| Cucumber (Cucumis sativus L.2n= 2x= 14) is cucurbitaceae annual creeping herb which originates from the tropical rain forest area in the south of Himalayan mountains. Cucumber is one kind of the most important vegetable in China. The culitivation area of cucumber in China was 98.9 hectares, and with annual production of 40.709 million tons in 2010. As global wanning and flood disasters occurred frequently, waterlogging has became one of the most frequent and extensive abiotic stresses that negatively influence crop growth and productivity, and in some case resulting in plant death. Cucumber is easily affected by heavey rain and subsequent periods of soil flooding in summber, especially in South China because of its shallow-rootedness, less developed aerenchyma, weak absorption ability and poor regeneration ability. However, the adventitious root could be formed in cucumber plants under waterlogging condition which could replace some function of taproot, for lightening the damage caused by waterlogging. Research relate the mechanism of the waterlogging stress to induce the formation of adventitious roots in cucumber seedlings is still very lack. Previous research showed that hydrogen peroxide played important roles in improving plant resilience and mitigating injury. One waterlogging resistant line "Zaoer N" was applied in present study to gain insight into the physiological response of cucumber under waterlogging, and find out the possible role of H2O2 during the adventitious roots formation of cucumber. The main results were as follows:1. The most important trait for survival in waterlogging environment is adventitious roots formation of cucumber plants. After 3 d of waterlogging, adventitious root primoidia were visible on the hypocotyl surface. After 4 d, a few of adventitious root primordia were elongate to emerge from the shoot epidermis. After 5 d, numerous adventitious roots protruded from the lower part of the submerged hypocotyl. Microscopic studies revealed that root primordial had already formed 12-24 h after the start of the experiment. Primordia continued to grow and most reached the epidermis after 48 h of submergence. After 72 h, the root primordial penetrates the hypocotyl surface.2. Compared with the control plants, the superoxide anion producing rate increased quickly in waterlogged cucumber, and reached the peak level at 8 h after treatment. H2O2 content also increased significantly and maintained high level in 4 h.3. The treatment of 10 mM H2O2 could promote the adventitious roots formation of cucumber seedlings under waterlogging stress. The number and length of adventitious roots increased 24.76% and 14.87%, respectively. The root activity was also significantly higher than control about 63.09%. However,5 μM DPI treatment obviously inhibit the adventitious root formation. The number and length of adventitious roots reduced 49.21% and 43.08%, respectively. The root activity was also significantly reduced 24.63%.4. The H2O2 content of H2O2 pretreatment cucumber increased compared with the control plants. There are no significant changes of superoxide anion producing rate. However, the content of H2O2 and the superoxide anion producing rate increased in the DPI pretreated plants. It might be due to the oxidative stress caused by DPI. The activities of SOD and CAT increased in H2O2 pretreatment cucumber indicated that the previous two kind of enzyme might be play important role in eliminating the ROS.5. qRT-PCR technology was applied to analyze the expression levels of 9 RBOH genes under waterlogging, H2O2 pretreatment and DPI pretreatment. The results showed that the expression levels of CsRboh02 and CsRboh06 increased under waterlogging condition, and the change was in accordance with the change of H2O2 content. The expression level of CsRboh06 was up-regultaed by H2O2 pretreatment. It indicated that CsRboh02 and CsRboh06 might play important roles for ROS accumulation and adventitious root formation of cucumber under waterlogging stress.6. qRT-PCR analysis showed that the expression level of MT2 was down-regulated under waterlogging and H2O2 pretreatment. It indicated that the inhibition of MT2 gene might cause the ROS accumulation of cucumber under waterlogging condition. |
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