Drought Tolerance Evaluation And Mechanisms Involved In Drought Tolerance Of Cut Chrysanthemum

Chrysanthemum is one of ten traditional famous flowers in China and four cut flowers in the world, it plays important roles in gardens. With the chrysanthemum cultivation area has increased, the scarcity of water has become a major chrysanthemum annual supply constraints. To studying the mechanisms for drought tolerance and the adaptation and regulatory mechanisms to drought in chrysanthemum is crucial for selecting and breeding drought-tolerant cultivars, which could be an important stratety to allevate the water shortage and the deterioration of the ecological environment. Several cultivars bred by NanJingy Agricultural University and the foreign cultivars were used in this study. Drought tolerance of20cut chrysanthemum cultivars were evaluated in this study, and then two cultivars of cut chrysanthemum, differing in drought tolerance,’Nannong Xuefeng’(drought-tolerant) and ’Nannong Jingyan’(drought-sensitive) were used to investigate mechanisms to drought stress. We compared the leaf epidermal surface morphology of the two cultivars. We also compared different drought-tolerant cultivars of antioxidant enzyme activity, its relative gene expression and photosynthetic in response to drought and recovery. The main results are as follows:1. The potted dry method was used to evaluate the drought tolerance of20cut chrysanthemum varieties. Stem diameter, plant height, under/above biomass, relative water content, MDA and relative conductivity were measured as morphological and physiological indices for drought-tolerance evaluation and the drought tolerance capacity of20cut chrysanthemum varieties were evaluated by variance analysis, principal components analysis, subordinate function value analysis and cluster analysis. The results indicated that6drought-tolerance indexes could be classified into two component parts according to principal components analysis. The indexes including stress indexes of stem diameter, plant height, under/above biomass, relative water content and MDA content were tightly related to drought tolerance of20cut chrysanthemum varieties. Cluster analysis showed that20cut chrysanthemum varieties could be divided into highly tolerant, tolerant, lowly tolerant and non-tolerant groups, respectively.’Nannong Xuefeng’was of highest drought tolerance,12cultivars represented by’Nannong Mogui’,’Nannong Jinlian’,’Nannong Hongque’were drought tolerant,6cultivars represented by’Nannong Xiaoli’,’Jingxin Zhicheng’,’Han2’ were of low resistance to drought,’Nannong Jingyan’was not tolerant to drought. According to cluster analysis and the average of subordinate function, drought tolerant of cut chrysanthemum cultivars was divided into four classes. The average value of subordinate function above0.8was the highest drought tolerance, from0.5to0.8was drought tolerance, from0.3to0.5was the lower drought tolerance, below0.3was the drought sensitive.2. Using drought tolerance cultivar’Nannong Xuefeng’and drought sensitive cultivar ’Nannong Jingyan’ as material, a comparative analysis of structural characteristics of leaf surface (trichomes, wax) and antioxidant enzyme activity and relative gene expression in response to drought stress and recovery, we found that drought tolerance cultivar’Nannong Xuefeng’had denser trichomes and more waxiness on the leaf epidermis than susceptible cultivar’Nannong Jingyan’, was2.3-and3-fold of’Nannong Jingyan’, respectively. It inferred that drought tolerance in chrysanthemum had related to densier leaf trichomes and higher wax content. After drought stress, the antioxidant enzyme activities and relative gene expression were enhanced in the two cultivars; in the drought tolerance cultivar ’Nannong Xuefeng’, the antioxidant activity (SOD, POD, CAT) and relative gene expression rapidly increased by day5and day7, and their level remained higher after re-watering than’Nannong Jingyan’(drought sensitive), however, in ’Nannong Jingyan’, under short-term stress (day5) APX enzyme activity was higher, with the drought development, APX activity in’Nannong Jingyan’ was lower than’Nannong Xuefeng’, inferred that APX played an important role in antioxidative defense mechanism of ’Nannong Jingyan’at day5. Morever, the change of enzyme activity followed the related gene expression in the two cultivars.3. Using drought tolerance cultivar ’Nannong Xuefeng’and drought sensitive cultivar ’Nannong Jingyan’as material, a comparative analysis of photosynthetic parameters and chlorophyll fluorescence parameters in response to drought stress and recovery, to explore the effect of photosynthetic response to drought stress and recovery. There was no decline or some reduction in leaf Fv/Fm under short-term (day3) drought stress in cur chrysanthemum. Pn declined with the decreasing of Gs, chlorophyll content and ΦDPSII in two cur chrysanthemum cultivars, but to a great extent for ’Nannong Jingyan’. Significant decrease was observed in photosynthetic parameters (except Ci) and chlorophyll fluorescence parameters under5d and7d of drought stress, with more dramatic decline in ’Nannong Jingyan’ than ’Nannong Xuefeng’. After re-watering,’Nannong Xuefeng’had higher resilience, meanwhile, the chlorophyll content restored to the control level, while those parameters were significantly lower than the control levels in ’Nannong Jingyan’, These results suggested that the recovery of photosynthetic after re-hydration was affected by stomatal limitation in ’Nannong Xuefeng’, affecting by stomatal limitation and non-stomatal limitation in ’Nannong Jingyang’.