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

Difference between extraradicular and intraradicular, What is the differenc...

What is the difference between extra. and intraradicular? Extraradicular means there is lesions came from periodontal or from the adjacent tissue and make periapical infection

What are the archenteron and the blastopore, What are the archenteron and t...

What are the archenteron and the blastopore? What is the stage of the embryonic development in which these structures are formed? What are the destinations of the archenteron and o

Protozoans and cnidarians, compare and contrast the structure of the follow...

compare and contrast the structure of the following: hyrda plain, hydra mematocysts, obelia, amoeba, euglena, paramecium caudatum conjugation, euglena acus.

Photosynthesis, photosynthesis moderates global warming, briefly explain th...

photosynthesis moderates global warming, briefly explain this statement

Multiple fission - types of asexual reproduction, Multiple Fission - Types ...

Multiple Fission - Types of Asexual Reproduction Multiple fission is a variation of fission where the parent divides mitotically into a number of smaller units that are the da

Fate maps, Fate Maps The details of the procedure of gastrulation are...

Fate Maps The details of the procedure of gastrulation are not simple to understand without the knowledge of positions of the cells of the future germinal layers in the blast

How is the blood typing concerning the abo system, How is the blood typing ...

How is the blood typing concerning the ABO system and the Rh usually done? In a blood typing for the ABO system and the Rh system a blood sample is collected from the person an

Explain about the dehydration or drying, Explain about the Dehydration or D...

Explain about the Dehydration or Drying? The technique of drying is the oldest method of food preservation practiced by mankind. The removal of moisture, which is actually dehy

What is the limitations of panoramic x-ray, Limitations of Panoramic X-Ray ...

Limitations of Panoramic X-Ray There are certain limitations to panoramic Xrays that you have to be awareof:  The amount of magnification  Fine details of structures arou

Define the objectives in the biochemistry of the eye, Define the objectives...

Define the objectives in the biochemistry of the eye. After going by this section, you should be familiar with: a. Dynamic of vascular supply of eye; b. The cornea metabo

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