Free Amino Acid Composition of Leaf Exudates and Phloem Sap: A Comparative Study in Oats and Barley

• Published in: Plant physiology (Bethesda) Vol. 92; no. 1; pp. 222 - 226
• Main Authors: Weibull, Jens, Ronquist, Fredrik, Sture Brishammar
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01-01-1990
• Subjects: Amino acids; Barley; Biological and medical sciences; Chemical composition; Chemical constitution; Elution; Exudation; Fundamental and applied biological sciences. Psychology; Insect stylets; Oats; Phloem; Plant physiology and development; Sap; Avena sativa; Aphidoidea; Monocotyledones; Exudate; Sap; Hordeum vulgare; Insecta; Interspecific comparison; HPLC chromatography; Plant leaf; Cereal crop; Homoptera; Gramineae; Arthropoda; Aminoacid; Angiospermae; Aphididae; Spermatophyta; Chemical composition; Invertebrata; Sampling
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.92.1.222

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.