Plant and Cell Physiology Advance Access published online on March 22, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm034
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Flowering in Tobacco Needs Gibberellins but is not Promoted by the Levels of Active GA1 and GA4 in the Apical Shoot
1 Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-CSIC, Avda. de los Naranjos s/n, 46022 Valencia, Spain; 2 Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Science, S-90183 Umeå, Sweden.
Corresponding Author; Name: Isabel López-Díaz, Present address: Instituto de Biología Molecular y Celular de Plantas, Universidad Politecnica de Valencia-CSIC, Avda. de los Naranjos s/n, 46022 Valencia, Spain. telephone: + 34 963877866; fax: + 34 963877859. E-mail: ilopez{at}ibmcp.upv.es
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Abstract |
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Flowering of Nicotiana tabacum cv Xhanti depends on gibberellins (GAs) because GA deficient plants, due to over-expression of a GA 2-oxidase gene (35S:NoGA2ox3; Ubeda-Tomás et al., 2006) or to treatment with the GA biosynthesis inhibitor Paclobutrazol, flowered later than wild type. These plants also showed inhibition of the expression of molecular markers related to floral transition (NtMADS-4 and NtMADS-11; Jang et al., 2002). To further investigate the role of GA on flowering we quantified its content in tobacco plants during development. We found a progressive reduction in the levels of GA1 and GA4 in the apical shoot during vegetative growth, reaching very low levels at floral transition and beyond. This excludes these two GAs as flowering promoting factors in the apex. The evolution of active GA content in apical shoots agrees with the expression patterns of GA metabolism genes: two encoding GA 20-oxidases (NtGA20ox1=Ntc12, NtGA20ox2=Ntc16), one encoding a GA 3-oxidase (NtGA3ox1=Nty) and one encoding a GA 2-oxidase (NtGA2ox1), suggesting that active GAs are locally synthesized. In young apical leaves, GA1 and GA4 content and GA metabolism gene expression were rather constant. Our results support that floral transition in tobacco, in contrast to Arabidopsis, is not regulated by the levels of GA1 and GA4 in apical shoots, although reaching a threshold in GA levels may be necessary to allow meristem competence for flowering.
Keywords: gibberellins - flowering - tobacco
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