Aminosaeuren und Zucker im Phloemsaft verschiedener Pflanzenteile von Hafer (Avena sativa) in Beziehung zur Saugortpraeferenz von Getreideblattlaeusen (Hom., Aphididae).
1989
Kuo Sell H. L.
Pure phloem sap of different parts of oats (Avena sativa) was collected by cutting stylets of feeding aphids using a ruby laser. Aphids and plants were kept under constant environmental conditions. Only parts of oats preferred by the cereal aphids, Sitobion avenae and Metopolophium dirhodum were selected for the collection of phloem sap. Sucrose was the only sugar transported in the phloem. The concentration of sucrose was almost equal in the phloem sap of spikelet (254.4 mug/mul), flag leaf (252.4 mug/mul) and the leaf next to the flag leaf (293.9 mug/mul). The total concentration of amino acids ranged between 174.9 nmol/mul in the spikelet, 127.8 nmol/mul in the flag leaf and 121.1 nmol/mul in the leaf next to the flag leaf. Differences, however, were not significant. The proportion of amino acids to sucrose was 1 to 11 in the spikelet, 1 to 14 in the flag leaf and 1 to 18 in the leaf next to the flag leaf. Apart from the discrepancies in total concentrations qualitative and quantitative differences in single amino acids were found between the plant parts, especially between spikelets and leaves. A total of at least 32 amino acids were detected in the phloem sap. The dominating amino acids were glutamic acid, aspartic acid, glutamine, aspargine, threonine, serine, alanine and valine. In spikelets the content of glutamine, asparagine, valine, methionine, ornithine and two unknown amino acids ("unknown-2" and "unknown-4") was significantly higher than that in the leaves, while the content of glutamic acid, aspartic acid, threonine, serine, glycine, ethalonamine and an unknown amino acid ("unknown-1") was significantly lower compared to the leaves. Differences between the spikelets and the leaf next to the flag leaf were in most cases higher than that between spikelets and flag leaf. Between the two leaves only the content of threonine and unknown amino acid "unknown-1" was significantly different. Possible reasons for the preference of spikelets by S. avenae and flag leaves by M. dirhodum are discussed with reference to the composition of phloem sap.
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