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

Pollutants, These are solid, liquid or gaseous substance present in the atm...

These are solid, liquid or gaseous substance present in the atmosphere in such concentrations, as may be or tend to be injurious to human beings or other living creatures, plants a

Explain the canal obstruction - endodontic retreatment, Explain the Canal O...

Explain the Canal Obstruction File work shorter than the normal apical and feel a great resistance to reach true length. a. A retained instrument o Canal calcification b.

Determine the postovulatory phase of x menstrual cycle, Healthy human femal...

Healthy human female X is 25 years old and not pregnant.  During the postovulatory phase of X's menstrual cycle,   A.  there are high blood plasma levels of LH and FSH.

Human respiratory system - bronchioles, BRONCHUS - In thorax trachea is...

BRONCHUS - In thorax trachea is devided in to 2 bronchi that enter into lungs of its own side. Rings present in it. BRONCHIOLES - These are branches of bronchus.

Explain the mechanical requirements of implant materials, Mechanical requir...

Mechanical requirements of implant materials Dental implant s must be able to sustain and transfer loads -It should have adequate mechanical strength in order to distribute th

Fluid mosaic model, FLUI D MOSAIC MODEL Proposed by Nicholson and ...

FLUI D MOSAIC MODEL Proposed by Nicholson and Singer (1972) Proteins and lipids are arranged in a mosaic fashion. Lipids and proteins are in a semi fluid structure.

Fragmentation, Normal 0 false false false EN-IN X-NON...

Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

The human impact on the environment, what are the principle sources of exce...

what are the principle sources of excessive nitrate and phosphate in rivers and lakes?

Explain posaconazole, Posaconazole  Posaconazole (SCH 56592), an unappr...

Posaconazole  Posaconazole (SCH 56592), an unapproved azole available from the manufacturer for compassionate use, isunder review by the FDA for oral treatment of invasive fung

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