Background and aims

Silicon (Si) is known to alleviate aluminum (Al) toxicity in a number of plant species; however, the mechanisms of Si-triggered Al detoxification have not been elucidated, especially in rice (Oryza sativa). We investigated the interactions between Si and Al in root and the role of cell wall polysaccharides in rice resistance to Al.

Methods

Rice seedlings were grown in 0.5 mM CaCl₂ solution with or without 50 µM Al and 1.0 mM H₄SiO₄ for 24 h. The cell expansion and oxidative injury of root were measured by histochemical analyses; Al accumulation and distribution in root apices were determined by inductively coupled plasma mass spectrometry (ICP-MS); the degree of pectin methylesterification was analyzed by immunofluorescence, and the expression of genes (e.g. OsPME) related to Al resistance was measured by quantitative real-time PCR.

Results

Si relieved the inhibition of cell elongation and oxidative injury caused by Al and significantly reduced Al content (by about 41 %) in cell wall (CW). Meanwhile, Si inhibited pectin methylesterase (PME) activity and its gene expression, thereby increasing the degree of pectin methylesterification, and reduced the content of hemicellulose, which was the main binding site for Al in CW, under Al stress. Furthermore, Si decreased the non-exchangeable Al fraction of CW in root, but did not change the cation exchange capacity of CW.

Conclusions

Si reduces the deposition of Al in the cell wall of rice root apex by decreasing both the degree of pectin demethylesterification and the content of hemicellulose, thereby alleviating Al stress.

中文翻译：

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硅通过减少铝在细胞壁中的沉积来缓解铝诱导的对水稻根尖细胞伸长的抑制作用

背景和目标

已知硅（Si）可以减轻许多植物物种对铝（Al）的毒性；然而，硅触发铝解毒机制尚未阐明，特别是在水稻（稻）。我们调查了硅和铝在根中的相互作用以及细胞壁多糖在水稻对铝的抗性中的作用。

方法

水稻幼苗在有或没有50 µM Al和1.0 mM H ₄ SiO _4的0.5 mM CaCl ₂溶液中生长24小时。通过组织化学分析测定根的细胞膨胀和氧化损伤。铝在根尖的积累和分布通过电感耦合等离子体质谱法（ICP-MS）测定。通过免疫荧光分析果胶甲基酯化的程度，并通过定量实时PCR测量与铝抗性相关的基因（例如，OsPME）的表达。

结果

Si减轻了由Al引起的细胞伸长和氧化损伤的抑制作用，并显着降低了细胞壁（CW）中的Al含量（降低了约41％）。同时，Si抑制了果胶甲基酯酶（PME）的活性及其基因表达，从而增加了果胶甲基酯化的程度，并降低了铝在铝胁迫下铝的主要结合位点半纤维素的含量。此外，Si降低了CW根中不可交换的Al含量，但并未改变CW的阳离子交换能力。

结论

Si通过同时降低果胶脱甲基酯化程度和半纤维素含量来减少铝在水稻根尖细胞壁中的沉积，从而减轻铝胁迫。