CHANGES IN PHENOLIC COMPOUNDS AND RELATED ENZYMES IN YOUNG PLANTS OF SORGHUM

The major flavonoid in vegetative green shoots of Sorghum vulgare var. Wheatland milo. has been identified as luteolin-7-glucoside. Minor amounts of apigenin-7-glucoside and possible diglycosides or C-glycosyl derivatives of the above flavones, as well as occasional production of the cyanidin glycoside present in seedlings, were detected. Luteolin-7-glucoside and the esters of phenolic acids, especially of caffeic acid, have similar developmental patterns, increasing to a maximum at about 10 days after germination and subsequently at a constant or slightly decreasing rate up to 30 days when based on fresh weight. Polyphenolase activity can be detected spectrophotometrically in only small amounts in etiolated seedlings; its activity begins to increase rapidly in green shoots 4-5 days after germination at a rate similar to that of the accumulation of the ester of caffeic acid. Chlorogenic acid was the most active substrate for the enzyme; others in order of decreasing activity were catechol, p-cresol, DOPA, and p-hydroxycinnamic acid. The presence of an inhibitor or latent enzyme in etiolated seedlings has not been ruled out, but the possibility of a second enzyme capable of hydroxylating p-hydroxycinnamic acid is discussed. Since a microsomal fraction contains phenylalanine and tyrosine ammonia lyase and cinnamic acid hydroxylase activities, this second hydroxylating enzyme of monophenols might be a part of an enzyme complex converting the amino acids to the C6-C3 phenolic acids. © 1970.