THE PROTEIN OF ROLB GENE ENHANCES SHOOT FORMATION IN TOBACCO LEAF EXPLANTS AND THIN CELL-LAYERS FROM PLANTS IN DIFFERENT PHYSIOLOGICAL STAGES

The objective was to determine whether the protein of rolB affects sho ot formation and whether this potential relationship depends on the de velopmental stages of the plant and/or on the culture conditions. Thin cell layers (TCL) and leaf explants were excised from tobacco plants in the vegetative and flowering stages and cultured under various horm onal conditions. In TCLs of vegetative-stage plants, the expression of rolB enhanced the formation of the shoot buds under hormone-free cond itions and with specific concentrations of auxin and/or cytokinin, His tological examination showed that the induction of the shoot meristemo ids was particularly enhanced by rolB protein and that meristemoid gro wth was accelerated. In leaf explants from vegetative-stage plants, th e expression of rolB increased the formation of shoot buds in the pres ence of 1 mu M IAA plus 1 or 10 mu M cytokinin, With BA alone, at a 0, 1 mu M concentration, shoot formation occurred in the transgenic expla nts only, whereas with concentrations ranging from 0.5 to in mu M, it was higher in these explants than in controls. RolB protein enhanced t he formation of shoot buds in TCLs from flowering plants under all hor monal conditions. In the presence of 1 mu M IAA and kinetin, the prote in also increased the flowering response. In leaf explants from flower ing plants, the expression of rolB increased the number of shoot buds in the presence of 1 mu M IAA with 10 mu M BA, In conclusion, rolB pro tein promotes shoot formation; it seems to have a positive interaction with cytokinin and an effect on the induction of the meristematic con dition.