The exine layer, Biology

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.

 

Posted Date: 1/23/2013 5:22:04 AM | Location : United States







Related Discussions:- The exine layer, Assignment Help, Ask Question on The exine layer, Get Answer, Expert's Help, The exine layer Discussions

Write discussion on The exine layer
Your posts are moderated
Related Questions
Explain the Uses of ISO in Seafood products  Seafood products  The most significant application in this category is the use of ISP in fish sausage and surimi based restructu

Syngamy - Protozoan The two gametes may be morphologically similar (isogametes) or dissimilar (anisogametes). The gametes also vary in form, they may be flagellated or amoeboi

Explain about the Autodispensor? This is used to transfer accurate quantities of liquids that are difficult to pipette like concentrated acids, alkalis, etc. You will also use

The left atrio-ventricular aperture in man is guarded by

In biology, a species is smallest and basic unit of classification. Each species is placed within a single genus. For example biological name of human being is homosapiens. Here ho


Leptospirosis It is a bacterial disease that occurs in many domestic and wild animals, is endemic worldwide, but the highest incidence is in tropical and subtropical areas. Tr

Q. Explain the communication process? Communication is a process by which information is exchanged between individuals through a common system of symbols, signs, or behavior. C

Q. Why is the nickname "dark reactions" not completely correct for the chemical stage of photosynthesis? "Dark reactions" is not a correct name for the chemical phase of photos

Shoot Multiplication -Clonal Propagation This is the most important step with respect to the rate of propagation and genetic uniformity of the product. The most reliable and