Plant growth promoting Rhizobacteria trigger isoflavone metabolismin early stages of development in Glycine max var Osumi


Abstract: At present, soybean is playing a crucial role both in the field of food and inpharmaceutical industry. Isoflavones (IF) have a remarkable therapeutic potential and can bedelivered either through the diet (bioactives or nutraceuticals) or as food supplements, and thishas opened a new market for industry. However, due to the inducible nature of secondarymetabolism, IF levels change according to environmental conditions leading to inconsistenteffects on health. This lack of reproducibility may be overcome by the means of elicitation.Biotic elicitation with plant growth promoting Rhizobacteria (PGPR) is proposed as a usefulstrategy to improve biomass production and to trigger secondary metabolism at the same time, byusing several mechanisms, being especially relevant those that necessarily involve plantmetabolism.The aim of this work was to evaluate the effects of nine PGPR isolated from differentbackgrounds to alter IF levels in Glycine max var. Osumi. Different experiments were carried outinoculating each strain on two-day old pregerminated seeds sown on sterile pots filled withvermiculite. Six days after inoculation, photosynthesis was measured and seedlings wereharvested. Weight of shoots, cotyledons and roots were registered and isoflavones in each organwere analyzed by HPLC.Although only one strain (N21.4) increased total IF contents as compared to controls, fivedifferent behaviours were detected when the daidzein and genistein families were analyzed.N21.4 has shown its ability to trigger defensive metabolism against leaf pathogens to a differentextent in the model plant A. thaliana and in tomato, and it was a systemic induction in both cases.Interestingly, only one strain caused significant decreases in total IF (M84), and three strainsincreased IF levels in leaves, two of them coupled to a decrease in roots (N11.37, L81) and onewas not accompanied by this decrease (Aur6). All strains triggered IF metabolism so furtherstudies have to be developed since the different beneficial effects of IF through the diet may bedue to the different IF profiles and also, they will have different physiological effects on plantperformance upon pathogen challenge or for symbiosis establishment.In conclusion, these are encouraging results from three points of view i) N21.4 increasesisoflavones in seedlings; ii) other strains trigger IF metabolism differentially, hence, both factscould be used to prepare food supplements or as enriched standardized foods after fulldevelopment of the biotechnological procedure and iii) Further studies need to be carried out torelate changes in IF with protection against leaf pathogens, unravelling the underlyingmechanisms of the systemic induction.

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