PROTOCATECHUALDEHYDE AND OTHER PHENOLS AS CELL WALL COMPONENTS OF GRAPEVINE LEAVES

摘要

Upon washing with dilute bicarbonate solution, quercetin glucuronide as well as the monotartaryl esters of 4-coumaric, caffeic and ferulic acids were released from extensively solvent-purified cell wall material (CWM) of Vitis vinifera leaves. Drastic alkaline hydrolysis additionally yielded protocatechualdehyde and protocatechuic acid. Digestion of bicarbonate-washed CWM with a commercial esterase liberated protocatechuic and 4-coumaric acids, but no protocatechualdehyde. The latter was, however, solubilized upon incubation of the same CWM with pectinase ('Macerase') and subsequent alkaline hydrolysis, together with some of the two phenolic acids. In contrast to this, the analogous set-up with cellulase was almost ineffectual, inasmuch as only traces of these acids were released. Thus, quercetin glucuronide and the tartaric esters of the hydroxycinnamic acids are only loosely associated with the cell wall, whereas part of the 4-coumaric and protocatechuic acids as well as the protocatechualdehyde are covalently ester-bonded. The phenolic acids probably act as the acyl parts of esters with polysaccharidic hydroxyl groups, and the aldehyde as the hydroxyl part of esters with glucuronic or galacturonic acid moieties. The contents of extractable protocatechualdehyde and protocatechuic acid decreased by about 60% from the early to the late exponential phase of leaf growth. The possibility is discussed that the decrease in covalently wall-bound protocatechuic compounds during leaf development is causally related to the age-dependent establishment of resistance to fungal disease.