Early responses to gibberellic acid in a dwarf maize mutant (Zea mays L. d 1)

Early effects of gibberellic acid (GA3) (1-4 h treatment) on the ion ratios in a dwarf maize mutant (Zea mays L. d 1) showing normal growth after hormone treatment, have been investigated by electron microprobe analysis. GA3 exerts a different effect on the ion ratios in plastids, cytoplasm and vacuoles in short term experiments. The Cl content of chloroplasts and cytoplasm increases without a lag phase after GA3 treatment. The K content of plastids increases after a lag phase of 2 h, whereas in the cytoplasm an increase can be observed immediately after GA3 addition. The hormone has only little influence on the Ca content of the cell compartments investigated. Control experiments with water and the physiologically inactive GA3 methylester confirm the specifity of the short-term actions of GA3 on the ion ratios. The primary action of GA3 at the membrane level is discussed.