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 A 3 (GA 3 ) reduced the number of leaf nodes at flowering and time to flowering and increased the stem height at flowering in three genotypes of spring rape ( Brassica napus var. annua L.). The responses to GA 3 were similar to those for long days (LD) and low-temperature treatments, suggesting that the effect of photoperiod and the vernalization response are probably mediated through gibberellins. The response to exogenous GA 3 was 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 small increase in the number of leaf nodes at flowering and time to flowering and a small decrease in the stem height at flowering, but unexpectedly, its effect was hardly influenced by the application of exogenous GA 3 . Genotypes that showed the clearest responses to the treatments with regard to the number of leaf nodes at flowering and time to flowering did not show the clearest responses with regard to the stem height at flowering; the pattern of responses of the number of leaf nodes at flowering and time to flowering was distinct from that of stem height at flowering. This indicates that flower formation and stem elongation are separable developmental processes which may be controlled by different endogenous gibberellins, different levels of a specific endogenous gibberellin, or different responses to gibberellin.