The Biochemical Behavior And Regulation Of Zn In The Rhizosphere Of High Zn Density Rice(Oryza Sativa L.)

Rice (Oryza sativa L.) is one of the major staples crops, feeding more than half of the world’s population. Zinc (Zn) is an essential micronutrient for humans. Zn deficiency affects nearly half of the world population, particular in developing countries, where high proportion of cereal crops consumed as a staple food. Therefore, it is important to investigate how to improve the accumulation and bioavailability of Zn in rice grain. Low content of available Zn in soil is the main restrictive factor for Zn bioavailability in rice grain. However, Zn availability is closely related with Zn fractions and transformations. In order to improve the content of soil Zn availability, the measurements of water management combined with Zn fertilizer and endophytic microbes were used to study the effects on soil Zn fractions, grain Zn accumulation, and Zn bioavailability. The main results are summarized as below:1. Zn fractions and plant-available Zn in rice rhizosphere soil were studied in a rhizobox experiment. The results demonstrated that soil Zn fractions were significantly changed during plant growth. The tendency of Zn fractions were the same between rhizosphere and bulk soil, and Zn concentrations were ordered as follows:Residual> Fe-Mn oxide bound> Organic Matter bound> Carbonate bound> Exchangeable. pH is the important influencing factor for the changes of Zn fractions and available Zn content in rhizospheric soil. The concentration of exchangeable Zn in rhizospheric soil was significantly higher than that of non-rhizosphere soil. The mobility factor in rhizospheric soil was significantly higher than that of non-rhizosphere soil, facilitating the change from unavailable to available, and thus improved the content of plant-available Zn.2. This study aimed to investigate the impact of different water regimes and and t Zn fertilizer source (ZnSO4and Zn-EDTA) on grain yield and Zn accumulation in rice grain. Different water managements, continuous flooding (CF), and alternate wetting and drying (AWD) were applied during the rice growing season. Compared with CF, the AWD regime significantly increased grain yield and Zn concentrations in both brown rice and polished rice. On an average, AWD increase grain yield of genotypes (Nipponbare and Jiaxing27), by11.4%, and grain Zn concentration by3.9%compared to CF regime. Zn fertilization significantly increased Zn density in polished rice, with a more pronounced effect of ZnSO4being observed as compared with Zn-EDTA, especially under an AWD regime. Decreased phytic acid content and molar ratio of phytic acid to Zn were also observed in rice grains with Zn fertilization. Besides, Zn bioavailability of polished rice was significantly increased. The above results demonstrated that AWD water regime combined with ZnSO4fertilizer was an effective agricultural practice to elevate grain yield, grain Zn accumulation and bioavailability of rice.3. This study is to investigate the possibility of zinc (Zn) biofortification in the rice grains by inoculation of endophytic strains isolated from a Zn hyperaccumulator Sedum alfredii Hance. Five endophytic strains, Burkholderia sp. SaZR4, Burkholderia sp. SaMR10, Sphingomonas sp. SaMR12, Variovorax sp. SaNRl, and Enterobacter sp. SaCS20, isolated from S. alfredii, were inoculated in the roots of Japonica rice variety, Nipponbare under hydroponic condition. Fluorescence images showed that endophytic strains successfully colonized in rice roots after72h. Improved root morphology and plant growth of rice was observed after inoculation with endophytic strains especially SaMR12and SaCS20. Under hydroponic conditions, endophytic inoculation with SaMR12and SaCS20increased Zn concentration by44.4%and51.1%in shoots, and by73.6%and83.4%in roots, respectively. Under soil conditions, endophytic inoculation with SaMR12and SaCS20resulted in an increase of grain yields and elevated Zn concentrations by20.3%and21.9%in brown rice, and by13.7%and11.2%in polished rice, respectively. After inoculation of SaMR12and SaCS20, rhizospheric soils of rice plants contained higher concentration of DTPA-Zn by10.4%and20.6%, respectively. In situ micro-XRF mapping of Zn confirmed the elevated Zn content in rhizosphere zone of rice treated with SaMR12as compared with the control. Besides, endophytic inoculation significantly reduced the phytic acid content, and increased Zn bioavailability by Caco-2cell model. The above results suggested that endophytic microbial isolated from S. alfredii could be successfully colonized rice roots, resulting in improved root morphology and plant growth, increased Zn bioavailability in rhizosphere soils, and elevated grain yields and Zn densities in grains.