Pollen tube structure, Biology

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.

Posted Date: 1/23/2013 4:28:36 AM | Location : United States







Related Discussions:- Pollen tube structure, Assignment Help, Ask Question on Pollen tube structure, Get Answer, Expert's Help, Pollen tube structure Discussions

Write discussion on Pollen tube structure
Your posts are moderated
Related Questions
Q. Wound Botulism? It is the rarest form of botulism. The illness results when C. botulinum by itself or with other microorganisms infects a wound and produces toxins, which re

What is an example of animal coming from the phylum arthropoda?

What is Fern Allies - Equisetum ? The earliest land plants are thought to have evolved from green algal ancestors, since they share many features. Both green algae and plants h

Q. What are the major parts of ferns? Ferns are constituted by small roots that come downwards from the rhizome stem and often horizontalized. The fronds also arise from the rh

What are the two groups of defense mechanisms of the body against foreign or harmful agents? What is the difference between them? The body has many defense mechanisms against f

TYPES OF CLEAVAGE - Depending upon the distribution & amount of yolk, cleavage is of following types - 1 .      HOLOBLASTIC EQUAL CLEAVAGE ( holos , whole ; blastos, ger

Stabilized forms of natural colourants The mimicking of the native environment in which a natural colour exists is just one way of producing a stabilized form. In this case, th

A solute passes from higher concentration on the left of a container to the right side of container thru a membrane. What would happen if a second solute of lower concentration was

#question.name any two plants having heterotrophic mode of nutrition .

What is Imbibition The ability of colloids to pick up water and swell when they come in contact with water is called imbibition. Imbibition is usually accompanied by the evo