Comparative Biological Effectiveness of the Gibberellins

SINCE the isolation 1 of gibberellin A (later identified 2 as a mixture of gibberellins A 1 , A 2 and A 3 ) and more recently the discovery 3 of gibberellin A 4 , numerous physiological responses have been induced in plants 4 with the gibberellins. Takahashi et al. 2 reported that A 1 , A 2 and A 3 all possessed strong physiological activities in stimulating the elongation of rice seedlings. Apart from this reference, the gibberellins have not been evaluated in terms of specific biological activities. The comparative effectiveness of gibberellins A 1 , A 2 , A 3 and A 4 and the methyl esters of A 1 and A 3 in promoting vegetative extension, flowering of facultative long-day annuals and in fruit setting is now reported 5 .