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Pyruvate kinase and a phosphatase as potential indicators of potassium and magnesium status of Tomato and Cucumber Plants

1975; Wiley; Volume: 26; Issue: 2 Linguagem: Inglês

10.1002/jsfa.2740260202

1097-0010

R. T. Besford,

Aluminum toxicity and tolerance in plants and animals

Abstract The activities of pyruvate kinase and a phosphatase in the leaves of tomato and cucumber may be used as indicators of the potassium and magnesium status of the plants and provide an estimate of the concentration of “available” magnesium in the leaves. Extracts were prepared from young, fully expanded leaves of tomato plants grown in the presence of two concentrations of nutrient potassium, and of cucumber plants receiving two concentrations of potassium and magnesium. The pyruvate kinase and phosphatase activities of the extracts were determined in the presence and absence of added potassium and/or magnesium. When assayed in the presence of added MgSO 4 (10 μmol/ml) the pyruvate kinase activity from tomato leaves containing 1.87 g K + /100 g dry matter was half that obtained from leaves containing 3.54 g K + /100 g dry matter. Similarly in cucumber leaves adequate in potassium, the activity was significantly higher than that from leaves containing insufficient potassium. In this assay an indication of suboptimal potassium levels in the leaves of both tomato and cucumber plants was obtained before the onset of visible deficiency symptoms. In the presence of added KC1(50μmoles/ml) the pyruvate kinase activity from cucumber leaves was related to the magnesium concentration in the leaves, the highest activity being obtained from leaves of highest magnesium status. Furthermore, the activity of extracts from two groups of tomato leaves containing the same magnesium concentrations was very similar. The phosphatase activity of cucumber leaf extracts assayed in the presence of added KC1 (50μmol/ml) also paralleled the magnesium concentrations in the leaves. These enzyme assays, which can be completed within 2 h, could offer a rapid means of assessment of the potassium and magnesium status of tomato and cucumber plants.