Effects of proline and betaine on heat inactivation of ribulose-1,5-bisphosphate carboxylase/oxygenase in crude extracts of rice seedlings

Activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) in hea ted crude extracts from seedlings of the rice cultivars Hitomebore and 1R28 was investigated in the presence of proline and betaine. Both solutes reta rded the inactivation of the enzyme extracted from the leaves of both culti vars at temperature-stress from 35 to 45 degrees C. At 50 degrees C, howeve r, betaine was effective in both cultivars. Stabilization of RuBPCO activit y was independent of die added solute from 1 to 2 M concentration