<< Chapter < Page Chapter >> Page >

ABA induces dormancy in seeds by blocking germination and promoting the synthesis of storage proteins. Plants adapted to temperate climates require a long period of cold temperature before seeds germinate. This mechanism protects young plants from sprouting too early during unseasonably warm weather in winter. As the hormone gradually breaks down over winter, the seed is released from dormancy and germinates when conditions are favorable in spring. Another effect of ABA is to promote the development of winter buds; it mediates the conversion of the apical meristem into a dormant bud. Low soil moisture causes an increase in ABA, which causes stomata to close, reducing water loss in winter buds.

Ethylene

Ethylene is associated with fruit ripening, flower wilting, and leaf fall. Ethylene is unusual because it is a volatile gas (C 2 H 4 ). Hundreds of years ago, when gas street lamps were installed in city streets, trees that grew close to lamp posts developed twisted, thickened trunks and shed their leaves earlier than expected. These effects were caused by ethylene volatilizing from the lamps.

Aging tissues (especially senescing leaves) and nodes of stems produce ethylene. The best-known effect of the hormone, however, is the promotion of fruit ripening. Ethylene stimulates the conversion of starch and acids to sugars. Some people store unripe fruit, such as avocadoes, in a sealed paper bag to accelerate ripening; the gas released by the first fruit to mature will speed up the maturation of the remaining fruit. Ethylene also triggers leaf and fruit abscission, flower fading and dropping, and promotes germination in some cereals and sprouting of bulbs and potatoes.

Ethylene is widely used in agriculture. Commercial fruit growers control the timing of fruit ripening with application of the gas. Horticulturalists inhibit leaf dropping in ornamental plants by removing ethylene from greenhouses using fans and ventilation.

Nontraditional hormones

Recent research has discovered a number of compounds that also influence plant development. Their roles are less understood than the effects of the major hormones described so far.

Jasmonates play a major role in defense responses to herbivory. Their levels increase when a plant is wounded by a predator, resulting in an increase in toxic secondary metabolites. They contribute to the production of volatile compounds that attract natural enemies of predators. For example, chewing of tomato plants by caterpillars leads to an increase in jasmonic acid levels, which in turn triggers the release of volatile compounds that attract predators of the pest.

Oligosaccharins also play a role in plant defense against bacterial and fungal infections. They act locally at the site of injury, and can also be transported to other tissues. Strigolactones promote seed germination in some species and inhibit lateral apical development in the absence of auxins. Strigolactones also play a role in the establishment of mycorrhizae, a mutualistic association of plant roots and fungi. Brassinosteroids are important to many developmental and physiological processes. Signals between these compounds and other hormones, notably auxin and GAs, amplifies their physiological effect. Apical dominance, seed germination, gravitropism, and resistance to freezing are all positively influenced by hormones. Root growth and fruit dropping are inhibited by steroids.

Questions & Answers

what is Alimentary canal?
Princess Reply
what is commenialism
jamex Reply
Do you mean commensalism?,it is a feeding relationship that has to do with two different species feeding, that is one is benefiting and the other is unaffected.
hamidat
commensalism is a feeding relationship that has to do with different species feeding, one is gaining and the other is unaffected.
hamidat
what is the work of phloem tissue
Rose Reply
What is osmoregulation?
Jacklin
osmoregulation is the maintenance of internal body through the aid of water
favour
mention four characteristics of enzymes
Leah
mention four characteristics of enzymes
Agorong
The phloem tissue is responsible for the distribution of manufactured food in the shoot.
hamidat
Enzymes speed up the rate of chemical reactions,they are catalytic protein.
hamidat
to transport the manufactured food
Ronald
A skeleton is any film structure that gives mechanical support to the body and provides protection to the softer parts of the body.
Patrick Reply
nice
Kabir
A skeleton is a frame or bony part of a body that aid in the movement of different parts of the body.
hamidat
What is a skeleton?
Chipo Reply
is a bone without meat
Stanley
is a frame work of d body that provide support nd rigidity 4 d body
tunz
is a structure of the body without the organs and the skin
Rose
what is an electron microscope?
Chr Reply
is a microscope that is used to study small organisms in the cell.
Rose
is a microscope which uses electricity to magnify
jamex
okay
Rose
what is commenialism
jamex
what is an antigen?
Luyando
an antigen is any thing that reduces the action of a gene
hamidat
what is biochemist
Lenard Reply
biochemistry:-is the study of chemical reaction with living organisms
Kabir
HOW MANY DNA STRANDS DOES CORONA VIRUS HAVE?
Baramox
GO AND ASK GOOGLE.
hamidat
what are the scientific method
Precious Reply
describe the functioning of the Golgi body in animal cells
Naiga Reply
used to package minerals in the cell
Rose
what features does red blood have that allows it to effectively move through the blood and transport oxygen? list at least four features and explain how they help RBC's carry out their functions.
Alice Reply
has nucleus, haemoglobin
favour
what is biology
kenneth Reply
it's the study of living organisms and their interactions with one another and the environment
Precious
Biology is the study of life.
hamidat
is the study of living organisms and there structure
Rose
describe the structure of DNA
Mafashion Reply
it a double helical structure negatively charged as a results of a phosphate backbone and the two strands are joined together by hydrogen bonds
Ebenezer
Bring out clearly the process of clothing
Irene Reply
How is the region of unwinding called
Irene
what is hoemositasis
Violet
homeostasis is the regulation of a constant internal environment
hamidat
what is DNA replication
jamex
is de maintance of constant internal environment
jamex
is an unfavourable conditions cost by capavic bacteria
hashim Reply
no idea
hamidat
no idea
Precious
Describe the following terms used in nutrition, parasitism, saprophytic, symbiosys
Meymo Reply
parasitism involves gaining and losing
hamidat
a saprophyte does not cause harm to it Host.
hamidat
in symbiosis the two organisms are benefiting
hamidat

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask