Sauvion Nicolas, Nardon Christiane, Febvay Gérard, Gatehouse Angharad M R, Rahbé Yvan
INRA-INSA de Lyon, UMR Biologie Fonctionnelle Insectes et Interactions, Bat. Louis-Pasteur, 20, ave. A. Einstein, 69621 Villeurbanne, France.
J Insect Physiol. 2004 Dec;50(12):1137-50. doi: 10.1016/j.jinsphys.2004.10.006.
Concanavalin A (lectin from Canavalia ensiformis L., ConA) has previously been shown to act as a feeding inhibitor for Acyrthosiphon pisum, the pea aphid. In the present study a range of histochemical and biochemical techniques were used to elucidate the target tissues and binding sites of the lectin in the aphid. Diet uptake was evaluated using a radioactive tracer (14C-methylated inulin) and demonstrated that adults were capable of ingesting high quantities of the toxin (approx. 1 microg over a 48 h period). Electophoretic analysis and enzyme-linked immuno-sorbent assay of honeydew samples confirmed these results and further demonstrated that only small levels of ConA were excreted. Histofluorescence and immunolocalisation studies on nymphs revealed that the stomach was the primary target for ConA. At concentrations up to 400 microg ml(-1), lectin binding only occurred in the stomach region, however, at high concentrations (800 microg ml(-1)) the whole digestive tract was stained, although there was no evidence of binding in either the oesophagus or rectum. In addition to binding, there was evidence to suggest that ConA was also causing systemic effects in that the lectin appeared to cross the intestinal epithelial barrier. Immunohistochemical and electron microscopy studies revealed that ConA induced severe cellular swelling of the epithelial cells, accompanied by hypersecretion and a progressive detachment of the apical membrane; however, the striated border itself did not appear to be directly affected. Furthermore, there was no lysis of the epithelium, nor loss of integrity of the epithelial cells themselves. Our results suggest that ConA interacts with glycosylated receptors at the surface of the stomach epithelial cells, interfering with normal metabolism and cell function, resulting in a rapid feedback response on feeding behaviour. Whilst our results provide a much greater understanding regarding the modes of action of ConA in insects, they suggest that different lectins, including other mannose binding lectins, have different modes of action at the cellular levels, and thus generalizations should be treated with caution.
刀豆球蛋白A（来自刀豆的凝集素，ConA）先前已被证明可作为豌豆蚜（Acyrthosiphon pisum）的取食抑制剂。在本研究中，一系列组织化学和生化技术被用于阐明凝集素在蚜虫体内的靶组织和结合位点。使用放射性示踪剂（14C-甲基化菊粉）评估食物摄取情况，结果表明成虫能够摄取大量毒素（48小时内约1微克）。对蜜露样本的电泳分析和酶联免疫吸附测定证实了这些结果，并进一步表明只有少量的ConA被排泄出来。对若蚜的组织荧光和免疫定位研究表明，胃是ConA的主要靶标。在浓度高达400微克/毫升时，凝集素结合仅发生在胃部区域，然而，在高浓度（800微克/毫升）时，整个消化道都被染色，尽管在食管或直肠中没有结合的证据。除了结合外，有证据表明ConA也在产生全身效应，因为凝集素似乎穿过了肠上皮屏障。免疫组织化学和电子显微镜研究表明，ConA诱导上皮细胞严重肿胀，伴有分泌亢进和顶端膜的逐渐脱离；然而，纹状缘本身似乎没有受到直接影响。此外，上皮没有溶解，上皮细胞本身也没有完整性丧失。我们的结果表明，ConA与胃上皮细胞表面的糖基化受体相互作用，干扰正常代谢和细胞功能，从而对取食行为产生快速反馈反应。虽然我们的结果为ConA在昆虫中的作用方式提供了更深入的理解，但它们表明不同的凝集素，包括其他甘露糖结合凝集素，在细胞水平上有不同的作用方式，因此进行概括时应谨慎。
