Abstract
Selenite and phosphate share similar uptake mechanisms, as a phosphate transporter is involved in the selenite uptake process. However, the mechanism by which selenium (Se) transformation in plants is mediated by phosphorus (P) remains unclear. In this hydroponic study, the absorption, translocation, and biotransformation of Se in selenite-treated rice (Oryza sativa L.) seedlings were investigated under varying P nutrient status. The results showed that P-deficient cultivation increased the Se concentration in roots with Se-only treatment by 2.1 times relative to that of the P-normal condition. However, co-treating roots with additional P caused the Se concentration to decline by 20 and 73% compared to Se treatment alone under P-normal and P-deficient cultivation, respectively. A similar pattern was also observed in Se uptake by rice roots. With an Se-transfer factor elevated by 4.4 times, the shoot Se concentration was increased by 44% with additional P supply compared to the concentration under Se-only treatment of P deficiency; however, no significant differences were observed regarding P-normal cultivation. P deficiency increased the Se percentage by 28% within the cell wall, but reduced it by 60% in the soluble fraction of Se-only treated roots relative to that of the P-normal condition. Contrarily, compared with the Se-only treatment under P deficiency, additional P supply enhanced Se storage in the root soluble fraction by 1.3 times. The opposite tendency was observed for rice shoots. Moreover, P deficiency reduced the proportion of SeMet by 22%, but increased MeSeCys by 1.3 times in Se-only treated roots compared to those under the P-normal condition. Interestingly, MeSeCys was not detected when additional P was added to the two cultivation conditions. Unlike in the roots, only SeMet was generally detected in the rice shoots. The results demonstrate that the P nutrient status strongly affects the Se biofortification efficiency in rice seedlings by altering the Se subcellular distribution and speciation.
Highlights
Selenium (Se), considered an essential trace element for humans and animals, is critical for antioxidation, immune system support, and disease prevention (Rayman, 2000)
The biomass of rice shoots slightly decreased under P-deficient cultivation, but a significant increase (P < 0.05) was observed in the roots compared to the biomass of the corresponding treatments under P-normal cultivation (Table 1)
The P concentration and uptake rate of roots exposed to P deficiency were much lower than those of roots exposed to P-normal cultivation, and these factors were elevated by 2.9 and 3.0 times, respectively, when only additional P was supplied to the P-deficient solution
Summary
Selenium (Se), considered an essential trace element for humans and animals, is critical for antioxidation, immune system support, and disease prevention (Rayman, 2000). Previous studies have shown that the absorption of selenite could be affected by the presence of phosphate (P) in the media (Hopper and Parker, 1999). Zhang et al (2014) reported that OsPT2, a phosphate transporter, is involved in selenite uptake, thereby indicating that a competitive relationship might exist between P and Se. Studies of wheat have suggested that selenite absorption in plants was suppressed by increasing P supply (Liu et al, 2018) and was stimulated by P deficiency (Li et al, 2008). Given the inconsistency of previous findings, further studies on the absorption mechanisms of selenite as mediated by P in plants are still needed, and the process of Se translocation from roots to shoots should be evaluated
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