The document discusses the shoot apical meristem, which generates the aerial organs of plants. It has three layers (L1, L2, L3) that contribute to stem and organ formation. The meristem also contains zones - a central zone of stem cells, a peripheral zone where leaves form, and a rib zone that forms the stem. The meristem maintains a population of stem cells and generates organs through coordinated cell division and differentiation.

1. Developmental Biology
Presentation by
Karthi.M
Topic: Organization of shoot and root apical meristem

2. Paleozoic Era
• The Paleozoic Era started 542 million years ago ,ended 251 million years ago
The era is usually broken down even further to six main periods.
• Cambrian: 542 to 488.3 million years ago
• Ordovician: 488.3 to 443.7 million years ago
• Silurian: 443.7 to 416 million years ago
• Devonian: 416 to 359.2 million years ago
• Carboniferous: 359.2 to 299 million years ago
• Permian: 299 to 251 million years ago

3. Introduction
• It is almost a point of definition for the algae that they are aquatic plants,
although some of them have invaded moist habitats on land.
• The useful fossil record begins with the Cambrian period of the Paleozoic
Era, over 500,000,000 years ago.
• Cambrian record, so far as plants are concerned, consists entirely of a wide
variety of algae and bacteria.
• In fact, the early Paleozoic is often referred to as the Age of Algae and
Invertebrates.
• But fossils from the Silurian period, beginning about 360,000,000 years
ago
• This include primitive land plants and it is probable that their first
appearance was in the preceding period, the Ordovician.
• When these first colonists left the waters to invade the more difficult.

4. …………
• But more varied habitats on land, the algae remained the dominant
members of the earth’s flora.
• But soon the land dwellers surpassed their aquatic progenitors.
• One of the crucial problem had to e solved before plants could invade
the land was the protection of the zygote against drying.
• In all land plants, this is accomplished, with important differences in
the details, by the retention of the zygote and the developing embryo
with in the sex organs of the maternal plants.
• For this reason, the land plants are known collectively as the
subkingdom Embryophyta.

5. The Meaning Of Evolution
 Is the process of change in living populations.
 The study of evolution – fundamentals branches of
biology – Evolutionary biology
 It is the study of biology as a historical science, or the
study of living systems as they change through time
 All living systems are products of evolutionary history

6. Evolution Of The Plant Kingdom
 Plants and their classification
 Algae
 Bryophytes
 Vascular Land Plants
 Plants with Naked Seeds
 Flowering Plants

7. Phylogeny Of The Eukaryotes
Amoeboid and flagellated protozoans
Origin of chloroplasts
Red algae
(Rhodophyta)
chrysophyta
Brown algae(Phaeophyta)
Pyrrophyta
Euglenophyta
Xanthophyta
Green algae(chlorophyta)
Mosses and
liverworts(bryophyte)
VASCULAR LAND
PLANTS(Tracheophyta)
Ciliated protozoans (ciliate)
TRUE
FUNGI(Eumycota)
Slime molds
Cnidaria
OTHER MULTICELLULAR
ANIMALS
Mesozoa
Sponges(Porifera)

8. Plants and their classification
• International Rules of Botanical Nomenclature specify that the plant
kingdom is to be separated into ‘divisions’ rather than ‘phyla’.
• Eichler (1883) and his contemporaries divided the entire plant
kingdom into four divisions, as follows:
• The kingdom plantae contains only those eukaryotic organisms possessing
chlorophyll pigments, plastids and also usually a cell wall .
• The ancestry of the plants is still an unsettled question

9. • Division Thallophyta: plants without embryos.
• class Algae: Thallophytes containing chlorophyll
• class fungi: Thallophytes without chlorophyll
• Division Bryophyta: plants with embryos but without vascular tissues: mosses and
their relatives
• Division Pteridophyta: vascular plants without seeds: ferns, horsetails, club mosses
and their relatives.
• Division Spermatophyta: seed plants
• class Gymnospermae: seed plants without flowers, the seed being naked
rather than enclosed in an ovary
• class Angiospermae: flowering plants, with the seeds protected in an ovary.

10. ………..
• The embryophyta include the traditional divisions Bryophyta, Pteridophyta and
spermatophyte.
• Klein and Cronquist (1967) have re-examined the classification of thallophytes and
• Cronquist,Takhtajan and Zimmerman (1966) have similarly re-examined the
classification of the embryophytes.
Division Pyrrophyta: dinoflagellates and cryptomonads
Division Chrysophyta: golden-brown algae and diatoms
Division Euglenophyta: euglena and its relatives
Division Rhodophyta: red algae
Division Phaeophyta: brown algae
Division Chlorophyta: green algae Euglena
Brown algae
Red algae
Diatoms

11. Bryophytes
• The phylum bryophyta is a relatively small group comprising the mosses, the
liverworts and the hornworts.
• These are the amphibians of the plant world.
• They have met only minimum requirements of adaptation to the terrestrial
environment.
• They are restricted to wet habitats and all of them require water for reproduction
• The embryos – multicellular-retained with female sex organs- it protecting them
from drying.

12. • All of the aerial parts of the plant are covered by a waxy cuticle
which protects the plant against drying

13. Phylogeny of the bryophytes
• Bryophytes of the many characters which they share with the
green algae.
• It is highly probable that the bryophytes were derived from an
ancestor among the green algae.
• One group of bryophytes, the hornworts, suggests relationships to
higher plants.
• While the gametophyte is a small, simple thallus, the sporophyte is
larger
• It is well supplied with chlorophyll
• But still depends upon the gametophyte for absorption of water
and minerals from the substrate

14. • The capsule has a central axis of elongate cells which suggests vascular tissue.
• The epidermis has stomata like those on the leaves of vascular plants.
• With such an array of traits suggesting those of vascular plants, it is difficult to
avoid the inference.
• that modern hornworts may be but little changed from an ancestral stock by which
bryophytes gave rise to vascular plants.
• This inference appears to misleading, for vascular plants appear in the fossil record
in the SILURIAN.
• The bryophytes appear more than 100,000,000 years later.
• Obviously if these data are correct, bryophytes cannot be ancestral to tracheophytes.
• So the weight of opinion among botanists now favors direct origin of the vascular
plants, the phylum Tracheophyta, from a chlorophytan ancestor.

15. The Shoot Apical Meristem
• Shoot system: above ground structures of
plants, leaves, buds, stems, flowers and fruits
• Nodes: where leaves are located
• Internodes: the spaces between nodes
• Buds: terminal, lateral, accessory
• Terminal Buds: located at the tip of the stem
• Terminal bud scar: indicate the amount of
growth over the past year
• Lateral Bud: found at the side of a stem
• Accessory Buds: found in pairs and are located
beside terminal or lateral buds

17. meristems
• Tissues of the stem capable of cell division
• Apical Meristem: found at the tip of the stem
• Lateral Meristem: found surrounding the stem
• Growth at the apical meristem is called as primary growth.
• The 3 types of tissues, apical meristem will be connect.
• Protoderm: will eventually make the epidermis of the stem.
• This is the outer protective covering of the stem.
• Ground meristem: will make the different types of ground tissue.
Parenchyma: stores water and food
Collenchyma: supports young stems and roots
Sclerenchyma: hard protection
• Procambium: will make the vascular tissue. It consist of both

19. The Shoot Apical Meristem Contains Different Functional Zones and Layers
• It consists of different functional regions that can be distinguished by the orientation of
the cell division planes and by cell size and activity
• The angiosperm vegetative shoot apical meristem usually has a highly stratified
appearance, typically with three distinct layers of cells
• These layers are designated L1, L2, and L3, where L1 is the outermost layer
• Cell divisions are anticlinal in the L1 and L2 layers; that is, the new cell wall separating
the daughter cells is oriented at right angles to the meristem surface
• Cell divisions tend to be less regularly oriented in the L3 layer
• Each layer has its own stem cells, and all three layers contribute to the formation of the
stem and lateral organs
• Active apical meristems also have an organizational pattern called cytohistological
zonation.
• Each zone is composed of cells that may be distinguished not only on the basis of their
division planes, but also by differences in size and by degrees of vacuolation

20. • The shoot apical
meristem generates the
aerial organs of the
plant.
(A) This longitudinal
section through the center
of the shoot apex of Coleus
blumei
• Shows the layered
appearance of the shoot
apical meristem
• Most cell divisions are
anticlinal in the outer
L1 and L2 layers, while
the planes of cell
divisions are more
randomly oriented in
the L3 layer.
• The outermost (L1)
layer generates the
shoot epidermis; the L2
and L3 layers generate
internal tissues.
(B) The shoot apical meristem also has cytohistological zones, which
represent regions with different identities and functions
• The central zone contains the stem cells, which divide slowly but are
the ultimate source of the tissues that make up the plant body
• The peripheral zone, in which cells divide rapidly, surrounds the
central zone and produces the leaf primordia
(A ©J.N. A. Lott/Biological Photo Service.).

21. • The center of an active meristem contains a cluster of relatively large, highly
vacuolate cells called the central zone.
• The central zone is somewhat comparable to the quiescent center of root
meristems.
• A doughnut-shaped region of smaller cells, called the peripheral zone, flanks the
central zone. A rib zone lies underneath the central cell zone and gives rise to the
internal tissues of the stem.
• These different zones most likely represent different developmental domains. The
peripheral zone is the region in which the first cell divisions leading to the
formation of leaf primordia will occur.
• The rib zone contributes cells that become the stem. The central zone contains the
pool of stem cells, some fraction of which remains uncommitted, while others
replenish the rib and peripheral zone populations (Bowman and Eshed 2000).

22. • The underground part of the plant is called
root system.
• The underground main axis of the plant body
is called root.
• It is the prolongation of radicle of the embryo.
• It is positively geotropic or negatively phototropic.
• It is not differentiated into nodes and internodes.
• It is non-chlorophyllous or brown coloured.
• It does not possess leaves, buds, flowers and fruits.
• Lateral roots are produced from main axis in
acropetal succession.
• Lateral roots are formed from inner region of the
• main axis (pericycle).
• So these are called ENDOGENOUS ORGANS.
Root System

23. • The small hair like outgrowth present on the tips of lateral roots and main axis
are called ROOT HAIRS.
• Root hairs are exogenous organs.
• Root hairs are found in mesophytes and xerophytes and absent in hydrophytes.
• The protective layer present around the root tip is called ROOT CAP.
• Root cap is made up of a dead tissue called CALYPTROGEN. Hence it is also called
CALYPTRA.
• It is also well developed in mesophytes and xerophytes, absent in hydrophytes.
• In free floating hydrophytes root pockets are present.

24. Types of root
system
• Tap root system
The central main axis is called tap root.
Tap root is formed by the prolongation of radicle of the embryo
Lateral roots are produced obliquely in all directions from tap root
in acropetal succession.
It is most commonly found in DICOTYLEDONS.
• Fibrous root system or adventitious root system
A bunch of new roots are produced from the base of the stem as fibres. So
these roots are called fibrous roots and the root system is called fibrous
root system.
In this, roots are not formed from radicle. So these are aslo called
adventitious roots, and the root system is called adventitious root system.
It is most commonly found in MONOCOTYLEDONS.
In angiosperms two types of
root systems are present.
They are:
1.Tap root system
2.Fibrous root system or
Adventitious root system

25. The Root Tip Has Four
Developmental Zones

26. Meristematic zone :
• lies just under the root cap
• quarter of a millimetre long
• root meristem generates only one
organ, the primary root
• It produces no lateral appendages.

27. Elongation zone:
• site of rapid and extensive cell
elongation
• Although some cells may continue
to divide while they elongate within
this zone
• the rate of division decreases
progressively to zero with increasing
distance from the meristem.

28. Maturation zone:
• cells acquire their differentiated characteristics
• Cells enter the maturation zone after division and elongation have
ceased
• Differentiation may begin much earlier
• but cells do not achieve the mature state until they reach this zone
• radial pattern of differentiated tissues becomes obvious in the
maturation zone

29. • Root Apical Meristems Contain Several Types of Stem Cells
• The patterns of cellular organization found in the root meristems of seed
plants
• It is substantially different from those observed in more primitive
vascular plants
• All seed plants have several stem cells
• Instead of the single stem cell found in Plants such as the water fern
Azolla.
• However, they are similar to Azolla

30. The Arabidopsis root apical meristem has the following structure:
• quiescent center is composed of a group of four cells
• Also known as the center cells in the Arabidopsis root meristem
• quiescent-center cells in the Arabidopsis root usually do not divide after
embryogenesis
cortical–endodermal stem cells:
• It form a ring of cells that surround the quiescent center.
• These stem cells generate the cortical and endodermal layers
• They undergo one anticlinal division (i.e., perpendicular to the
longitudinal axis)
• these daughters divide periclinally (i.e., parallel to the longitudinal axis)
to establish the files that become the cortex and the endodermis

31. • each of which constitutes only one cell layer in the Arabidopsis root
columella stem cells :
• the cells immediately above (apical to) the central cells
• They divide anticlinally and periclinally to generate a sector of the
rootcap known as the columella
root cap–epidermal stem cells:
• are in the same tier as the columella stem cells but form a ring
surrounding them
• Anticlinal divisions of the root cap–epidermal stem cells generate the
epidermal cell layer
• Periclinal divisions of the same stem cells, followed by subsequent
anticlinal divisions of the derivatives, produce the lateral root cap

32. stele stem cells:
• Are a tier of cells just behind the quiescent-center cells
• These cells generate the pericycle and vascular tissues
• The stem cells, together with their immediate derivatives in the apical meristem, are called the
promeristem
(From Schiefelbein et al.1997, courtesy of J. Schiefelbein, © the American Society of Plant Biologists, reprinted with permission.)

33. Reference
• 1.Book Title:Plant Physiology:Zeiger and Taiz, Edition-3rd
2002,Publishers:sinauer associates Massachusetts, Page no:Chapter
16:340,350-352,354,356.
• 2.http://www.els.net/WileyCDA/ElsArticle/refId-a0020121.html
• 3.shoot system review:
https://www.youtube.com/watch?v=pSMwZJS9JfE
• 4.Root system review:
https://www.youtube.com/watch?v=pSMwZJS9JfE