| Chrysanthemum morifolium, a traditional famous flower in China, is a main floriculture crop with high ornamental value, and took over a vital position in production of cut flowers. From the perspective of ecological habits, a cold climate is suitable for its growing development, and the temperature of 15-25℃ is the best. Generally, when temperature exceeds 32℃, it will be subjected to inhibition on some level,i.e. lower rate of inflorescence growth and later flowering, moreover, higher temperature (>40℃) will cause deformity and blind flowers obviously. Therefore, high temperature in summer has been an fatal factor during the normal growth and development of chrysanthemum. Cut-flower is one of the most important types in chrysanthemum cultivation, including big and small inflorescence size, and ’Youxiang’ belongs to the former which is one of the main varietiesof summer cultivation. However, summer high temperature often created some negative impacts on flowering buds and its growth.In this study,’Youxiang’ seedlings were incubated with 45℃ high temperature for 2h, and then we discussed the heat resistance of adult plants from physiology, proteomics and epigenetics. As a result, we discovered that heat treatment in seedling stage can significantly improve the heat resistance of adult plants. The main results are as follows:1.Physiological mechanism associated with heat treatment inseedling to improve heat resistance of chrysanthemumIn the experiment, cut chrysanthemum cultivars ’Youxiang’ seedlings were incubated with 45℃ for 2h, and then recovered at room temperature for 24h, were selected to analysethe physiological indicators, respectively. The results indicated that there were higher SOD activity, more malondialdehyde and proline in the seedlings under high temperature stresses, while the content of soluble protein and water, maximal photochemical efficiency of PS Ⅱ (Fv/Fm) and net photosynthesis rate (Pn) were decreased significantly. After recovery for 24h, we measured all physiological indicators using leaves from two groups (treatment and control) again and significant difference only existed in the content of soluble protein. The results illustrated that heat shock treatment achieved the effect of thermal exercise,meanwhile, after recovery for 24h, we excluded the damage of seedlings by heat shock.Next, we field seedling of two groups to routine management.By measuring budding time, the vase life of cut flowers, flowering morphological, physiological and biochemicalof the leaves, we further explored the effects of chrysanthemum flowering after heat acclimation on seedling stage.The results showed that treatment group delayed budding time and had preferable effect of vase. In leaves, there were higher soluble sugar content, water content and SOD activitythan the control group. In petals, soluble sugar content, proline content was significantly higher while MDA was lower. Moreover, we observed that the degradation rate was lower than the control group by transmission electron microscopy. Next, we conducted 50℃ high temperature stress during flowering processing. It was obvious that Pn, PS Ⅱ, the content of chlorophyll, soluble sugar, SOD and proline was significantly higher while the opposite is MDA compared with control group.After recovery for 24h at room temperature, the content of soluble protein and proline in treated group was significantly greater.In conclusion, the treatment of heat shock during seedling stage can significantly improve the heat resistance in the flowering when was suffered high temperature stress.2.Proteomics research concerning heattreatment inseedling to improve chrysanthemum heat resistanceWe appliedisobaric tags for relative and absolute quantitation (iTRAQ),chose leaves as materials, which were control and treated by heat shock in seedlings stage, control and treated by high temperature stress in flowering, in order to identify some key proteins related with heat resistance.Based on iTRAQ proteomic investigation, in seedlings stage, we obtained 21 proteins with significant changes in abundance in treated group relative to control,15 of which were up-regulated and 6 of which were down-regulated. Parts of these were stress-related proteins, such as ubiquitin, Rubisco activating enzyme and S-adenosylmethioninesynthetase were up-regulated, and the ATP synthase was down-regulated.During flowering,we found that the expression of 14 proteins was significantly different, and all of them are upregulated, some of them are also associated with resistance, i.e. glutamine synthetase, ribulosecarboxylase and catalase. These results showed that the heat treatment in seedling evidently improved the expression level of some heat-related protein when suffered high temperature stress, which may related to the improvement of heat resistance after seedling pretreatment of chrysanthemum.3.Research between seedling heat shock treatment and epigeneticDNA methylation patterns were used by methylationsensitive amplified polymorphism (MSAP) technology to analyse the different samples from group of control and treatment.The results showed that seedling heat shock treatment led to increasing level of genomic DNA cytosine methylation and the rate of full methylation is higher than the half, moreover, this phenomenonstatealso was detected in flowering stage after heat stress. In conclusion, we speculated that the reason of changes in genomiic DNA methylation was a kind of molecular mechanisms that heat shock treatment could improve the heat resistance in chrysanthemum ’Youxiang’ and also related to delayflowering. |
