Pollen morphology

1. POLLEN GRAINS
Submitted by
Cathy Surya
2nd M.Sc. Botany
St. Teresa’s College, Ernakulam.
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Submitted to
Dr. Chandini V K
Department of Botany
St. Teresa’s College, Ernakulam

2. CONTENTS
• Pollen morphology
• Exine sculpturing
• Pollen kitt
• NPC
• Palynology
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3. POLLEN MORPHOLOGY
• Pollen Units
• Polarity
• Shape
• Size
• Apertures
• Exine sculpturing
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4. POLLEN GRAIN
• Male gametophytes or reproductive cells of a
plant.
• Size – nearly 10 -100nm.
• Shape – Round, oval, disc or bean shaped
sometimes filamentous.
• Texture – From smooth to spiky.
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5. Pollen Units
• The pollen grains do not always remain united as tetrad during
maturity.
• They are dissociated into single pollen grain called monad.
• Sometimes rarer types like dyads (two pollen grains), Octads (eight
pollen grains) and Polyads (many pollen grains) are also observed.
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6. Polarity of Pollen
• Identified at microspore tetrad stage.
• The pole nearest to centre of tetrad – Proximal pole
• The pole farther from the centre of tetrad - Distal pole
Polar axis - Line of connecting the two poles.
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7. POLLEN MORPHOLOGY
• Pollen grains consist of hard outer wall
(exine) and soft inner wall (intine).
• Two nuclei occur in each pollen grain:
• One is tube nucleus
• One is generative nucleus.
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8. POLLEN WALL
• Exine (sporopollenin) is acetolysis resistant.
• Intine (callose) is non resistant to acetolysis.
Sporopollenin (function) –
• For resistance to biodegradation.
• Preserved for long periods during fossilization.
• It is a polymeric substance of carotenoids.
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9. EXINE SCULPTURING
• Four basic substrata seen in exine
Exine
Tectum
Columellae/
baculae
Foot
layer/sole
Endexine
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10. EXINE SCULPTURING
• The exine consist of two layers outer sexine (sculptured layer) and inner
nexine (non sculptured layer).
• Sexine containining roof like outer layer called tectum.
• Upright rod like elements on the inner layer is Columellae or baculae.
• Nexine – Foot layer and endexine.
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11. EXINE SCULPTURING
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12. The exine is of three types -
1. Tectate : The exine consists of nexine, columellae and the tectum in which the tectum
is continuous and roof-like.
2. Semitectate : The exine consists of nexine, columellae and the tectum in which the
tectum is perforated.
3. Intectate or Atectate : The exine consists of nexine and columellae only and the
tectum is absent.
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13. Functions of Exine
• Prevent prolonged exposure to dry air during dispersal and
transmission to female gametophyte.
• Protective against adverse atmospheric conditions, like desiccation
and UV radiation.
• Reservoir function is connected with cavities that are seen in pollen of
many angiosperms.
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14. Pollen Grain Surface Pattern
Psilate
• Completely smooth surface.
• The surface appears as a mat that may have small depressions or pits that
are less than one micron in diameter.
Example: Aconitum, Betula.
Scabrate
• Pollen surface with small isodiametric rough spots.
• Less than 1μm in diameter (shape may vary)
Example : Populus, Urtica
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15. Verrucate
• Rounded projection on the tectum where breadth is greater than length.
• The surface can be round, flat or irregular.
• The diameter is more than 1μm .
Example: Plantago, Fumaria
Gemmate
Sculpturing elements (gemma) higher than
1μm
• Same width as height (constricted base)balloon-like.
• Pollen is intectate.
Example: Juniperus, Linum and some elements
of Nymphaea etc.
CONTINUOUS…
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16. Clavate/Pilate
Club-shaped sculpturing elements (clavae), or rods with knob heads, appearing “lollipop-
like”.
• Height is greater than 1μm.
• Diameter is smaller than its height
(thicker at apex than at base).
• Pollen is intectate.
CONTINUOUS…
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17. Baculate
• Rod-shaped sculpturing elements (bacula)
• Height is greater than width (height greater than
1 μm high)
• Thickness is same from top to bottom.
• Pollen is intectate.
• Example : some of Nympheae.
CONTINUOUS…
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18. Echinate
• Pointed sculpturing elements (echini).
(Can be cylindrical to cone shaped) 1μm or greater in
height.
Example : Malva, Lonicera.
Rugulate
• Elongated sculpturing elements.
• Greater than 1μm long.
• Pattern irregularly arranged.
• Example : Apium, Erodium
CONTINUOUS…
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19. Striate
• Sculpturing elements elongated having ridges and furrows running more or
less parallel.
• Surface may look like a fingerprint.
• This ornamentation can also be said and muri(ridges)
and grooves(space between).
CONTINUOUS…
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20. Reticulate
• Seen as ridges arranged in a network which has gaps (lumina).
• Muri (breadth of ridges) equal to or narrower
than the width of the lumina.
CONTINUOUS…
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21. Foveolate
• The surface is provided with more or less circular pits.
• 1μm or greater in diameter.
• The distance between two adjacent lumina is larger than their diameter.
Example: Fagopyrum, Tilia.
Frustillate
• The surface is provided with grooves.
• Grooves are irregular on the surface and do not anastomose.
• They may be straight or sinus
• Example : Pteris tripartita
CONTINUOUS…
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22. 22

23. APERTURE
• The weak areas in pollen wall where is thin exine deposition.
• Two different types - Pores and fissures (colpi).
• Fissures- More primitive, they are elongated
with pointed ends.
• Pores – Isodiametric.
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24. APERTURE
• In some pollen grains, the exine around the apertures is either thicker or thinner.
• In pores this border is termed annulus (typical in grass pollen) and in colpi- margo
(e.g. in Hedera helix)
• Pollen grains with pores are porate , with colpi are colpate.
• If both pore and colpus are combined in the same aperture, the pollen grain is
colporate.
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25. Exine Formation
• Involves the deposition of sporopollenin from the surrounding cells of the
tapetum.
Done in many ways
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Tapetal cells possess a highly
active secretory system
containing lipophilic
globules, these contain the
precursors of sporopollenin
these get deposited onto the
surface.
Centripetal accumulation of
sporopollenin onto
previously formed layers.
In seed plants where
sporopollenin accumulates
within a pre-patterned cell
surface glycocalyx referred to
as the primexine

26. • Primexine model-
Pollen wall development – Angiosperms
5. A section of the
primexine is then adapted
to form probaculae.
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1. Meiosis and
tetrad
formation
2. Microspores are
surrounded by a
callose wall.
3. A cellulose primexine forms
between the plasma membrane
and callose wall of each
microspore.
4. Callose wall and primexine are
deposited at the surface of the
microspore through processes
mediated by the plasma membrane.
6. Sporopollenin deposition and
accumulation on probaculae,
then form baculae and the
tectum.
7. The callose wall then degrades and
the developing baculae and tectum
are exposed to the fluid of the locule.
8. Wall formation is
complete when the nexine
and intine layers are
formed and the primexine
disappears.
9. The mature pollen grain is
then coated by tryphine and
pollenkitt, which are
synthesized by the tapetum.

27. Continuous…
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28. • Undulation Model- Takahashi, (1989, 1993, 1995) in Caesalpinia and Lilium.
2. In Lilium the
plasma membrane
assumes a reticulate
pattern which
matches the pattern
of the mature exine.
4. Probaculae are
later formed in
between the plasma
membrane and the
protectum.
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1. Tetrad stage
3. Fibrous threads together
with granules aggregate at
the regions of protuberances
of the plasma membrane and
slowly these aggregates
develop into a smooth
protectum.
5. Callose wall dissolves, thus
releasing the microspores and
further differentiation of the
exine continues.

29. INTINE
• The intine usually starts to develop at the vacuolated stage, beneath the apertures.
• It is a flexible layer made of cellulose and pectin.
• When a pollen is in the germination stage the intine leans toward the exine itself,
comes out from the apertures and winds itself round the germinative duct like an
integument.
• Although the intine does not change colour when treated with iodine and aniline
compounds, it is extremely sensitive to treatment with acids and to boiling.
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30. INTINE
• The intine is sometimes rather thick (Laurus, Canna), and sometimes
so thin that it is practically invisible under a microscope (Lotus).
• It is usually uniformly distributed.
• It is often thicker near apertures (Oncus).
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31. POLLENKITT
• Oily, pigmented and sticky coating on pollen grain.
• Mainly seen in insect pollinating plants.
• It is derived from tapetum (mixture of dissolved carotenoids, piments,
lipids).
• Carotenoids responsible for its yellow or orange colour and contains
some proteins making sticky.
• Acting as insect attractant.
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32. • Honey bees have special body parts where they pack pollen to be
carried back to the hive - called corbiculae or “pollen baskets.”
• Other bee species carry pollen in hairy receptacles called scopae.
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33. Not all pollen is sticky
• The pollen from many wind pollinated plants, such as grass, is much drier and
not nearly so sticky.
• Dry pollen has to be carried in smaller clumps.
• This wastes both time and energy.
• Insect pollinated plants have sticky pollen and lots of pollen.
• The bees benefit from lots of pollen that is easy to carry home.
• In addition, pollenkitt contains lipids, proteins, and phenolic compounds which
are important to honey bee health.
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34. FUNCTIONS
• To hold pollen in the anther until dispersal.
• To facilitate pollen dispersal.
• To protect pollen from water loss.
• To protect pollen from ultra-violet radiation.
• To protect pollen protoplasts from fungi and bacteria.
• To keep together pollen grains during transport.
• To enable adhesion to insect bodies.
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35. NPC
• NPC refers to number (N), position (P) and character (C) of apertures.
• Proposed by Erdtman and Straka (1961)
• According to NPC system each pollen grain has an arithmetic cardinal number consisting
of three digits.
1. First digit reveals the absence or presence of aperture
2. Second one illustrates the position of aperture i.e. distal, proximal, and latitudinal,
meridonial, equatorial etc.
3. Third digit explains the character of an aperture, i.e. circular/oval or elongated, simple
or compound etc
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36. Classification of Aperture Based on Number
• Pollen having apertures are divided into seven groups.
• The groups are mentioned as N1 to N7.
• N1 has one aperture and N2 has two apertures and so on.
• N1 to N7 groups are also referred to respectively as monotreme, ditreme,
tritreme, tetratreme, pentatreme, hexatreme, and polytreme (Greek trema
means hole, opening, aperture)
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37. Classification of Aperture Based on Number
• Pollen grains where apertures are absent are termed as inaperturate
or atreme and they are placed in N0 group.
• Another special group N8—termed anomotreme is created where the
pollen grains and spores have one or several irregular or irregularly
spaced apertures.
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38. Classification of Aperture Based on Position
• There are seven groups of aperture based on position namely –P0 to
P6.
• Pollen grains having P0 group have uncertain or unknown position of
aperture.
• P1 groups of pollen and spores are catatreme.
• Catatreme pollen grains have one aperture that occurs on the
proximal (near centre of tetrad ) part of a grain.
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39. Continuous…
• P2 groups of pollen and spores are anacatatreme (Greek ana = up).
• Anacatatreme pollen and spores have two apertures. Here one aperture is on
the proximal pole and the other is on the distal pole
• P3 groups of pollen and spores are anatreme, i.e. the aperture is distal in
position.
• P4 groups of pollen and spore are zonotreme.
• A zonotreme pollen grain is having apertures on equator or sub-equator.
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40. Continuous…
• P5 groups of pollen and spore are dizonotreme.
• Dizonotreme pollen grains have apertures arranged in two or more zones.
• These apertures occur parallel to equator.
• P6 groups of pollen and spore are pantotreme
• Pantotreme pollen grains have apertures scattered over the whole surface
uniformly.
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41. Classification of Apertures Based on Character
• The character groups of pollen and spore are seven and they are mentioned as C0 to C6.
• C0 groups have apertures whose character cannot be established with certainty.
• C1 groups of pollen and spore have leptoma. It is a thin aperture like region functions
as aperture.
• C2 groups are trichotomocolpate.
• Trichotomocolpate is a three- branched aperture, the branches of which are more than
two times longer than breadth.
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42. Continuous…
• The group C3 has colpate grains.
• The group C4 comprises porate pollen grains.
• The group C5 comprises colporate pollen.
• The group C6 comprises pororate pollen.
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43. Continuous…
• In NPC classification a grain is mentioned in
three-digit number
e.g. Pollen grains having NPC 764 characterizes
those pollen grains that are polytreme
pantoporate.
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44. Palynology
• Study of various aspects of pollen grains and spores.
• Term suggested by Hyde and William (1957).
Subdivided into
Basic Palynology- Deals with pollen and spore morphology, physical and chemical
properties of pollen wall etc
Applied Palynology- Comprises geopalynology, aeropalynology, mellitopalynology,
latropalynology, pharmacopalynology, forensic palynology.
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45. APPLICATIONS AND SYSTEMATICS
• Used in phylogenetic analysis.
• Used in identification of extant plants.
• Used to study about past climate, biogeography etc.
• The morphology of pollen grains forms the basic criteria for identification.
• Pollen data provides information of changes in vegetation, climate, human
disturbance of terrestrial ecosystems.
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46. Palynology in relation to taxonomy
The roles are:
1. Stenopalynous and Eurypalynous Taxon
2. Family Level
3. Generic Level
4. Species Level
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47. Stenopalynous and Eurypalynous Taxon
Stenopalynous
• In many taxon, the type of pollen is characteristic and constant.
e.g.Asclepiadaceae, Cruciferae, Poaceae etc.
Eurypalynous
• The taxon in which the types of pollen may vary in size, aperture, stratification
e.g. Acanthaceae, Rubiaceae, Verbenaceae etc.
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48. Family Level and Generic level
• Based on pollen characters, Podophyllum - pollen grains remain united, has
been removed to a separate family Podophyllaceae. The pollen grains are free
in the other members of Berberidaceae
Generic level
• Pollen Characters have been used in classifying the genera of the Acanthaceae
and the Primulaceae.
• The two genra Phytolacca and Rivinia of the Phytolaccaceae, can be recognized
on the basis of palynological characters. The pollen of Phytolacca is
3-zonocolpate, whereas that of Rivinia is pantocolpate.
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49. Species Level
• The exine pattern has been useful in recognizing different species of Bauhinia. According to
Nair (1974),pollen are psilate in B. acuminata, striate in
B. krugii, spinulate in B. malabarica, reticulate tuberculate in
B. purpurea, reticulate in B. racemosa, and verrucate in B. retusa.
• Pollen size is helpful in distinguishing two species of Malva,
M. rotundifolia (pollen 74- 84 µm) and M. sylvestris (pollen 105-126 µm). 49

50. References
• Pandey S.N, Chadha A, Plant Anatomy and Embryology, Vikas Publishing House, 1996.
• Shivanna K.R, Johri B.M, The Angiosperm Pollen Structure and function, Wiley Eastern
Limited, 1989
• Wang R and Dobritsa A, Exine and Aperture Patterns on the pollen surface:Their
formation and roles in plant reproduction, Department of Molecular Genetics, Ohio
State University, 2018.
• W. Simon, F. Andrew, H.W Charles, J.B David Evolutionary development of the plant
spore and pollen wall ,AoB PLANTS, 2011.
• https://www.biologydiscussion.com/palynology/
• https://www.honeybeesuite.com/
• https://research.fit.edu/
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51. THANK YOU
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