水稻化感品种根分泌物中非酚酸类化感物质的鉴定与抑草活性

Non-phenolic allelochemicals in root exudates of an allelopathic rice variety and their identification and weed-suppressive activity

水稻化感品种能从根系分泌释放化感作用物质 ,长期以来 ,酚酸类物质被认为是水稻根分泌的主要化感物质 ,但这一结论常常被质疑。利用连续循环和直接树脂吸收两种方法采集典型的水稻化感品种 PI31 2 777幼苗的根分泌物 ,并用液相色谱 /质谱(L C/ MS)联用技术鉴定了根分泌物中的非酚酸类物质。结果显示 ,水稻 PI31 2 777幼苗根系能分泌释放 7-甲氧基羟基肟酸、羟基肟酸、3-异丙基 - 5 -乙酰氧基环己烯酮 - 1、5 ,7,4′-三羟基 - 3′,5′-二甲氧基黄酮、二萜内酯 A和二萜内酯 B6个非酚酸类化合物。经液相色谱 (HPL C)定量分析 ,这些化合物在水稻生长 1 0 d的根分泌物中的浓度为 5～ 1 9μmol/ L。进一步的生测结果显示 ,这些化合物在其释放的浓度范围能对稻田常见的稗草和异型莎草有抑制活性 ,尤其是这些化合物的等摩尔混合物的抑草活性增加 ,同时水稻根分泌物的抑草活性与土壤载体显著相关。表明羟基肟酸、环己烯酮、黄酮和二萜内酯四类非酚酸类物质是水稻的主要化感物质 。

Rice (Oryza sativa L.) production is often characterized by a heavy application of herbicides, which may cause environmental problems, while rice allelopathy can potentially be used to improve weed management. This allelopathy can be achieved by the allelochemicals produced by released from living rice roots. Therefore, searching for the allelochemicals from rice has been extensively studied. A range of phenolic acids, such as p-hydroxybenzoic, vanillic, p-coumaric and ferulic acids, were identified as the primary allelochemicals in rice root exudates but are unlikely to explain rice allelopathy, since their concentrations in soil never reach phytotoxic levels. More recently, an increasing number of studies have shown that some flavones, diterpenes, and other types of compounds are potent allelochemicals in rice. In this study, non-phenolic allelochemicals 7-methoxyhydroxamic and hydroxamic acids, 3-isopropyl-5- acetoxycyclohexene-2-one-1, momilactone A, momilactone B, and 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone, were identified from the root exudates of an allelopathic rice accession PI312777 by means of LC/MS. Further studies with continuous root exudates trapping system (CRETS) and direct resin adsorption methods showed that these compounds were released from the living roots of PI312777 seedling after 10 days of its transplanting, and their concentrations were ranged from 5～19 μmol/L by HPLC quantitative analyses. Bioassays indicated that all of these compounds at their released concentrations could inhibit the growth of weeds Echinochloa crus-galli and Cyperus difformis associated with rice, and their equimolar mixtures had a much stronger inhibitory activity than their individuals. In addition, the weed-suppressive activity of these compounds was varied with the media of bioassays. It was much stronger in pot culture with soil than in Petri dish with filter paper, suggesting that microorganisms could biodegrad root exudates, and hence, the weed-suppressive activity of the allelochemicals were enhanced. This study also showed that the concentrations of non-phenolic allelochemicals in rice root exudates were obviously depended on collection methods, suggesting that how to trap and identify the active allelochemicals in rice root exudates should be the priority in the future research on rice allelopathy. So far, there has been limited success in finding allelochemicals whih can really explain the allelopathic action in the field. Therefore, it is needed to further clarify the chemical principles and release mechanisms of rice allelochemicals.