Effect of α-Tocopherol, β-Carotene, Monogalactosyldiglyceride and Phosphatidylcholine on Light-Induced Degradation of Chlorophyll a in Acetone

The effect of α-tocopherol, β-carotene, monogalactosyldi-glyceride and phosphatidylcholine on red light induced degradation of chlorophyll a was studied in acetone at 4°C. Monogalaclosyldi-glyceride was ineffective up to a molar ratio of monogalactosyldi glyceride to chlorophyll of 1:10. α-Tocopherol, β-carotene and phosphatidylcholine inhibited chlorophyll degradation. Maximal protection by α tocopherol and β-carotene was similar (76%) but on a molar basis a tocopherol was less effective. Protection by phosphatidylcholine was less than by a tocopherol and α-carotene but the lipid was effective at a lower ratio of chlorophyll to protectant. Inhibition by phosphatidylcholine was independent of the degree of unsaturation of the fatty acids. Effects of β-carotene and α-tocopherol were additive at suboptimal concentrations, but addition did not increase the maximal protection of 76% by these substances alone. Phosphatidylcholine increased the effectiveness of α-tocopherol and β-carotene independent of their concentrations. It is suggested that interactions between lipids participate in the mechanism protecting chlorophyll a against photooxidation in the chloroplast membrane.