Gibberellic acid induced elongation of lettuce hypocotyls and its inhibition by colchicine

Lettuce (Lactuca sativa L.) seedlings treated with gibberellic acid (GA) for 72 h produced hypocotyls 600% longer than the water controls. The process of elongation was accelerated by GA. Also, for maximum elongation, presence of GA was not necessary after 20 h. Short term treatments of seedlings with GA indicated that the seedlings were most 'sensitive' to GA after 8 h of growth in water. Colchicine inhibited the GA-induced elongation. Its effect was maximal if it was applied within the first 2 h after GA treatment irrespective of the stage of hypocotyl development; the inhibition was progressively lessened after 2 h and lost after 36 h. These kinetic data are presented together with measurements of hypocotyl cell lengths and widths and provide a basis for correlated ultrastructural studies.