不同生境盐地碱蓬适应高盐低氮生境的生理生态机制

Currently, much more attentions were focused on cations, e.g., Na+ compared to Cl- in the physiological and molecular mechanisms which may be involved in salt tolerance of plants. The content of nitrate nitrogen is very low, while the Cl- content is high in the soils of saline land. However, the mechanisms of nitrate uptake and maintaining of NO3- and Cl- homeostasis under high salinity and low nitrate nitrogen conditions are still unclear in halophytes. The euhalophyte Suaeda salsa L. can be used in the restoration of contaminated saline land. Therefore, S. salsa is regarded as ecological green belt along the coastal zone. Meanwhile, the species is economically important because its fresh branches have high value as a vegetable and its seed oil is edible and rich in unsaturated fatty acids, i.e., the species can be used for developing saline agriculture. The present study will use the species to investigate how halophyte adapt to high salinity and low nitrate nitrogen environments. Firstly, to investigate the different physiological characteristics of Cl- exclusion and nitrate uptake in S. slasa from the intertidal zone and on inland saline soils . Secondly, to clone genes that may involve in Cl- exclusion and nitrate uptake in S. salsa according to former transcriptome sequencing analysis in the species. Thirdly, to investigate the expression of these genes in S. slasa from the intertidal zone and on inland saline soils under high salinity and low nitrate nitrogen conditions, and to test the roles of these genes in Cl- exclusion and nitrate uptake in Arabidopsis thaliana by gene overexpression in wide type or transferring them to A. thaliana mutants.

目前，植物响应盐胁迫的生理及分子机制主要集中在Na+等阳离子，对Cl-的研究却很少。盐碱地区土壤氮素含量很低而Cl-含量较高，但盐生植物高效获取硝态氮以及维持NO3-/Cl-稳态的机制并不清楚。真盐生植物盐地碱蓬（Suaeda salsa L.）是盐碱地区环境修复的优良植物资源，可以作为海岸带生态屏障和污染物消解的实地系统，同时也是发展盐地农业的优良种质资源。本研究课题拟以盐地碱蓬为材料，在前期研究的基础上，1）对不同生境盐地碱蓬幼苗根系拒Cl-以及硝态氮高效获取的生理特性进行比较研究；2）利用前期转录组分析得到的盐地碱蓬根系高亲和力NO3-转运蛋白以及氯离子通道蛋白的基因片段，克隆得到相关的全长基因；3）比较分析高盐低氮条件下不同生境盐地碱蓬上述基因的表达，并通过超表达以及转拟南芥突变体验证其生物学功能。探明不同生境盐地碱蓬适应高盐低氮生境的生理生态机制。

探明不同生境盐地碱蓬适应高盐低氮生境的生理生态机制，可以为合理开发利用我国大面积滩涂和内陆盐碱地提供理论依据。该课题研究发现，低氮水平上， 200 mM NaCl显著增加盐地碱蓬根和木质部汁液中的NO3- 含量。说明高盐低氮条件下盐地碱蓬能够高效吸收和转运NO3-。比较两种不同生境盐地碱蓬，300 mM NaCl处理下，潮间带生境比内陆生境根中积累更多Cl-，而木质部汁液中Cl- 的含量较内陆生境中的更低。非损伤微测技术结果分析显示潮间带生境盐地碱蓬比内陆生境的根部排出更多Cl-，表明潮间带生境盐地碱蓬比内陆生境盐地碱蓬根系具有更强的排的能力。. 克隆得到了SsNRT2.1和SsCLCc全长基因。低氮水平上，随着盐浓度的升高，盐地碱蓬中与硝态氮吸收相关的基因SsNRT2.1的表达量被盐分上调的，200 mM NaCl条件下其上调量尤其显著，说明该基因可能参与了盐地碱蓬硝态氮高效吸收的过程；盐处理显著诱导了两种生境盐地碱蓬根中SsCLCc 基因的相对表达。无论是对照组还是盐处理组，该基因在潮间带生境盐地碱蓬根中的相对表达量都高于内陆生境根中的表达量，上述结果说明盐地碱蓬根中SsCLCc可能参与了其根系拒Cl- 的过程。. 获得了SsNRT2.1和SsCLCc纯合的过表株系、回补株系以及突变体。0和100 mM NaCl处理下，通过分析比较SsCLCc各个株系的生理指标，过表达植株受盐胁迫影响最小，突变体受盐胁迫影响最大，回补株系与野生型受盐胁迫相似，初步判定SsCLCc将细胞质中过量的Cl-转移到液泡中，有利于保护细胞质中的结构及物质不受Cl-的毒害作用，提高植物的耐盐性；一定的盐分对SsNRT2.1过表达株系的表达量是促进的，对回补株系的短时间表达量是促进的。无论在根中还是叶片中NO3-离子的含量都高于野生型，突变体株系的离子含量明显低于野生型植株，回补株系的NO3-含量高于或者接近野生型植株。初步证明低氮条件下SsNRT2.1在盐地碱蓬中起到吸收硝态氮的作用。上述结果为理解盐地碱蓬适应高盐低氮生境的生理生态机制提供了理论依据。