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Pollen morphology, exine sculpturing, pollen kitt,NPC and palynologypptx

The document discusses the morphology and characteristics of pollen grains, detailing their structure, including exine and intine layers, and variation in shapes and sizes. It introduces the NPC classification system for pollen apertures, outlines the roles of palynology in taxonomy and ecological studies, and describes how pollen morphology can aid in the identification of plants at different taxonomic levels. Additionally, it highlights the significance of pollenkitt and the ecological functions of pollen in reproduction and dispersal.

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POLLEN GRAINS Submitted by Cathy Surya 2nd M.Sc. Botany St. Teresa’s College, Ernakulam. 1 Submitted to Dr. Chandini V K Department of Botany St. Teresa’s College, Ernakulam
CONTENTS • Pollen morphology • Exine sculpturing • Pollen kitt • NPC • Palynology 2
POLLEN MORPHOLOGY • Pollen Units • Polarity • Shape • Size • Apertures • Exine sculpturing 3
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. 4
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. 5
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. 6
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. 7
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. 8
EXINE SCULPTURING • Four basic substrata seen in exine Exine Tectum Columellae/ baculae Foot layer/sole Endexine 9
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. 10
EXINE SCULPTURING 11
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. 12
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. 13
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 14
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… 15
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… 16
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… 17
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… 18
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… 19
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… 20
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… 21
22
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. 23
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. 24
Exine Formation • Involves the deposition of sporopollenin from the surrounding cells of the tapetum. Done in many ways 25 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
• Primexine model- Pollen wall development – Angiosperms 5. A section of the primexine is then adapted to form probaculae. 26 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.
Continuous… 27
• 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. 28 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.
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. 29
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). 30
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. 31
• 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. 32
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. 33
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. 34
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 35
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) 36
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. 37
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. 38
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. 39
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. 40
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. 41
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. 42
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. 43
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. 44
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. 45
Palynology in relation to taxonomy The roles are: 1. Stenopalynous and Eurypalynous Taxon 2. Family Level 3. Generic Level 4. Species Level 46
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. 47
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. 48
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
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/ 50
THANK YOU 51