Release of microspores, Biology

Assignment Help:

Release of Microspores

Up to the tetrad stage, there is no cellulosic wall around the microspores. As you will come to know in the next unit, a unique feature of the pollen is the ornamentation of the pollen wall. This ornamentation is seen on the outer layer of the pollen or exine. The exine is made up of sporopollenin, one of the most resistant (to physical and biological decomposition) substances known in the biological world. Pollen grains of prehistoric plants are well preserved as fossils because of their exine. There is enormous variation in the ornamentation of the exine, and it is a characteristic feature of a given species. Often pollen grains of particular group of plants can be identified on the basis of their exine pattern.

The blue print of exine, termed primexine is laid down below the callose wall after the basic structural features of the exine including the position of the germ pore (a region in the pollen wall through which the pollen tube emerges) are demarcated in the primexine. This important morphogenetic event takes place while the microspores are still enclosed in the callose wall, in groups of four or at the tetrad stage. Thus, the pattern of mature exine is laid down before the spores are set free. The callose wall seems to play an important role in the orderly deposition of primexine. You will read more about this in the next unit. After the development of exine, the callose wall dissolves. The enzyme callase which dissolves the callose wall is produced by the surrounding tapetal cell pen plasmodium. The development of the male gametophyte begins after the liberation of individual microspores.


Related Discussions:- Release of microspores

Animals of the littoral zone, Animals of the littoral zone Animals of...

Animals of the littoral zone Animals of this zone may be herbivores, carnivores or detritus feeders and are as diverse as plants. Many of them such as rotifers, protozoans, i

Explain thalamus and hypothalamus, Q. Explain Thalamus and Hypothalamus ? ...

Q. Explain Thalamus and Hypothalamus ? Thalamus and Hypothalamus: The thalamus is situated in the forebrain at the uppermost part of the diencephalon (posterior part of the for

What is a biome, What is a biome? A biome is the prevailing ecosystem c...

What is a biome? A biome is the prevailing ecosystem constituted by similar abiotic and biotic factors present in one or more regions of the planet.

Crisis due to deforestation, Crisis due to Deforestation Due to conti...

Crisis due to Deforestation Due to continuing deforestation we are faced with a major ecological and socio-economic crisis. To reverse this trend of deforestation a National

How do grasslands differ from savannas, How do grasslands differ from Savan...

How do grasslands differ from Savannas? Name the two main categories of plant forms that dominate the desert vegetation.

Observation of bumpus, An interesting observation made by an American biolo...

An interesting observation made by an American biologist H.C. Bumpus (1899) provides a good explanation for normalising selection. Bumpus collected some 136 injured house sparrows

Zoology, general characteristics of phylum chordata

general characteristics of phylum chordata

Protozoa, what are disadvantage of protozoa

what are disadvantage of protozoa

Amino acids and peptide bonds-protein structure, Amino Acids and Peptide Bo...

Amino Acids and Peptide Bonds, Protein Structure - The graduate can construct models of the structure and function of amino acids and peptide bonds, predict ionization of an amin

Phylum protozoa, Classification of the phylum protozoa

Classification of the phylum protozoa

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd