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

Are the arterial pulsations normal, Are the arterial pulsations normal? ...

Are the arterial pulsations normal? Is the pulse volume normal or increased? Is there a discrepancy of pulsation in any of the four extremities? A careful evaluation of pulsati

Transmissible gastroenteritis of swine, Transmissible gastroenteritis of sw...

Transmissible gastroenteritis of swine The disease, first reported from the USA in 1964, is caused by antigenic group 1 mamalian coronavirus, a member of genus Coronavirus of

Respiration in animal, what is respiration in animals ,its functions ,types...

what is respiration in animals ,its functions ,types of respiration

Symptoms and complications of atherosclerosis, Q. Symptoms and Complication...

Q. Symptoms and Complications of atherosclerosis? Symptoms Excessive weight, hypertension, high levels of cholesterol and triglycerides. Complications Myocardia

Give the introduction of genesis of coronary artery diseases, Give the intr...

Give the introduction of genesis of coronary artery diseases and risk factors? Cardio-vascular diseases have their roots in the structure and functional alterations in the vasc

Explain the process of growth factors, Explain the process by which growth ...

Explain the process by which growth factors promote angiogenesis. Add citation or links.

Can you define termination of the stress test, Q. Can you define terminatio...

Q. Can you define termination of the stress Test? Test should be terminated when: 1) PVCS develop in pairs or with increasing frequency or when ventricular tachycardia devel

What would be a very wrong way to tell the difference, You have accidentall...

You have accidentally mixed up 3 beakers of solutions. One is water. One is pure methanol. One is pure phosphoric acid. What would be a very wrong way to tell the difference betwee

What is deplasmolysis of plant cells, What is deplasmolysis of plant cells?...

What is deplasmolysis of plant cells? The plant cell when placed under hypertonic medium loses a huge amount of water and its cell membrane detaches from the cell wall. In that

Bacteria, write six characteristics of bacteria

write six characteristics of bacteria

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