Poster: Plant Pathogen/Symbiont Interactions

Abs # 694: Nitrosylating-Activity is Evolved in Phytoalexin Production by Soybean Cotyledons

Presenter:	Salgado, Ione , ionesm@unicamp.br
Authors	Salgado, Ione  (A)   Braga, Marcia R (B)   Modolo, Luzia V (A)   Alcantara, Susana F (A)   Kuniyoshi, Tais M (A)
Affiliations:	(A): Universidade Estadual de Campinas (B): Instituto de Botânica de São Paulo

Nitric oxide (NO) has been shown to influence various developmental processes and also to play a role in plant defense responses against pathogens. In soybean, the phenylpropanoid pathway that leads to the synthesis of phytoalexins, has been shown to be induced by NO. The broad range of NO bioactivity is many times attributed to its ability to be rapidly oxidized or reduced to species, which have distinct chemical properties and different biological effects. The aim of this study was to investigate the effects of different NO donors on the phytoalexin biosynthesis in soybean cotyledons and compare them to those induced by the pathogenic fungus Diaporthe phaseolorum f. sp. meridionalis (Dpm). We used "true" NO donors (NOC-18 and NOC-5); the nitrosyl complex sodium nitroprusside (SNP) and S-nitrosothiols, such as, S-nitrosoglutathione (GSNO). The overall production of phytoalexins, using the soybean cotyledon assay, was estimated in the diffusates at 286 nm and quantified by HPLC. The effectiveness of the various NO donors in inducing phytoalexin accumulation in soybean cotyledons depended on the time course of NO releasing and the nitrosylating activity of these compounds. Daidzein, genistein, glyceollins, apigenin and luteolin were the main compounds identified. The phenylpropanoid production induced by GSNO was very similar to that one evoked by Dpm. On the other hand, glyceollins, which are derived from daidzein, were not induced by SNP, except when reducing agents, such as glutathione and dithiothreitol, were added. These results suggest that transnitrosylation reactions seem to play an important role during the biosynthesis of antimicrobial flavonoids, which is the main defensive response of soybean cotyledons to Dpm infection. Supported by FAPESP and CNPq.