| Drought Juglans mandshurica is one of the "Three valuable hardwood trees" in the northeast of China and has high commercial and medicinal value.Soil drought is the major stress limiting factor in its growth.In this study,we take 2-year-old Juglans mandshurica seedlings as the object to research the response trends of leaf morphological structure and physiology indexes under continuous soil drought stress(0 d.5 d,10 d,15 d,20 d,25 d).Comparative analysis of transcriptome was carried out on the leaves with obvious physiological changes,and the response mechanism of Juglans mandshurica leaves against drought stress was initially discussed at the molecular level,which provided a theoretical basis for studying the response mechanism of tree to drought resistance and the reasonable cultivation and utilization of Juglans mandshurica.The primary research results are as follows:As the degree of drought stress gradually deepened,the leaf water content and relative water content decreased,and the thickness of upper and lower epidermis cells,palisade tissue and sponge tissue decreased gradually.The arrangement of mesophyll cells becomes loose,the xylem structure becomes compact and the area decreases.The ratio of palisade tissue to sponge tissue increased slightly.The length,width and opening rate of stomata in the lower epidermis of leaf decreased significantly with the aggravation of drought stress.Under drought stress,by changing leaf structure and stomata size,Juglans mandshurica actively closed stomata to reduce transpiration and respiration loss and improve drought resistance.Drought stress caused the response to the physiological level of Juglans mandshurica mainly including changes in photosynthetic capacity,osmotic regulation and antioxidant regulation.Under drought stress,Pn and Tr decreased,Gs decreased but Ci increased,the photosynthesis was limited by non-stomatal factor.As the degree of drought deepened,the water use efficiency increased first and then decreased,reaching a peak at 15d.The contents of chlorophyll a,chlorophyll b and carotenoids showed a trend of increasing first and then decreasing,and reached a peak at 1 Od.Drought stress caused the accumulation of proline,soluble sugar and soluble protein osmotic adjustment substances in the leaves,which reached the peak of accumulation at 20d were 2.78,1.78 and 2.07 times of the control group respectively.Persistent drought caused peroxidation of the leaf cells,cell membrane permeability and MDA content continued to increase,and caused the accumulation of harmful reactive oxygen species such as H2O2 and O2-in the leaves,which induced the response of the antioxidant enzyme system.The activities of SOD,POD,and CAT increased significantly,which reached the peak of activity at 20d were 3.04,3.16 and 4.14 times of the control group respectively.To achieve the role of timely removal of active oxygen and other harmful substances,to avoid oxidative damage caused by the accumulation of active oxygen.Drought stress caused differential expression of different functional genes of Juglans mandshurica.A total of 4787 differentially expressed genes were screened.Among them,the differential expression of genes in response to abiotic stimuli and membrane components were significant,which played a particularly important role in resisting drought stress.Through further functional annotation and analysis of differentially expressed genes,153 transcription factor genes,58 plant hormone signal transduction genes,30 drought response genes,and 29 genes related to changes in physiological indicators were obtained.These functional genes played an important role in the resistance to drought stress,and reduces the damage caused by drought to Juglans mandshurica. |
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