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

How are the main classes of arthropods classified, How are the main classes...

How are the main classes of arthropods classified according to the presence of larval stage in their embryonic development? In crustaceans there are species with direct and oth

Explain the s1m filament theory of muscle contraction, Explain the s1M fila...

Explain the s1M filament theory of muscle contraction. What is special of "FlavrSavr" variety of tomato? Why is it preferred to its normal native variety? Illustrate a label

Characteristic features of phylum arthropoda, Characteristic Features of Ph...

Characteristic Features of Phylum Arthropoda Well-developed muscular system along with striated muscles attached to the exoskeleton, and visceral organs having smoot

What the two pcr amplified strands, You now want to express the gene in E c...

You now want to express the gene in E coli, but unfortunately it has an intron in it that will not be processed out in bacteria, hence it must be removed. (a)  Design P

Phase (different interference) contrast microscopy, Phase (different interf...

Phase (different interference) Contrast microscopy: Living cells are mostly   transparent. For viewing under ordinary light microscope, therefore, live cells must be stained wi

Food chain and types of food chain, In an ecosystem various trophic levels ...

In an ecosystem various trophic levels are interlinked with each through a food chain. ( the transfer of food energy from green plants through a series of organism with repeated ea

What are the vessels that carry blood to the kidneys, Q. What are the vesse...

Q. What are the vessels that carry blood to the kidneys? Is this blood venous or arterial? The renal arteries are ramifications of the aorta and so the blood filtered by the ki

How does the synthetic theory of evolution explain this fact, In hospitals ...

In hospitals where many tuberculosis patients are treated the population of the tuberculosis mycobacteria may be constituted of multiresistant (to antibiotics) strains. How does th

Describe the distae dissection techniques of surgery , Describe the DistaE ...

Describe the DistaE Dissection Techniques of Surgery? DistaE Dissection (De Bakey Type ZII or Stanford Type B) :  Techniques of Surgery :  The approach is through a left p

Why is vision important for life on earth, Q. What is vision? Why is vision...

Q. What is vision? Why is vision important for life on earth? Vision is the ability of some living beings to distinguish, to perceive and to interpret luminous stimuli. Visi

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