Role of phytoprostanes and phytofurans in the protection and defense mechanisms of rice (Oryza sativa L.) against oxidative stress caused by abiotec agents and different technological practices

Abstract

Rice plays a key role in food safety of more than half of the world's population. At least 60% of cultivated soils have abiotic stress limitations caused by mineral deficiencies, temperatures, extremes, drought or acidity. Specific technological practices can help to reduce the damage. The phytoprostanes (FPs) and phytofurans (FFs) produced by the non-enzymatic oxidation of the linolenic acid present in the plant membranes and participate in the protection of cells and tissues against the deleterious effects of oxidative stress. Thus, the present Thesis is aimed at studying the profile and content of FPs and FFs in white rice, whole rice and rice bran, in different genotypes, as well as its role in the protection and defense mechanisms against oxidative stress caused by abiotic agents and diverse technological practices. In order to understand the levels of oxidative stress induced by specific agronomic practices, three (3) trials were established during the growing season (October-2015/April-2016 and October-2016/April-2017), in an experimental field, in the Mid-East of Argentina, belonging to the Faculty of Agricultural Sciences and Forestry of the National University of La Plata (34˚ 52’S, 57˚ 57’W, 9.8 m of altitude). The experimental design was, in all cases, random blocks with 3 repetitions. In the first trial, polished grain, whole grain and rice bran flours from 14 varieties were analyzed. The grains were ground and sieved. The second trial consisted in sowing 1 control variety, and 4 genotypes of high protein content in grain; treatments were 0 and 0.3 Lha-1 of foliar fertilizer (micronutrient solution). In the third trial, 7 genotypes were sown. The treatments were two environments (open field and plastic cover) and the spray application of three doses of salicylic acid (0, 1, and 15 mM). The extraction and adequacy of the samples was carried out by extraction in solid phase and its qualitative-quantitative analysis by UHPLC-ESI-QqQ-MS / MS. The statistical differences were obtained by means of multivariate or one-way analysis of variance (ANOVA) and the means were compared using the Tukey test. The FPs and FFs analyzed were: 9-F1t-PhytoP; Ent-16-F1t-PhytoP + Ent-16-epi-16-F1t-PhytoP; 9-epi-9-F1t-PhytoP; 9-epi-9-D1t-PhytoP; 9-D1t-PhytoP; Ent- 16-B1-PhytoP + 16-B1-PhytoP; Ent-9-L1-PhytoP + 9-L1-PhytoP; Ent-16-(RS)-9-epi-ST-Δ14-10-PhytoF; Ent-9-(RS)-12-epi-ST-Δ10-13-PhytoF y Ent-16-(RS)-13-epi-ST-Δ14-9-PhytoF. The implementation of the tests and the indicated methodology allowed obtaining the following results: 1) Regarding the impact of the technological process developed to obtain rice flours on the levels of FPs and FFs, it was observed that both classes of compounds exhibited average concentrations higher in the rice bran than in the brown grain flour and white grain flours. The recovered concentrations suggested that rice bran is a valuable dietary source of FPs and FFs that should be considered in further studies on bioavailability and bioactivity in vitro and in vivo. 2) When analyzing the impact of foliar fertilization on the content of FPs and total FFs, significant effects were found. The relative abundance of average FPs of the treatments and genotypes was between 213.3 and 3.1 ng g-1dw; while in the FFs, it was between 19.2and 3.5 ng g-1 dw. With the foliar fertilization treatment, the total content of FPs and FFs decreased by 31.9% and 20.0%, respectively. 3) Finally, regarding the effect of the different environments and the application of salicylic acid, it was observed that both treatments produced a reduction in the concentration of the biomarkers, differential according to the compounds and genotypes.