( 1955), Canright (1955), Bailey (1956), Fahn and Bailey
(1957) and others observed that there are two traces in a leaf and
these two traces are associated to single gap. They recognized this as
fourth nodal type and termed as Unilacunar two traces
Clerodendron, two-trace unilacunar
node; two opposite leaves to a node.
They considered unilacunar two trace condition as
the primitive nodal type for angiosperm
Subsequently, many other anatomists supported
this concept of nodal evolution.
Unilacunar node with two distinct traces is
characteristic not only of some gymnosperms and
ferns but also occur in several dicotyledons, such as
Laurales, Verbenaceae, Labiatae and Solanaceae.
It is also found in cotyledonary nodes of several
angiosperms.

125. In the light of the above facts it is now interpreted that the evolution of this
primitive nodal type ( Unilacunar two trace) preceded in the following two
sequences:
(i) Two trace unilacunar gave rise to trilacunar, which get terminated to
multilacunar condition :
(ii) Two trace unilacunar, by the loss of one trace, gave rise to one trace
uniacunar that formed trilacunar node by the addition of two new gaps
associated with two traces.
The multilacunar condition is derived from the trilacunar type by the
addition of more new traces and gaps.
The trilacunar type may also give rise to one trace unilacunar condition. This
evolutionary sequence may be observed in a single family Chenopodiaceae

126. Possible ways of evolution of nodal vasculature
from a unilacunar two trace node.
Unilacunar
two trace node.
Unilacunar
one trace node
Multilacunar
multitrace node
Trilacunar
three trace node.

127. Pant and Mehra ( 1964) did not favor the above interpretation as a vast
majority of gymnosperms and angiosperms do not show two trace
unilacunar node.
Benzing (1967) also pointed out that the unilacunar two trace node
considered to be primitive by many workers is confined to a new families
and these families have derived from decussate phyllotaxy and several
specialized floral characters. Thus, he considered unilacunar three trace
node to be the primitive nodal type for the angiosperms than the
unilacunar two trace node.

128. Philipson and Philipson (1968) also maintain that trilacunar node of
Rhododendron is derived from unilacunnar type.
Takhtajan ( 1964) also discussed probable course of evolution of nodal
structure in dicotyledons. He considers that trilacunar node with two
traces from the central gap is the basic type of angiosperm node.
Other type of nodal structures are derived from this hypothetical
synthetic fifth type of node by reduction and amplification

129. A. tri-structure node with a double trace
at the median leaf gap.
B. trilacunar node with three traces.
C. unilacunar node with one trace.
D. multilacunar node with multitraces.
G. unilacunar node with one trace.
Possible course of solution of nodal structure in dicotyledons
from a primitive tri-multilacunar type.

130. Examples
Unilacunar: Single gap, single trace : Ocimum, Eucalyptus, Nerium, Lantana
camara, Justicia
: Single gap, two traces : Clerodendron splendens
: Single gap, three traces: Chenopodium album, Withania somnifera
Trilacunar: Three gaps, three traces : Brassica, Annona, Azadirachta
Multilacunar: Several gaps and traces: Polygonum, Aralium, Coriandrum
(

131. WOOD

133. Wood

134. Manoxylic wood
Pycnoxylic wood
Ring porous wood
Diffuse porous wood
Sap wood
Heart wood
Duramen
Alburnum
Soft wood
Hard wood
WOOD

135. Vessels (all equal size)
Trachieds
Ray
One year growth
DIFFUSE POROUS
WOOD

136. Large vessels
Trachieds
Small vessels
One year growth
RING POROUS
WOOD

137. Ring porous & diffuse porous wood

140. Heartwood & Tyloses

141. Heart wood sap wood

142. Annual rings

143. Tension wood & Compression wood
Compression wood forms on the underside of branches and contains
more lignin than normal wood.
Wood with a high lignin content is especially strong in compression.
Tension wood forms on the upper sides of hardwoods and contains
more cellulose than normal wood.

144. Reaction Wood:
•Formation due to Mechanical Stress: Reaction wood (either compression
wood in softwoods or tension wood in hardwoods) develops as a response to
mechanical stress. It's formed to counteract the effects of gravity or other external
forces.
•Counteracting Leaning or Bending: When a tree leans or bends due to
environmental factors like wind, slope, or other structural stress, reaction wood helps
to reorient the tree to grow more vertically, maintaining its stability.
•Restoring Balance: The primary function of reaction wood is to restore the tree
to an upright position by exerting a force against gravity. Compression wood forms on
the underside (or the inside of a curve) to push or contract, while tension wood
forms on the upper side (or the outside of a curve) to pull or expand, helping to
maintain balance.

145. Tension Wood:
•Gravitational Response: Tension wood specifically develops in response to gravitational
stimuli. It occurs in hardwoods, mostly angiosperms, and forms on the upper side of
leaning or bending branches or stems.
•Cellular Elongation: The cells in tension wood elongate, leading to its characteristic high
cellulose content and different anatomical structure, causing the wood fibers to exert a
tensile force.
•Restoring Upright Growth: Tension wood assists in pulling the inclined branch or stem
upward, helping it return to a more vertical growth orientation.
•Assisting Water Transport: Additionally, tension wood might play a role in enhancing
water and nutrient transport in some tree species.
Both types of wood, though different in their structural and anatomical characteristics,
serve the common purpose of allowing the tree to adapt and maintain its position against
mechanical stresses, contributing to the overall stability and survival of the plant. The
formation of these woods showcases the incredible ability of trees to adapt to
environmental stressors.

146. Compression wood is a specialized type of wood formed in coniferous trees as a
response to mechanical stresses or gravitational stimuli.
Primary reasons for the development of compression wood:
1. Mechanical Stress Response:
•Gravitational Forces: Coniferous trees often grow in various orientations, and these
trees encounter mechanical stress due to factors like wind, snow, or leaning.
Compression wood develops as a response to counteract these stresses, particularly on
the lower side of leaning branches or stems.
•Counterbalancing Bending or Leaning: When a conifer tilts or bends, compression wood
forms on the underside (the side facing the ground) or the inside of a curve to push or
contract, aiming to counterbalance the gravitational force.
2. Restoring Upright Growth:
•Stabilization: Compression wood assists in stabilizing the tree's position and promoting
a more vertical growth orientation, thereby helping the tree resist the forces that cause it
to lean or bend.

147. 3. Anatomical and Physiological Characteristics:
•Higher Lignin Content: Compression wood has higher lignin content and altered cell wall
properties compared to normal wood, providing it with different mechanical properties
that aid in resisting bending and compression.
•Asymmetrical Growth: The cells in compression wood are typically smaller and more
irregularly shaped, contributing to its distinctive characteristics and strength.
4. Water and Nutrient Transport:
•Some research suggests that compression wood may also play a role in water and
nutrient transport, helping to maintain the flow of vital substances within the tree despite
the gravitational challenges it faces.
Compression wood, with its unique anatomical and mechanical properties, is vital for
coniferous trees to resist gravitational forces, maintain their stability, and ensure proper
growth, contributing significantly to the overall structural integrity and survival of these
trees in challenging environments

148. Gravitropism and reaction wood

149. Tension wood
Normal wood
Tension wood
Upper side of the branch
Lower side of the branch
TENSION WOOD

150. COMPRESSION WOOD
Tension wood
COMPRESSION wood
Normal wood
Upper side
Lowerside

151. BIRDS EYE
Bird's eye wood is
characterized by small,
round, dark knots or
"eyes" that resemble the
appearance of bird's
eyes.

152. LEAF ANATOMY

154. UNIFACIAL & BIFACIAL LEAF

155. Bifacial Leaf
A dicotyledonous leaf is also called dorsiventral or bifacial leaf. For
example, mango leaves, banyan leaves and oleander leaves. These
leaves are hypostomatic (stomata mostly on the lower epidermis).
Mesophyll tissues present in these leaves are differentiated into
palisade and spongy.
Unifacial leaf
Unifacial leaves perform all the same functions as bifacial leaves, but
are anatomically a single side. Unifacial leaves are more common in
plants that grow tubular leaves, like chives and onions
Unifacial leaf is also called as isobilateral or amphistomatic

156. ANATOMY
OF
SEEDLINGS

158. The epicotyl is located above the cotyledons and below the plumule. It is
important in hypogeal germination where it extends above the soil.
The hypocotyl is below the cotyledons and goes to the tip of the radicle.
The basal part of the hypocotyl is root-like in structure while the middle
and upper parts are stem-like.
The transition of vascular tissues occurs in the basal part of the hypocotyl.
The vascular bundles are collateral in arrangement in the middle and
upper parts and radial in the basal part.
Hypocotyl is the main extension organ, it gradually develops into the stem
as the plant continues to grow

170. CELL WALL
Ultrastructure, Components & Organization
CELL WALL

171. LAYERS
Primary wall
Intercellular substances or middle lamella
Secondary wall.

174. Cell wall layers

175. Cell wall layers

178. Cell Wall Chemical Constituents
• Cellulose
• Hemi-cellulose
• Pectic substances
• Lignin
• Proteins
• Waxes
• Cutin
• Suberin
• Sporopollenin

179. A. Structural Components
•1) Cellulose:
• The most abundant substance in the plant kingdom
• A polymer of ß -glucose residues joined in long chains by 1-4 links.
• These chains lie parallel to each other and are very regularly spaced, to form
long crystalline microfibrils.
• Microfibrils may be arranged randomly or in a regular fashion.
• Cellulose chains lie antiparallel in such a way that alternate chains point in
opposite directions.
• Within the microfibrils themselves, are smaller units, the micelles, which
are small aggregations of cellulose molecules that lie parallel to one another
and thus confer a crystalline structure upon the microfibrils.

181. A. Structural Components
•1) Cellulose:
• About 100 cellulose molecules form a bundle to make one micelle.
• Bundles of cellulose molecules are interconnected and form a porous
coherent system, the micellar system, interpenetrated by an
equally coherent inter micellar system, in which various wall
substances other than cellulose are found.
• A bundle of about 20 micelle makes a microfibril and a bundle of
many microfibrils make a macrofibril or fibril or elementary fibril.
• The microfibrils are necessary to bear the stress in the wall due to turgor
pressure.
• One cotton fibre consists of such 1500 fibrils.

183. • 2) Pectic Substances:
• These consist of polymers of d-galacturonic acid, l-arabinose, d-galactose and l-
rhamnose.
• These substances are found mainly in the middle lamella of primary walls.
• The metabolic changes which occur in the pectic substances deposited in the wall
involved the formation of strongly acidic polygalacturonic acid (pectic acid - a
water soluble transparent gelatinous acid seen in overripe fruits).
• 3) Hemi Celluloses:
•These are amorphous and consist of linear or branched polymers of
d-xyloses, d-galactose, d-mannose, l-arabinose, and l-rhamnose.
•In contrast to cellulose they shorter, branched and are not crystalline in their
natural condition.

184. 4) Lignin
• Occurs as an incrustation between cellulose microfibrils.
• The concentration is highest in the middle lamella and falls off towards the
lumen.
• It is an important structural material and it is this substance that gives strength
to wood.
• Because of this deposition of lignin between the existing cellulose frameworks
there is always a swelling of the cell wall during lignification.
• Lignin is the most abundant plant polymer after cellulose.
• It consists of large amorphous molecules built up from a variety of penyl-
propane derivatives such as sinapyl, coniferyl and ß -coumaryl alcohols.
• The presence of lignin confers great rigidity and resistance to chemical
degradation.
• Lignin comprises 15-35% of the dry weight of the supportive tissues in higher
plants

185. 5) Protein:
• Primary wall of dicots contains 5-10% of proteins.
• Seen cross linked into the wall
• Recent work has demonstrated the occurrence of a group of proteins
containing aminoacid hydroxyproline in the primary walls of various tissues.
• The amount present increases during growth.
• Arabidogalactan proteins play a major role in cell – cell interactions.

186. Components of secondary wall
• The primary and secondary walls differ in their chemical composition and in fine
structure.
• In most cases the secondary walls have a higher percentage of cellulose and lignin while
the pectic substances are present only in trace quantities as compared to the primary
walls.
• 6) Cutin and suberin:
• The excessive loss of water from plant body is-prevented by the presence of two families
of polymers known as cutin and suberin.
• Cutin
• A mixture of polyesters of hydroxylated palmitic and oleic acids.
• The precursors of cutin are synthesized in the epidermal cells and they are secreted
through the cell walls and are probably assembled.
• Suberin
• A mixture of polymers containing long chain acids and alcohols.
• Seen attached to cell walls of epidermis, in endodermis and bundle sheath of grasses.

187. • 7) Waxes:
• Waxes are non-polymeric
• consisting of complex mixtures of paraffin, long chain alcohols, ketones and
acids.
• Waxes together with cutin, provide the water retaining properties of the
cuticle
• 8) Callose :
• Callose is a polysaccharide built up from glucose units linked by ß -I,3 bond
(ß 1,3 glucan).
• It is found in sieve plate and in association with plasmodesmata connecting
the sieve element to its companion cell.
• Callose is remarkable for the speed at which it appears in response to wound
especially in phloem.
• Callose may be produced when pollen grain lands on an unreceptive stigma
resulting in the prevention of pollen tube growth.

188. • 9) Gums and Mucilage :
• they are also the compound carbohydrates of the cell walls.
• They possess the property of swelling in water.
• Gums exude as a result of physiological or paathological disturbances.
• Mucilage occur in some gelatinous type of cells.
• 10) Mineral substances:
• Silica, calcium carbonate, calcium oxalate and several organic compounds like tannins,
resins, fatty substances, volatile oils etc. may impregnate cell walls.
• Water:
• The universal component of the primary wall
• Water forms 80% of the fresh weight.
• Water is required for the operation of hydrogen bonding.
• The outer surface of cellulose microfril is disorganized by the presence of water for bonding
with other substances.
• Water acts as a solvent for a range of ions and small molecules.

189. Dehydration of cell wall

190. Cytokinesis & Biosynthesis of Cell Wall Materials
• As a cell finishes karyokinesis and begins cytokinesis, a complex (phragmoplast) of
microtubules and ER forms between the two daughter nuclei.
• The microtubules appear to be capable of trapping dictyosome vesicles that then
fuse into one large flat cisterna.
• Carbohydrates that the vescicles had contained are synthesized into the two new
primary walls and the middle lamella that binds them together.
• As the new walls form inside the cisternae, the membrane becomes transformed into
plasmalemma.
• The new structure - middle lamella, two primary walls and plasmalemmas - is termed
the cell plate
• Cell plate continues to grow at its margins as the phragmoplast expands outward,
trapping more vesicles that fuse with the cell plate. The position of phragmoplast and
cell plate vary, sometimes place asymmetrical. The phragmoplast disassembles as it
approaches the margins of the cell, and the plasmalemma of the cell plate fuses with
the existing plasmalemma of the mother cell. The two primary walls meet the
existing wall as does the new middle lame

191. Synthesis of Cellulose
• In the biogenesis of cellulose and other cell wall components, two main
pathways have been described.
• One involves the Golgi complex, and the other appears to be directly
associated with the Plasmamembrane.
1. The golgi membranes with their glycosyl transferase content are able to
polymerize glucan chains into cellulosic microfibrils. The mode of synthesis of
cellulose microfibril is thought to be the basis of crystallization.
2. Complexes of cellulose synthesizing -enzymes (glycosyl transferase) are
embedded in the plasmalemma in the form of rosettes (globular complexes).
The enzymes are believed to receive activated glucose from the cytoplasm side
and add it to growing molecules of cellulose which extend out of the other side
of the plasmalemma. Because the cellulose synthases are aggregated in the
rosettes, the growing molecules are automatically aligned, and they crystallize
immediately

196. • The growing microfibrils will interact with pre existing wall material and
will be anchored rather solidly.
• As growth of the molecules continues, the synthase rosettes float forward
in the plane of the plasmalemma, which is fairly easy according to the
fluid mosaic model of membrane structure.
• If there is no mechanism to orient the movements of the rosettes, the
microfibrils should be deposited random, which indeed does occur in
most primary walls.
• The rosettes can also aggregate into very large arrays that have as many
as 16 rows of rosettes. The entire array moves as a unit through the
membrane, depositing parallel rows of cellulose crystals.

197. • The process of biosynthesis and orientated deposition of cellulose
fibrils is considered to consist of four steps:
• (a) Polymerisation (of the activated monomeric precursor) to
form a cellulose molecule of high molecular weight
• (b) Transport of the molecule from the site of synthesis to that
of crystallisation
• (c) Crystallisation or fibril formation
• (d) Orientation of fibrils during deposition.

198. The middle lamella:
• The intercellular substance which cements together the primary
wall of two adjacent cells is called middle lamella.
• This is a complex layer in structure and morphology.
• It is amorphous, colloidal and optically inactive.
• It is composed mainly of pectic compounds especially calcium and
magnesium pectates.

199. Growth of Cell Wall
• The expansion of cell wall is a complicated process involving the synthesis and
arrangement of wall material
• The rate of expansion of walls parallel to the long axis of the organ especially in
an elongating organ like root will be much greater than the cross walls.
• Formerly two theories were held regarding the method of cell wall growth in
thickness:
• that of growth by intussusception, where new microfibrils were held to be laid
down between existing microfibrils and that of growth by apposition where
new microfibrils were laid down on top of the existing ones, forming a new
layer.
• With respect to longitudinal growth, the theory now most widely held is the
multi-net theory of cell wall growth, which also accounts for the observed
orientation of microfibrils in successive layers of the wall.

200. Secondary Walls
• Formed after cell expansion has stopped.
• The secondary wall may be considered as a supplementary wall whose
principal function is mechanical support.
• The secondary walls, particularly of fibres and tracheids, show microscopic
layering. The microscopic layers are commonly known as the S1 (outer), S2
(middle) and S3 (inner)
• The S3 layer is usually thinner than either the S1or S2 and may be absent
altogether.
• The S1 layer normally consists of four submicroscopic lamellae, alternate
ones having microfibrils in opposed helices.
• The S2 layer, the middle of the secondary wall, consists of numerous lamellae
in which the orientation of the microfibrils is at only a small angle to the long
axis of the cell. There seems to be a tendency for the microfibrils of this very
thick and conspicuous wall layer to be aggregated into macrofibrils.
• The S3 layer is always poorly developed in contrast to the S2 layers and there
is evidence too that the S3 layer may differ chemically in some way from
S1and S2.

201. • The secondary wall is developed from the primary wall by the addition of
new materials.
• Secondary walls contain much cellulose than do primary walls and,
correspondingly, less matrix materials.
• However Secondary walls also contain a number of classes of chemical
substances which are-not commonly found in primary Walls, like linin,
cutin, suberin, callose etc.
• Secondary wall materials are deposited in annular, spiral scalariform,
reticulate or pitted form.

207. • The SI layer appears to consist of perhaps two sets of crossed microfibrils running in a
helix around the long axis of the cell.
• In the S2 layer the direction of the microfibrils is predominently at a small angle to the
long axis of the cell. This therefore approaches a right angle with respect to the
orientation of the SI layer.
• The S3 layer is again comprised of microfibrils with a slow helical arrangement around,
the cell axis.
• The SI and S2 layers are highly laminated, and this geometrical complexity serves to
provide the strength and resistance which is needed.

208. • The SI layer appears to consist of perhaps two sets of crossed microfibrils
running in a helix around the long axis of the cell.
• In the S2 layer the direction of the microfibrils is predominantly at a
small angle to the long axis of the cell. This therefore approaches a right
angle with respect to the orientation of the SI layer.
• The S3 layer is again comprised of microfibrils with a slow helical
arrangement around, the cell axis
• Reaction wood changes in the pattern of microfibrils in the secondary
wall layers.
• Compression wood …lower side of branches of conifers
• Tension wood upper side of the branches of angiosperms
• Changes in the angle of microfibrils in the S2 layer.
• The S3 layer is frequently absent.

209. Reaction wood
• In mechanical terms, the vertical trunk of a tree, feels the normal stress
due to gravity & will tend to compress all the cells at a given level to an
equal degree.
• In a horizontal branch however, the cells in the upper part of the tissue
will be in tension, where as those in the lower part will be in
compression.
• Tissue produced under such conditions is known as reaction wood, and
shows changes in the pattern of microfibrils in the secondary wall layers.
The wood is called, reaction wood (compression wood in conifers /
tension wood in dicotyledons) because its development is assumed to
result from the tendency of the branch or stem to counteract in the
force induced in the axis. Reaction wood occurs in roots also.

210. Compression wood & Tension wood
Reaction wood is of two types namely compression wood and tension wood.
Compression wood is produced a on the lower side of branches of conifers
Tension wood is produced along 'the upper side of the branch of angiosperms.
Compression wood is characterized by marked shortening of the individual
cells and changes in the angle of microfibrils in the S2 layer. The S3 layer is
frequently absent.
In the tension wood there is again a shortening of cell length but, in this case
the three S layers of wall may be replaced by a so called
G (gelationus) layer, which is unlignified. Alternatively S3 may be absent or S2
and S3 may be absent.
Consequently reaction wood is more dense and more brittle than normal
wood and unsuitable for use in construction

211. • Certain depressions or cavities found in the secondary wall.
• Primary wall are also have depressions here and there. Which
correspond to what is called primary pit fields.
• When the secondary materials are added, the primary pit fields are
not covered and these regions later form pits. Plasmodesmata extend
through these.
• A pit consists of two opposing thin areas in the cell walls. The portions
of the cell wall separating the two unthickened areas is called closing
membrane or pit membrane.
• This comprises middle lamella and a thin layer of the primary wall.
• The opening of the pit is called pit aperture and the cavity forming
between the pit membrane and the aperture is the pit cavity.
PITS

212. PITS

213. Types of pits
• 1. Simple pits:
• The secondary wall does not arch over the pit
cavity in these depressions.
• Diameter of the pit aperture is the same as that of
the pit cavity and the closing membrane.
• In stone cells the pit cavities may branch and such
simple pits are called ramiform pits.

215. • 2 Bordered pits:
• . The pit cavity is enclosed by overarching portions of secondary wall
which limit the diameter of the pit aperture.
• The pit is called bordered because in surface view a ring of secondary
wall forms a border around the aperture.
• Diameter of the pit aperture is smaller than that of the pit cavity and
the closing membrane.
• The closing membrane of bordered pits, especially of gymnosperms
has a thickened central part called the torus surrounded by a thin
marginal area.
• The diameter of the torus is always greater than that of the aperture.
Hence, by its adjustments, the torus can open or close the pit.

216. Simple and Bordered pits

217. Torus

218. Pit Pair
• The bordered pits in tracheids can function as valves, which controls the
flow of water.
• In some dicots vestured pits occur. Such pits contain small outgrowths from
the pit wall which project into the pit cavity.
• These vestures consist of accumulations of cytoplasmic materials.
• Usually the pits are developed in pairs each of which is constituted of two
pits lying opposite to each other of the contiguous cells.
• A pit pair has two pit cavities, two pit apertures and one pit membrane.
• If two bordered pits make a pair, it is called a bordered pit pair and two
simple pits constitute a simple pit pair.
• If a bordered pit and a simple pit form a pair, it is called a half-bordered pit
pair.
• Sometimes a pit occurs opposite to an intercellular space. Such a pit is called
a blind pit.
• If two or more pits are developed opposite to one large pit, such an
arrangement is called unilateral compound pitting

223. Desmotubule

224. Plasmodesmata
• Threads of cytoplasm with which the protoplast of one cell remains
connected to the protoplast of other.
• Maintains protoplasmic continuity.
• All the primary pit fields on the wall are traversed by plasmodesmata.
• Formed during cytokinesis, apparently at sites in the cell plate where
strands of ER-present prevent fusion of vesicles.
• Secondary plasmodesmata can form between more mature cells
which are not undergone division, which have undergone post genital
fusion, or between the haustoria of certain parasites and the host
cells. In this case, wall degrading enzymes must be present.

226. ANATOMY
TAXONOMY

227. 1. Identification and Description:
•Distinctive Structural Features: Plant anatomy helps in the identification and
description of plant species based on unique structural characteristics.
Features such as leaf arrangement, shape, venation patterns, types of stomata,
trichomes, presence of specialized tissues, and the structure of reproductive
organs (flowers, fruits, seeds) are crucial for distinguishing and characterizing
different plant taxa.
2. Taxonomic Classification:
•Species Discrimination: Anatomical details aid in differentiating between
species, genera, families, and higher taxonomic ranks. Taxonomists use specific
anatomical characteristics to group plants into taxonomic categories.
•Use of Diagnostic Characters: Unique anatomical traits are employed as
diagnostic characters for various plant groups, contributing to their
classification within the broader taxonomic system.

228. 3. Evolutionary Relationships:
•Phylogenetic Inference: Comparative plant anatomy is instrumental in
elucidating evolutionary relationships among different plant species.
Homologous structures (inherited from a common ancestor) and
analogous structures (evolved independently but serving similar
functions) help in inferring the evolutionary history of plants and
constructing phylogenetic trees.
4. Adapting to Modern Techniques:
•Integration with Molecular Data: While plant anatomy provides
fundamental information, it is often combined with molecular data and
genetic studies for a more comprehensive understanding of evolutionary
relationships. This integration helps to refine and validate taxonomic
classifications.

229. 5. Palaeobotany and Fossil Analysis:
•Plant anatomy is crucial in palaeobotany, the study of ancient plant
fossils. Anatomical features of fossilized plant structures are studied to
understand the evolutionary history and relationships between extinct
and existing plant groups

230. ANOMALOUS
SECONDARY GROWTH

231. Generally due to
• Modification of the common type of vascular cambium
• Unequal activity of the vascular cambium
• Successive cambia.
• Anomalous placement of vascular cambium
• Discontinuous, unidirectional and bidirectional activity
of cambium.

232. In storage roots to produce the required tissue to store the food, adaptive type
of anomalous secondary growth takes place; e.g., Beta vulgaris, Daucus carota
etc. The young stem has a wavy outline with alternate ridges and furrows

233. Anomalous secondary growth in storage roots

234. Beet root
Abnormal activity of cambium
Abnormal position of cambium
Cambial ring formed from pericycle
Produces secondary xylem and parenchyma in alternate groups
To outer side, it produces secondary phloem outer to secondary xylem
and parenchyma outer to inner parenchyma.
Results in a ring of conjoint collateral vascular bundles embedded in
parenchyma cells
Parenchyma function as storage regions
Cambium cease its activity after some time and accessary cambium arises
from phloem parenchyma cells or outer ring of pericycle.
With passage of time, more proliferative parenchyma cells are formed.

235. Sweet potato

236. Formation of cambium is normal as in any dicot
Later it behave abnormally
Produces separate strands of secondary xylem and secondary phloem
separated by parenchyma
Each strand of xylem get embedded by an individual ring of secondary
cambium
These cambia originate from parenchyma that surrounds secondary
xylem
Secondary cambium behave abnormally
Produces few elements of secondary xylem internally and few sieve
elements and laticifers externally