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In plants, hydrogen sulfide (H₂S) is an emerging novel signaling molecule that is involved in growth regulation and abiotic stress responses. However, little is known about its role in the regulation of arsenate (As^V) toxicity. Therefore, hydroponic experiments were conducted to investigate whether sodium hydrosulfide (NaHS; a source of H₂S) is involved in the regulation of As^V toxicity in pea seedlings. Results showed that As^V caused decreases in growth, photosynthesis (measured as chlorophyll fluorescence) and nitrogen content, which was accompanied by the accumulation of As. As^V treatment also reduced the activities of cysteine desulfhydrase and nitrate reductase, and contents of H₂S and nitric oxide (NO). However, addition of NaHS ameliorated As^V toxicity in pea seedlings, which coincided with the increased contents of H₂S and NO. The cysteine level was higher under As^V treatment in comparison to …