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

Determination of neural ectoderm by induction, Determination of Neural Ecto...

Determination of Neural Ectoderm by Induction Earlier you know that the dorsal mesoderm induces the ectoderm to differentiate into neural tissue. Spemann and his co-workers co

Respiration, explain why expired air contain co2

explain why expired air contain co2

What is oxidative phosphorylation, What is oxidative phosphorylation? O...

What is oxidative phosphorylation? Oxidative phosphorylation is  the process by which ADP is phosphorylated by Pi  to ATP  in  the  respiratory chain.

Placement of implant with improper axial angulation, Placement of implant w...

Placement of implant with improper axial angulation Surgical placement of the implant improperly can lead to a prosthetic rehabilitation that compromises esthetics and the dist

Why biologists use comparative method, Normal 0 false false ...

Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

Cell cycle, What can stop a normal cell from growing?

What can stop a normal cell from growing?

Fructose-1, Fructose-1,6-bisphosphate  and Fructose-6-phosphate : The  conv...

Fructose-1,6-bisphosphate  and Fructose-6-phosphate : The  conversion of  fructose-1,6- bisphosphate  to fructose-6-phosphate is  catalysed by fluctose-1,6-bisphosphatase  which  i

What is increase in the second messenger, When glucagon binds its receptor ...

When glucagon binds its receptor there is an increase in the second messenger, cAMP. cAMP levels can be decrease by which of the following enzymes? -adenylate cyclase -PDK1

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