POLYAMINE METABOLISM AND ETHYLENE BIOSYNTHESIS IN NORMAL AND HABITUATED SUGAR-BEET CALLUS

The optimal assay conditions and the trend with time in culture (28 da ys) of arginine decarboxylase (ADC; EC 4.1.1.19), ornithine decarboxyl ase (ODC. EC 4.1.1.17) and diamine oxidase (DAO; EC 1.4.3.6) activitie s in habituated (I-I) and normal (N) auxin- and cytokinin-requiring su gar beet callus were compared. Although the response to variations in buffer pH and EDTA and pyridoxal phosphate (PLP) concentrations varied for ADC and ODC activities between the two callus types, pH 8.3, 50 m u M PLP and 5 mM EDTA were generally optimal or near-optimal for both H and N callus. In most cases the addition of ornithine or arginine in the ADC and ODC assays, respectively, given to block the interconvers ion between the two substrates, resulted in lower (CO2)-C-14 recovery. DAO activity was very differently affected in H and N callus by the p resence of polyvinylpyrrolidone in the extraction buffer. However, in both cases, this activity increased with time in culture. ADC activity was always predominant in both cell lines and always higher in N call us. In the latter, ADC activity rose sharply between days 14 and 21 an d then leveled off while in H callus it increased steadily from day 14 onwards. ODC activity was also higher in N callus and peaked sharply on day 21 while in H callus it was not detectable in the second half o f the culture period. In both cell lines this activity was low or nil on day 28. 3,4-[C-14]-methionine incorporation into ethylene and polya mines was also compared in N and H callus. In the latter, ethylene syn thesis was lower and [C-14]-spermidine formation higher than in N call us. This is in accord with the significantly higher spermidine titres found in H callus.