What is the role of Gibberellins on plant metabolism?

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1. Dormancy and seed germination:

Gibberellins are known to break dor­mancy in seeds and thus hasten the process of germination (Ross and Bradbeer, 1968) Dormancy in potato tubers is also broken by GA.

2. Root Growth:

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Genrally GA inhibits the growth of roots (Stow and Yamaki, 1957). It has been reported that in lettuce and cucumber, radicle gets elon­gated due to GA action.

3. Stem elongation (Internodal elongation):

By far the most pronounced physiological effect of GA is in stem elongation particularly at the intern- odes. Seedlings of tomato, lettuce etc sprayed with GA show elongation of stem. This property of GA has been made use of in treating genetic dwarf­ism in plants. Moose, Osgood and Ginoza (1980) have reported that rosette sugarbeet treated with GA3 reached normal height with improved sugar con­tent. Similar have been the results of experimentation with dwarf varieties of pea and corn.

4. Apical dominance:

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The role of gibberellins in apical bud dominance is not certain. While the reports of Scott et al (1967) suggest that decapitatated shoots supplied with GA continued growth, the work of Hillman (1970 suggests an opposite effect. But in some instances at least gibberellins might promote apical growth by blocking the action of dormins (endogenous growth retardants that promote dormancy).

5. Bolting:

Development of elongated shoot (bolting) in dwarf plants is encouraged by the use of GA3.

6. Role in flowering:

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GA treatment to plants can substitute long day expo sure necessary for flowering. GA can also replace the effect of verbalization.

7. Cell division:

GA is known to activate cell division in vascular cambium The work of Lin and Loy (1976) has demonstrated that GA promotes cell division by stimulating cells in the G1 phase to enter the S phase and short­ening the S phase itself.

8. Male Sterlity:

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GA3 is known to induce male sterility in plants by sup­pressing the growth of androecium. Spraying of gibberellins in grapes supreses the development of stamens.

9. Parthenocrapy:

GA promotes the synthesis of the enzyme amylase in the aleurone layer of endosperm in germinating barly grains. This has been experimentally proved by the in vitro treatment of aleurone layer by GA.

10. Synthesis of amylase:

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GA promotes the synthesis of the enzyme in the aleurone layer of endosperm in germinating barley grains. This has been experimentally proved by the in vitro treatment of aleurone layer by GA.

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