Aminosäuren und Zucker im Phloemsaft verschiedener Pflanzenteile von Hafer (Avena sativa) in Beziehung zur Saugortpräferenz von Getreideblattläusen (Hom., Aphididae)

Abstract

Amino acids and sugars in phloem sap of different parts of oats (Avena sativa) in relation to feeding sites of cereal aphids, Sitobion avenae and Metopolophium dirhodum (Hom., Aphididae) 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 μg/μl), flag leaf (252.4 μg/μl) and the leaf next to the flag leaf (293.9 μg/μl). The total concentration of amino acids ranged between 174.8 nmol/μl in the spikelet, 127.8 nmol/μl in the flag leaf and 121.1 nmol/μl in the leaf next to the flag leaf. Differences, however, were not significant. The proportion of amino acids to sucrose was 1:11 in the spikelet, 1:14 in the flag leaf and 1:18 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, asparagine, 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, ethanolamine and an unknown amino acid (“unknown‐1”) was significantly lower compared to the leaves. Differences between the spikelet and the leaf next to the flag leaf were in most cases higher than that between spikelet 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. Zusammenfassung Unter konstanten Bedingungen wurden mit Hilfe einer Rubin‐Laser‐Apparatur inserierte Stechborsten von Getreideblattläusen Sitobion avenae durchtrennt und der austretende reine Phloemsaft verschiedener Pflanzenteile von Hafer (Avena sativa) gewonnen. Die Auswahl der Pflanzenorgane orientierte sich an der Saugortpräferenz von S. avenae und Metopolophium dirhodum. Saccharose war die einzige Transportform des Zuckers im Phloemsaft. Die Zuckerkonzentration im vorletzten Blatt war mit 293,9 μg/μl tendentiell höher als im Ährchen (254,4 μg/μl) oder Fahnenblatt (252,4 μg/μl). Bei der Gesamtkonzentration der Aminosäuren bestanden ebenfalls nur tendentielle Unterschiede zwischen den Pflanzenteilen (im Ährchen 174,8 nmol/μl, Fahnenblatt 127,8 nmol/μl und vorletzten Blatt 121,1 nmol/μl). D...

Amino Acid and Sucrose Content Determined in the Cytosolic, Chloroplastic, and Vacuolar Compartments and in the Phloem Sap of Spinach Leaves

“…Of both plants the determined average sucrose concentrations in the phloem sap were about 1 M (G Lohaus, manuscript in preparation). Similar sucrose concentrations have been determined by other authors in phloem sap from maize (20) and oat (17). The similarity of these results with the sucrose concentrations assayed in phloem sap from spinach leaves shown here, indicates that the estimation of the sap volume yielded reasonable results and that the amino acid concentrations listed in Figure 5 are realistic values.…”

“…It is feasible that the observed imbalance in neutral amino acid concentrations between the vacuoles and the cytosol may be due to an active extrusion of amino acids across the tonoplast. In vacuoles from barley leaves specific transport of phenylalanine (16) and of alanine, leucine and glutamine (6) (8,14), oat (17,27), barley (27), maize (20,28), and rice (10). Table III shows the relative distribution of amino acids in the phloem sap of spinach and for comparison also the amino acid distribution in the cytosol.…”

“…In contrast to monocotyledons like oat (17,27), barley (27), wheat (8,14), maize (20,28), or rice (10) where, after severing of the stylet, the phloem sap can be collected for many hours, with spinach leaves the exudation of the sieve tube sap occurred only for about 10 to 15 min after severing of the stylet. Therefore, only relatively small amounts of phloem sap (about 5 nL) could be collected at a time.…”

Nutritional quality of phloem sap in relation to host plant-alternation in the bird cherry-oat aphid

“…H. 6ulgare phloem, dominated by glutamic acid and aspartic acid and low levels of asparagine, resembled phloem typically collected on other cultivated grasses, e.g. oat (Kuo-Sell 1989), wheat (Fisher & MacNicol 1986), and rice (Hayashi & Chino 1990). Large differences in the concentrations of these amino acids are apparently encountered by R. padi during alternation between P. padus and H. 6ulgare.…”

“…Cysteine and proline are not detectable by this method. They are present in low amounts in the phloem from cultivated grasses and other plants (Fisher & MacNicol 1986;Kuo-Sell 1989;Hayashi & …”