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

Causes of gerd, In addition, pregnancy or constipation may worsen GERD by i...

In addition, pregnancy or constipation may worsen GERD by increasing intra-abdominal pressure. Secondary causes of GERD include reflux caused by acid hypersecretory states, connec

Explain diagnostic approach to congenital heart disease, Explain Diagnostic...

Explain Diagnostic Approach to Congenital Heart Disease ? It is often easy to recognise the presence of CHD in older children and adults. As in any other form of heart disease

What do protozoans eat, Q What do protozoans "eat"? Do they move in search ...

Q What do protozoans "eat"? Do they move in search for food? Protozoans are heterotroph beings that are they do not make their own food and thus they need to search for it in t

What are the three main types of passive transport, What are the three main...

What are the three main types of passive transport? The three main kinds of passive transport are a)  simple diffusion, b)  osmosis and c)  Facilitated diffusion. C

Mental health, Mental Health For physiological health & social status, ...

Mental Health For physiological health & social status, it is necessary to maintain mental health. Mental illness is characterised by - Depression Insomnia Exces

How fever, How Fever,Illness,Infections,Injury affects the BMR? Any ill...

How Fever,Illness,Infections,Injury affects the BMR? Any illness or fever caused by an illness influences the metabolic rate. Fevers increase the metabolic rate by about 7% for

Agro industrial-enrichment of soil, Enrichment of soil Indirect provis...

Enrichment of soil Indirect provision of minerals to grazing livestock includes mineral fertilization of  pasture and altering soil pH, however this may not be always feasible

Brain, What are the types of brain?

What are the types of brain?

Egestion, After the food intake is over, the food gets digested, assimilate...

After the food intake is over, the food gets digested, assimilated and finally egested through the kidneys and anus. The urinary system: • Filters waste materials from the blood

Zoology, structural adaptation of mammalian alimentary canal

structural adaptation of mammalian alimentary canal

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