Question

How were gibberellins discovered? Explain two experiments in order to show the effects of gibberellins.

Answer 1

Kurosawa, a Japanese botanist, discovered gibberellin while investigating the rice foolish seedling disease in which spindly seedlings are formed due to GA like compounds produced by the fungus ( Gibberella fujikuroi) infecting the plant. ( see text for more information) .
Experiment 1:
Several suitable seedlings of Vigna or Phaseolus are grown in two Petri dishes. One lot of seedlings is sprayed with 20 ppm gibberellic acid (GA3) solution with the help of an ato­miser or a sprayer. The other lot is sprayed with distilled water which serves as a control. Observations are made after one week by measuring the height of the seedlings.
Observation
It is observed that the height of the gibberellin-treated seedlings has increased considerably compared to that of control seedlings.
Experiment 2:
Three lots of Vigna or Phaseolus seedlings are grown in three Petri dishes. One lot is kept in dark and the other two lots are kept in light of which one lot is sprayed with 20 ppm gibberellic acid (GAg) solu­tion. The stem growth of the seedlings in each case is measured and com­pared.
Observation
Light has an inhibitory effect on stem elongation. Appli­cation of gibberellin to the plants growing in light greatly increases their stem growth. Reversal of light-induced inhibition of stem elongation by application of gibberellin suggests that endogenous gibberellin is the limiting factor in stem growth.
It may be concluded that light causes inhibition of stem growth by lowering the level of endogenous gibberellin and this inhibi­tion is erased by applying exogenous gibberellin to the plants.