Flowering in tobacco [Nicotiana tabacum] needs gibberellins but is not promoted by the levels of active GA1 and GA4 in the apical shoot

Gallego Giraldo, L.; Garcia Martinez, J.L.; Moritz, T.; Lopez Diaz, I.

Flowering in tobacco [Nicotiana tabacum] needs gibberellins but is not promoted by the levels of active GA1 and GA4 in the apical shoot

2007

Gallego Giraldo, L.(Universidad Politecnica de Valencia (Spain)) | Garcia Martinez, J.L. | Moritz, T. | Lopez Diaz, I.

Flowering of Nicotiana tabacum cv Xhanti depends on gibberellins because gibberellin-deficient plants, due to overexpression of a gibberellin 2-Oxidase gene (35S:NoGA 2ox3) or to treatment with the gibberellin 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). To investigate further the role of gibberellin in flowering, we quantified its content in tobacco plants during development. We found a progressive reduction in the levels of GAsub(1) and GAsub(4) in the apical shoot during vegetative growth, reaching very low levels at floral transition and beyond. This excludes these two gibberellins as flowering-promoting factors in the apex. The evolution of active gibberellin content in apical shoots agrees with the expression patterns of gibberellin metabolism genes: two encoding gibberellin 20-oxidases (NtGA20ox1=Ntc12, NtGA20ox2=Ntc16), one encoding a gibberellin 3-oxidase (NtGA3ox1=Nty) and one encoding a gibberellin 2-oxidase (NtGA2ox1), suggesting that active gibberellins are locally synthesized. In young apical leaves, GAsub(1) and GAsub(4) content and the expression of gibberellin metabolism genes were rather constant. Our results support that floral transition in tobacco, in contrast to that in Arabidopsis, is not regulated by the levels of GAsub(1) and GAsub(4) in apical shoots, although reaching a threshold in gibberellin levels may be necessary to allow meristem competence for flowering.

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