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

Phases of cell cycle, The cell goes through many discrete phases before and...

The cell goes through many discrete phases before and after cell division. From this understanding, scientists then identified the four characteristic phases of the cell cycle:

What is fern allies - equisetum, What is Fern Allies - Equisetum ? The ...

What is Fern Allies - Equisetum ? The earliest land plants are thought to have evolved from green algal ancestors, since they share many features. Both green algae and plants h

Discovery of the cell, Q. Describe the Discovery of the Cell? Ans: The ...

Q. Describe the Discovery of the Cell? Ans: The discovery that living organisms are composed of cells was made by an Englishman, Robert Hooke, in 1665. Hooke used the light mic

Circuitry and priming -procedures of oxygenators, Circuitry and Priming : ...

Circuitry and Priming : The cardio pulmonary bypass circuit consists of oxygenator, tubings, cannulae, cardiotomy reservoirs and cardioplegia attachments. The first step is to pri

Rna molecule have two polynucleotide chains like the dna, Q Does RNA molecu...

Q Does RNA molecule have two polynucleotide chains like the DNA? Only DNA has two polynucleotide chains. The RNA is formed by just one polynucleotide chain.

Explain about ia muscle-spindle, Which of the following occur in response t...

Which of the following occur in response to an increase in the length of the right knee extensors in response to a quick tap applied to the right patellar tendon?  An increase in t

Name which part of the seed in other monocotyledons, The scutellum observed...

The scutellum observed in a grain of wheat or maize is comparable to which part of the seed in other monocotyledons? 1. Cotyledon 2. Endosperm 3. Aleurone layer 4. Plum

Explain cell signaling, In multicellular organisms there is a requirement f...

In multicellular organisms there is a requirement for the cells to communicate with one another in order to coordinate their metabolism and growth.  The principal way by  that  cel

Adults with infective endocarditis, Mitral valve prolapse (MVP) has emerged...

Mitral valve prolapse (MVP) has emerged as a prominent, predisposing structural cardiac abnormality and in adults accounts for 7 to 30 per cent of NVE in cases not related to drug

Define characteristics of probiotics, Define Characteristics of probiotics?...

Define Characteristics of probiotics? Are microorganism Promote a healthy intestinal microflora Ensure colonization resistance to pathogens Destruction of ge

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