ASCORBIC ACID-DEPENDENT REGULATION OF REDOX LEVELS OF CHLOROGENIC ACID AND ITS ISOMERS IN THE APOPLAST OF LEAVES OF NICOTIANA-TABACUM-L

There is a question whether ascorbic acid (AA) can control redox level s of phenolics in the apoplast. The present study was designed to answ er this question. AA, dehydroascorbic acid (DHA), chlorogenic acid (CG A) and its two structural isomers were present in the apoplast of leav es of tobacco (Nicotiana tabacum L. cv. BelW3). The levels of AA plus DHA (AA + DHA) and the ratios of AA to (AA + DHA) decreased while the levels of CGA plus its isomers increased during leaf aging. o-Quinones of CGA plus its isomers were found in the apoplast only in aged leave s of which apoplastic level of AA was nearly zero. In addition, activi ty of apoplastic peroxidase that could oxidize CGA and its isomers inc reased during leaf aging. From the observations, it is concluded that AA can regulate the accumulation of the o-quinones of CGA and its isom ers in the apoplast. Based on the conclusion, it is proposed that solu ble peroxidase in the apoplast has two functions, namely, (i) scavengi ng of H2O2 and/or regulation of the level of apoplastic H2O2 in the pr esence of AA, and (ii) accumulation of oxidation products of the pheno lics in the absence of AA.