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

BIOLOGY, 100 WORDS NOT COMPLETED

100 WORDS NOT COMPLETED

How the sodium-potassium pump present in the cell membrane, How does the so...

How does the sodium-potassium pump present in the cell membrane work? What is the importance of this protein for the cell? The sodium-potassium pump is the transport protein th

Meiosis, Why is it necessary to have the second division in meiosis even th...

Why is it necessary to have the second division in meiosis even though cells have already been reduced to haploid number after the first division?

Pbpk modeling during human drug development, Early human studies are normal...

Early human studies are normally conducted in healthy subjects to assess acute safety and, if applicable, to monitor biochemical and pharmacological responses. These studies also p

Anatomical reason for the left bronchus to be more elevated, Q. What is the...

Q. What is the anatomical reason for the left bronchus to be more elevated than the right bronchus? Why in most cases of aspiration of foreign material by children is the object fo

Polar bear is adapted to its environment, Give three ways in which a polar ...

Give three ways in which a polar bear is adapted to its environment. A polar bear is adapted to its environment by its high ratio of bulk to surface area, a thick water-repelle

Zooflagellates – protozoan, Zooflagellates – Protozoan Zooflagellates ...

Zooflagellates – Protozoan Zooflagellates are heterotrophs that are free living, commensals or symbiotic or parasitic in other animals. A number of species eg. Trichonynzpha a

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

Role of hormones in regeneration, Role of Hormones in Regeneration Se...

Role of Hormones in Regeneration Several neurosecretory effects in regeneration are integrated into a neuroendocrine feedback system. It is frequently difficult to distinguis

Explain wire loop and tube method, Explain Wire loop and Tube Method 1....

Explain Wire loop and Tube Method 1.  Use a 25-gauge dental injection needle, cut to remove beveled end 2. Both ends of-mm diameter steel ligature wire passed through the ne

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