The study of pollen is highly useful in paleoecology. The observation by sem clearly demonstrate that the pollen in. Pollen grains germi nate on the female stigma surface by forming a pollen tube, which emerges through one of the apertures in the pollen grain wall. The generative cell of the gametophyte will divide forming 2 sperm. Pollen formation development of the pollen wall and. The generative wall consists of a finely fibrillar component sandwiched between the 2 unit membranes figs.
To survive this process, pollen grains possess a variety of physiological and structural adaptations. A diverse range of pollen morphologies occurs within the large, paraphyletic legume subfamily caesalpinioideae, especially among earlybranching lineages. Apr 27, 2010 harmomegathy is the characteristic folding of pollen grains to accommodate the decrease in cellular volume due to water loss. The four microspores then form the double wall of the pollen grain within a structure made of callose.
The aperture is simple, occurs on the distal face of the pollen grain, is usually long and narrow, and extends to the ends of the grain plates i, 118. Pollen definition, structure and formation biology dictionary. Pdf morphology of hibiscus rosasinensis pollen grain. Edlund,1 robert swanson, and daphne preuss2 howard hughes medical institute, molecular genetics and cell biology department, university of chicago. Pollen morphology, bee plants, pollen wall, exine structure, spinolous, echinate. Pdf how to describe and illustrate pollen grains researchgate. Apr 27, 2010 upon release from the anther, pollen grains of angiosperm flowers are exposed to a dry environment and dehydrate.
Pollen structure of kelussia odoratisima umbelliferae from iran leila amjad, hamidreza akkafi abstract kelussia odoratissima mozaff. The inner layers are the endospore and exospore, the outer layer, which often peels off. Structure of stamen, anther, pollen sac and pollen grain in. Pollination is the transfer of pollen from a male part of a plant to a female part of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Describe the formation and structure of a pollen grain. Pdf morphology of hibiscus rosasinensis pollen grain from. Pollen morphology and ultrastructure of selected species of. Study of pollen grain, pollen morphology, pollen germination. They vary in size, shape, and surface characteristics depending on the plant species.
Pollen grains are microscopic structures that vary in size and shape. B wall structure of a typical tricolpate tri aperturate pollen grain. Pollen morphology is studied using lm and sem and is important to visualize the general features of a. Cf sem images of pollen grains in their unfolded hydrated and folded states.
Structures within the furrows of some grains are described. Both inner and outer cell wall of pollen grains often have a typical structure that depends on the species. Fine structure of developing pollen 291 borders the intine of the pollen grain. Pollen grains contain several lipidic structures, which play a key role in their development as male gametophytes. Abstract the pollen grains of seed plants are both remarkable and intensively studied structures that have evolved to ensure delivery of the male gametes to the embryo sac during sexual reproduction. Foldable structures and the natural design of pollen grains. Pdf pollen identification using morphological characters. Pollen structure of kelussia odoratisima umbelliferae. Structure, development and function twell major reference works wiley online library. Pollen biology pollen grains consist of a hard outer wall exine and an inner softer wall intine which encloses the cytoplasm with its cells nuclei and organelles. Accompanying the text, but not in a convenient position for comparison with the. Structure of stamen, anther, pollen sac and pollen grain in plants. Stamen in a flower consists of two parts, the long narrow stalk like filament and upper broader knoblike bilobed anther fig. Structure of pollen pollen itself is not the male gamete, but each pollen grain contains vegetative nonreproductive cells only a single cell in most flowering plants but several in other seed plants and a generative reproductive cell containing two nuclei.
The structure of both pteridophyte and bryophyte spores is very similar to pollen. We observe two pollen loculi and four pollen sacs connected by the connective at the centre of which a vascular bundle is. Such a container is an evolutionary adaptation for life out of water because it protects male gametes from adverse atmospheric influence while transferring from anthers to pistils. Of course, in the case that the plant is tetraploid, then the pollen grains will be diploid. The deposition of these walls begins already during meiosis and continues until final maturation of. Species belonging to family astraceae pollen are spinolous spherical in shape. Chemical maps of selected molecular groups in sections of rye pollen grains four examples. A pollen grain contains the male gamete of the angiosperm plant.
Pollen grains are microscopic structures that carry the male reproductive cell of plants. The number and length of stamens vary in different species. Pollen is a powdery substance consisting of pollen grains which are male microgametophytes of seed plants, which produce male gametes sperm cells. Jan 28, 2018 in this video structure of pollen grain is explained in very short. The diagram below illustrates the release of pollen grains from the callose structures. During this process, the callose is digested by callase and the pollen grains are able to grow and complete the formation of the endospore and exospore. Each pollen grain is formed in the male structures of seedbearing plants and is transported by various means to the female structure to facilitate fertilization of the ovules. Pollen structure and function in caesalpinioid legumes. The apertures on the pollen surface provide the main routes for exchange with the environment 3 and serve as exit points for the pollen tube. The outer wall of the pollen grain the exine, sometimes called the pollen. The pollen grain is uninucleate has one nucleus in the beginning. The pollen grain is the carrier of the male gametes or their progenitor cell, in higher plants. They also have variation in symmetry, position and distribution of apertures, exine structure and sculpture of the pollen wall. Perhaps the most striking of these adaptations is the ability of the pollen wall to fold onto itself to prevent further desiccation.
Pollen grains tectate, tectum sculpturing slightly rugulose, longest axis 45 m or larger. A pollen grain is a microscopic body that contains the male reproductive cell of a plant. The pollen occurs in monads of bilaterally symmetrical, heteropolar, monocolpate grains, with the colpus oriented parallel to the long equatorial axis. Pollen, a mass of microspores in a seed plant, usually appearing as a fine dust and varying greatly in shape and structure. The wall of the pollen grain always consists of two layers. The inside of the grain contains cytoplasm along with the tube cell which becomes the pollen tube and the generative cell which releases the sperm nuclei. Transmission electron micrograph showing the point of contact between a pollen grain p and a stigma papillus s, colorized to highlight the pollen. Pmc free article sarker rh, elleman cj, dickinson hg. The apertures on the pollen surface provide the main routes for exchange with the environment 3 and serve as. Pdf biogenesis and function of the lipidic structures of. The study of pollen should encompass all structural and ornamental aspects of the grain.
In this video structure of pollen grain is explained in very short. When the pollen germinates, the pollen tube emerges through one of the apertures pores in the pollen grain wall. Pollen biology encompasses pollen production, its transfer to the stigma or pollination, and details of pollenpistil interaction leading to fertilization and seed set. The tube cell will produce the pollen tube in the megasporangium, the microsporocyte divides by meiosis, producing 4 megaspores. Pollen structure and function in caesalpinioid legumes article pdf available in american journal of botany 1033. Pollinating agents are animals such as insects, birds, and bats. In the nutrient medium, the pollen grain germinates. Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the female cone of coniferous plants. The tube cell enlarges and comes out of the pollen grain through one of the germ pores to form a pollen tube. Pollen identification using morphological characters unpublished.
Pollen grains are microscopic structures that vary in. Pollen grains are male gametophytes or reproductive cells of a flowering plant. Crosssection of the cell wall structure of a pollen grain and a spore. The pollen grains do not remain united at maturity, and are dissociated into single pollen grain called. Pollen structure and morphology struktura i morfologia pylku giuseppe frenguelli department of plant biology, university of perugia, borgo xx giugno 74, 06121, perugia, italy introduction the pollen grain is the male gametophyte in gymnosperms and angiosperms, i. Pollen grains have a hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male cone to the female cone of coniferous plants. Mar 14, 2020 pollen has an extremely long geological history, as it is well preserved in rocks as old as 400 m.
A folding of aperturate pollen grains in response to change in humidity allows a partial dehydration of the cellular material while preventing complete desiccation and death. Springer vienna acalymmate feature describing a dispersal unit of two or more monads enclosed by an exine, which is discontinuous at the junctions between the monads. Viewed through a microscope, a pollen grain hardly looks real. Pollen grain ultrastructure comparative of two species. The origin and genetic control of the synthesis of the two pollen wall layers is different. The exine is developed through the contribution of the early microspore cytoplasm and the inner anther wall cell layer, the tapetum, which plays a dominant role in the synthesis and deposition of sporopollenin on the pollen grain outer surface. We analyzed the hibiscus rosasinensis pollen morphology in three stages. The chemical composition of pollen, the physiological containers that produce the male gametes of seed plants, has been a subject of research of plant physiologists, biochemists,1,2 and lately even materials scientists3,4 for various. Wind pollinated, airborne pollen grains normally range from 10 m to 80 m. Each pollen grain is a minute body, of varying shape and structure, formed in the male structures of seedbearing plants and transported by various means wind, water, insects, etc. For example, the brassica pollen coat can constitute 10 to 15% of the mass of the pollen grain dickinson et al.
Pollen has an extremely long geological history, as it is well preserved in rocks as old as 400 m. Foldable structures and the natural design of pollen. The maps were constructed by plotting the intensities of the respective band as a function of lateral position. Structure, development and function wiley online library. Pollen is a biological structure functioning as a container, in which is housed male gametophyte generation of the angiosperms and gymnosperms.
They also possess a sporopollenin cell wall consisting of several layers. This video just gives an overview for revision purpose only. The diversity in form and structure of pollen grains suggest they have arisen by remarkable processes of adaptation. Learn more about this tiny structure and take a short. The pollen grain of plants belonging to family malvaceae is echinate. The outer wall of the pollen grain the exine, sometimes called the pollen coat. Pollen grain pollen is a fine to coarse powder containing micro gametophytes produce male gametes sperm cells. A route for the transfer of materials through the pollen grain wall.
At the time of liberation, it becomes 2 celled, with a small generative cell and a vegetative cell. Pdf for the description of a pollen grain, a number of features are used. Pollen grains tectate, tectum sculpturing coarsely rugulose. The pollen grains are produced within the anther of the flower. The two celled pollen grains have a longer life span because of their more resistant wall structure, low plasma water content and reduced metabolic activity, whereas the trinucleate pollen grains are shortlived due to their less resistant wall and high moisture content, which can easily be lost by desiccation. Examples are given of the surfaces of various pollen specimens, and a distinction between the submicroscopic structures of corylus and myrica is reported. As we will discover, pollen plays a crucial role in the plant world. Pollen mother cells originate from the sporogenous tissue of the anther which later divide meiotically to form four pollen grains called tetrad. Pdf pollen structure and function in caesalpinioid legumes. This is an exhaustive study of the history and basic principles of pollen morphology, with a key and descriptive classification of the pollen grains of 450 species of the wind pollinated plants of north america. Pollen biology encompasses pollen production, its transfer to the stigma or pollination, and details of pollen pistil interaction leading to fertilization and seed set. Pollen was acetolyzed using the method of erdtman 1969. The pollen wall structure, especially the exine part, is one of the characters used in identification 15.
Species of family myrtaceae pollen are colporate and prolate. The proximal end of the filament is attached to the thalamus or petal of the flower. The different species in families fabaceae has a great morphological diversity. Mature angiosperm pollen grains are unusual vegetative cells that contain within themselves sperm cells, complete with. The elaborate extracellular pollen wall, the exine, is largely formed from acyl lipid and phenylpropanoid precursors, which together form the exceptionally stable biopolymer sporopollenin. Structure of pollen grain definition, examples, diagrams. The deposition of these walls begins already during meiosis and continues until final maturation of the pollen grain. Pollen shape and sexine ornamentation the pollen occurs in monads of bilaterally symmetrical, heteropolar, monocolpate grains, with. Ic, the structure consists of essentially short ca.
In a single unit, each grain contains all the genetic information required to specify an entire haploid plant organism for example, pollen embryoids in tissue culture, or to unite with the female gamete at fertilization and form a diploid zygote and, hence, a new sporophyte. Jul 05, 2017 pollen grains are male gametophytes or reproductive cells of a flowering plant. Pollen and stigma structural features and their roles structural feature proposed functional signi. Control of pollen hydration in brassica requires continued protein synthesis, and glycosylation in necessary for intraspecific incompatibility. Biology practicals class xii r k maliks newton classes. Two carbon replica methods suitable for the study of pollen grain surfaces are briefly described. The structure of the pollen coat also is adapted to different delivery mechanisms. The semithin sections show that the anther of lygeum spartum l. Harmomegathy is the characteristic folding of pollen grains to accommodate the decrease in cellular volume due to water loss. The aim of this project was study the structure of.
These differences include type of aperture, shape and exine ornamentation of pollen grain erdtman, 1952, kosenk, 1992, kuprianova, 1983, maassoumi, 2005. Pollen, a mass of microspores in a seed plant appearing usually as a fine dust. Illustrated pollen terms pictures from paldat are the main source for the illustrations. Insect pollination is correlated with an abundant pollen coat pacini and franchi, 1996. Apr 09, 2004 a route for the transfer of materials through the pollen grain wall. Pollen morphology and ultrastructure of selected species. The partial desiccation of the pollen grain following its release from the anther results in the grain falling into a dormant state that ensures the cellular material survives until the pollen grain reaches the stigma of a flower. Any break in these sequential events affects seed and fruit set.
1162 1619 975 1211 631 1032 388 833 1291 34 32 961 170 1242 365 1067 1502 867 353 355 656 150 1657 1474 1081 86 869 1200 355 295 703 924 814 650 397 522 990