| To fulfill the natural human needs of selenium (Se), I further improved the agronomic biofortification of rice (Oryza sativa) with less Se fertilizers and comprehensively evaluated Se bioaccessibility and bioavailability in the Se-enriched rice. Se-enriched rice grains were prepared by foliar application of selenite after rice heading. As compared with control, low amount of sodium selenite (10.5 g Se/ha) significantly increased Se content in rice grains by up to 51 times; at the same time, rice yield was also up-regulated by up to 1.24 times. Furthermore, by Se speciation analysis, in vitro gastrointestinal digestion and antioxidant assays, the Se-enriched rice grains contain readily absorbable selenomethionine as the major Se species and have significantly higher antioxidant bioactivities. This Se-enriched rice has enormous potential for Se supplementation in humans.;Se shows both beneficial and toxic effects on plant growth. Treatments with lower concentrations of sodium selenite enhanced the growth of rice seedlings, whereas higher concentrations of sodium selenite repressed seedling growth. To reveal the regulatory mechanisms underlying these effects, a comparative proteomics study combining 2-dimensional gel electrophoresis (2-DE) and matrix assisted laser desorption ionization (MALDI)-tandem time of flight (TOF/TOF) mass spectrometry (MS) were performed. By comparison of gel images between Se treatments and control, 66 and 97 differentially expressed proteins were identified in shoot and root, respectively. Gene Ontology and Clustering analysis reveal primary metabolism, photosynthesis and redox homeostasis are the most highly affected biological processes by Se treatments. Lower Se treatments (2 and 6 mg/L sodium selenite) activated antioxidative system, enhanced photosynthesis and primary metabolism. However, higher Se treatment (10 mg/L sodium selenite) damaged photosynthesis apparatus, inhibited photosynthesis and primary metabolism. This study provided novel insights into Se response in rice at the proteome level, which are expected to be highly useful for dissecting the Se response pathways in higher plants and for producing of Se enriched rice cultivars in the future.;To better understand the regulatory mechanism under Se accumulation in rice grains, a comparative proteomics study using 2-DE coupled MALDI-TOF/TOF MS and 1-dimensional gel electrophoresis (1-DE) coupled liquid chromatography (LC) - Fourier transform-ion cyclotron resonance (FT-ICR) MS were carried out. By comparison of Se treatments and control, 62 and 250 differentially expressed proteins were identified by 2-DE/MALDI-TOF/TOF MS and 1-DE/LC-FT-ICR MS, respectively. By gene functional classification, proteins involved in the processes of sulfur metabolism, carbon metabolism, cell redox regulation, and seed nutritional storage were the most highly affected by Se accumulation in mature rice grains. In addition, there were 6 proteins identified to contain fragments of selenoamino acid modification, which was the first identification of selenoproteins in higher plants.;Genetic engineering of Se-enriched rice will have important implications for human health in Se deficient regions. Therefore, to acquire appropriate rice genes as candidates for bioengineering of Se-enriched rice cultivars, I overexpressed three of the rice O-Acetylserine(thiol)lyase (OASTL) genes encoding cytosolic OASTLA, plastic OASTLB and mitochondrial OASTLC, individually in the model plant Arabidopsis (Arabidopsis thaliana ) to characterize the effects of Se accumulation in transgenic plants. The results showed that compared to the wild type plants, overexpression of all these genes significantly increased Se content in transgenic plants under treatments of different selenite concentrations. By real-time RT-PCR analysis, I found that the whole metabolic pathway of selenite assimilation was activated by overexpressing rice OASTL genes, especially the genes involved in cysteine and methionine biosynthesis, which may give rise to more Se accumulation in the transgenics. In addition, overexpression of rice OASTL genes also activated the antioxidative system by activating the glutathione reductase, which may be responsible for the increased biomass of Se-enriched transgenic plants. Therefore, OASTL genes could be good candidate for the future genetic engineering of Se-enriched rice. |
