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

Physiological condition for growth, PHYSIOLOGICAL CONDITION FOR GROWTH - ...

PHYSIOLOGICAL CONDITION FOR GROWTH - It depends on anabolism and cetabolism. If anabolism is more positive growth. If both are balanced growth is zero. If cetabolism is more

Explain the bases, The bases in DNA have carbon-nitrogen ring structures; d...

The bases in DNA have carbon-nitrogen ring structures; due to the nitrogen atoms they are known as nitrogenous bases. There are two parts of ring structure. Adenine and guanine are

Obligate anaerobic beings and facultative anaerobic beings, Q. What is the ...

Q. What is the difference between obligate anaerobic beings and facultative anaerobic beings? Obligate anaerobic beings are those that cannot survive when oxygen is present. So

Volvox Colonial Existence, Necessity of interdependence of Volvox organisms...

Necessity of interdependence of Volvox organisms in the colonial existence

What is bioremediation, What is bioremediation? Bioremediation is the u...

What is bioremediation? Bioremediation is the use of microorganisms, as bacteria, protists and fungi, to degrade noxious substances turning them into non toxic or less toxic su

What are the genotypes of a man with normal pigment, 1. A man with normal p...

1. A man with normal pigment, whose father was an albino, marries an albino. What chance is there that their first child will be an albino? 2. A man with normal pigment marries

What is the structural depiction of a carboxyl group, Q. What is the struct...

Q. What is the structural depiction of a carboxyl group? Carboxyl groups have a carbon attached to one hydroxyl group by a simple bond and one oxygen by a double bond. The othe

Hydrocarbons do not readily evaporate at room temperature, The fact that so...

The fact that some pure solutions of hydrocarbons do not readily evaporate at room temperature is a result of- Select one: a. London dispersion forces. b. The hydrophobic

Concentration of noradrenergic cell bodies, The major concentration of nora...

The major concentration of noradrenergic (and adrenergic) cell bodies is found in locus ceruleus a nucleus in the reticular formation. The axons of these neurons project through t

What is the approximate number of amino acids, What would be the approximat...

What would be the approximate number of amino acids of a protein with a mass of 203 kd? Assume an average molecular weight for amino acids of 110 grams/mol.

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