南湖新闻网讯（通讯员 闫磊）近日，资源与环境学院姜存仓教授课题组连同园艺林学学院刘继红教授在Journal of Hazardous Materials杂志发表题为“Boron contributes to excessive aluminum tolerance in trifoliate orange (Poncirus trifoliata (L.) Raf.) by inhibiting cell wall deposition and promoting vacuole compartmentation”的研究论文，相关研究为揭示硼对南方酸性红壤中柑橘砧木（枳）铝毒害的缓解机制提供了新见解。
柑橘是世界第一大类水果，我国的柑橘产量和种植面积居世界首位，其主要种植于长江中下游和长江以南的酸性土壤地区。其中，铝（Al）毒是酸性土壤中限制柑橘生长的主要胁迫因子之一。硼（B）是植物正常生长发育所必需的微量元素。研究表明，硼和铝之间具有一定的相互作用，且多项研究表明硼对植株铝毒害具有一定的缓解作用，但是更深入的缓解机制还有待探索。
图1 图形摘要
枳（Poncirus trifoliata (L.) Raf.）作为柑橘的近源属植物，是柑橘栽培中的主要砧木。因此，本研究以枳为研究对象，利用水培体系，首先分析硼添加对根系有机酸分泌种类及根际pH变化分析，结果表明，铝主要诱导枳根系分泌苹果酸以响应铝毒；铝胁迫下，施硼可促进根系苹果酸的分泌（螯合根际铝）及碱化根际pH（改变根际铝形态），共同降低根系对铝的吸收，进而减弱铝对植株的毒害作用。另外，对细胞壁果胶组分含量及特性变化分析发现，硼通过抑制低甲基酯果胶合成（较低的JM5荧光强度）、降低果胶甲酯酶活性以降低细胞壁中铝的结合位点，从而减少细胞壁中铝的积累。不同亚细胞组分中铝含量及分配表明，硼可促进液泡中铝的分配，且调控细胞质Al3+转运至液泡的PtALS1和PtALS3基因在加硼之后表现出较高的表达量。因此，结果得出铝胁迫下加硼抑制根尖对铝的吸收，降低细胞壁中铝的积累，且进一步促进液泡对进入细胞质中的铝区隔存贮，最终减轻铝对植株的毒害作用。本项目研究结果将为酸性土壤施用硼肥提高铝毒抗性、丰富柑橘逆境胁迫的调控提供理论基础和实践参考。
图2 硼缓解枳铝毒具体机制模式示意图
博士研究生闫磊为本文的第一作者，我校园艺植物生物学教育部重点实验室、园艺林学学院刘继红教授和资源与环境学院姜存仓教授为本文共同通讯作者。浙江大学刘于老师以及我校博士研究生李双、程锦也参与了该项研究。该研究得到了国家自然科学基金和中央高校基本科研业务费专项基金资助。
审核人：姜存仓 刘继红
【英文摘要】
Boron (B) is an indispensable micronutrient for plant growth that can also alleviate aluminum (Al) toxicity. However, limited data are available on the underlying mechanisms behind this phenomenon. Here, we found that a certain range of B application could alleviate the inhibitory effects of Al toxicity on citrus. Transcriptome analysis revealed that several Al stress-responsive genes and pathways were differentially affected and enriched, such as coding for the secretion of organic acid and the distribution of Al in subcellular components after B addition. Specifically, B application enhanced rhizosphere pH and induced malate exudation by expressing PtALMT4 and PtALMT9 genes occurred in Al-treated root, which ultimately reduced the absorption of Al and coincided with down-regulated the expression of PtNrat1. Moreover, B supply suppressed the pectin methyl-esterase (PME) activity and displayed a lower level of PtPME2 expression, while enhanced the PtSTAR1 expression, which is responsible for reducing cell wall (CW) Al deposition. Boron addition enhanced the PtALS1 and PtALS3 expression, accompanied by a higher proportion of vacuolar Al compartmentation during Al exposure. Collectively, the protective effects of B on root injury induced by Al is mainly by subsiding the Al uptake in the root apoplast and compartmentalizing Al into vacuole.
