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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. [ABSTRACT FROM AUTHOR]

Abstract: Ceratophyllum demersum L. is known to be a potential accumulator of arsenic (As), but mechanisms of As detoxification have not been investigated so far. In the present study, we analyzed the biochemical responses of Ceratophyllum plants to arsenate (AsV; 0–250μM) exposure to explore the underlying mechanisms of As detoxification. Plants efficiently tolerated As toxicity up to concentrations of 50μM AsV and durations of 4 d with no significant effect on growth by modulating various pathways in a coordinated and complementary manner and accumulated about 76μgAsg−1 dw. Significant increases were observed in the levels of various thiols including phytochelatins (PCs), the activities of enzymes of thiolic metabolism as well as arsenate reductase (AR). These primary responses probably enabled plants to detoxify at least some part of AsV through its reduction and subsequent complexation. The maximum proportion of As chelated by PCs was found to be about 30% (at 50μM AsV after 2 d). Simultaneously, a significant increase in the activities of antioxidant enzymes was observed and hence plants did not experience oxidative stress when exposed to 50μM AsV for 4 d. Exposure of plants to higher concentrations (250μM AsV) and/or for longer durations (7 d) resulted in a significant increase in the level of As (maximum 525μgg−1 dw at 250μM after 7 d) and an inverse relationship between As accumulation and various detoxification strategies was observed that lead to enhanced oxidative stress and hampered growth. [Copyright &y& Elsevier]

Abstract: Copper, though essential, is potentially toxic heavy metal at supraoptimal level and has widespread contamination. The present investigation was carried out to study the responses induced by lower as well as higher doses of copper (0.1–25μM) in an aquatic macrophyte, Hydrilla verticillata (L.f.) Royle for a period of 1–7 days. The plants accumulated copper in high amount with a maximum of 770μgg−1 dw on day 7 at 25μM. Biomass and photosynthetic pigments showed less alteration up to 1μM while at higher concentrations, significant decline occurred. Malondialdehyde (MDA) content and electrical conductivity (EC) also showed sharp increase at higher concentrations indicating oxidative stress. In response to copper exposure, plants showed significant induction of proteins and enzymes like superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT) and glutathione reductase (GR), however, only up to moderate exposures. Total non-protein thiols (NP-SH) and cysteine levels increased significantly up to 5μM copper exposure while at 25μM, their level declined drastically. Reduced glutathione (GSH) showed decrease at all concentrations while oxidized glutathione (GSSG) simultaneously increased. Phytochelatins (PCs) were also induced significantly at studied concentrations of 1 and 5μM on day 4 in comparison to control. However, copper chelation depicted by PC-SH to copper ratio was found to be low (6.5% at 1μM and 2.4% at 5μM) suggesting that PCs play only a part in integrated mechanisms of copper homeostasis and detoxification. Tolerant response of plants to moderate copper exposures and high accumulation potential warrants their suitability for remediation of moderately copper polluted water bodies. [Copyright &y& Elsevier]

In the present study, the level of thiols and activity of related enzymes were investigated in coontail (Ceratophyllum demersum L.) plants to analyze their role in combating the stress caused upon exposure to cadmium (Cd; 0–10μM) for a duration up to 7d. Plants showed the maximum accumulation of 1293μgCdg−1 dw after 7d at 10μM. Significant increases in the level of total non-protein thiols (NP-SH) including phytochelatins (PCs) as well as upstream metabolites of the PC biosynthetic pathway, cysteine and glutathione (GSH) were observed. In addition, significant increases in the activities of cysteine synthase (CS), glutathione-S-transferase (GST), glutathione reductase (GR), as well as in vitro activation of phytochelatin synthase (PCS), were noticed in response to Cd. In conclusion, under Cd stress, plants adapted to a new metabolic equilibrium of thiols through coordinated synthesis and consumption to combat Cd toxicity and to accumulate it. [Copyright &y& Elsevier]