Developmental Changes in Flavonoids and Enzyme Activities of Primary Leaves from Field-Grown Barley

Abstract

C-glycosylflavone levels, fresh weight, soluble protein, and activities of eight enzymes of phenolic and general metabolism were investigated in primary leaves of field-grown Atlas 68 barley over a 35-day period from juvenility to leaf senescence. Three distinct patterns of metabolic activity were found. Phenylalanine ammonia-lyase and shikimate dehydrogenase levels were highest during the earliest stages of leaf development and decreased progressively as the leaves matured. Catalase, malate dehydrogenase, cytochrome c oxidase, soluble protein, the flavonoids saponarin and lutonarin, and fresh weight showed dramatic increases during the early development of the leaves, reached maximum levels around 15-20 days, and decreased progressively as the leaves senesced. Peroxidase, polyphenol oxidase, and chalcone-flavanone isomerase activities were maximal at 15-20 days, decreased, but exhibited a surge of activity just prior to death of the primary leaves. When 15-day-old leaves were divided into apical, middle and basal sections of equivalent lengths, the basal portion had the highest levels of peroxidase and chalcone-flavanone isomerase while the apical sections had the highest activities of the other enzymes. At the stages of maximum flavonoid accumulation, saponarin levels were about 4 times higher than lutonarin levels. As saponarin content decreases, isovitexin, the 7-O-aglycone of saponarin, was detected. The results are discussed in terms of the balance of biosynthesis and degradation of flavonoids in the primary leaf throughout its development from juvenile to senescent stages under field conditions.