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

Assignment, Write short note onApplications of apical dominance in horticul...

Write short note onApplications of apical dominance in horticulture and agriculture

Define dietary management for burns, Define Dietary Management for Burns? ...

Define Dietary Management for Burns? Nutritional support is a major part of therapy for a patient with burns in view of the large catabolic losses, essential anabolic demands a

Explain diabetic diets, Explain Diabetic  diets Diabetic  diets :  Th...

Explain Diabetic  diets Diabetic  diets :  There  are  therapeutic modification  in  the  quantity1 quality of  various macronutrients  particularly carbohydrates.

Explain atp molecules in photophosphorylation, Q. How is photic energy abso...

Q. How is photic energy absorbed by chlorophyll transfered to ATP molecules in photophosphorylation and How will be the resulting ATP used? Light excites energizes and chloroph

Explain food applications of gum karaya, Explain Food Applications of gum k...

Explain Food Applications of gum karaya The water absorbing and water-holding capacity of Karaya, together with an excellent acid compatibility made it suitable for its use

Explain cell membrane and plasma membrane, Explain cell membrane? The...

Explain cell membrane? The Cell Membrane :  The cell membrane, or plasma membrane, separates the cell from neighboring cells or from the external environment. Both prokaryot

Portal hypertension, Portal Hypertension: If you review the portal cir...

Portal Hypertension: If you review the portal circulation you may recall that normal blood flow to and from the liver depends on proper functioning of  the portal vein, the he

What is the menstrual cycle, What is the menstrual cycle? The menstrual...

What is the menstrual cycle? The menstrual cycle is the periodic succession of interactions among hormones and the organs of the female reproductive system that, after the star

Define the best describes this autopsy finding, A 70-year old woman present...

A 70-year old woman presents with a 1-hour history of crushing substernal chest pain. Shortly after admission, the patient expires. An autopsy reveals calcium deposits in the intim

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