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 are alleles of a gene, What are alleles of a gene? Diploid individ...

What are alleles of a gene? Diploid individuals have paired chromosomes. For instance in humans there are 23 pairs of chromosomes totalling 46 chromosomes. Each pair comprehend

Explain the colorimetric method glucose estimation, Explain the Colorimetri...

Explain the Colorimetric Method Glucose Estimation? Alkaline copper reduction methods are by far the most commonly used methods for glucose estimation. This time honoured metho

Define the starch gel electrophoresis, Define the Starch gel electrophoresi...

Define the Starch gel electrophoresis? Starch gel has the advantage of fine texture and absence of protein adsorption with a molecular sieving effect retarding proteins of larg

Is there a exchange of cells between the mother, Is there a exchange of cel...

Is there a exchange of cells between the mother and the fetus through the placenta? Under normal conditions, there is not a passage of cells across the placenta during gestati

Explain heat preservation - method of food preservation, Explain Heat Prese...

Explain Heat Preservation - Method of Food Preservation? The process of heating was used centuries before its action was understood. Food is heated up or cooked. Heat kills mi

Mechanism of blood coagulation, GENERA L MECHANISM OF BLOOD COAGULATION - ...

GENERA L MECHANISM OF BLOOD COAGULATION - All researchers agree that blood clotting is a cascade mechanism and involves three essential steps - (a) Formation of prothrombin ac

Ovule, Ovule The ovule, also known as the megasporangium is the forer...

Ovule The ovule, also known as the megasporangium is the forerunner of the seed. It consists of a central mound of tissue called the nucellus, which is enveloped by one or tw

Illustrate spoilage of milk and milk products, Q. Illustrate Spoilage of Mi...

Q. Illustrate Spoilage of Milk and Milk Products? Milk is a wholesome food and so it is generally consumed in its basic form or with the addition of a beverage supplement. Mil

Egg type, why their is different amount of yolk is present in eggs.

why their is different amount of yolk is present in eggs.

Determine the occurrence of vitamin A, Determine the Occurrence of vitamin ...

Determine the Occurrence of vitamin A In the vegetable kingdom, vitamin A  probably occurs in the form of its provitamins which belong to the group of carotenes. Carrots, spina

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