The influence of growth conditions and leaf maturity in relation to the chlorogenic acid stimulation of glycollate oxidase from tobacco leaves
Glycollate oxidase (glycollate: oxygen oxidoreductase EC. 1.1.3.1) levels in tobacco leaves from plants grown under three different photoperiods and three different temperature regimes were compared. Leaf extracts obtained from mature plants grown at moderate temperatures (25–20C; day/night) and with intermediate day lengths (10 h) showed highest activity. In contrast, peroxidase (EC. 1.11.1.7) was highest in extracts from plants grown at low temperatures and short days while chlorogenic acid oxidase (EC. 1.10.3.1) was highest in leaf extracts from plants grown at high temperatures. Other investigations revealed that old leaves contained consistently lower glycollate oxidase levels than young leaves from the same plant. The addition of chlorogenic acid to the assay medium tended to equalize differences in enzyme activity. Photosynthetic efficiency as determined by O2 evolution (Hill reaction) and photophosphorylation in isolated chloroplasts improved with leaf maturity but this development did not appear to be a direct consequence of low photorespiratory activity. Measurements of the conversion of glycollate-1-14C to 14CO2 by leaf disks under light or dark conditions indicated that chlorogenic acid affects glycollate metabolism in vivo. It is postulated that chlorogenic acid moderates photorespiration by interacting with glycollate oxidase.