Resumen de Tècniques químiques i de sincrotró per a la caracterització i el desenvolupament d aliments funcionals. Efectes d un bioestimulant en l enriquiment de blat amb seleni
Selenium is vital to human health. The resources of Se are largely obtained from edible plants since the human body cannot synthesize assimilable organic Se species effectively. Selenite and selenate are the predominant inorganic Se forms that are taken up by plants. Afterwards, they are mostly metabolized to organic forms which are the forms of Se effectively assimilable for animals and human intake. Although crop enrichment with Se-containing fertilizers to obtain Se-biofortified food in Se-deficient regions is becoming a common practice, there are still issues to be addressed regarding the Se-induced toxicity to the plant itself. In this respect, plant biostimulants are used to enhance nutrition efficiency, abiotic stress tolerance and crop quality. In this study we have applied a biostimulant based on a complex of hybrid hetero-polyoxometalates of Keggin structure molecules mixed with humic acids. Our aim is to assess the effect of this product in counteracting the toxicity of Se which hampers the normal development of wheat plants, and second, to evaluate a possible modification on the Se speciation in the presence of the biostimulant.
Xylem sap analysis showed that inorganic Se species have different metabolic pathways in the plant tissue. Translocation is a key process to control Se and nutrient elements accumulation in wheat shoots. A quick and low-cost method based on acid-base potentiometric titrations for testing the sap response to the Se species has been established. Furthermore, the studies regarding the application of the biostimulant on wheat plants are performed on short-term and long-term plant growth periods.
Short-term wheat plants were exposed to either selenite, selenate or a mixture of both species (Se(MIX)) in presence or absence of the biostimulant either by foliar (FA) or by root application (RA). Our results show that the FA did not modify the plant biomass but RA significantly increased the root biomass in all treatments as well as the shoot biomass under Se(VI) and Se(MIX). The biostimulant accelerated the translocation of Se in the presence of Se(VI) and Se(MIX). XAS allowed to identify organic Se as the main Se species formed in the shoots being the influence of the plant biostimulant almost negligible on the Se speciation. These results indicate the potential of this biostimulant in the Se-enrichment of crops while avoiding the possible stress induced by this element.
In a long-term assay we targeted on the co-application of the Se-treatments together with the foliar application of the biostimulant at different growth stages (tillering or heading stage) until harvesting. The biostimulant had a key role in the enhancement of both the amount of grains produced per spike and their biomass without diminishing the total amount of Se and maintaining Se speciation as in the absence of the biostimulant. The use of μ-XAS showed that organic Se is the main Se species in wheat grain and that, Se application stage influence the proportion of organic Se. This information will be useful for biofortification programs to minimize economic costs towards a more effective Se supplementation since the productivity of crops would not be affected and the necessary dietary amount of organic Se forms in edible parts will reach an adequate range.
