Far-red light stimulates internode elongation, cell division, cell elongation, and gibberellin levels in bean

The contributions of cell division and cell elongation and the potential role of gibberellins in the far-red light stimulation of bean internode elongation were investigated. When bean plants, Phaseolus vulgaris cv. Kentucky Wonder, were grown in white light supplemented with far-red light a significant increase, up to threefold, in internode elongation was observed. Microscopic examination revealed that cell lengths were also increased but by a lower magnitude than internode length. Cell-labeling studies with [H-3]thymidine showed that nuclei labeling was increased in internodes receiving supplemental far-red light. Thus far-red light induced increased internode elongation is a result of both increased cell elongation and increased cell division. Gibberellins A(1), A(20), A(19), A(44), and A(4) and kaurenoic acid were identified in extracts of internode tissue by gas chromatography - mass spectroscopy using [H-2(2)]-labeled internal standards for quantification. It thus appears that the early C-13 hydroxylation pathway is operative in the elongating internode. Endogenous GA(1) and GA(20) were approximately twofold higher in the first internodes of plants receiving supplemental far-red light. A comparison of the metabolism of exogenously supplied [H-2(2)]GA(19) suggested that GA turnover was greater in tissues exposed to supplemental far-red light. These results indicate that both cell division and elongation contribute to the enhanced elongation response of bean internodes to far-red light and that these processes are correlated with an increase in CA levels and (or) metabolism.