硅调节植物抗病性的机理：进展与展望

宁东峰， 梁永超

(1 中国农业科学院农田灌溉研究所， 河南新乡 453003； 2 中国农业科学院农业资源与农业区划研究所， 北京 100081；3 浙江大学环境与资源学院， 浙江杭州 310029)

矿质营养可以影响作物对病害的防御能力，被认为是调控作物病害的重要影响因素之一，通过矿质营养元素调节可以降低许多作物病害发生程度[1-2]。虽然迄今为止，并未证实硅是植物生长发育所必需的矿质营养元素，但是硅对植物生长发育的有益作用，国内外已有大量的研究报道。研究表明，硅可以促进植物生长并提高产量[3-9]，增强植物抵抗病害及虫害的防御能力[10-16]，同时也可以减轻盐分胁迫[17-20]，干旱胁迫[21-22]，重金属毒害[23-27]，辐射[28]，养分失衡[5]，冻害[29]等非生物胁迫对植物的危害。促进环境友好型农业生产是农业科学研究面临的最大的挑战，而探索农业生态系统自身对病害的调节，减少化学农药的施用，是实现农业绿色生产的重要环节。硅素营养增强作物对病虫害的防御能力已得到充分证实，但其中的作用机理非常复杂，至今仍然没有明确。本文对国内外有关硅素营养与作物病害发展的相互关系及相关机理的最新研究进展进行了归纳总结，为通过植物营养调节技术来提高作物病害防御能力的研究提供理论支撑。

1 概述

1.1 土壤中的硅

1.2 植物中硅的积累、形态和分布

同一植物不同器官硅积累量差异较大，以水稻为例，水稻各器官SiO2含量顺序，谷壳(15%)>叶片(12%)>叶鞘(10%)>茎(5%)>根(2%)[36]。对同一器官而言，如叶片，则依赖于叶片的年龄，一般老叶的硅含量高于新叶，水稻体内硅的含量随着生育时期的推移以指数形式增加[7]。

2 硅与植物病害

2.1 硅与水稻稻瘟病

稻瘟病是由真菌的稻梨孢菌[Magnaporthegrisea(Hebert Barr) ]引起的，该病在世界许多水稻栽培国家和地区广泛发生和流行，在高温灌溉或热带旱作水稻地区尤为严重[38]，是我国水稻三大病害之一。稻瘟病菌可以感染水稻地上部的任何组织，在营养生长期常发生在叶片上，引起叶片稻瘟病，在生殖生长期则发生在茎节点或穗分枝上，引起穗稻瘟病[39]。Onodera等[40]早在1917年首次提出植株叶片含硅量与水稻稻瘟病病害程度成负相关。Inokari和Kubota[41]在1930年研究证实，向腐殖化土和水稻土中施入硅肥可以降低稻瘟病的发病率。Volk等[42]研究表明，水稻叶片稻瘟病病斑数量与叶片中硅含量的增加呈线性负相关关系。Rabindra等[43]研究发现，在相同的生长环境下，地上部硅积累量高的品种其稻瘟病发生率低。但也有研究指出地上部硅含量高的品种，对稻瘟病的防御能力也不一定总是高于硅含量低的品种[38,44]。Seebold等[45]研究了施硅对敏感型、中抗和高抗型水稻品种抵抗稻瘟病的作用，发现无论品种抗性如何，施用硅肥后，病原真菌潜伏期延长，病斑个数、形状大小与病斑膨胀率等都显著降低[45]。在佛罗里达土壤缺硅严重的稻作地区，硅肥被当做有效的杀菌剂来抑制稻瘟病[10]。在哥伦比亚东部地区的旱作水稻田，当稻瘟病病情较轻时，单施硅肥抑制水稻稻瘟病的效果与三环锉杀菌剂全量施用的效果相当；稻瘟病严重时，硅肥同时配施10%的杀菌剂效果最好[46]。在苗圃中施用硅肥显著抑制了水稻幼苗稻瘟病的侵染[47]。

2.2 硅与水稻纹枯病

水稻纹枯病是由真菌(Thanatephoruscucumeris)引起的，无性态为RhizoctoniasolaniKühn，属半知菌亚门真菌，致病的主要菌丝融合群AG-1占95%以上，该病多在高温、高湿条件下发生和流行，是水稻生产的主要病害之一。水稻苗期和穗期都可能感病，抽穗前多发生在叶鞘，抽穗后向叶片、穗颈部扩展。Rodrigues等[48]研究发现在缺硅土壤中施用硅肥后，中度敏感性和敏感性水稻品种，比不施硅肥的高抗病品种的纹枯病发病率降低。施硅显著增加水稻秸秆中的硅含量，病原真菌潜伏期随着施硅量的增加而延长，纹枯病病斑个数、形状大小与病斑膨胀率等都显著降低[11]。在水稻孕穗期和开花期，施硅可以显著降低纹枯病的病情[49-50]。

2.3 硅与水稻胡麻叶斑病

胡麻叶斑病由稻平脐蠕孢(Bipolarisoryzae)引起，在高温高湿和有雾露的条件下发病严重，水稻苗期最易感病，分蘖期抗性增强，分蘖末期抗性又减弱。在日本，研究报道指出硅肥的施用可以降低水稻胡麻叶斑病的发病率[51]。在美国佛罗里达缺硅的有机土壤中，连续两年施用炉渣硅钙肥，胡麻叶斑病相比对照分别降低15.0%和32.4%[11]。在巴西缺硅的土壤中施用硅肥，可以显著降低胡麻叶斑病的发生，而不受土壤中Mn含量的影响[52]。Dallagnol等[53]利用水稻吸硅缺陷的变异种进行了研究，发现施硅可以显著增加叶片中硅含量，而硅含量与病菌潜伏期成正相关关系，与病斑个数、病斑大小等呈负相关关系，并且提出水稻根系对硅的主动吸收对胡麻叶斑病的预防有重要作用。

2.4 硅与水稻白叶枯病

白叶枯病由细菌[Xanthomonasoryzaepv.oryzae(Ishiyama)Zoo]引起[54]，是稻黄单胞杆菌水稻变种，为革兰氏阴性菌。水稻的全生育期均可能感染白叶枯病，尤其是在苗期和分蘖期；水稻各个器官均可感染该病，叶片最易染病。Chang等[55]报道TNI是对这种病害敏感型品种，其叶片中硅含量低于抗性育种线；选用TSWY7品种做水培试验，研究发现其对病害的抵抗能力随着硅肥用量的增加而同步增强。薛高峰等[56]研究同样表明施硅可以提高水稻易感病品种对白叶枯病的防御能力。

2.5 硅与白粉病

白粉病是由(Sphaerothecajuligin)病原菌感染引起的，在麦类作物和园艺作物多发生。Miyake和Takahashi[57]通过增加培养液中硅的浓度，黄瓜地上部硅含量随之增加，白粉病的发病率降低。Menzies等[58]研究发现当黄瓜生长在硅含量高的营养液中时，白粉病感染率、菌落大小、孢子发芽都有降低。草莓叶片硅含量与培养液中硅浓度成比例地增加，白粉病的发病率降低[59]。当大麦和小麦缺硅时，对白粉病的敏感性增加[60]。杨艳芳等[61]研究指出，施硅能显著降低小麦感病品种植株的白粉病病情指数，提高其对白粉病的抗病能力。有研究报道，叶面施用硅肥也可以有效抑制黄瓜、甜瓜、葡萄叶片白粉病的发生[62]。梁永超等[15]研究认为，叶面施肥虽然能够通过硅的物理防御作用降低病害的侵染，但不能提高植物系统获得抗性的能力，而根部施肥则可以提高黄瓜对白粉病感染的诱导抗性。

2.6 硅与其他病害

除了上述主要病害外，硅对植物其他多种病害的发生也有防御能力。如根腐病，由细菌Pythiumspp引起，在许多农作物上都有发生。Heine等[63]研究发现硅可以降低番茄和苦瓜腐霉菌的发病率。大豆锈病，由真菌Phakopsorapachyrhizi引起，是影响大豆产量的主要病害之一。Lemes等[64]研究表明，施用硅肥可以替代杀菌剂的使用，硅肥与杀菌剂配合可以更有效地抑制病情的发展。

3 抗病机制

3.1 物理防御机制

3.2 生物化学防御机制

虽然硅提高植物抗病性的物理防御机制不可忽视，但被动的机械防御在解释一些现象时受到限制和质疑，继而研究提出了新的生物化学防御假设。认为植物体内可溶性硅在植物病害防御中起着积极的作用，可以归结为两点。

第一，硅诱导感病植物细胞产生抗毒素物质。Fawe等[71]研究提出施硅处理增加了感病的黄瓜叶片中黄酮类植物抗毒素的积累，从而增强了黄瓜叶片抵抗白粉病的能力。Bélanger等[72]研究认为，施硅与不施硅处理植物细胞化学的最大差异是，施硅处理植物表皮细胞沉积大量酚醛类物质，该物质沿着细胞壁和临时的吸器膜积累，类似植物抗毒素，因而提出硅对小麦抵抗白粉病起着积极的防御作用。Rodrigues等[14]研究同样提出，施硅处理的感病水稻叶片浸出的植物抗毒素的含量要高于不施硅处理，认为硅在提高水稻抗稻瘟病中起着积极的防御作用。Ghanmi等[73]以拟南芥为研究对象，提出施硅诱导产生了电子-密集的抗毒素物质产生，该类物质在感病表皮细胞的真菌母器周围积累，提出硅提高植物的抗病性是复杂的过程，而不是简单的物理防御。Re′mus-Borel等[74]通过薄层色谱法(TLC)分析叶片浸出物质，发现施硅处理与不施硅处理小麦叶片浸出物质中抗毒素苷配基存在差异，通过高效液相色谱(HPLC)分析认为，施硅处理的叶片中至少三种抗毒素物质要高于不施硅处理，提出硅诱导小麦产生抗毒素物质来应对白粉病的侵染。

第二，硅诱导感病植物组织中病程相关蛋白酶活性的提高。Chérif等[75]研究发现黄瓜感染霉腐病(Pythiumspp)后，施硅处理可以显著促进叶片内几丁质酶及过氧化物酶和多酚氧化酶的活性，并且提高了β-葡糖苷酶的活性。这些研究表明，硅参与提高植物抗病性是积极的、复杂的生物化学过程。Cai等[66]研究发现水稻感染稻瘟病后，施硅处理可以显著增加水稻叶片中过氧化物酶、多酚氧化酶、苯丙氨酸解氨酶的活性。孙万春等[16]研究指出，施硅处理提高了感病叶片过氧化氢酶的活性，降低了体内过氧化氢的积累和脂质过氧化反应，从而提高了对真菌菌丝(OryzasativaL)的防御能力。梁永超等[15]对叶面施硅与根系施硅对黄瓜白粉病的抗性机制进行了研究，发现无论对抗性品种或敏感品种，在感染白粉病后，根系施硅处理可以提高病程相关蛋白酶的活性(过氧化物酶、多酚氧化酶、几丁质酶)，而叶面施肥虽然也可以降低白粉病的病情，但其对相关蛋白酶的影响不显著，而主要是通过物理防御作用。

3.3 分子水平防御机制

硅提高植物对病害的防御过程是非常复杂的，许多科学家借助现代分子技术，从分子水平上阐明防御机制。Rodrigues等[76]首次在分子水平上研究了硅的抗病机理，提出硅增强了感稻瘟病水稻M201与抗病密切相关的PR-1，过氧化物酶基因的转录水平。Fauteux等(2006)通过基因芯片，从转录组水平分析了对照、对照+施硅、对照+感染白粉病、施硅+感染白粉病四个处理间拟南芥基因表达差异。结果表明，在没有白粉病胁迫下，拟南芥仅有两个基因受到施硅影响；但是在感染白粉病后，施硅处理与不施硅处理比较近4000个基因表达存在差异。通过功能分析发现，很多上调基因与防御功能相关，而大部分下调基因与新陈代谢相关。在没有病害胁迫时，施硅对拟南芥的新陈代谢没有影响，在感染白粉病后，施硅植物通过上调防卫基因和病程相关基因来应对病菌侵染[77]。Brunings等[78]通过基因芯片技术分析了水稻四个处理间的基因表达差异。研究表明，对于不感病水稻，施硅与不施硅处理间存在221个基因表达上的差异，其中28个参与植物防御或响应逆境胁迫。由此推断硅参与了水稻的新陈代谢，并在水稻增强抗稻瘟真菌(M.oryzae)中起到了分子信号传导的作用。对于感病水稻，不施硅处理，真菌(M.oryzae)侵染引起738基因表达差异，而施硅处理只有239个。如编码植物生长素水解酶基因Os01g0706900与编码植物生长素SAUR响应家族蛋白基因Os08g0452500，无硅处理，两基因被上调，而施硅处理不受影响。无硅处理水稻18个编码钙调信号传导相关的基因表达上调，而施硅处理只有10个上调。说明，施硅对水稻应对病害胁迫起到了预调节的作用，从转录水平上影响水稻对真菌(M.oryzae)侵染的响应。Chain等[79]也通过基因芯片分析了小麦四个处理间基因表达的差异。研究认为，在没有感病胁迫时，施硅对小麦基因表达差异影响较小，但是在感染病害时，施硅会显著地减少由真菌侵染引起的基因转录的变化。Ghareeb等[80]研究认为，施硅可以增强番茄对青枯病(由细菌Ralstoniasolanacearum引起)的防御能力，通过RT-PCR技术跟踪12种防御标记基因表达。结果表明，施硅处理番茄在细菌Ralstoniasolanacearum侵染时，茉莉酸/乙烯标记基因，以及氧化胁迫标记基因和过氧化物酶标记基因表达上调。认为在番茄受到细菌侵染时，硅诱导植物产生乙烯、茉莉酸、活性氧等系列信号，使植物处于预激活化状态，从而减轻生物胁迫。

4 研究展望

综上大量研究表明，硅对水稻稻瘟病、纹枯病、白叶枯病、胡麻叶斑病等病害都有显著的抑制作用，硅也被认为是水稻的“准必需营养元素”[3,10,78]。在缺硅土壤中施用硅肥，可以增强作物对病害的抵抗能力，从而大量降低杀菌剂的使用。在中国南方热带和亚热带稻作地区，高温高湿的环境条件，土壤脱硅富铝化现象严重，加之水稻常年连种，每年吸收带走大量的硅，土壤缺硅现象严重[31]。但在我国农业生产中，硅肥施用的价值没有引起重视，农民很少自发的施用硅肥，长此以往，势必造成土壤中硅素亏缺，而成为水稻生产的障碍因子。所以，农业生产中推广硅肥的施用，对作物稳产、无公害生产和生态环境保护都具有重要意义。

虽然已有大量研究阐明了硅提高植物抗病性可能存在的物理和生物化学机理，在受到病害胁迫时，植物体内的活性硅可以诱导细胞产生防卫响应，以及通过增加胁迫荷尔蒙物质来诱导植物产生系统防御。硅在植物防御病害响应时，可能起到增强剂或战略信号蛋白的激活剂的作用。所以，硅可能与关键的植物胁迫信号系统相互作用，而最终诱导产生对病原菌的抵抗。但是硅在调节植物信号转导方面的确切机制尚不清楚，仍需要深入研究。

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