Action of gibberellic acid on the mitotic activity of the different zones of the shoot apex ofRudbeckia bicolor andPerilla nankinensis

Summary The influence of GA on the mitotic activity of each zone of the shoot apex is studied in two species having strikingly different morphogenetic responses to the chemical.InRudbeckia bicolor, the stimulation of mitoses mostly occurs in the central zone. This fact is related to the subsequent flowering of the plant. InPerilla nankinensis, the activation is more general and affects the central and the peripheral zones. It is connected to an acceleration of the plastochronic functioning.Therefore, the action of GA differs following the species and following the meristematic zones.In the pith, no increase of the length of the cells is apparent in either case, but the mitotic activity is enhanced. This increase of the number of cell divisions provokes the bolting ofRudbeckia and the elongation ofPerilla.With 1 Figure in the Text