# Usage of Si, P, Se, and Ca Decrease Arsenic Concentration/Toxicity in Rice, a Review
### Selenium (Se) and As
Rice is the primary source of selenium in the human diet, and although rice essentially requires selenium, the molecular mechanism of Se uptake is not yet well understood. Research shows that selenite is adsorbed via silicon _Lsi1_ (OsNIP2; 1), a silicon attack carrier in rice. _Lsi1_ defects lead to a significant reduction in the concentration of Se in shoots when using selenite. However, there was no difference in Se concentration between wild-type rice and _Lsi1_ mutant rice line when treated with selenite (Figure 1) [113]. Se is a known antagonist for arsenic toxicity, and Se is believed to detoxify arsenic plants [116]. Researchers have analysed Se efficacy application on arsenic uptake, transcript dynamics, antagonistic between arsenic and selenium in rice varieties, and antioxidant responses [126]. In the periodic table, As and Se are close to each other and play the same role in prokaryotic plant metabolic functions [127], and it should be noted that As and Se are usually paired in biochemical cycles [128]. Furthermore, studies have shown that Se and As are predominantly inorganic in paddy soils, while trace amounts of organic forms are also present because of microbial biological transmission [129]. Researchers have suggested that silicon transmitters may drive competition between As (III) and Se (IV) adsorption [113]; while As (V) and Se (IV) compete for the phosphate uptake system, arsenic (V) in general may inhibit selenium (VI) transport in vessel element [130; 131]. Researchers have also shown that Se reduces As toxicity in rice via reduction of arsenic accumulation, by reducing oxidative stress through nutrient status, and increasing antioxidant efficiency [132]. A study was performed to consider the interaction between selenium and arsenic, which showed that adding As via irrigation water significantly decreased rice straw, grain yield, and roots. However, selenium assisted in reducing the detrimental efficacy of As and offset the decrease in performance due to the arsenic toxicity, while the impact of selenium was more significant on the dry yield at higher doses. The observations also showed that Se application might reduce the accumulation and toxicity in the rice crop [133]. A similar study also showed that selenium application showed a significant reduction in fluorescent nitric oxide (NO) intensity, H\({}_{2}\)O\({}_{2}\) content, arsenic accumulation, reactive oxygen species (ROS), and superoxide radical (O\({}_{2}\)\({}^{-}\)) associated with cell death, indicating a protective role of Se in rice as a possible ROS igniter [134]. Besides, research has suggested a positive role for Se in increasing the enzymatic activity of thiol metabolism, which induces a pattern of differential accumulation of sulphur-related genes and improves arsenic toxicity through selenium completion, including a stable balance of sulphur-containing compounds and nutrients. Furthermore, nutrient levels are positively dependent on the differential expression pattern of genes related to NPK involved in nutrient availability and metabolism [134; 136]. Overall, some studies are providing new insights into the role of Se in different rice genotypes under arsenic stress via changes in thiol-related genes and nutrient transport. Of course, the researchers' new view is that Se may affect arsenic transfer to the stem, but it does not affect its uptake process [134; 137].