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

Endocrine glands - gastro-intestinal mucosa, GASTRO-INTESTINA L MUCOSA - ...

GASTRO-INTESTINA L MUCOSA - It develops from the endoderm of the embryo. Inner most layer of the wall of the alimentary canal is called mucosa. Certain cells of the mucosa

Determine the central thermoreceptor neurons, Which of the following serves...

Which of the following serves as a sensor, or as part of a sensor, that functions in a negative feedback system? A. Central thermoreceptor neurons whose peripheral terminals ar

Name which part of the seed in other monocotyledons, The scutellum observed...

The scutellum observed in a grain of wheat or maize is comparable to which part of the seed in other monocotyledons? 1. Cotyledon 2. Endosperm 3. Aleurone layer 4. Plum

Osmoregulation in animals, Osmoregulation in Animals Osmoregulation as...

Osmoregulation in Animals Osmoregulation associates to the regulation of water and ionic content of the body of non-chordate metazoans. These might be osmoconformers / osmoreg

Embryology, what is meaning of haustoria

what is meaning of haustoria

How can the immune memory lead to the efficacy of vaccines, Q. How can the ...

Q. How can the immune memory lead to the efficacy of vaccines and also produce allergies? Vaccines are controlled inoculations of fragments of inactive infectious agents or of

Cow-pox (vaccinia), C o w - po x (vaccinia) E p ide...

C o w - po x (vaccinia) E p idemiology: This infection, although mostly occurring in cows, sometimes also occurs in buffaloes. Under natural conditions, t

Phylum protozoa, classification of organisms in phylum protozoa according t...

classification of organisms in phylum protozoa according to their class,order,family,genus,species.

Explain about types of insulin, Q. Explain about types of Insulin? Thre...

Q. Explain about types of Insulin? Three types of Insulin is available. The type varies in how quickly it starts working (lowering blood glucose), time of peak activity (when t

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