CO,NO Alleviate The Oxidative Damage And Delay Programmed Cell Death Of Aleurone Layer In Rice Seed Germination Under Drought Stress

It is well known that drought stress is a key factor that reduces crop production in agriculture. Overproduction of reactive oxygenous species (ROS) caused by drought stress usually leads to oxidative damage, which will inhibit growth and development of many plant species. In the study, rice(Oryza sativa L.) variety, 'YouⅡ128'seeds were treated with 1.0μmol·L-1 hematin (CO donor) and 200μmol·L-1 SNP (NO donor) to explore the effects of exogenous carbon monoxide (CO) and nitric oxide (NO) on atttenuating oxidative damage in rice seed germination under drought stress.The results showed that exogenous CO and NO significantly raised seed germination rate, shoot and root length, activated amylase activity, increased soluble sugar content, soluble protein and proline content. Meanwhile, the results also indicated that CO and NO apparently and differentially up-regulated the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), resulting in the apparent decrease of membrane permeability and MDA content. These results suggested that CO and NO may alleviate drought-induced oxidative damage in seed germination and significantly induce rice seed germination.The aleurone layer cells with strong activity synthesize and secrete various enzymes to decompose the storage nutrients of endosperm in cereal seed germination, which providing for embryo growth. When this secretion is finished, the cells of aleurone layer occurring programmed cell death. By using pharmacology, anatomy combined with staining and microscopy, the cell morphologic feature of PCD was observed in aleurone layers under normal conditions. The results indicated that the PCD of aleurone layer is closely correlated with the degree of vacuolization, displaying the position and time effects companied with the growth and distance of embryo, and final shapes of vacuole were different. Forthermore, CO and NO slowed down the rate of DNA degradation, increased the surviaval rate of cell and delayed the occurrence of PCD in aleurone layers under drought stress. However, CO-specific synthetic inhibtor zinc protoporphyrin IX (ZnPPIX), CO scavenger hemoglobin (Hb), and NO-specific scavenger cPTIO effectively reversed above effects. Therefore, we deduced that CO induced rice seed germination probably mediated by NO and NO may act downstream of CO signaling under drought stress.