RESUMO
The expression of the Agrobacterium rhizogenes rolD oncogene induces precocious floral transition and strong flowering potential in tobacco and tomato. Here, we describe specific developmental effects induced by expression of rolD in Arabidopsis. We show that floral transition, as histologically monitored, occurred in rolD- plants earlier than in wild type, and this was coupled with a premature and enhanced formation of vegetative and reproductive axillary bud meristems. Furthermore, CYP79F1/SUPERSHOOT/BUSHY (SPS), a gene that negatively controls shoot branching in Arabidopsis and involved in glucosinolate metabolism and in cytokinin and auxin homeostasis, was down-regulated in rolD plants. The multiplication of post-embryonic meristems was also observed in the root system, with enhanced adventitious root formation. This result was confirmed by thin cell layer response in vitro, both under hormone-free and standard rooting conditions. However, the formation of lateral root meristems was not affected by rolD expression. Our results show that rolD accelerates and enhances specific post-embryonic meristems in Arabidopsis.
Assuntos
Arabidopsis/genética , Proteínas de Bactérias/genética , Meristema/genética , Plantas Geneticamente Modificadas/genética , Arabidopsis/crescimento & desenvolvimento , Sistema Enzimático do Citocromo P-450/genética , Flores/genética , Flores/crescimento & desenvolvimento , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Meristema/crescimento & desenvolvimento , Fenótipo , Folhas de Planta/genética , Folhas de Planta/crescimento & desenvolvimento , Raízes de Plantas/crescimento & desenvolvimento , Brotos de Planta/genética , Brotos de Planta/crescimento & desenvolvimento , Caules de Planta/genética , Caules de Planta/crescimento & desenvolvimento , Plantas Geneticamente Modificadas/crescimento & desenvolvimento , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Rhizobium/genéticaRESUMO
Long-sized oligogalacturonides (OGs) are cell wall fragments that induce defence and developmental responses. The Ca(2+)-dependent "egg-box" conformation is required for their activity, and polyamines may prevent them from adopting this conformation. Although OGs are known to inhibit auxin-induced growth processes, their effect on cytokinin-induced ones requires investigation. In the present work OGs were shown to promote cytokinin (benzyladenine, BA)-induced vegetative shoot formation from tobacco leaf explants, independent of the presence of CaCl(2) in the medium and of auxin (indoleacetic acid, IAA) supply. The effect of polyamines, putrescine (PU) and spermidine (SD) supplied with/without their biosynthetic inhibitors (DFMO, CHA) was also investigated, and showed that spermidine enhanced adventitious vegetative shoot formation, but only on medium containing Ca(2+) and IAA. Treatments with inhibitors blocked this promotive effect. OGs did not alter free polyamine concentrations, but caused a moderate increase of conjugated ones, and exhibited an early inhibitory effect on polyamine biosynthetic gene expression. OGs, but not SD, caused long-term changes in calcium-associated epifluorescent signals in the cell walls, and, later, inside the cells of specific tissues. Electron microscopy analysis (ESI system) demonstrated that calcium accumulated in the cell walls and vacuoles of OG-cultured explants. The relationship between OGs, cytokinin, calcium, and polyamines in adventitious vegetative shoot formation is discussed.