THERMOMORPHOGENIC AND PHOTOMORPHOGENIC CONTROL OF STEM ELONGATION IN FUCHSIA IS NOT MEDIATED BY CHANGES IN RESPONSIVENESS TO GIBBERELLINS

Stem elongation in Fuchsia x hybrida was influenced by cultivation at different day and night temperatures or in different light qualities. Internode elongation of plants grown at a day (25 degrees C) to night (15 degrees C) temperature difference (DIF+10) in white light was almo st twofold that of plants grown at the opposite temperature regime (DI F-10). Orange light resulted in a threefold stimulation of internode e longation compared with white light DIF-10. Surprisingly, internode el ongation in orange light was similar for plants grown at DIF-10 and DI F+10. Flower development was accelerated at DIF-10 compared with DIF+1 0 in both white and orange light. To examine whether the effects of DI F and light quality on shoot elongation were related to changes in gib berellin metabolism or plant sensitivity to gibberellins (GAs), the st em elongation responses of paclobutrazol-treated plants to applied gib berellins were determined. In the absence of applied gibberellins pacl obutrazol (>0.32 mu mol plant(-1)) strongly retarded shoot elongation. This inhibition was nullified by the application of about 10-32 nmol of GA(1), GA(4), GA(9), GA(15), GA(19), GA(20), GA(24), or GA(44). The results are discussed in relation to possible effects of DIF and ligh t quality on endogenous gibberellin levels and gibberellin sensitivity of fuchsia and their effects on stem elongation.