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

Cell with a euploid number of chromosomes, A cell with a euploid number of ...

A cell with a euploid number of chromosomes contains: A.one half of a complete set of chromosomes B.several complete sets of chromosomes C.the correct number of chromosomes D.two c

Tumours of kidney - wilm''s tomour, Tumours of kidney - Wilm's Tomour ...

Tumours of kidney - Wilm's Tomour So  far you have learnt about the disorders in glomerular dysfunctioning, now you will learn about the tumours in kidney the wilm's  tumour.

Cell surface receptors, Hydrophilic and some lipophilic hormones bind to ce...

Hydrophilic and some lipophilic hormones bind to cell surface receptors. These are necessary  membrane  proteins  located  in the plasma  membrane  which  bind  the  signaling  mol

Explain fixed-dose combination of tuberculosis, Fixed-Dose Combinations  ...

Fixed-Dose Combinations  A combination formulation of rifampin, isoniazid and pyrazinamide (Rifater) is approved by the FDA for the initial 2 months of daily anti-tuberculosis

Disposal-lab animals, Disposal : Opaque bags are the recommended for dispo...

Disposal : Opaque bags are the recommended for disposing off carcasses. You should also put freshly dissected animals and tissues into opaque plastic bags, seal them and dispose t

Threshold for an action potential in neuron a, Neuron A is a healthy neuron...

Neuron A is a healthy neuron with all the usual ion channels.  When at rest with a membrane voltage of R millivolts, neuron A produces no action potentials.  The voltage thresh

Explain counter stain - ziehl-neelsen method, Explain Counter Stain - Ziehl...

Explain Counter Stain - Ziehl-Neelsen Method? Methylene blue is used to stain previously decolourized cells. All non acid-fast bacteria de-stained by acid alcohol now absorbs c

How are fishes characterized, Q. Fish identity card. How are fishes charact...

Q. Fish identity card. How are fishes characterized according to examples of representing beings, skin, basic morphology, circulation, nitrogen waste, respiration, thermal control

steps of c-dna creation and mrna, C dna is made from a mature m rna of euk...

C dna is made from a mature m rna of eukaryotic cell with the utilization of enzyme called as reverse transcriptase. Steps in c dna creation 1. m rna is made and purified f

Passage of pollen tube, Passage of Pollen Tube In cotton, the pollen p...

Passage of Pollen Tube In cotton, the pollen produces a tube within an hour which grows on the surface of the stigmatic hairs, and then between the cells of the stigma at the

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