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

Define mobilization of bone calcium and phosphorous, Define Mobilization of...

Define Mobilization of bone calcium and phosphorous? It is now firmly established that vitamin D 3 is metabloized first in the liver to 25-hydroxyvitamin D (25 OH- D) (calcicl

Define e-ptfe suture material, Define e-PTFE suture material The e-PTF...

Define e-PTFE suture material The e-PTFE suture material is a nonabsorbable monofilament that has high tensile strength, good handling properties, and good knot security, but

How to convert 3.5°f to celsius four hundred pounds, Convert 3.5°F to Celsi...

Convert 3.5°F to Celsius Four hundred pounds is how many kilograms?

Explain zymogen, Zymogen :- an  inactive form of an  enzyme; becomes active...

Zymogen :- an  inactive form of an  enzyme; becomes active prior to its action.

Define classification of carbohydrates - polysaccharides, Define classifica...

Define classification of carbohydrates - Polysaccharides? This classification is based on the number of monosaccharide units they contain, Polysaccharides are those polymers of

Structure of human spermatozoon, Structure of human spermatozoon: Na...

Structure of human spermatozoon: Nature: Human sperms are minute, microscopic and motile. Structure: Each sperm have an oval shaped head piece, a neck, a middle piece and

Inferior epigastric artery-other arterial conduits, Inferior Epigastric Art...

Inferior Epigastric Artery (I.) :  This is a branch of external iliac artery supplying the abdominal wall. It is raised as a free graft for CABG. The usual length availab

What is enzyme assay, What is Enzyme assay Enzyme assay may also be use...

What is Enzyme assay Enzyme assay may also be used to determine whether stored plant products are suitable for use as food commodities, for e.g.  α-amylase should be present

Respiration – protozoan, Respiration – Protozoan Gas exchange occurs b...

Respiration – Protozoan Gas exchange occurs by the diffusion of oxygen across the cell membrane. Some protozoan utilize this oxygen but are also capable of anaerobic respirati

Metabolic events, Metabolic Events Let us now examine the changes that...

Metabolic Events Let us now examine the changes that occur in the seeds after they imbibe water. In general, the most important metabolic events are: Degradation

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