Clarification of role of silicon on the enhancement of manganese tolerance in higher plants.

以南瓜和豌豆叶片为材料，研究了硅提高植株耐锰性的机理，在不降低总锰含量的情况下，过量施硅可明显避免南瓜植株出现毒害症状。施硅植物的质外体洗涤液中的锰含量低于不施硅植物的10%。细胞壁中锰的交换态、氧化态和残渣态表明，在过量锰处理后2天，施硅植株的交换态锰大于不施硅植株。在处理后的第4天，施硅的植株中发现了更多的氧化锰。这些植物的细胞壁中的纤维素组分中也显示出更多的硅和锰。因此，施硅提高了南瓜植株的耐锰性，除了增加细胞壁对锰的吸附外，还通过将过量的锰掺入细胞壁来减少质外体中的可溶性锰。硅的供应还缓解了豌豆的锰毒害，而不降低叶片总锰。供硅植物AWF中的锰含量约为不供硅植物的40%。在过量锰的条件下，从不同供硅时间处理的植株叶片中提取AWF，以研究AWF中锰和硅的浓度与锰的毒性程度之间的关系。锰毒害的严重程度与AWF中的Mn不显著相关，而与Si显著相关。结果表明，供硅引起的AWF中锰含量的降低不足以解释豌豆耐锰性的提高。提出了质外体可溶性硅的重要作用。

Mechanisms of Si-enhanced Mn tolerance were investigated in leaves of pumpkin and cowpea.When pumpkin plants were supplied with Si under excess Mn, toxicity symptoms were clearly avoided without decreasing the total Mn. Manganese in the apoplastic washing fluids (AWF) of the plants supplied with Si were lower than 10% of those without Si supply. Fractionation of Mn in the cell walls into exchangeable, Mn oxide, and residual forms indicated that at 2 days after excess Mn treatment, the exchangeable Mn of the plants supplied with Si was larger than that of the plants without Si supply. At 4 days after the treatment, larger amounts of Mn oxide were found for the plants supplied with Si. These plants also showed larger amounts of Si and Mn in the cellulose fraction from their cell walls. Thus, Si supply enhances Mn tolerance of the pumpkin plants by decreasing the apoplastic soluble Mn through the incorporation of excess Mn into the cell walls, in addition to the enhanced adsorption of Mn on, the cell walls.Silicon supply also alleviated Mn toxicity of cowpea without decreasing the total leaf Mn. The Mn in the AWF of the plants supplied with Si was about 40% of those without Si supply. The AWF were extracted from the leaves of the plants treated at different timing of Si supply under excess Mn to examine the relationships between the severities of Mn toxicity and the concentrations of Mn and Si in the AWF. The severities of Mn toxicity were not significantly correlated with Mn in the AWF but were significantly correlated with Si. The results indicated that the decrease of Mn in the AWF caused by Si supply was insufficient to explain the enhanced Mn tolerance in cowpea. An important role of apoplastic soluble Si was suggested.