水稻幼苗对外源硫氰化物污染的吸收、转化和降解机理的研究

Thiocyanate is commonly used in a variety of industrial processes and exists as major constituent of waste water from coke-oven factories. Because of its strong binding tendency to protein, thiocyanate causes inhibition of halide transport to the thyroid gland. It also acts as non-competitive inhibitors to block a variety of enzymatic reactions and affects the central nervous system on humans. Removal of thiocyanate is of crucial importance to environment health. Indeed, various efforts have been devoted to the clean up of thiocyanate-contaminated effluents, including physical/chemical processes and biotreatments. Due to un-avoidable drawbacks, these remediation approaches have not been accepted as a good alternative to large scale implementation. This project is intended to investigate mechanisms involved in uptake, assimilation and accumulation of exogenous thiocyanate by rice seedlings, using isotope techniques and real-time quantitative PCR. The objectives of this study are to: i) investigate uptake, accumulation, and assimilation of 13C and15N labeled thiocyanate by rice seedlings; ii) clarify phyto-degradation pathway of exogenous thiocyanate and possible metabolites in rice seedlings using RT-PCR analysis; iii) investigate availability of thiocyanate as supplementary N and S sources to support growth of rice seedlings.

本项目以水稻幼苗降解外源硫氰化物为核心研究内容，运用同位素（13C 和15N双标记）示踪技术结合分子生物学（RT-PCR扩增）研究手段，深入研究水稻幼苗吸收、迁移、降解和富集外源硫氰化物的机理，从分子水平上解析外源硫氰化物在植物体内的代谢途径和可能的代谢产物，探讨外源硫氰化物作为水稻幼苗生长所需的辅助氮源和硫源的可能性，为其生物可利用性提供有价值的理论依据。

硫氰化物（SCN−）污染对生态环境存在危害性。水稻幼苗对外源SCN−吸收、迁移、累积和代谢的规律是本研究的核心内容。水稻能有效吸收和转化外源SCN−，残留的SCN−主要富集在根部；稳定同位素结合PCR分析显示，“COS途径”和“CNO途径”都参与转化SCN−，且存在明显的组织特异性；水稻叶片CYN和COSase不足以进一步降解SCN−的中间代谢产物CNO−和COS。外源SCN−胁迫显著地提高编码IAA氧化酶基因（OsDAO）和不可逆的IAA-氨基酸共轭反应基因（OsGH3.2、OsGH3.8、OsGH3.9、OsGH3.10）的表达，继而诱导不可逆型IAA的形成，引起根系总长度、根系分叉数、根系表面积和根系体积显著减少，从而抑制水稻幼苗根系的生长发育；JA、IAA和NaHS能有效缓解SCN−胁迫对水稻幼苗根系生长发育的影响，建模分析NaHS缓解外源SCN−胁迫的效果优于IAA和JA。外源SCN−攻击水稻幼苗线粒体呼吸链电子传递中的复合物I（NADH脱氢酶）和复合物III（细胞色素c还原酶），引起水稻幼苗体内O2-•和H2O2过量累积，诱导氧化胁迫；SCN−在根系的破坏位点是复合物III，在叶片中的破坏位点是复合物I和复合物III；SCN−胁迫诱导水稻幼苗体内MDA的累积，根系中MDA的累积是氧化损伤和LOX共同作用的结果，而叶片中MDA的累积则是氧化损伤的结果；SCN−胁迫诱导的氧化胁迫导致水稻蛋白质修饰，表现为PCO含量增加，且叶片中PCO含量明显高于根系中；SCN−胁迫诱导氧化胁迫通过抑制水稻体内DNA复制关键基因（DNA复制许可因子：OsMCM和DAN复制因子：OsRPA）的表达而导致DNA损伤。硝态氮培育水稻幼苗对外源SCN−的转化略优于铵态氮培育水稻幼苗，且外源SCN−对水稻吸收介质中的硝态氮和铵态氮无明显差异；SCN−胁迫对硝态氮培育水稻幼苗体内编码氮代谢关键酶（NR、GS、GOGAT和GDH）的基因表达和活性没有明显的抑制，而明显抑制铵态氮培育水稻幼苗体内编码GOGAT基因的表达和酶活性；两种N源培育下，SCN−胁迫水稻的RGR和NUE与SCN−胁迫浓度间存在负相关性，且对铵态氮培育水稻幼苗的影响要大于对硝态氮培育水稻幼苗；外源SCN−作为水稻生长辅助N源对硝态氮培育水稻幼苗的效果要优于对铵态氮培育水稻。