Regulatory Mechanisms in Anthocyanin Biosynthesis in First Internodes of Sorghum vulgare: Effect of Presumed Inhibitors of Protein Synthesis.

There was a 6 to 24-hour lag in the production of anthocyanins in the light after excision of 4-day-old etiolated internodes of Sorghum vulgare variety Wheatland milo. In internodes infiltrated with water, apigeninidin was formed first at 12 to 24 hours and continued to be produced slowly. Luteolinidin was formed slightly later, but its formation rapidly exceeded that of apigeninidin. Cyanidin was the last type to be produced, but equaled the amounts of luteolinidin by 4 days. In noninfiltrated internodes, the production of cyanidin was greatly accelerated, beginning at about 6 hours.Data from experiments with inhibitors that presumably affect protein synthesis at different loci indicated that protein synthesis was necessary for maximum production of all 3 anthocyanins, but that different steps were rate limiting. Light independent synthesis of apigeninidin and luteolinidin was inhibited by chloramphenicol and l-ethionine but not by actinomycin D and 8-azaguanine. However, the synthesis of these 2 anthocyanins was not inhibited by puromycin, but was sometimes stimulated. The light-induced synthesis of cyanidin was inhibited by actinomycin, azaguanine, chloramphenicol and ethionine. Actinomycin no longer was inhibitory if added after incubation for 6 hours in air. All inhibitors were capable of inhibiting to various degrees either the incorporation of (14)C-uracil into RNA or (14)C-leucine into protein. The inhibitor data suggest that the light insensitive synthesis of apigeninidin and luteolinidin may be controlled by enzyme synthesis at the level of ribosomes via stable mRNA, while the light-induced production of cyanidin is dependent initially on the production of mRNA. The latter hypothesis is similar to that recently proposed by Lange and Mohr for a cyanidin produced in Sinapis seedlings.