Chromate (Cr­[VI]) is a highly phytotoxic contaminant that is ubiquitous in soils. However, how Cr­(VI) is taken up by plant roots remains largely unknown. Here, we show that the high-affinity sulfate transporter Sultr1;2 is responsible for Cr­(VI) uptake by the roots of Arabidopsis thaliana. Sultr1;2 showed a much higher transport activity for Cr­(VI) than Sultr1;1 when expressed in yeast cells. Knockdown of Sultr1;2 expression in Arabidopsis markedly reduced the Cr­(VI) uptake rate, whereas knockout of Sultr1;1 had no or little effect. A double-knockout mutant (DKO) of the two genes lost the ability of Cr­(VI) uptake almost completely. The Sultr1;2 knockdown mutant or DKO plants displayed higher resistance to Cr­(VI) under normal sulfate conditions as a consequence of the lower tissue Cr accumulation. Overexpression of Sultr1;2 substantially increased Cr­(VI) uptake with shoot Cr concentration being 1.6–2.0 times higher than that in the wild-type. These results indicate that Sultr1;2 is a major transporter responsible for Cr­(VI) uptake in Arabidopsis, while Sultr1;1 plays a negligible role. Taken together, our study has identified a major transporter for Cr­(VI) uptake in plants, providing potential strategies for engineering plants with low Cr accumulation and consequently enhanced Cr­(VI) resistance and also plants with enhanced accumulation of Cr for the purpose of phytoremediation.

The present study aimed to test a hypothesis that acid invertases in root of metallophytes might play important roles in root growth under heavy metal stress. Plants of two contrasting populations, one from an ancient Cu mine (MP) and the other from a non-contaminated site (NMP), of metallophyte Elsholtzia haichowensis were treated with Cu in controlled experiments. The results showed that MP was Cu tolerant under 10 μM Cu2+ treatment. Cu treatment resulted in a higher root/shoot biomass ratio in MP compared to NMP. Scaling exponent in root/shoot allometric function in MP was lower than NMP. More complicated root architecture was observed in MP under Cu stress. Four full-length cDNAs (EhNcwINV, EhCcwINV, EhNvINV and EhCvINV) encoding cell wall and vacuolar invertases were cloned. Both of the transcript level and activity of the acid invertase in MP elevated under Cu treatment. There were positive correlations between root acid invertase transcript level, activity and root/shoot biomass ratio. The results indicated important roles of acid invertase in governing root growth under Cu stress. It also suggested that there was a possible interrelation between acid invertases and Cu tolerance mechanisms in MP of E. haichowensis.

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Lanthanum (La), calcium (Ca), and cadmium (Cd) have similar physical and chemical properties because of their similar ionic radius. Although the interactions between La, Ca, and Cd have been frequently reported in plants, few studies have investigated the interactive effects of La and Ca on the growth and Cd accumulation in plants. Therefore, we investigated the interactive effects of La and Ca on the growth and Cd accumulation in wheat under Cd exposure by a hydroponic experiment. The results indicated that wheat growth was significantly affected by La−Cd and La−Ca interactions. The accumulation of Cd in wheat was significantly affected by La−Ca and La−Cd interactions and La−Ca−Cd interplay. Correlation analysis indicated that Ca deficiency stimulated La to promote wheat growth and mitigate Cd toxicity. Simultaneously, a low Ca supply stimulated La to decrease Cd accumulation in wheat and induce TaNramp5 expression. In addition, Cd accumulation in wheat was significantly affected by the W7−La interaction and W7−La−Ca interplay. All of the results suggested that La, Ca, and Cd probably share the same binding sites in calmodulin (TaCaM) and La could affect Cd accumulation in wheat by interacting with TaCaM and then downregulating the expression of TaNramp5.

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