| Maize is the most important cultivated crops in northern China, high yield, simple management, etc., but the growing maize areas in northern spring often encountered "late spring" weather, resulting in the seeds do not germinate for a long time, due to low temperatures, and lead to reduce seed vigor, poor emergence, emergence of arrhythmia, large differences between plant growth. So, it is very important on improving corn seed germination under low temperature stress. Brassinosteroid in plant plays an important role in responsing low temperature stress, but the mechanism of its function on cold tolerance in the corn seed germination is unclear. In this study, Xianyu 335, a maize hybrid, was used to investigate the effects of 24-Epibrassinolide (EBR) on maize embryo germination under low temperature (LT) stress. The results shows:1. Maize seeds were soaked by EBR under chilling stress, after response surface analysis (RSA), the combination 0.01037mM and 23.924h of soaking concentration and time, the corn seed germination rate, germination index, vigor index, seedling coleoptile long, root length, seedling fresh and dry weight were optimal by comprehensive evaluation, so the optimum concentration of EBR that promoted maize seed germination under low temperature stress was 0.01 mM.2. After EBR soaking, the germination potential and vigor index were significantly higher than those without the EBR pretreatment, increased by 22.2% and 14.1%, the biomass on corn seedling was significantly higher than that without EBR treatment, seedling total fresh weight increased 26.9%, plant fresh weight increased 24.2%, seedling total dry weight increased 53.3% and plant dry weight increased 57.1%, which indicates the application of exogenous EBR can effectively relieve the inhibition of seed germination and seedling growth under low temperature stress.3. After EBR soaking, compared with the control, the soluble protein content was increased by 19.4% on 2d, the total soluble sugar content was increased by 17.2% on 4d, the proline content was increased by 69.0% on 8d, while the nucleotide content of seed leachate overall less than the control treatment, but its seed amylase activity higher than control, which suggested that EBR could promote the accumulation of osmotic adjustment material content under low temperature stress in corn embryo, contributing to corn seed germination, and enhance the ability of resistance to low temperatures.4. After EBR soaking, compared with the control, the superoxide radicals (O2)in seed embryo significantly decreased by 17.6%, the relative conductivity significantly decreased by 14.7%, MDA content significantly decreased by 54.7%, while the antioxidant enzymes (including SOD, POD, CAT and GR, etc.) activity were significantly increased, the maximum increase rate were 96.7%,24.8%,28% and 61.7%, meanwhile the content of non-enzyme antioxidant GSH also significantly increased by 30.0%, reducing the oxidative damage on the embryo, which showed that EBR could improve anti-oxidative capacity to alleviate the injuries of low temperature stress in maize seeds.5. EBR soaking induced the accumulation of nitric oxide (NO), when using the NO scavenging c-PTIO and NOS inhibitor L-NAME, the enzyme activities of CAT and POD, and the content of proline decreased, but NO donor SNP increased the enzyme activities and the content of proline, indicating NO mediated the EBR-induced antioxidant capacity. The gene expression pattern analysis showed that the expression of P5CSI, CBFl, CBF3 and COR15α was induced by LT stress, and further increased by EBR treatment in maize embryo, while their expression were suppressed by c-PTIO and L-NAME, and improved by SNP, which implied LT-responsed genes were regulated by NO. These results demonstrated that NO was mediated in the BR-induced LT tolerance in maize embryo by modulating the antioxidative capacity and the expression of LT-responsive genes. |
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