Effects of Interactions between Low-temperature Treatments, Gibberellin (GA3) and Photoperiod on Flowering and Stem Height of Spring Rape (Brassica napus var. annua)

Exogenous gibberellin A₃(GA₃) reduced the number of leaf nodesat flowering and time to flowering and increased the stem heightat flowering in three genotypes of spring rape (Brassica napusvar.annua L.). The responses to GA₃were similar to those forlong days (LD) and low-temperature treatments, suggesting thatthe effect of photoperiod and the vernalization response areprobably mediated through gibberellins. The response to exogenousGA₃was greatest in non-cold-treated plants in short days (SD)suggesting that endogenous GAs are limiting in these conditions.CCC, an inhibitor of gibberellin biosynthesis, caused a smallincrease in the number of leaf nodes at flowering and time toflowering and a small decrease in the stem height at flowering,but unexpectedly, its effect was hardly influenced by the applicationof exogenous GA₃. Genotypes that showed the clearest responsesto the treatments with regard to the number of leaf nodes atflowering and time to flowering did not show the clearest responseswith regard to the stem height at flowering; the pattern ofresponses of the number of leaf nodes at flowering and timeto flowering was distinct from that of stem height at flowering.This indicates that flower formation and stem elongation areseparable developmental processes which may be controlled bydifferent endogenous gibberellins, different levels of a specificendogenous gibberellin, or different responses to gibberellin.Copyright 1999 Annals of Botany Company Brassica napus var. annua, gibberellin, photoperiod, spring rape, vernalization.