High-resolution Analysis of the Effect of DIF and Growth Regulators on Stem Elongation in Zinnia

Abstract

Instantaneous stem elongation rates (SER) in zinnia (Zinnia elegans cv. Pompon) treated with daminozide (B-Nine) or gibberellic acid (GA3) were recorded in 3 DIF regimes (+5, –5, 0; daily average 18.7C). Two developmental stages were chosen for study: Stage 1 was vegetative growth before flower bud formation Stage 2 was the period before anthesis. At both stages, patterns of SER and total diurnal growth were influenced by DIF regime. The application of GA3 increased SER in a more or less additive manner over all phases of the diurnal growth cycle and daminozide similarly reduced SER. Neither GA3 or daminozide application transformed growth patterns to match those of positive or negative DIF plants, respectively. Instead. the growth regulators only enhanced or reduced total diurnal growth without modifying the effects of DIF. This suggests that DIF can influence stem elongation growth in a manner which is independent of the effects of gibberellin.