Effects of interactions between low-temperature treatments, gibberellin (GA(3)) and photoperiod on flowering and stem height of spring rape (Brassicanapus var. annua)

Exogenous gibberellin A(3) (GA(3)) reduced the number of leaf nodes at flow ering and time to flowering and increased the stem height at flowering in t hree 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 trea tments, suggesting that the effect of photoperiod and the vernalization res ponse are probably mediated through gibberellins. The response to exogenous GA(3) was greatest in non-cold-treated plants in short days (SD) suggestin g that endogenous GAs are limiting in these conditions. CCC, an inhibitor o f gibberellin biosynthesis, caused a small increase in the number of leaf n odes at dowering and time to flowering and a small decrease in the stem hei ght at flowering, but unexpectedly, its effect was hardly influenced by the application of exogenous GA(3). Genotypes that showed the dearest response s to the treatments with regard to the number of leaf nodes at flowering an d time to flowering did not show the dearest responses with regard to the s tem height at flowering; the pattern of responses of the number of leaf nod es 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 end ogenous gibberellins, different levels of a specific endogenous gibberellin , or different responses to gibberellin. (C) 1999 Annals of Botany Company.