Non‐Reversibility of Gibberellin‐Induced Inhibition of Regeneration in Begonia Leaves

Abstract

AbstractWith applied to the petioles of detached Begonia x cheimantha leaves before planting, Gibberellic acid (GA3) inhibited the formation of adventitious buds and roots ill an apparently irreversible manner. Bud formation was entirely suppressed by 10−6M and higher concentrations and a significant inhibition was still present at 10−9M the lowest concentration tested. Root formation was not affected by GA3 below 10−7M and was possible even at 10−4 M GA3. Petiole elongation was stimulated by GA3 with an optimum at 10−5M.GA3 also blocked the action of 6‐benzyiamino‐purine (BAP) and 1‐naphthaleneacetic acid (NAA), compounds which are potent stimulators of bud and root formation, respectively. When applied simultaneously with GA3 they were, at their optimal concentrations, devoid of any effect in counteracting or reversing the gibberellin‐induced inhibitions. Abscisic acid and the growth retardants CCC and Phosfon also were unable to restore bud and root formation.In leaves initially treated with water or 10−5M BAP, endogenous bud and root formation as well as BAP‐induced bud formation were entirety suppressed when 10−5M GA3 was applied 8 days after the initial treatments. Even when delayed for 14 days GA3 treatment inhibited BAP‐induced bud formation, while treatment after 21 days bad little effect on bud and root formation. Development of pre‐existing, visible bud primordia was not inhibited by GA3.BAP and NAA competitively inhibited the action of GA3 in petiole extension growth.The results are discussed in relation to results obtained in other plant systems. It is suggested that GA3 acts by blocking of the organized cell divisions initiating the formation of bud and root primordia.