Seed coat effects, Biology

Assignment Help:

Seed Coat Effects

In some seeds dormancy is imposed by the presence of the seed coat; if this is removed, the seed germinates. Two possible types of mechanisms could be involved, one biochemical or physiological and the other purely mechanical.

Scarification

The seed coat is nearly impervious to the diffusion of gases. Wareing's group found that seeds of Birch (Betula Pubescens), which would not germinate intact, would do so if the seed coat were scratched or broken. Moreover, added oxygen greatly stimulated germination of such damaged seeds. Evidently the embryos themselves were not dormant; they would germinate if isolated from the seed An alternative possibility is that the seed coat might prevent the leaching out of a diffusible inhibitor. The second, or mechanical alternative has been investigated by Y. Esashi and A.C. Leopold using seeds of Xanthium pennsylvanicum (also called Xanthium strumarium), the cocklebur.

This plant produces two kinds of seeds in each fruit large, non dormant ones and small, dormant ones. The investigators used the specially designed apparatus to show that neither type of seed generates enough force to rupture the testa during imbibitions. During growth, however, the large, non dormant seeds generate sufficient force to break it whereas the smaller dormant seeds do not. This shows, for Xanthium at least, that the long held opinion that the embryo must generate sufficient force during germination to rupture the seed coat is correct. Moreover, it is clear that the forces generated by imbibitions alone are not sufficient. Active growth is also needed.


Related Discussions:- Seed coat effects

Zoology, what is hydrostatic skeleton?

what is hydrostatic skeleton?

Causes of non-ketotic hyperosmolar diabetic coma, Q. Causes of Non-Ketotic ...

Q. Causes of Non-Ketotic Hyperosmolar Diabetic Coma? The causes of NKHDC are given below: 1) Infections 2) Trauma 3) Burns 4) Myocardial Infarctions (heart attack)

What is katal, What is katal katal : the amount of  enzyme that  tran...

What is katal katal : the amount of  enzyme that  transforms  1 mol  of substrate into product in one second.

Respiratory system, whats the difference in respiratory system in mammals,r...

whats the difference in respiratory system in mammals,reptilia and amphibian?

............., notochotr is absent in the group ...........

notochotr is absent in the group ...........

Mixed mitral stenosis and regurgitation, Mixed Mitral Stenosis and Regurgit...

Mixed Mitral Stenosis and Regurgitation The most common cause for a combined lesion is rheumatic, Very rarely; it could be of congenital origin. Regurgitation in a stenotic val

Define erythropoietin, Erythropoietin (EPO) A. acts by increasing the p...

Erythropoietin (EPO) A. acts by increasing the production of red blood cells by cells in the bone marrow. B. is secreted by peritubular interstitial cells of the kidney cort

Explain the procedure for morphological study of fungi, Explain the Procedu...

Explain the Procedure for Morphological Study of Fungi? Now carry out the exercise, following the steps enumerated herewith: 1. Prepare a humid chamber by placing two-three

Carpentier -edwards valve-biological valves, Carpentier -Edwards Valve (C-E...

Carpentier -Edwards Valve (C-E) :  This is porcine aortic valve preserved in gluteraldehyde and mounted on flexible stent made of cobalt-chromium-nickel alloy (ELGILOY). Glut

Explain the absence of passive fit of the prosthesis, Absence of Passive Fi...

Absence of Passive Fit of the Prosthesis A passive fit of the prosthesis reduces long term stresses in the superstructure, implant components and the bone adjacent to the impla

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