THERMOPERIODIC CONTROL OF STEM ELONGATION AND ENDOGENOUS GIBBERELLINSIN CAMPANULA-ISOPHYLLA

The effect of day/night temperature regimes on stem elongation and on the content of endogenous gibberellins (GAs) in vegetatively propagate d plants of Campanula isophylla cv. Hvit have been studied. Compared w ith a constant temperature regime at 18 degrees C (18/18 degrees C), s tem and internode elongation was enhanced sig nificantly by a combinat ion of high day/low night temperature (21/15 degrees C) and inhibited by an opposite regime (15/21 degrees C). Gibberellins A(1), A(19), A(4 4), A(53), and A(97) were identified as endogenous components in Campa nula. (GA(97) was earlier referred to as 2 beta-OH-GA(53).) Quantitati ve analysis of the endogenous GAs indicates that temperature regimes t hat stimulate elongation growth are accompanied by an increase in the level of GA(1), GA(19), and GA(44). On the other hand, in plants grown under conditions that reduced stem elongation growth, there was an in creased level of GA(97).