a) Make a comparative chart of the function of all the plant hormones.
b) Describe practical applications of plant hormones.
a) All plant hormones have diverse chemical composition & action at low concentration they regulate growth, differentiation & development by promoting or inhabiting the same. They are synthesized from one region & translocated to another region for regulating one or more physiological function. Functions of all the plant hormones (Auxins, Gibberellins, Cytokinins, Ethylene, Abscisic acid) represented as follows:
1. Gibberellin has pronounced effect on leaf growth.
2. It induces elongation of the stem in dwarf plants.
3. It breaks dormancy of seeds, buds & tubes.
4. Gibberellin checks adventitious root production at the cut ends of branches.
5. Promotes flowering in long day plants.
6. Gibberellin promotes stomatal opening.
7. It prevents leaf senescence.
8. It can bring about changes in the sexuality of flowers.
1. Auxin promotes root formation.
2. It has a little effect on leaf growth.
3. It causes apical dominance.
4. Auxin has no effect on genetically dwarf plants.
1. Cytokinin plays an active role in cell division.
2. It stimulates the germination of seed.
3. Cytokinin stimulates adventitious root production at the cut ends of branches.
1. Abscisic acid induces dormancy of seeds, buds & tubes.
2. Promotes flowering in some short day plants.
3. Abscisic acid promotes stomatal closure.
4. It promotes leaf senescence.
1. Fruit growth: The growth of fruit is stimulated by ethylene in some plants.
2. Triple response: Ethylene changes the growth patterns of plants by (i) inhibition of stem elongation (ii) stimulation of radial swelling of stems & (iii) horizontal growth of stems with respect to gravity.
3. Breaking of dormancy: It breaks bud & seed dormancy in many plants.
Note: These are the functions of plant hormones. There should be one comparative chart for all hormones.
b) Plant hormones have found practical applications in agriculture. Auxins are used for weed control, initiation of rooting cuttings, in tissue culture, parthenocarpic fruit set, thinning of fruit trees to obtain larger fruit size & inducing flowering. They are also used for inhibiting sprouting & bud growth. Ethylene is used for fruit ripening any synchronizing flower formation. Gibberellins are used for stalk elongation of sugarcane to increase sugar content.
There is a world wide attempt to develop commercial plant growth regulators which will be able to increase basic productivity or yield of a crop such as wheat, rice or peas. The hormone to be applied at the proper concentration at the right stage of development, & then develop a criterion to measure the increase in yield. Success in promoting yields has always occurred when a specific goal is recognized such as an increase in sugar content of sugarcane, promote the flow of latex in Hevea & prevent lodging of small grains. Applications of plant hormones have found use mainly in horticultural crops.