Plant Physiology 92:222-226 (1990)
© 1990 American Society of Plant Biologists
Metabolism and Enzymology
Free Amino Acid Composition of Leaf Exudates and Phloem Sap 1
A Comparative Study in Oats and Barley
Jens Weibull2,
Fredrik Ronquist3 and
Sture Brishammar
Swedish University of Agricultural Sciences, P. O. Box 7044, S-750 07 Uppsala, Sweden,
Department of Plant and Forest Protection, P. O. Box 7044, S-750 07 Uppsala, Sweden
Comparisons were made between the free amino acid composition in leaf exudates and that in pure phloem sap, using twin samples taken from a single leaf of two oat (Avena sativa L.) and three barley (Hordeum vulgare L.) varieties. Leaf exudate was collected in a 5 mM EDTA-solution (pH 7.0) from cut leaf blades and phloem sap was obtained through excised aphid (Rhopalosiphum padi L.) stylets. Fluorescent derivatives of amino acids were obtained using 9-fluorenylmethyl chloroformate and were separated by means of high performance liquid chromatography. The total concentration of free amino acids varied considerably in the exudate samples. There was no correlation between the total amino acid content in the exudate samples and that of the corresponding phloem sap samples, but the amino acid composition of the corresponding samples was highly correlated (median R2-value 0.848). There was only limited between-plant variation in phloem sap amino acid composition. Nevertheless, in comparisons involving all samples, many of the amino acids showed significant correlations between their relative amounts in exudate and phloem sap. The results presented here indicate that the exudate technique holds great promise as an interesting alternative to the laborious and time-consuming stylet-cutting technique of obtaining samples for comparative studies of phloem sap.
2 Present address: Weibullsholm Plant Breeding Institute, P. O. Box 520, S-261 24 Landskrona, Sweden.
3 Present address: Uppsala University, Department of Zoology, Section of Entomology, P. O. Box 561, S-751 22 Uppsala, Sweden.
1 This work was supported by the Swedish Council for Forestry and Agricultural Research.
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