Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

Abstract

The possible involvement of gibberellins (CAs) in the regulation of hypocotyl elongation by phytochrome was examined. Under white light the tal1 long hypocotyl (Ih) cucumber (Cucumis sativus L.) mutant, deficient in a type B-like phytochrome, shows an increased "responsiveness" (defined as response capability) to applied CA, (the main endogenous active CA) compared to the wild type. Supplementing far-red irradiation results in a similar increase in responsiveness in the wild type. Experiments involving application of the precursor GA, and of an inhibitor of CA, inactivation suggest that both the GA, activation and inactivation steps are phytochrome independent. Endogenous C A levels of whole seedlings were analyzed by combined gas chromatography-mass spectrometry using deuterated interna1 standards. The levels of GA, (and those of CA,,, the inactivated CA,) were lower in the //I mutant under low-irradiance fluorescent light compared with the wild type, similar to wild type under higher irradiance light during the initial hypocotyl extension phase, and higher during the phase of sustained growth, in which extension involved an increase in the number of cells in the upper region. In all cases, growth of the Ih mutant was more rapid than that of the wild type. It is proposed that CA, and phytochrome control cell elongation primarily through separate mechanisms that interact at a step close to the terminal response.

O afilhamento da aveia afetado pela qualidade da luz em plantas sob competição

“…A giberelina, porque pode alterar o alongamento celular em função de efeitos da qualidade da luz (WELLER et al, 1994;FOSTER et al, 1994;LÓPEZ-JUEZ et al, 1995;REED et al, 1996) e a citocinina por estimular a iniciação da divisão celular em afilhos (WANG & BELOW, 1996). Outra possibilidade é o fato de o fitocromo estar envolvido no controle de genes ligados à fotossíntese, codificando a síntese de clorofila a/b, pequenas subunidades da Rubisco e outros componentes do maquinário fotossintético (DALE, 1988).…”

Phytochrome Regulates Gibberellin Biosynthesis during Germination of Photoblastic Lettuce Seeds

“…In the case of phytochrome-deficient mutants of Brassica rapa (ein mutant) (Rood et al, 1990) and sorghum (ma 3 R mutant) (Beall et al, 1991), internode elongation of pea (Campell and Bonner, 1986;Sponsel, 1986), epicotyl elongation of cowpea (Martínez-García and García-Martínez, 1992), and hypocotyl elongation of lettuce (Toyomasu et al, 1992), it was proposed that phytochrome may affect the endogenous levels of GA through its affects on GA biosynthesis and turnover. It was also suggested that phytochrome may affect the response of tissue to GA, as in epicotyl elongation of cowpea (Martínez-García and García-Martínez, 1992), mesocotyl elongation of rice (Nick and Furuya, 1993;Toyomasu et al, 1994), and hypocotyl elongation of cucumber (lh mutant) (Ló pez-Juez et al, 1995). Phytochrome could, therefore, affect GA biosynthesis and/or response of tissue to GA in elongation growth.…”

The highs and lows of plant life: temperature and light interactions in development

“…It is likely that phyB contributes to this response in fuchsia as it been shown to have a prominent role in the control of hypocotyl and stem elongation in several other species. Indeed, phyB mutants in Arabidopsis, pea (lv) and cucumber (lh) all have constitutively elongated phenotypes (Reed et al, 1993;Weller, 1994;López-Juez et al, 1995). In pea and cucumber the phyBmediated differences in hypocotyl elongation seem to result from differences in GA responsiveness of endogenous levels and not GA levels per se.…”