Quantitative analysis of protein changes during meristem intiation and bud development in protoplast-derived Petunia hybrida callus

Small calluses from Petunia hybrida leaf protoplasts differentiated into meristems and then vegetative buds in the presence of high cytokinin concentrations. Total proteins from calluses grown at two cytokinin concentrations, of which only the highest induced bud formation, were analysed for molecular markers of cytokinin action by two-dimensional electrophoresis. The protein patterns were also compared to those of differentiated shoots and roots and to those of calluses grown under various hormonal conditions. Five percent of the total proteins detected by this method varied significantly in their level of expression according to the treatment. Quantification by image analysis demonstrated the occurrence of five groups of polypeptides with different expression patterns. Polypeptides from group 1 marked the development of buds and were abundant in young photosynthetic organs from whole plants. Polypeptides from group 5 increased only in calluses grown on control medium, i.e. in the presence of the lowest cytokinin concentration. No protein increased specifically during meristem formation. The possible action of cytokinin on regeneration is discussed in relation to these results.