Molecular Mechanism Of Thymol In Regulating Cadmium Stress And Salt Stress In Rice

Thymol acts as a natural plant compounds, and is primarily applied to medical and clinical research. In order to study the thymol regulation mechanism in plant physiology, this study takes rice seedings as materials, combining with the biochemical reagents, fluorescent probe and real-time fluorescence quantitative?qRT-PCR?, briefly analyzes the thymol regulation of rice resistance to cadmium stress and salt stress related mechanism research. It provides the theory and foundation for safety production of heavy metal pollution and soil salinization in the rice. The main results are shown below:1. Compared to the control, treatment with NaCl concentrations ?100 mM? and CdCl₂ concentrations ?4 ?M? resulted in the significantly inhibit the growth of rice seedlings roots ?lethal status?. However, simultaneous treatment with thymol concentrations ?20 ?M? pronouncedly alleviated the growth inhibition induced by salt stress and cadmium stress. This shows that thymol pronouncedly alleviated Cd/Salt-induced the growth stunt in rice seedings.2. Physiological, biochemical, and histochemical analysis indicated that thymol concentrations ?20 ?M? significantly decreased Cd/Salt-induced Oxidative damage,lipid peroxidation, total of ROS accumulation and cell death.3. Cd²⁺ in roots was detected in situ by using specific probe Leadmium Green AM. It was discovery that thymol pronouncedly decreased Cd-induced Cd²⁺accumulation in roots. Endogenous NO in root was detected in situ by using specific probe DAF-FM DA. It was found that cadmium stress pronouncedly increased endogenous NO accumulation. The application of NO releasing compound SNP?sodium nitroprusside?, not only increased endogenous NO level in roots,but also aggravated Cd toxicity. However, compared to the cadmium treatment alone,simultaneous treatment with thymol or NO scavenger ?cPTIO? and inhibitor?L-NMMA, Tungstate? could decrease NO accumulation and alleviate Cd-induced phytotoxicity ?e.g. root inhibition, ROS accumulation, cell death?. Furthermore, Cd treatment alone stimulated endogenous NO ?nitric oxide? generation by enhancing NOS ?nitric oxide synthase? and NR ?nitrate reductase? activities in roots, which could be suppressed by the addition of thymol. Thymol at proper concentrations confers plant tolerance against Cd toxicity by suppressing a list of NO-mediated downstream events, such as oxidative injury, cell death, and Cd accumulation.4. Thymol could significantly increase Cd-induced antioxidant enzymes ?SOD,APX and CAT? activity and antioxidants substance content ?glutathione and ascorbic acid?. Meanwhile, it could induce Mn-SOD, Cu/Zn-SOD, Fe-SOD, APX1/2, CATa/b genes associated with antioxidant enzyme activity up-regulation. This shows that thymol could alleviate salt stress by regulating the reactive oxygen species homeostasis in the root of rice seeding.5. Gene expression associated with salt stress ?OsSOS1,OsHKT1; 1,OsNHX1,OsNHX2, OsNHX3, OsNHX5? shows that: Salt treatment alone could induce OsSOSl,OsNHX1 OsNHX2, OsNHX3, OsNHX5 genes up-regulation and induce OsHKT1;1 gene down-regulation. Compared to the salt treatment alone, simultaneous treatment with thymol could significantly up-regulated the genes, which was related to salt stress ?OsSOS1, OsHKT1;1, OsNHX1, OsNHX2, OsNHX3, OsNHX5?. This shows that thymol could alleviate salt stress by regulating the ionic balance in the root of rice seeding.In conclusion, this study first identified the key role of thymol in the regulation of Cd/Salt tolerance. This research provides significant reference information for development of thymol as a broad spectrum of biological pesticide.