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

Determine immunodeficiency presented by aids patients, What is the cause of...

What is the cause of the immunodeficiency presented by AIDS patients? The cause of the immunodeficiency shown by AIDS patients is the destruction of CD4 T helper lymphocytes by

Exstrophy of the bladder, Exstrophy of the Bladder This is the most c...

Exstrophy of the Bladder This is the most common major congenital defect of lower urinary and genital tract. This is found more frequently in males than in females. Exstr

What compound composes most of the cell membrane, What compound composes mo...

What compound composes most of the cell membrane? How is this compound suited to the function of the membrane? Phospholipid composes most of the cell membrane. The hydrophob

Explain about the spectrophotometer, Explain about the Spectrophotometer? ...

Explain about the Spectrophotometer? The spectrophotometer, a key instrument today in biomedical laboratories, was invented in 1939 by the American chemist Arnold O. Beckman (1

Differences between prokaryotic & eukaryotic cells, DIFFERENCES BETWEEN PRO...

DIFFERENCES BETWEEN PROKARYOTIC & EUKARYOTIC CELLS   S . N o .   CHA R AC T ERS   P R O K AR Y O T I C CELL

Explain isozymes, ISOZYMES Sometimes an  enzyme present  in  the  same ...

ISOZYMES Sometimes an  enzyme present  in  the  same  organism is  found  to  have different molecular forms but  catalyzing the  same  reaction. These are called  isozymes. Th

Mammalian lungs - respiration, Mammalian Lungs - Respiration In this w...

Mammalian Lungs - Respiration In this we will study mainly mammalian lungs as it is the best representative of a respiratory surface adapted for terrestrial respiration. For t

Illustrate ploidies of zygote, Q. What are the respective ploidies of zygot...

Q. What are the respective ploidies of zygote, gamete and somatic cells in a species with gametic meiosis? Adopting as pattern an "x" quantity of chromosomes for gametes, somat

Define iron - the micronutrient, Define Iron - The Micronutrient Iron, ...

Define Iron - The Micronutrient Iron, as you may be aware, is a trace element present in the body. The body contains approximately 3 - 3.5 g of iron of which about two thirds i

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