The Role Of Nitric Oxide And MAPK In Brassinosteroids-induced Antioxidant Defense In Cucumis Sativus

In recent years, with the rapid growth and development, protected agriculture has become the dominant industry in agricultural production in China. Latest data showed that the area of protected agriculture make up about 85% of the total area in the world. However, the overall level of development of protected agriculture is not high because of lacking of capital investment, insufficient agricultural facilities system, less capacity to withstand natural risks and unstable product quality. Increasing investment to improve the structure of agricultural facilities and technology innovation to improve the controllability of plants to the relatively weak agricultural infrastructure is two main aspects to improve the development level of horticulture in China. The plasticity of horticultural plants to adapt to adverse environmental provides a good path to reduce our capital investment to improve technological innovation. Therefore, it is of great significance to investigate the adaptation mechanism of horticultural plants respond to adverse environmental. In this paper, cucumber (Cucumis sativus L.) were used to investigate the effects of NO involved in BR on the low temperature stress tolerance of oxidative stress, and relationship between NO, and H2O2 as a signal molecule in BR regulation of plant stress. MAPK inhibitors were used to discuss the effect of kinase on the BR-induced oxidative stress. The main results are as follows:1. We have studied the role of NO signal in BR-induced tolerance to multiple stresses. We demonstrated that exogenous BR induced NO production by confocal laser scanning microscopy (CLSM) and spectrometric methods, tungstate (an inhibitor of NR),L-NAME(a specific inhibitor of nitric oxide synthase) and PTIO(a scavenger of NO) inhibited BR-induce NO accumulation. The results demonstrated that there were two paths in BR-induced NO production.2. We have studied whethert NO was involved in BR-induced plant responses to stresses and the underlying molecular mechanisms. Exogenous BR and SNP(a NO donor) significantly increased the tolerance to photo-oxidative and cold stresses. The protective effects of BR were blocked by inhibitor and scavenger of NO. BR and SNP-induced tolerance to chill and oxidative stress were associated with enhanced antioxidant capacity. The inhibitor and scavenger of NO also reduced BR-induced expression of genes encoding antioxidant enzymes such as SOD, CAT, POD, GR and APX.3. We have studied the relationship between NO, and H2O2 as a signal molecule in BR-induced systemic resistance. Exogenous H2O2 and NO donor SNP treatment significantly increased antioxidant enzymes activities of APX, CAT, GR and SOD activities and their corresponding genes expression. NO scavenger PTIO inhibited H2O2-induced antioxidant capacity. It indicated that the NO was involved in H2O2-induced changes in antioxidant metabolism incucumber. DPI and the H2O2 scavenger (DMTU) inhibited BR-induced production of NO, but NO inhibitors and scavengers did not affect the BR-induced H2O2 accumulation. It indicated that the there are some linearity relations between H2O2 and NO in induction of plant stress signaling pathways. H2O2 may play a role in the NO upstream.4. We have investigated whether NO was involved in BR-ieduced tolerance against PQ oxidative stress. NO is essential for the BR-induced changes in lipid peroxidation and improved APX, CAT, SOD and GR antioxidant activity, and increased antioxidant and detoxification-related glutathione-S-transferase activity,which enhanced plant tolerance against oxidative stress in cuucmber. By using tomato BRs mutant (Dim) and wild-type (Condinred) as supplementary material, we further elucidated that NO was assiociated with BR-ieduced PQ oxidative stress tolerance.5. We have studied the redox effects of BR-induced of MAPK protein kinase. MAPK inhibitor PD98059 and U0126 showed high activity against BR-induced stress resistance to light oxidative stress, in regard to BR-induced antioxidant enzymes activities of APX, CAT, GR and SOD and their corresponding genes expression. These two MAPK inhibitiors also alleviate the changes in cellular redox state induced by BR, as indicaded by the decrease in GSH/GSSG ratio. In addition BR-induced GST activity was significantly inhibited with both of the inhibitors. The results supported that MAPK was involved in the regulation of antioxidant capacity by BR.6. At last, we studied the effect of NO on the photosynthesis parameters, chlorophyll biosynthesis genes and related genes in the Calvin cycle. The results showed that NO increased light-saturated CO2 assimilation rate (Asat), upregulated chlorophyll synthesis gene MgCH, FeCH and three carboxylic acid cycle Rbc S, PGK, FBPase and TPI genes expression,but inhibited chlorophyll synthesis gene rbcL. These results showed the possible involvement of NO in the regulation of plant photosynthesis.