Developmental Effects of Sandoz 6706 on Activities of Enzymes of Phenolic and General Metabolism in Barley Shoots Grown in the Dark or under Low or High Intensity Light

The activities of three enzymes of phenolic biosynthesis and six of general metabolism were studied at 24-hour intervals between the 3rd and 8th day after planting in barley shoots treated with the chlorosis-inducing herbicide Sandoz 6706 and grown in the dark or under high or low intensity light. The herbicide had no effect on fresh weight or soluble protein (per shoot) in plants grown in the dark or under low intensity light, but slightly decreased these parameters in plants grown for more than 5 days under high intensity light. In dark-grown seedlings the herbicide had no detectable effects on plastid ultrastructure or on the activity of malate dehydrogenase, cytochrome c oxidase, NADP-cytochrome c reductase, triose phosphate isomerase, peroxidase, catalase, shikimate dehydrogenase, phenylalanine ammonia-lyase, or chalcone-flavanone isomerase. Under low intensity light, Sandoz 6706-treated plants developed plastids with single thylakoids extending across the organelle, and the activity of all enzymes examined was increased to varying degrees. When the herbicide-treated plants were grown under high intensity light, plastid lamellar organization was severely disrupted. Activities of shikimate dehydrogenase and chalcone-flavanone isomerase were markedly enhanced, phenylalanine ammonia-lyase activity slightly promoted, and catalase activity severely inhibited. The other enzymes were not appreciably affected by Sandoz 6706 under high intensity light. It is concluded that the changes in plastid ultrastructure and enzyme activities of the herbicide-treated plants are largely secondary photomorphogenetic or photooxidative responses in the carotenoid-free plants in which chlorophylls accumulate in reduced amounts (low intensity light) or are completely absent (high intensity light).