CHEMICAL-COMPOSITION OF PHLOEM EXUDATE OF MYCOPLASMA-INFECTED APPLE-TREES

Abstract Phloem exudate was obtained by incision from different apple cultivars affected by apple proliferation disease. The exudate was analyzed by high–performance liquide chromatography (HPLC), some compounds also by thin–layer chromatography, gel filtration chromatography and polyacrylamide gel electrophoresis. Sorbitol and sucrose were the most prevalent sugar, alcohol and sugar, respectively, while stachyose, raffinose, fructose, and myo–inositol were present to a much lower extent. Glucose was absent or occurred at very low concentrations only. All common amino acids with the exception of arginine and cysteine were detected, aspartic acid and glutamic acid together with the corresponding amides being predominant. Citric acid and malic acid werether major organic acids while shikimic, succinic and fumaric acid were present at considerably lower amounts. The inorganic constituents were (in decreasing order) potassium, magnesium, sodium, sulphate, chloride, phosphate, calcium, and nitrate. Approximately 100 ppm protein were found consisting mainly of two major fractions with a molecular weight of 110,000 and 28,000 Dalton, respectively. Only two lipid classes were detected which were represented by 0.4 ppm β–sitosterol and by 50 ppm of a sterylester with a long chain fatty acid moiety. DNA and RNA could not be found, but all RNA nucleotides were present and also UPD–glucose, which was predominant. The significance of the results obtained for culturing mycoplasma–like organisms (MLOs), is discussed. Copyright © 1990, Wiley Blackwell. All rights reserved