Promotion of Cell Division in Tissue Cultures by Gibberellic Acid

Abstract

IT is well established that gibberellic acid (GA) stimulates not only cell extension but also cell division in intact plants^1,2. It has been shown that cambial division is stimulated when GA is applied to disbudded woody shoots (including those of Acer pseudoplatanus)², but that the derivative cells do not undergo further expansion and differentiation unless indolyl-3-acetic acid is also supplied; moreover, the rate of cambial division is greatly enhanced when both hormones are applied simultaneously. Reports on the effects of GA on the growth of tissue cultures are more contradictory. Netien³ states that GA inhibits callus tissue growth while Schroeder and Specta⁴ obtained an increase in callus tissue growth in the presence of GA. Nickell et al.⁵ investigated a large number of tissues grown in callus culture and found that GA (10 p.p.m.) in some cases caused promotion and in other cases caused inhibition of growth. These experiments were carried out on callus cultures grown on agar and in all cases the results were expressed in terms of fresh weight increase. It cannot be said from this whether GA is effecting cell division or cell enlargement, though Schroeder et al. suggest from anatomical observations that there was an increase in cell number in their experiments.