The Evaluation And Analysis Of Resistance To Water Stress In Six Cultivars Of Small Ornamental Chrysanthemum

Water stress is a common abiotic stress in plant growth and development,which has a serious impact on the production of ornamental chrysanthemum.The adaptability of ornamental chrysanthemum to water stress can provide theoretical guidance for its later application.In this study,six ornamental chrysanthemum varieties were used as materials to conduct waterlogging and drought stress experiments respectively.By analyzing the differences of morphological characteristics,physiological and biochemical characteristics,photosynthetic characteristics and other changes of ornamental chrysanthemum varieties after water stress,the six small ornamental chrysanthemum varieties were evaluated for waterlogging tolerance and drought tolerance,and the varieties with strong tolerance were screened out.Chrysanthemum cultivars with obvious differences in waterlogging tolerance and drought tolerance were selected to study the variation of photosystem performance of different tolerance cultivars after water stress.Transcriptome analysis of different drought tolerance ornamental chrysanthemum was conducted to explore the metabolic regulation pathways in response to drought stress.It provides theoretical basis for further study on molecular response mechanism of drought stress.The main results are as follows:1.After waterlogging stress,the PSI end electron acceptor reduction efficiency(φ_Ro),the performance index(PI_abs,PI_total),the P_n and RWC of the 6 species of small ornamental chrysanthemum decreased significantly,especially the decrease of PI_total,and there was a great difference among the varieties.The PI_total of‘BJQDH’and‘BJZJL’decreased by 75.77% and 80.95%,respectively.The decrease of ‘BJFY’and ‘BJYZF’ was smaller,only decreasing by 35.87% and 25.33%.The REC,MDA content,the Pro content,the soluble sugar content,the soluble protein content,the POD activity increased in different degrees,while the SOD activity decreased only in ‘ BJQDH ’ and ‘ BJZJL ’,which decreased by 5.56% and 6.21%,respectively.2.After drought stress,the maximum photochemical efficiency of PSII（F_v/F_m）,φ_Ro,PI_abs,PI_total,P_n and RWC of 6 species of ornamental Daisy significantly decreased.Among them,PI_abs,PI_tota and P_n of ‘BJQDH’decreased the most obviously and the most,which decreased 89.97%,90.61% and 114.23%,respectively.The REC,the MDA content,the Pro content,the soluble sugar content,the soluble protein content,the SOD activity and the POD activity were increased in different degrees.Among them,the increase of the Pro content was the most significant,and the increase of Pro content in‘BJQDZ’was the largest,which increased by 2173.55% compared with the control.3.Through comprehensive evaluation and analysis,it can be seen that the tolerance of six ornamental chrysanthemums to water stress :‘BJYZF’and ‘BJFY’have strong waterlogging tolerance,but poor drought tolerance;‘ BJQDZ’ has strong drought tolerance,but its waterlogging tolerance is general.The tolerance of ’‘BJZM’and‘BJZJL’to water stress was at a medium level;‘BJQDH’had the worst tolerance to water stress,and its waterlogging tolerance and drought tolerance were the weakest.4.After waterlogging stress,the structure and function of PSII were damaged,the activity of PSI was decreased,the OEC damaged,the PSI and PSII are inhibited in electron transport,resulting in decreased photochemical activity and overall photosynthetic performance,and reduced photosynthetic capacity.The variety‘BJQDH’with weak waterlogging tolerance was severely hindered in PSⅡ electron transfer,and a large amount of QA-was accumulated.The electron transfer efficiency of PSI decreased significantly,and the degree of photoinhibition increased.By maintaining the activity of PSII reaction center and electron transfer,‘ BJYZF ’maintained high photosynthetic performance and reduced the degree of photoinhibition,thus showing high waterlogging resistance.5.Drought stress damaged the reaction center of PSII,the antenna structure was destroyed,the oxygen releasing complex was inhibited,the electron transfer between the optical systems was limited,and the activity of the optical system was decreased.The reversible inactivation of PSII in ‘ BJQDH ’ variety with weak drought tolerance led to the formation of energy trap,imbalance of energy distribution in the reaction center,limited electron transfer at the end of PSI,and significantly decreased the performance index of the optical system.By maintaining normal PSII energy generation and PSI energy utilization,‘ BJQDZ ’ maintains high photosystem activity,thus maintaining photosynthesis ability and enhancing tolerance to drought stress.6.Through transcriptional data analysis,1591 and 1204 differentially expressed genes（DEGs）were identified in ‘ BJQDZ ’ and ‘ BJQDH ’,and the downregulated genes were significantly more than up-regulated genes.KEGG analysis showed that metabolic process was the main pathway in response to drought stress,and differentially expressed genes were mainly involved in carbohydrate metabolism,lipid metabolism,amino acid metabolism and secondary metabolism.Compared with‘BJQDH’,drought stress promoted the expression of genes related to carbohydrate metabolism（amino sugar and nucleotide sugar metabolism）,lipid metabolism（berberine and wax biosynthesis and lipid synthesis pathway）,amino acid metabolism（amino acid biosynthesis）and secondary metabolism（phenylpropane biosynthesis）,thus enhancing the drought tolerance ability of ‘BJQDZ’.This study explored the physiological response mechanism of ornamental chrysanthemum after water stress through the analysis of photosynthetic characteristics,physiological and biochemical characteristics.The evaluation system of tolerance to water stress was established,and it was found that‘BJQDH’had the worst tolerance to water stress,‘BJYZF’ and ‘BJQDZ’ showed the strongest tolerance to flood and drought,respectively.After waterlogging stress,the structure and function of the photosynthetic system of ornamental chrysanthemum were damaged,leading to the decline of photosynthetic capacity.Drought-tolerant varieties improve their drought tolerance by promoting the expression of genes in related metabolic pathways.The research results have certain guiding significance for the production and application of ornamental chrysanthemum.