Modolo Luzia Valentina, Cunha Fernando Queiroz, Braga Márcia Regina, Salgado Ione
Departamento de Bioquímica, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, SP, 13083-970, Brazil.
Plant Physiol. 2002 Nov;130(3):1288-97. doi: 10.1104/pp.005850.
Phytoalexin biosynthesis is part of the defense mechanism of soybean (Glycine max) plants against attack by the fungus Diaporthe phaseolorum f. sp. meridionalis (Dpm), the causal agent of stem canker disease. The treatment of soybean cotyledons with Dpm elicitor or with sodium nitroprusside (SNP), a nitric oxide (NO) donor, resulted in a high accumulation of phytoalexins. This response did not occur when SNP was replaced by ferricyanide, a structural analog of SNP devoid of the NO moiety. Phytoalexin accumulation induced by the fungal elicitor, but not by SNP, was prevented when cotyledons were pretreated with NO synthase (NOS) inhibitors. The Dpm elicitor also induced NOS activity in soybean tissues proximal to the site of inoculation. The induced NOS activity was Ca(2+)- and NADPH-dependent and was sensitive to the NOS inhibitors N(G)-nitro-L-arginine methyl ester, aminoguanidine, and L-N(6)-(iminoethyl) lysine. NOS activity was not observed in SNP-elicited tissues. An antibody to brain NOS labeled a 166-kD protein in elicited and nonelicited cotyledons. Isoflavones (daidzein and genistein), pterocarpans (glyceollins), and flavones (apigenin and luteolin) were identified after exposure to the elicitor or SNP, although the accumulation of glyceollins and apigenin was limited in SNP-elicited compared with fungal-elicited cotyledons. NOS activity preceded the accumulation of these flavonoids in tissues treated with the Dpm elicitor. The accumulation of these metabolites was faster in SNP-elicited than in fungal-elicited cotyledons. We conclude that the response of soybean cotyledons to Dpm elicitor involves NO formation via a constitutive NOS-like enzyme that triggers the biosynthesis of antimicrobial flavonoids.
植物抗毒素的生物合成是大豆（Glycine max）植株抵御真菌菜豆间座壳南方变种（Dpm）（茎溃疡病的病原体）侵袭的防御机制的一部分。用Dpm激发子或一氧化氮（NO）供体硝普钠（SNP）处理大豆子叶，会导致植物抗毒素大量积累。当SNP被铁氰化物（一种不含NO部分的SNP结构类似物）取代时，这种反应不会发生。当子叶用一氧化氮合酶（NOS）抑制剂预处理时，真菌激发子诱导的植物抗毒素积累会受到抑制，但SNP诱导的则不受影响。Dpm激发子还能诱导接种部位近端大豆组织中的NOS活性。诱导的NOS活性依赖于Ca(2+)和NADPH，并且对NOS抑制剂N(G)-硝基-L-精氨酸甲酯、氨基胍和L-N(6)-(亚氨基乙基)赖氨酸敏感。在SNP激发的组织中未观察到NOS活性。一种针对脑NOS的抗体在激发和未激发的子叶中标记了一种166-kD的蛋白质。在暴露于激发子或SNP后，鉴定出了异黄酮（大豆苷元和染料木黄酮）、紫檀烷（大豆抗毒素）和黄酮（芹菜素和木犀草素），尽管与真菌激发的子叶相比，SNP激发的子叶中大豆抗毒素和芹菜素的积累有限。在Dpm激发子处理的组织中，NOS活性先于这些黄酮类化合物的积累。这些代谢物在SNP激发的子叶中的积累比在真菌激发的子叶中更快。我们得出结论，大豆子叶对Dpm激发子的反应涉及通过一种组成型的类NOS酶形成NO，该酶触发抗菌黄酮类化合物的生物合成。
