The Effects of Linolenic Acid and Extracts of Ricinus Leaf on System I and System II

Abstract

The action of extracts of Ricinus communis leaf (RLE) and of linolenic acid (LINO) on System I and System II of corn and spinach chloroplasts were investigated by an amperometric method. RLE induced a time dependent decrease in the rate of oxygen production by corn chloroplasts (half time about one hour) at low white light intensity (900 ergs/cm2 sec.). At high white light intensity (7 x 103 ergs/cm2 sec.) the maximum value of the oxygen gush, V0, was observed to decrease with time in the presence of RLE; the steady state rate of oxygen production, Vm, also decreased under these conditions. The ratio, V0/Vm, decreased immediately upon addition of RLE, then increased with time. The effect of RLE on System I was much more rapid than on System II. In less than one hour all activity of System I disappeared. At high white light intensity addition of 1.6 x 10-4 M LINO to spinach chloroplasts induced a time dependent decrease of V0 and increase of Vm. The latter effect is indicative of uncoupling of phosphorylation. The ratio V0/Vm decreased both with time of incubation and concentration of LINO. On the other hand, at concentrations less than 10-4 M, LINO has little effect on System I. It is concluded that both RLE and LINO may be acting on the reaction center of System II. It appears that RLE contains a fraction that specifically acts to immediately reduce the number of System I reaction centers.