Release of microspores, Biology

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.

Posted Date: 1/23/2013 1:02:19 AM | Location : United States







Related Discussions:- Release of microspores, Assignment Help, Ask Question on Release of microspores, Get Answer, Expert's Help, Release of microspores Discussions

Write discussion on Release of microspores
Your posts are moderated
Related Questions
Q. What are the main available vaccines against poliomyelitis? The vaccines (medicines) used against poliomyelitis are the Sabin vaccine and the Salk vaccine. The Sabin vaccine

Nucellus - Ovule Enclosed within the integuments lies a homogenous mass of tissue which is termed as the nucellus. This is the tissue in which the female gametophyte differen

PHYLUM  NEMATODA (= NEMATHELMINTHES ) Definition and Introduction                                                                             Bilateral  and protostomial

Q. What are taenias? What are the diseases caused by them? The Taenias, as well know as tapeworms, are platyhelminth animals (flatworms). The major diseases caused by taenias a

Explain Associated Mitral Regurgitation and their role in miscellaneous conditions? Normal 0 false false false EN-IN X-NONE X-NONE

Define role of Vitamin A in controlling gene expression? Vitamin A as retinoic acid has widespread effects on the synthesis of a variety of important proteins. These diverse ef

Q. What do you mean by Echinodermata? You will recall that Pliylum Echinodermata includes spiny skinned animals which are exclusively marine (Gr, echinus : spiny; derma: ski

Q. What are some factors that can lead to protein denaturation? Protein denaturation can be caused by temperature variation, pH change, changes in the concentration of surround

what is the biological significance of skeleton