Aims

The contribution of sulphur (S)-induced responses to chromium (Cr) tolerance of rice plants is not yet fully elucidated. It is hypothesised that S nutrition mitigates the accumulation and toxicity of Cr through enhanced formation of iron plaque (IP) and S-containing chelators. This study aimed to investigate the responses of iron (Fe) and Cr availability and transfer in the hydroponic rice system to added S levels.

Methods

We explored the influence of S nutrition on Cr accumulation in rice under a combination of Cr (VI) (+Cr, –Cr) and S (0, 1.75, 3.5, 7 mM) treatments.

Results

S additions at rates of 1.75 and 3.5 mM gave the least decline in root and shoot growth of rice seedlings under Cr stress. Fe concentration in shoots was consistent with the level of Cr uptake. The subcellular distribution of Cr in roots and shoots differed with varying S supply levels. Our results also revealed that S treatment at a moderate level (3.5 mM) was more effective in suppressing the bioavailability of Cr in rice shoots than were the other levels.

Conclusions

S-induced reduction in shoot Cr concentration, particularly from 1.75 to 3.5 mM, was likely attributed to the enhanced biosynthesis of glutathione (GSH) and phytochelatins (PCs) in roots than the enhanced physical resistance of IP induced by S. The poor barrier capacity of IP to Cr absorption in rice plants primarily ascribed to the level of applied Cr concentration and partly to the competition between Cr and S at the absorbing sites.

Graphical abstract

中文翻译：

---

水稻幼苗根部的硫营养和铁斑形成及其对溶液培养中铬的固定和吸收的影响

目的

尚未完全阐明硫（S）诱导的水稻植物对铬（Cr）耐受性的贡献。假设S营养通过增强铁斑（IP）和含S螯合剂的形成来减轻Cr的积累和毒性。这项研究旨在调查水培水稻系统中铁（Fe）和Cr的有效性和转移对添加S的响应。

方法

我们探讨了在Cr（VI）（+ Cr，–Cr）和S（0，1.75，3.5，7 mM）处理的组合下，S营养对水稻中Cr积累的影响。

结果

以1.75和3.5 mM的比例添加S可使Cr胁迫下水稻幼苗的根和茎生长下降最小。枝条中的铁浓度与铬的吸收水平一致。Cr在根和芽中的亚细胞分布随硫供应水平的变化而不同。我们的结果还表明，中等水平（3.5 mM）的S处理比其他水平抑制水稻芽中Cr的生物利用度更有效。

结论

S诱导的芽Cr浓度降低，尤其是从1.75降低至3.5 mM，这可能归因于根系中谷胱甘肽（GSH）和植物螯合素（PCs）的生物合成增强，而S诱导的IP物理抗性增强。水稻对IP吸收Cr的影响主要归因于所施加的Cr浓度水平，部分归因于吸收位点上Cr和S之间的竞争。

图形概要