Photochemical dimerization of ferulic Acid by chloroplasts from sorghum.

Sorghum (Sorghum bicolor) chloroplasts, lamellar fragments, and Triton X-100 solubilized preparations catalyze a blue and red light-sensitized oxidation of ferulic acid to its beta-beta-linked dimer and its hydrolysis product, the acid dimer. Exogenous superoxide dismutase had no effect, and catalase and 1 to 10 mm KCN inhibited this photooxidative dimerization only in detergent-treated chloroplasts. It is postulated that the final oxidant is H(2)O(2), formed by light-induced photosystem I electron transport, followed by an unidentified peroxidatic activity. The reaction differs, however, from that catalyzed by horseradish peroxidase in the presence of H(2)O(2).