CONTROL OF CARROT SOMATIC EMBRYOGENESIS BY AGNO3, AN INHIBITOR OF ETHYLENE ACTION - EFFECT ON ARGININE DECARBOXYLASE ACTIVITY

The effects of AgNO3 and ethylene, released by exogenous supplied 2-chloroethylphosphonic acid (Ethephon), were studied on somatic embryogenesis by carrot (Daucus carota L.) cell suspension cultures. AgNO3, at concentrations of 10-20 μM, caused a 2-fold increase in the number of somatic embryos. At these concentrations AgNO3 did not cause adverse effects on cell survival, medium pH or growth; only a slight increase in ethylene production was observed. However, 1 mg·1-1 or 10 mg·1-1 Ethephon provoked a substantial decrease in the somatic embryo formation: inhibitory rates of 15% and 50% were recorded, respectively. The activity of arginine decarboxylase (ADC) (EC 4.1.1.19), a key enzyme of the polyamine pathway, was significantly stimulated by AgNO3 during the first 4 days of somatic embryogenesis, whereas Ethephon reduced it: 30% inhibition was recorded at 10 mg·1-1 Ethephon. On the basis of these findings, it is suggested that AgNO3 stimulates carrot somatic embryogenesis by inhibiting ethylene action; its implication in the control of ADC activity is discussed. © 1990.