Kinetics of Endogenous Cytokinin, IAA and ABA Levels in Relation to the Growth and Morphology of Tobacco Crown Gall Tissue

Abstract

The kinetics of endogenous cytokinin, IAA and ABA levels during the growth cycle of a wild-type tobacco crown gall (W38-B6S3) were compared with that of a shoot-inducing (Shi-) mutant. In both tumor types, high IAA and cytokinin (essentially ribosyl-trans-zeatin and its corresponding glucoside) levels were built up by the end of the linear growth phase and maintained during the greater part of the exponential growth period. The stationary phase was preceded by a very drastic decrease in the endogenous level of both hormones. Quantitatively, the wild-type tumour showed a higher IAA level and a reduced cytokinin level compared with the Shi- mutant. No significantly different endogenous ABA pattern was observed. The reduced cytokinin level might correspond to the ratio of transformed/untransformed cells in the wild-type tumour whereas the reduced IAA level in the Shi- mutant may be correlated with the deletion of gene 2 in the T-DNA of the pGV 2206 Ti plasmid. The elevated cytokinin/IAA ratio induced shooting mainly of the untransformed cells in the Shi- mutant tissue whereas in the wild-type, the shoot suppression was compatible with the reduced cytokinin/IAA ratio.