INTERACTIONS BETWEEN BIOMASS PRODUCTION AND ETHYLENE BIOSYNTHESIS IN COPPER-TREATED RICE

Rice (Oryza sativa L.) plants were grown over a 30-day-period in nutrient solutions containing increasing copper (Cu) concentrations (0.002, 0.01, 0.05, 0.25, 1.25, and 6.25 mg/L). It was observed that in both root and leaf tissues the total activity of 1-aminocyclopropane-1-carboxylate synthase decreased at concentrations above 0.05 mg/L Cu treatment, whereas the total activity of the ethylene forming enzyme slightly increased until the 1.25 mg/L Cu treatment. In the root and leaf tissues, the 1-aminocyclopropane-1-carboxylic acid concentrations decreased after the 0.05 mg/L and 0.01 mg/L Cu treatments, respectively, whereas the ethylene production decreased in both tissues after the 0.05 mg/L Cu treatment. It is proposed that excess Cu in both root and leaf tissues decrease the conversion of S-adenosylmethionine to 1-aminocyclopropane-1-carboxylic acid through the inhibition of the total 1-aminocyclopropane-1-carboxylate synthase activity. The concomitant effect of this inhibition on adventitious root formation and leaf senescence is evaluated.