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

Write two functions of proteins in biological system, Write two functions o...

Write two functions of proteins in biological systems. The important functions of proteins in biological systems are as follows: enzymes membrane carriers anti

What functions regulates by hypothalamus, Q. What functions regulates by hy...

Q. What functions regulates by hypothalamus? HYPOTHALAMUS - Main visceral control center of the body (yet small in size). Central to virtually all homeostatic control . Th

Development of pollen in cyperaceae, Development of Pollen in Cyperaceae ...

Development of Pollen in Cyperaceae In all members of the Cyperaceae out of the four nuclei formed after meiosis, only one functions, the others degenerate. The functional nuc

What are cerebrovascular accidents, Q. What are cerebrovascular accidents? ...

Q. What are cerebrovascular accidents? The Cerebrovascular accident (CVA), as well known as stroke, is the generic name given to infarction (tissue and cellular death by hypoxi

Symptoms of oesophagitis, Q. Symptoms of oesophagitis? The symptoms of ...

Q. Symptoms of oesophagitis? The symptoms of oesophagitis include heartburn or pyrosis, iron-deficiency anaemia due to chronic tissue bleeding, aspiration, which may cause coug

What is the adnexal organ of the digestive system, Q. What is the adnexal o...

Q. What is the adnexal organ of the digestive system in which bile is stored? How does this organ react to the ingestion of fat rich food? Bile is concentrated and stored in th

Investigations of food borne diseases, Q. Investigations of food borne dise...

Q. Investigations of food borne diseases? Most important aspect of food borne disease would be to collect the right sample. Now, what procedure to follow while collecting th

Define larval stage of taenia cystcercus, Define Larval Stage of Taenia Cys...

Define Larval Stage of Taenia Cystcercus? The pork tapeworn (T: solium) and beef tapeworn (T : saginata , which are endoparasites of humans who are the final hosts

Zoology , canal system in porifera

canal system in porifera

What are clotting factors, What are clotting factors? Clotting factors ...

What are clotting factors? Clotting factors are substances (enzymes, coenzymes, reagents) essential for the clotting stages to happen. Besides those triggering factors and reag

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