The role of silicon in metabolic acclimation of rice plants challenged with arsenic

• Silicon alleviates the negative impact of arsenic.
• No major metabolic reprogramming was observed.
• Arsenic toxicity was apparently unrelated to oxidative stress.
• Both silicon and arsenic could directly trigger varying patterns of gene expression.

Silicon (Si) plays key roles in alleviating various abiotic stresses, including arsenic (As) toxicity, via physiological mechanisms that remain poorly understood. Here, we combined photosynthetic measurements with analyses of central metabolism and gene expression to explore the consequences of As-related alterations on primary metabolism and examined whether these consequences could be affected by the application of Si to rice (Oryza sativa L.) plants challenged with As but supplemented with Si. The negative effects of As on photosynthesis and carbohydrate status were largely reversed by Si. However, no major metabolic reprogramming was observed, as denoted by minor, if any, significant changes in (i) the activities of a range of enzymes associated with C metabolism; (ii) the levels of a wide range of organic acids and amino acids; and (iii) the pools of NAD(P)H/NAD(P)+ and the redox states of ascorbate and glutathione. Arsenic toxicity was apparently unrelated to oxidative stress. We suggested that the search for As-tolerant plants under real field conditions should not focus solely on oxidative stress, and hence the focus on photosynthesis might be of higher significance. In conclusion, we identified Si nutrition as a central player that restricts photosynthetic impairment in As-treated plants, in addition to limiting As uptake via modulation of the expression of genes with prime importance in As uptake and translocation.