Glycolate metabolism of three submersed aquatic angiosperms during ageing [aquatic weeds]

The glycolate metabolism of three submersed aquatic macrophytes, Potamogeton pectinatus L., Vallisneria spiralis L. and Hydrilla verticillata (L.f.) Royle, was studied by estimating the endogenous levels of glycolate and hydrogen peroxide (H(,2)O(,2)) and assaying the activities of glycolate oxidase and catalase. The highest rate of glycolate oxidase activity was recorded at pH 8.0, 7.6 and 7.4 for Potamogeton, Vallisneria and Hydrilla, respectively, while pH levels above and below this value markedly reduced the glycolate oxidase activity. The optimum glycolate oxidase activity of the three species was obtained when the reaction time was restricted to 10 min. Both the glycolate content and the activity of glycolate oxidase in the three leaf age groups (young, mature and old) were highest in mature leaves of these aquatic species. The glycolate content in mature leaves was highest in Hydrilla which also showed the lowest glycolate oxidase activity. Lowest glycolate content and highest glycolate oxidase activity were recorded in Potamogeton. An intermediate picture was observed in Vallisneria. The H(,2)O(,2) content gradually increased with leaf age, while the catalase activity decreased. The content of H(,2)O(,2) in mature leaves was highest in Vallisneria and lowest in Hydrilla. The catalase activity was also lowest in the former of the three species. During ageing of isolated mature leaves in the dark, there was a gradual decline in glycolate metabolism with increase in leaf age in Vallisneria and Hydrilla, but not in Potamageton which showed a rise in glycolate oxidase activity after 3 days of induced ageing. Kinetin promoted glycolate metabolism in mature leaves of the three submersed plants during induced ageing, while ethrel and abscisic acid (ABA) showed an opposite effect.