Effects Of Waterlogging Stress On Physiological And Biochemical Indexes Of Brassica Napus L.

In order to meet the demand of vegetable protein and oil and improve the situation of self-sufficiency in rapeseed production,it is very important to carry out the production capacity improvement project of soybean and oil and expand the oil crop.By exploiting the resources of idle winter fields in the middle reaches of Yangtze River and developing winter rape and other advantageous cash crops rich in protein and oil,more than 30%of the protein and oil import substitution capacity can be achieved.However,due to rice-rape as the main planting mode in the Yangtze River Basin,the paddy soil has high water content,and the subtropical monsoon climate leads to high rainfall in spring and autumn,which is easy to cause waterlogging.Long-term formation of waterlogging in plant roots.Rape is a xerophilic plant,which lacks aerenchyma and is very sensitive to waterlogging.Therefore,it is of great importance for the development of rapeseed industry in the Yangtze River Basin to study the mechanism of rapeseed response to waterlogging stress and improve the waterlogging resistance of rapeseed varieties.In this study,100 germplasm resources of Brassica napus which participated in the national winter rapeseed strain comparison experiment were used as experimental materials.Waterlogging stress was treated at seedling stage,seedling formation rate was counted,and the damage resistance index was calculated.The ultrastructure changes of root cells of different waterlogging resistant rapeseed strains were observed,and the differences of active oxygen scavenging system,photosynthetic traits,endogenous hormone content and gene transcription levels among different strains were compared.The gibberellin,ethylene,and abscisic acid synthesis were inhibited by spraying inhibitors in ethylene,respectively.The mechanism of endogenous hormones in response to waterlogging stress was analyzed in terms of morphology,enzyme activity,photosynthetic characters,and hormone levels in ethylene plants with different water tolerance.The main research results are as follows:1.Waterlogging stress affects the effective number of corner fruit per plant,oil production,sclerotinia disease incidence and plant height,leading to yield loss and quality decline of rape.2.Waterlogging stress leads to plasmolysis and organelle fragmentation in the root cells of rapeseed.The organelle damage of moderately strong waterlogged rapeseed is relatively small,and it can maintain a relatively normal cell morphology under waterlogging stress.In addition,waterlogging caused a significant downregulation of the expression level of cytoskeleton related genes in rapeseed,which decreased to 0.2-0.3 times of normal conditions.3.There are differences in physiological metabolism levels in response to waterlogging stress at seedling stage of B.napus with different waterlogging tolerance.Compared with no waterlogging tolerant strains,the antioxidant enzyme activity of strong waterlogging tolerant rapeseed is relatively higher,and the degree of membrane lipid peroxidation is lower.The expression of anaerobic respiration genes induced by waterlogging stress was significantly upregulated,and the moderate to strong waterlogging tolerant rapeseed had a high level of regulation.In this study,it was found that the POD and SOD enzyme activities of rape with different waterlogging tolerance increased first and then decreased with the extension of waterlogging time,while the CAT enzyme activity and MDA content increased.The enzyme activity of strong waterlogging resistant strains was relatively high,and the increase in MDA was small,indicating that the higher the enzyme activity of the active oxygen scavenging system,the stronger the stress resistance ability of rape.In addition,waterlogging caused a significant increase in the expression of anaerobic respiration related genes PDC,LDH,and ADH in various strains of rapeseed,which was 3-6 times higher than the normal level.4.There were differences in photosynthesis in response to waterlogging stress at seedling stage in B.napus with different waterlogging tolerance,and the photosynthetic rate and chlorophyll content of waterlogging tolerant rapeseed decreased significantly.Waterlogging stress has seriously affected the chlorophyll content and photosynthetic characteristics of rape leaves with different waterlogging tolerance,leading to a significant decrease in chlorophyll content,photosynthetic rate,stomatal conductance,and transpiration rate in rape leaves as a whole,and a significant increase in intercellular CO₂ concentration.In addition,waterlogging tolerant rape has a relatively large range of changes,resulting in relatively severe stress.5.There were differences in hormone levels among different water-resistant B.napus seedlings in response to waterlogging stress.ET and ABA contents increased significantly due to waterlogging,and ethylene content was higher in more water-resistant varieties and abscisic acid content was higher in less water-resistant varieties.Under waterlogging stress,the transcription levels of ET related genes were significantly up-regulated in cultivars with strong tolerance to waterlogging,and the up-regulated levels of ABA synthesis related genes were the largest in cultivars with low tolerance to waterlogging.6.Spraying exogenous hormone inhibitors can regulate the damage of waterlogging stress to rapeseed by improving the level of active oxygen species,the degree of membrane lipid peroxidation,the accumulation of osmoregulation substances,and photosynthesis.Spraying NDGA significantly decreased the POD,CAT activity,and soluble protein content of each strain,significantly reduced the photosynthetic rate and chlorophyll content of the strong waterlogging resistant strain under waterlogging stress,and significantly increased the intercellular CO₂ concentration,aggravating the damage of waterlogging stress to rapeseed.Spraying STS significantly increased the POD activity of strong and moderate waterlogging tolerant strains,increased the proline content and transpiration rate of rape under waterlogging stress,and decreased the chlorophyll content of strong waterlogging tolerant strains and the photosynthetic rate of rape under waterlogging stress.Spraying uniconazole reduced the intercellular CO₂concentration of strong and no waterlogging tolerant strains under waterlogging stress,effectively increased the transpiration rate of each strain under waterlogging stress,and increased the chlorophyll content of no waterlogging tolerant strains under waterlogging stress.