Xylem Sap from Actinidia chinensis: seasonal Changes in Composition

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Abstract
Seasonal variation was followed in the content of total a-amino acids, arginine, calcium, total carbohydrate, β-galactosidase activity, magnesium, nitrate, phosphatase activity, phosphate and sulphate in vacuum-extracted xylem sap from Actinidia chinensis var. hispida, the Chinese gooseberry or kiwifruit. There was a marked increase in the concentration of most sap components just prior to leaf emergence followed by a rapid decrease after the leaves had expanded. Experiments with excised extension shoots showed that much of this spring-time increase in concentrations of sap components was due to mobilization of nutrients within the shoot itself. Sap from the trunk and the older branches changed less in composition than did sap from the younger parts of the plant. The amplitude and direction of trends in concentration of sap from the different parts of the plant varied with nutrient and with time. Analysis of vacuum-extracted xylem sap collected during periods of rapid transpiration from early summer onwards gives a reliable indication of the composition of the transpiration stream.

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