| Cupressus gigantea Cheng et L.K.Fu,also known as Yarlung Zangbo River juniper,is the longest of tree-age and thoracic among the cypress species in China.It is one of the endemic and rare tree speeies in Tibet.The cupressus population has a narrow distribution range,which will be distributed along the Yarlung Zangbo River or its tributaries.Due to its greater adaptability to drought,it has served as a soil and water conservation in the area.However,in recent years,environment change on both sides of the river valley and lack of effective protection measures,it has been listed as an endangered plant in China.In this study,the eypress from the coast of the Yarlung Zangbo River was chosen as main experimental material.Here,using natural stress treatment to investigate the response mechanism of drought stress.In addition,using ISSR technology to exhibit the genetic diversity of germplasm resources.The investigated to elucidate a theoretical basis for the scientifie protection and utilization of resources.The main conclusions were as follows:1.With the declined of the SRWC of pot culture,the leaves gradually yellow and injuris from top to bottom,the branches gradually curled,and the plants water loss and withered.SRWC and LRWC were gradually declined.The SRWC and LRWC content declined to 15.95%and 44.7%at the later stage of drought,and had significant difference compare with the control group,respectively.After rewatering,the withered leaves and curled branches was significantly recovered.2.With the declined of the SRWC of pot culture,the contents of Pn,GS and Tr were declined,while Ci gradually increased.The total and alternative respiration rapidly increased,and reached the peak at the later stage of drought,and had significant difference compare with the control group,and gradually recovered to the control level after rewatering.This indicated that the cypress had the stronger drought resistance and can be recovered from rehydration quickly.3.With the declined of the SRWC of pot culture,the function of cell membrane was impaired,and the relative conductivity was gradually increased.The content increased to 1.26 ?S·cm-1,which was 1.73 times higher than the control.At the same time,the accumulated the content of osmotic adjustment substances,the contents of soluble sugar and proline were rapidly increased at the later stage of drought,while the content of H2O2 and O2-gradually increased and the DAB and NBT staining gradually deepened,and gradually recovered to the control level after rewatering.This indicated that the metabolism of reactive oxygen species was disordered,resulting in the degree of membrane lipi peroxidation was enhanced,with the cell membrane was impaired.The cypress had stronger resistance to drought,and can be recovered from rehydration.4.With the declined of the SRWC of pot culture,the enzymatic antioxidant activities of SOD,POD and CAT increased first and then decreased.The non-enzymatic antioxidant ASA/GSH cycle and the antioxidant enzyme that maintained the circulating steady-state gradually increased,and reached the peak at the later stage of drought,and had significant difference compare with the control group,and gradually recovered to the control level after rewatering.This indicated that the enzyme activity system could be used to resist drought5.A total of 78 fragments were scored using 10 ISSR primer combinations,and from these,67 fragments(85.9%)were polymorphic and could differentiate the populations analzsed.The genetic diversity of eight populations was 11>13>12>8>14>4>10>15.The AMOVA analysis indicated that the genetic variation of population was mainly occurred intergroup variation.Dendrogram was constructed by the UPGMA method,all the individuals were separated into three categories.In the analysis of genetic structure,when K(best group number)=3,the individuals were separated into three groups.Thus,this indicated that the genetic characteristics of cypress population were accorded with geographical distribution. |
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