Srivastava A K, Srivastava S, Mishra S, D'Souza S F, Suprasanna P
Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Metallomics. 2014 Sep;6(9):1718-30. doi: 10.1039/c4mt00039k.
Arsenic (As) is a ubiquitously present environmental carcinogen that enters into the human food chain through rice grains. In our previous research, the application of thiourea (TU; a non-physiological thiol based ROS scavenger) has been demonstrated to enhance salt and UV stress tolerance as well as the crop yield under field conditions. These effects were associated with the ability of TU to maintain plant redox homeostasis. Since As stress also induces redox imbalance, the present research was initiated to evaluate the efficiency of TU in regulating As tolerance/accumulation in rice. The supplementation of TU (75 μM) to As(V) (25 μM) improved the root growth and also reduced the As concentration by 56% in the aerial parts, which could be attributed to significant downregulation of the Lsi2 transporter responsible for the translocation of As from root to shoot. The fact that these effects were not due to direct interaction between As and TU was confirmed from complexation studies using HPLC-(ICP-MS)-(ESI-MS). Short-term kinetic studies of GSH levels and the GSH/GSSG ratio confirmed the establishment of differential redox states in As and As + TU treated seedlings. The real-time RT-PCR based comparative expression profiling under As with/without TU treatment identified Sultr1;1 and Sultr1;2 as major redox-regulated sulfate transporters. Their specific induction in shoots coupled with enhanced root-to-shoot sulfate translocation (analyzed using (35)S-sulfate as a radiotracer) was observed under TU supplementation. Furthermore, the level of thiolic metabolites (PC2 in roots and GSH and PC3 in shoots) and activities of sulfur metabolism enzymes (ATP sulfurylase and cysteine synthase in roots and 5'-adenylylsulfate reductase in shoot) were also increased with As + TU as compared to As treatment. Thus, this study utilizes the interaction between As and TU to identify the critical redox regulated components of As tolerance in rice.
砷（As）是一种广泛存在的环境致癌物，可通过米粒进入人类食物链。在我们之前的研究中，已证明施用硫脲（TU；一种基于非生理性硫醇的活性氧清除剂）可增强田间条件下的耐盐性和耐紫外线胁迫能力以及作物产量。这些效应与TU维持植物氧化还原稳态的能力有关。由于砷胁迫也会诱导氧化还原失衡，因此开展了本研究以评估TU调节水稻对砷的耐受性/积累的效率。向25 μM的五价砷（As(V)）中添加75 μM的TU可改善根系生长，并使地上部分的砷浓度降低56%，这可能归因于负责将砷从根部转运到地上部分的Lsi2转运蛋白的显著下调。使用高效液相色谱-电感耦合等离子体质谱-电喷雾质谱（HPLC-(ICP-MS)-(ESI-MS)）进行的络合研究证实，这些效应并非由于砷与TU之间的直接相互作用。对谷胱甘肽（GSH）水平和GSH/GSSG比值的短期动力学研究证实，在砷处理和砷+TU处理的幼苗中建立了不同的氧化还原状态。基于实时逆转录聚合酶链反应（real-time RT-PCR）的在有/无TU处理的砷胁迫下的比较表达谱分析确定Sultr1;1和Sultr1;2是主要的氧化还原调节硫酸盐转运蛋白。在添加TU的情况下，观察到它们在地上部分的特异性诱导以及根到地上部分的硫酸盐转运增强（使用³⁵S-硫酸盐作为放射性示踪剂进行分析）。此外，与砷处理相比，砷+TU处理还提高了硫醇代谢物的水平（根部的PC2以及地上部分的GSH和PC3）和硫代谢酶的活性（根部的ATP硫酸化酶和半胱氨酸合成酶以及地上部分的5'-腺苷硫酸还原酶）。因此，本研究利用砷与TU之间的相互作用来确定水稻中耐砷性的关键氧化还原调节成分。
