Comparative study on the influence of silicon and selenium to mitigate arsenic induced stress by modulating TCA cycle, GABA, and polyamine synthesis in rice seedlings

Arsenic contamination of groundwater is a major concern for its usage in crop irrigation in many regions of the world. Arsenic is absorbed by rice plants mainly from arsenic contaminated water during irrigation. It hampers growth and agricultural productivity. The aim of the study was to mitigate the toxic effects of arsenate (As-V) [25 μM, 50 μM, and 75 μM] by silicon (Si) [2 mM] and selenium (Se) [5 μM] amendments on the activity of the TCA cycle, synthesis of γ-aminobutyric acid (GABA) and polyamines (PAs) in rice (Oryza sativa L. cv. MTU-1010) seedlings and to identify which chemical was more potential to combat this threat. As(V) application decreased the activities of tested respiratory enzymes and increased the levels of organic acids (OAs) in the test seedlings. Application of Si with As(V) and Se with As(V) increased the activities of respiratory enzymes and the levels of OAs. The effects were more pronounced during Si amendments. The activities of GABA synthesizing enzymes along with accumulation of GABA were increased under As(V) stress. During joint application of Si with As(V) and Se with As(V) the activity and the level of said parameters were decreased that indicating defensive role of these chemicals to resist As(V) toxicity in rice and Si amendments showed greater potential to reduce As(V) induced damages in the test seedlings. PAs trigger tolerance mechanism against As(V) in plants. PAs such as putrescine, spermidine and spermine were synthesized more during Si and Se amendments in As(V) contaminated rice seedlings to combat the toxic effects of As(V). Si amendments substantially modulated the toxic effects caused by As(V) over Se amendments in the As(V) challenged test seedlings. Thus, in future application of Si enriched fertilizer will be beneficial to grow rice plants with normal vigor in arsenic contaminated soil.