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

Concerning the body temperature how reptilia classify, Q. Concerning the ma...

Q. Concerning the maintenance of body temperature how do beings of the class Reptilia classify? Like amphibians and fishes, beings of the class Reptilia are heterothermic anima

Invertibreats, genral charecter and classificatin of porifera

genral charecter and classificatin of porifera

Which heavy metals cause toxic pollution, Besides mercury which other heavy...

Besides mercury which other heavy metals cause toxic pollution? Examples of other heavy metals that cause toxic pollution are lead, cadmium and chromium.

How gender affects the bmr, How Gender affects the bmr? We have already...

How Gender affects the bmr? We have already emphasized earlier that sex difference in metabolic rates are primarily attributable to difference in body size and composition. Wom

Are bacteria the only prokaryotic beings, Q Are bacteria the only prokaryot...

Q Are bacteria the only prokaryotic beings? Prokaryotic beings are classified into two big groups: bacteria and archaebacteria (this last also known as eubacteria). Compared

Regernation, Give ditail account on regernation in invertebrates and verta...

Give ditail account on regernation in invertebrates and vertabrites

Phylem protozoa, how does these phylem parasites????

how does these phylem parasites????

Scientific activity, describe the factors which decide the broad area of sc...

describe the factors which decide the broad area of scientific activity?

Illustrate the functioning of comprehensive model, Illustrate the functioni...

Illustrate the functioning of comprehensive model 1) Provide continuity in understanding developmental progress, or lack thereof, in those disorders that affect neurological de

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