OCR Biology: Plant Hormones

OCR Biology: Plant Hormones

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Auxins

Function

Regulates phototropism(direction of plant growth), leaf formation, gravitropism, abscission, apical dominance, root initiation, fruit development, and development. Found abundantly in the meristem. Phototropism is due to inhibition of auxin by light.

Commercial Uses

Auxin is widely used to produce vigorous growth of plant, to promote cell elongation, to promote apical dominance, to promote fruiting, promote flowering, formation of root in the plants which not easily propagated by stem cuttings, weed control, to prevent fruit drop (premature fruit dropping), and also to produce fruits without seed (e.g. seedless varieties tomatoes)

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Gibberellins

Function

 Gibberellins are the plant growth hormones, which were first reported in rice by T. Yobuta and T. Hayashi. Gibberellins are those growth hormones which cause cell elongation of intact plants. Apical shoot buds, root tips, and developing seeds are known to synthesize gibberellins.They promote plant growth, overcome dormancy, promote germination, induce flowering, helps in fruit growth and it also helps in the prevention of senescence

Commercial Uses

Delay senescence in citrus fruit(fruit can be left unpicked longer), Brewing (speeds up barley seed germination for producing malt), Sugar production (stimulates growth between the nodes, making the stems elongate), Speed up breeding by inducing seed formation in young trees

 

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Cytokinins

Function

Cytokinins are plant growth hormones . The first natural cytokinin was obtained from unripe maize grains by Letham et al,1964. Roots are the major source of cytokinin synthesis; they pass upwardly through the xylem. They promote cell division, cell elongation, essential for differentiation of tissues and organs, delay senescence of leaves, essential for apical dominance, to overcome seed dormancy, help in phloem transport and increases resistance to pathogens

Commercial Uses

Used for tissue culturing of plants, to increase shelf life of vegetables, they can increase the chances of a plants survival as they increase resistance to pathogens and also they delay senescence of intact plant parts.

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Ethene

 

Function

Promotes fruit ripening

Commercial Uses

Speeds up fruit ripening in apples, tomatoes...; it also promotes fruit drop in cotton, cherry...; Promotes female sex expressions in cucumbers; Promotes lateral growth in some plants.

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Abscisic Acid

Function

Absicissic acid is a growth inhibitor which retards or suppresses growth and metabolism. Induces bud dormancy, accelerates senescence in leaves, functions as a stress hormone by inducing temporary closure of stomata, promotes abscission of leaves, flowers and fruits, inhibits cell division and cell elongation, promotes rootings of stem cuttings, inhibits flowering but is sed in inducing flowering in short day plants.

Commercial Uses

Inhibits lateral bud growth - resulting in taller and thinner trees rather than shorter and fatter trees.

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