ROLE OF ETHYLENE ON INDUCTION AND EXPRESSION OF CARROT SOMATIC EMBRYOGENESIS - RELATIONSHIP WITH POLYAMINE METABOLISM

The effects of ethylene on somatic embryogenesis were investigated dur ing the induction phase (with auxin) and expression phase (without aux in) in carrot (Daucus carota L.) cell cultures. The addition of 2-chlo roethylphosphonic acid (CEPA), an exogenous source of ethylene, during the induction phase or after day 7 of the expression phase did not af fect the level of somatic embryogenesis. However, an increase of ethyl ene concentration at the begining of the expression phase inhibited em bryo formation. During this same period, ethylene reduced the polyamin e formation from [U-C-14]arginine by inhibiting the activities of argi nine decarboxylase (ADC, EC 4.1.1.19) and S-adenosylmethionine decarbo xylase (SAMDC, EC 4.1.1.50). Furthermore, the addition of exogenous sp ermidine to ethylene-treated cells can restore the embryogenic potenti al of carrot cells. The results demonstrate that there is a physiologi cal relationship between ethylene, polyamine biosynthesis and somatic embryogenesis.