铝胁迫下玉米分泌异羟肟酸的研究

Cyclic hydroxamates are found as major secondary metabolites in Poaceae plants，and plants have the capability to produce and exude high levels of cyclic hydroxamates into their rhizosphere. Hydroxamates siderophores have been found to alleviate Al toxicity in bacteria. In plants, there is considerable experimental evidence that high tissue levels of ?avonoid-type phenolics are quite common in Al accumulator plants. Such tolerance to Al in shoots of the acidophilus species Zea mays L. has been related to high levels of ?avonoid-type phenolics and cyclic hydroxamates in root tissue and exudation from roots. These benzoxazinoids are cyclic hydroxamates in roots and roots exudates have a high affinity for ion. However, a role for Al-induced exudation of cyclic hydroxamates from roots in amelioration of Al toxicity in Zea mays L. has not been reported. Our previous study evidences have been found a critical clue in terms of Al-detoxify effect of cyclic hydroxamates secreted from roots in Zea mays L.. To elucidate the possible role and mechanisms for cyclic hydroxamates secreted from roots in Al resistance in Zea mays L., studies are carried out including: (1) investigations of relationships between Al resistance and Al-induced exudation of cyclic hydroxamates from roots of Zea mays L. varieties. (2) the role of Al-induced secretion of cyclic hydroxamates in resistant to Al toxicity and correspond mechanism. (3) under Al stress, characteristic of secretion of cyclic hydroxamates from roots in Zea mays L.. (4) The influence of Al on cyclic hydroxamates metabolism, and relationships between the response of cyclic hydroxamates metabolism induced by Al and cyclic hydroxamates exudation from roots. This study results would be demonstrated that Al-induced secretion of cyclic hydroxamates from roots is a new mechanism for the difference in Al-tolerance between cultivars of Zea mays L. The study has very important consequences for breeding aluminum-resistant Zea mays L. cultivars and solving the problem of Al toxicity in Zea mays L. on acid soils.

异羟肟酸是禾谷类植物的重要次生代谢物，可大量分泌到根际土壤。微生物中的异羟肟酸可与铝络合形成异羟肟酸－铝复合物而缓解铝毒。植物的研究也发现，耐铝植物普遍含有较高量的异羟肟酸结构类似物类黄酮类酚醛。嗜酸耐铝玉米品种的根和根系分泌物中均有丰富的异羟肟酸，且对离子有高度的亲和力。然而，玉米根系分泌的异羟肟酸对铝的解毒作用及机制研究国内外均未见报道。我们前期的研究已掌握了玉米根系分泌异羟肟酸解除铝毒害的重要线索。为揭示玉米根系分泌异羟肟酸解铝毒的作用及机制，本项目拟开展以下研究：（1）玉米根系分泌异羟肟酸与其耐铝性关系；（2）异羟肟酸的解铝毒作用机制；（3）玉米根系分泌异羟肟酸的特性；（4）铝胁迫对根尖细胞中与异羟肟酸合成、分解有关的新陈代谢的影响及其与根系分泌异羟肟酸的关系。项目研究的成功将有助于发现玉米解铝毒新物质和阐明玉米耐铝新机制，对玉米新品种培育及酸性土壤中铝毒害问题的解决有重要意义。

铝毒是植物在酸性土壤中生长的主要限制因子，由于生长环境的差异，植物进化出不同的策略来抵抗铝毒害。阐明这些机理，将有助于我们开发抗Al农作物新品种。大部分陆生植物利用根系分泌有机酸，比如柠檬酸，苹果酸，琥珀酸来应对铝毒害，但有关玉米根系分泌的异羟肟酸对植物的解毒作用及机制的研究国内外均未见报道。本项目主要研究了玉米根系分泌异羟肟酸与其耐铝性关系，异羟肟酸解铝毒的作用，玉米根系分泌异羟肟酸的具体特性，以及水杨酸（SA）和β-D-葡萄糖苷酶（异羟肟酸代谢中的关键酶）在铝诱导根系分泌异羟肟酸中的作用。主要研究结果如下：1、铝可诱导玉米根系分泌异羟肟酸，铝处理后，玉米根伸长受阻，根尖铝含量和胼胝质含量增加。铝胁迫下根相对伸长率与异羟肟酸分泌量呈极显著正相关（r丁布=0.4550**，r门布=0.6008**），而根尖铝含量与异羟肟酸分泌量呈显著负相关（r丁布=-0.3542**， r门布=-0.4841**），根尖胼胝质含量与异羟肟酸分泌量也呈负相关（r丁布=-0.3651**， r门布=-0.1351）。并且，聚类分析表明耐铝型的30个玉米品种，如泰玉11号、费玉3号等在铝胁迫下根系分泌异羟肟酸的能力显著高于7个铝敏感品种，如郑单958、北育288等，表明不同基因型玉米品种的异羟肟酸分泌量与耐铝性显著相关。2、荧光淬灭法和邻苯二酚紫染色－试纸法检验均表明异羟肟酸能络合铝；且铝溶液中添加外源异羟肟酸后，玉米根的相对伸长率增加和根尖铝含量下降，有效的缓解了铝对玉米根尖表皮细胞的伤害。3、铝诱导耐铝品种根系分泌的异羟肟酸量随着铝浓度（10、15、20 μmol•L-1）的增加和处理时间（3、6、9、12、24 h）的延长而显著增加，但铝（10、15、20 μmol•L-1）不能诱导铝敏感品种根系分泌异羟肟酸4、铝诱导耐铝玉米品种叶中的β-D-葡萄糖苷酶活性上升，异羟肟酸合成增加；耐铝品种叶中合成的丁布由叶运输到根部，参与根系异羟肟酸类物质分泌。5、铝胁迫下，外源水杨酸(SA) 降低了 Al在玉米根尖中的积累、缓解了Al对玉米根尖细胞的伤害，显著提高了玉米根尖内异羟肟酸的含量和β-D-葡萄糖苷酶的活性，同时根系异羟肟酸的分泌增加。. 上述研究结果表明，铝诱导玉米根系分泌异羟肟酸是玉米抵御铝毒害的有效新机制，β-D-葡萄糖苷酶和SA介导了铝诱导玉米根系异羟肟的分泌。