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

Explain the confirmed test - most probable number test, Explain the Confirm...

Explain the Confirmed Test - Most Probable Number Test? Confirmed test is carried out to rule out the possibility of any positive presumptive test because of the presence of no

What is meant by bioassay, What is meant by bioassay? Name the two bio...

What is meant by bioassay? Name the two bioassays that are used to determine auxin activity in plants.

What are the antigen-presenting cells of the immune system, What are the an...

What are the antigen-presenting cells of the immune system? The antigen-presenting cells of the immune system, also called as APC cells, are cells that do phagocytosis and dige

What do you mean by primary visual and auditory cortex, Q. What do you mean...

Q. What do you mean by Primary Visual and Auditory Cortex? Primary Visual Cortex - in posterior aspects of occipital lobes.  Receives visual information from optic nerve (crani

Assortment, Assortment is a method in which the meiosis produces new combi...

Assortment is a method in which the meiosis produces new combinations of the genetic information. The paternal and maternal chromosomes line up randomly during the process of syna

Explain the working principle of spectrophotometer, Explain the Working Pri...

Explain the Working Principle of Spectrophotometer? The working principle of spectrophotometer is graphically presented in Figure. Figure: Working princip

How to devise a series of dilutions, A solution was prepared by dissolving ...

A solution was prepared by dissolving 25g NaOH powder in 100 ml water. Using not more than 15 ml water, devise a series of dilutions that will give a concentration of 5mg/ml NaOH.

What is the role of radiographic evaluation, What is the role of radiograph...

What is the role of radiographic evaluation in implant treatment? Radiographic examination is very different with implants than with teeth. Radiographs are frequently used in i

Zoology, characteristics of class mamalias

characteristics of class mamalias

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