低钾胁迫对水稻(Oryza sativa L.)化感潜力变化的影响

研究以国际公认的化感水稻P1312777和非化感水稻Lemont为供体，稗草（Echinochloa cru-galli L.）为受体，采用稻／稗共培体系，研究低钾胁迫对水稻化感潜力变化的影响及其机制。受体稗草的形态指标分析结果表明，低钾胁迫促使化感水稻P1312777对共培稗草的根长、株高和干重的抑制率均升高，增幅远大于非化感水稻Lemont。受体稗草生理生化指标分析结果表明，低钾胁迫下化感与非化感水稻对受体稗草保护酶系（SOD、POD、CAT）及根系活力的抑制作用增强，但化感水稻P1312777比非化感水稻Lemont的抑制程度大，且达极显著差异。实时荧光定量PCR分析结果表明，低钾胁迫下，化感水稻P1312777根部与叶部中酚类代谢的关键酶——苯丙氨酸解氨酶、肉桂酸-4-羟化酶、羟化酶、O-甲基转移酶的基因均上调表达，而非化感水稻根部相应酶均下调表达，叶部除苯丙氨酸解氨酶上调，其余酶也下调表达。而萜类代谢途径关键酶——HMG—CoA还原酶、角鲨烯合酶、单萜烯环化酶、倍半萜烯环化酶、二萜烯环化酶的基因，在两种水稻根部中呈现出相同或相似的表达方式（上调或下调），即HMG—CoA还原酶上调表达，角鲨烯合酶、单萜烯环化酶、倍半萜烯环化酶、二萜烯环化酶下调表达；而在水稻叶部，非化感水稻Lmont相应酶基因表达方式仍然不变，化感水稻P1312777除了角鲨烯合酶下调表达，其余4个酶均上调表达。水稻根系分泌物中酚类物质的HPLC分析结果表明，低钾胁迫下，化感水稻P1312777根系分泌物中，所检出的酚酸类物质总量是正常营养条件下的2．30倍，而非化感水稻Lemont则是正常营养条件下的0．91倍。综合分析认为低钾胁迫下，化感水稻P1312777抑草能力增强主要是由于酚类代谢途径关键酶基因表达上调，导致酚类代谢途径旺盛，分泌出更多的酚类物质，进而破坏受体稗草保护酶系统，抑制了稗草的正常生长。

Effects of potassium stress on allelopathic potential of rice (Oryza sativa L.)

In order to explore the changing mechanism of rice allelopathic potential under potassium deficiency, allelopathic rice PI312777 and non-allelopathic rice Lemont were employed as donor plants and the morphological and physiobiochemical characteristics of receiver plant branyardgrass(Echinochloa crus galli) mediated by the two donor plants were investigated under low potassium stress (5 mg·L-1 K, denoted as K-) and normal potassium (40 mg·L-1 K, denoted as K+). The result showed that, under K- condition, the two rice accessions inhibited the growth of barnyardgrass to different extents. The inhibitory effect (IR, %) of allelopathic rice PI312777 on barnyardgrass was greatly higher than that of non-allelopathic rice Lemont, showing 56.19% (IR, the same below) VS 14.67% in the suppression of root length of barnyardgrass, 35.78% VS 9.27% in plant height, and 46.24% VS 9.47% in dry weight. Under K- condition, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and the root activity of barnyardgrass were descended at a higher rate when the target plants were co-cultured with allelopathic rice PI312777 than those with non-allelopathic rice Lemont. Furthermore, analysis of Real time Fluorescent Quantitative PCR(FQ-PCR) showed that, under K- condition, phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, hydroxylase, and O-methyltransferases, which are the key enzymes in phenolic metabolic pathway, were all up-regulated in root and leaves of allelopathic rice PI312777. But all these enzymes were down-regulated in non-allelopathic rice Lemont except phenylalanine ammonia-lyase in leave. HMG-CoA reductase, squalene synthase, monoterpenes cyclase, sesquiterpene cyclase, and diterpene cyclase, which are the key enzymes in isoprenoid metabolic pathway, performed the same expression pattern in roots of the two rice accessions, and it was also found that in leaves of non-allelopathic rice Lemont, HMG-CoA reductase was up-regulated and the other four enzyme genes were down-regulated. But in allelopathic rice PI312777, only squalene synthase showed down-regulated, the reverse was true in the other enzyme genes. The result from the analysis of phenolic acids in two rice root exudates by using HPLC showed that, the total amount of ten phenolic acids concerned in allelopathic rice PI312777 under K- condition, was 2.30 times as those as under the K+ condition. However it was only 0.91 times in non-allelopathic rice Lemont under the same condition. It is therefore suggested that enhancement of rice allelopathic potential in the suppression of the target weeds under K deficiency might be attributed to the up-regulation of the key enzymes involved in phenolic metabolism, which leaded to the activation of phenolic metabolism, and increased phenolic allelochemicals, consequently inhibited growth of barnyardgrass.