Pollen tube structure, Biology

Assignment Help:

Pollen Tube Structure

The pollen tube in the stigma is filled with cytoplasm containing numerous mitochondria and dictyosomes. The number of dictyosome cisternae is reduced in the tubes. Large vesicles associated with dictyosome seem to be incorporated in the tube wall. Abundant ER and polysomes which are either in free form or attached to ER can also be seen. The pollen tube wall in the stigma and style show two distinct regions: the outer part of the wall (PAS positive), and the inner portion which is thicker, more homogeneous (much less reactive to PAS), and rich in callose. The dense cytoplasm contains vesicles of various sizes, ER, ribosomes, and a few poorly-developed plastids with swollen outer membranes. Dictyosomes are quite numerous with 4 or 5 cisternae, and produce vesicles.

The vesicles appear to fuse with the plasma membrane of the pollen tube. A very large population of small, spherical vesicles are scattered throughout the pollen tube cytoplasm. The ER in the pollen grains and during early growth of the pollen tube has extended cisternae and apparently serves as a storage site for proteins. As the pollen tube grows down the style, the ER shows the common variety of narrow cisternae indicating that protein present is being gradually utilized during tube growth. The ultra structure of the distal region of the pollen tube and the wide variety of cell organelles are indicative of active carbohydrate and protein metabolism. The part of the tube immediately behind the tip region shows less dense cytoplasm and more dispersed organelles. The more mature parts of pollen tube contain only a thin layer of cytoplasm closely appressed to the wall and a large vacuole occupies the rest of the space. Plugs of the wall material, mostly callose serve to separate the older parts of the pollen tube from the growing distill region. The plugs originate as rings on the inner side of the wall and grow inwards like the closing of an iris diaphragm.


Related Discussions:- Pollen tube structure

Anticoagulants, ANTICOAGULANTS (a ) Heparin (hepar = liver) . It is ...

ANTICOAGULANTS (a ) Heparin (hepar = liver) . It is synthesized by mast cells of connective tissue and liver cells. It is a heteropolysaccharide. It increases the effectivit

Sources of variability, Mutations and genetic recombination (in sexually re...

Mutations and genetic recombination (in sexually reproducing organisms) are major sources of variations in natural populations, In this section we will briefly mention the various

Failure of public production, Normal 0 false false false ...

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

Explain procedure for simple staining of bacterial cultures, Explain Proced...

Explain Procedure for Simple Staining of Bacterial Cultures? Now carry out the exercise following the steps given herewith: (1) Prepare thin bacterial smear on clean glass s

What is difference between analogous and homologous organs, What is the dif...

What is the difference between analogous and homologous organs? The Characteristics of different species are said to be analogous when having the same biological function, for

Refining of crude oil, The crude oil obtained from earth's crust is refined...

The crude oil obtained from earth's crust is refined by following steps. Step 1: separation of water Cottrell's process is used for separation of water. Crude oil is an emu

Steroids, STEROID S - These are derived lipids. Cholesterol is m...

STEROID S - These are derived lipids. Cholesterol is must in formation of steroid hormones. In steroids cyclopentanoperhydrophenentherene nucleus ring present. S

Fatty acids, F A TT Y ACIDS They are monocarboxylic organic acids...

F A TT Y ACIDS They are monocarboxylic organic acids (R.COOH) having a hydrocarbon chain of 4 - 30 carbon atoms. The polar carboxylic group is hydrophilic (Gk. hydro

What is enteral feeding, Tube or Enteral Feeding Ideally the patient mu...

Tube or Enteral Feeding Ideally the patient must be fed orally, but in cases where the patient is unable to take solid foods, a part or all of intake is usually given by the tu

Define types of circulatory systems, Q. What are the two kinds of circulat...

Q. What are the two kinds of circulatory systems? The circulatory systems can be classified into closed circulatory system and open circulatory system.

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