Phloem sap collection from lettuce (Lactuca sativa L.): Chemical comparison among collection methods.
The chemical composition of phloem sap from lettuce, collected by three different methods, was compared. Phloem sap from stylectomy samples contained sucrose and 14 amino acids. Honeydew and EDTA chelation samples showed considerable breakdown of sucrose into fructose and glucose, several additional amino acids, and large differences in relative concentrations of amino acids, when compared to stylectomy samples. Honeydew contained considerable amounts of other oligosaccharides, and few proteins in low amounts, while EDTA showed many proteins. HPLC chromatograms showed numerous unidentified secondary plant compounds in honeydew and EDTA samples. Comparison of phloem sap samples from near-isogenic susceptible and resistant lines showed no relation of phloem sap composition with monogenic resistance to the aphidNasonovia ribisnigri.
Department of Entomology, Wageningen Agricultural University, PO Box 8031, 6700 EH, Wageningen.
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van Helden
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Tjallingh
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van Beek