Skip to main content Accessibility help
×
Home
Hostname: page-component-684899dbb8-67wsf Total loading time: 0.216 Render date: 2022-05-21T10:25:05.525Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "useRatesEcommerce": false, "useNewApi": true }

Chapter 16 - Plant Hormones and Signal Transduction

Published online by Cambridge University Press:  12 May 2020

S. L. Kochhar
Affiliation:
University of Delhi
Sukhbir Kaur Gujral
Affiliation:
University of Delhi
Get access

Summary

Hormones are naturally occurring molecules, in plants and animals that function as messengers and signalling agents and thus impact growth and behaviour of the organism.

Plant hormones are classified as being of five major types: auxins, gibberellins, cytokinins, abscisic acid and ethylene (Table 16.1). Besides these plant hormones; various compounds such as salicylic acid, jasmonates, polyamines, strigolactones, brassinosteroids and nitric oxide (NO) have been reported to act as signalling molecules in hormonal and defence responses.

Auxin: The Growth Hormone

Historical background

The way auxins were discovered is quite fascinating and deserves a special discussion because it was the first and foremost growth hormone to be discovered in plants (Figure 16.1).

In later years of his career, the great evolutionary biologist Charles Darwin became increasingly interested in the study of plants. In 1881, Darwin along with his son Francis authored a book called ‘The Power of Movement of Plants’ in which they highlighted a series of experiments on the growth response of plants to light – Phototropism. For their experiments, they used germinating oat (Avena sativa) and canary grass (Phalaris canariensis) seedlings. Both the Darwins found that if seedlings were exposed to light from one direction, they would bend strongly towards it. If the coleoptile tip was covered with foil, it would not bend. The zone of coleoptile responsible for bending toward the light – ‘the growth zone’–is many millimetres below the tip. Thus, they came to the conclusion that some kind of stimulus produced in the tip region travels to the growth zone and causes the non-illuminated (shaded) side to grow more quickly compared to the illuminated side. For 30 years, the Darwin's experiments remained the only source of information about this interesting phenomenon.

Later in 1913, the Danish plant physiologist Peter Boysen-Jensen and the Hungarian plant physiologist Arpad Paal (1919) independently proposed that the growth-promoting signal generated in the tip region was chemical in nature.

They decapitated the coleoptile of Avena seedling and in one experiment (a) inserted a small gelatin block between the stump and cut tip and in other (b) a thin sheet of mica. The coleoptile bending was observed in (a) but not in (b) because the growth stimulus passes across the gelatin block but not through a water-impermeable barrier such as the mica sheet.

Type
Chapter
Information
Plant Physiology
Theory and Applications
, pp. 468 - 525
Publisher: Cambridge University Press
Print publication year: 2020

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Save book to Kindle

To save this book to your Kindle, first ensure coreplatform@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Available formats
×

Save book to Dropbox

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.

Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

Available formats
×