The exine layer, Biology

Assignment Help:

The Exine Layer

It consists of two layers, inner (nexine) which is continuous and an outer (sexine) the sculptured one. The outer layer has ornamentations comprising rod-like bacula showing terminal expansion which sometimes fuses to form a roof like tectum perforated by micropores. During pollen development, the tapetum releases a mixture called tryphine, consisting of carotenoid lipid droplets and fibrogranular proteins into the thecal cavity. These fibrogranular proteins are enclosed in membrane bound cisternae. In tectate pollen, the released substances of tapetum become incorporated on the surface of pollen grains where cisternae membrane ruptures and protein released through micropores enter the tectum and accumulate in the interspaces of bacula.

Pollenkitt is the pigmented lipid fraction left on the surface of the tectum. Unlike intine, the exine held proteins exhibit only one enzymatic activity. The hydration of pollen is described to be stimulatory in releasing the proteins held in the pollen wall layers. The calculated time taken by the exine held proteins of sporophytic origin to pass out is 30 seconds while the intine of gametophytic origin takes a few minutes. This time difference in the protein release has made it easy to collect both samples separately. In SSI systems therefore the rejection reaction is faster than in GSI system.

 


Related Discussions:- The exine layer

What is working memory, Q. What is Working Memory? Working Memory: It h...

Q. What is Working Memory? Working Memory: It has often been suggested that memory does not always work in three stage sequence and the model of memory system comprising of sen

Describe what types of results describe hypothesis, Why did giraffes develo...

Why did giraffes develop long necks? 1) Describe an experiment to test this hypothesis. Be explicit about the methods you will use, the setting, the time that the experiment wil

Explain electron transport chain, Explain Electron transport chain El...

Explain Electron transport chain Electron transport chain :Transport of high-energy electrons through a series of carriers in mitochondria.

Cellulose is not consumed by human beings but some animals, Since Some anim...

Since Some animals, particularly ruminants and termites, can digest cellulose with the help ofsymbiotic micro-organisms that live in their guts. Humans can digest cellulose to some

Bergmann's method of cell plating, Bergmann's Method of Cell Plating I...

Bergmann's Method of Cell Plating In this method free cells are suspended in a liquid medium at a density twice the finally desired plating density. Melted agar containing med

Human impact on environment, questions and answers on human impacts on envi...

questions and answers on human impacts on environment

What are venous vessels and veins, What are venous vessels, veins and venul...

What are venous vessels, veins and venules? Venous vessels are each blood vessel that carries blood from the tissues to the heart. Veins and venules are venous vessels. Venules

How to decreases the rate limiting, When the product of a metabolic pathway...

When the product of a metabolic pathway decreases the rate limiting earlier in the pathway it is called?

Briefly explain about phase of the plasmodium life cycle, Q. To which phase...

Q. To which phase of the plasmodium life cycle do the typical chills and fever of malaria correspond? The typical fever and chills episodes of malaria correspond to the phase w

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