Arsenic toxicity in rice (Oryza sativa L.) is influenced by sulfur supply: Impact on the expression of transporters and thiol metabolism

• Rice plants could combat As stress for 15 days in depleted sulfur supply conditions.
• Subcellular distribution of As played an important part in coping up the stress.
• Expression of transporters was altered so as to reduce As uptake and transport.
• Thiol metabolism also played significant role in stress tolerance.

Arsenic (As) is a non-essential element whose entry into rice grains is an issue of public concern. The need, therefore, exists to understand the regulatory mechanisms of As accumulation and distribution patterns in plants. This study analyzed the effect of sulfur (S) supply on As accumulation and distribution in rice (Oryza sativa L. var. IR64) plants. Nine day old seedlings were grown in 0.798 mM S (Normal S), 0.2 mM S (Low S) and 0.003 mM S (Zero S) for 7 days and then subjected to AsIII (20 μM) exposure for 7–15 days. The concentration of As varied significantly in different S treatments with a consistent trend of decrease in As concentration in depleted S supply treatments on both 7 days and 15 days. Arsenic concentration declined from 726 μg g− 1 DW to 537 μg g− 1 DW in roots and from 29 μg g− 1 DW to 8 μg g− 1 DW in shoots at 7 days, and from 1536 μg g− 1 DW to 1062 in roots and from 58 μg g− 1 DW to 16 μg g− 1 DW in shoots at 15 days, when S supply declined from normal to zero. The subcellular distribution of As was also found to vary with alteration in S supply and also differentially in shoot and root. In general, an up-regulation of sulfate transporters of groups 1 and 2 was observed while As transporters (Lsi1 and Lsi2) were down-regulated in response to As exposure to maintain sulfate and to regulate As levels. In spite of S depletion, an increase in cysteine, glutathione (GSH) and phytochelatin (PC) levels was observed upon As exposure. However, some negative impact of S depletion and As could be seen on the growth of plants. The study concluded that even in conditions of decreased S availability, plants continue to rely on thiol metabolism to tackle As levels and its toxicity effectively and altered subcellular distribution of As contributes only partially.