Basic Study On Mechanisms Of Thermotolerance And Chemical Regulation In Dahlia

Dahlia pinnata Cav. is a perennial bulbous flower in the genus Dahlia, family Composite, as one of the world’s famous flowers, widely cultivated in application. Dahlia pinnata Cav. is originated in Mexican plateau area, and likes warm and cool weather. But due to the global warming, the high temperature especially in the southern provinces of China in summer seriously affects the growth and development of dahlia, and also affects its landscape application and ornamental value.Salicylic acid(SA) is an important plant growth regulator, which can increase the resistance of plants to biotic and abiotic stresses. But there is no reports of dahlia.Therefore, this study selection Dahlia pinnata Cav. ‘ Danbanhuang’, respectively taking tissue culture dahlia, growth and flowering potted dahlia as materials, investigated the growth and flowering characteristics of dahlia, and determined the physiological and biochemical indexes, photosynthetic characteristics and the expression of senescence associated gene XTH of dahlia in high temperature stress and exogenous SA treatment.Through the index analysis, the physiological mechanisms of the response to high temperature and the induced effects of SA in dahlia were obtained. The main experiment results are as follows:1. Taking tissue-cultured dahlia as test materials, investigated the physiological response of dahlia to high temperature and exogenous SA, and the results showed that there is significantly difference between effects of different concentration of SA on the growth and rooting of dahlia plantlets. 0.05 mmol·L-1 SA can promote the rooting of dahlia in vitro, whereas higher concentations of SA inhibits the growth and rooting of dahlia.Besides, under high temperature stress(35℃/30℃, day/night), the SOD activity was first increased and then decreased, and the POD activity did not change significantly in the early stress and increased in the late, meanwhile CAT activity decreased all the time. In contrast, SOD, POD and CAT activities of dahlia which of culture medium added 0.05mmol·L-1 SA were significantly increased. It shows that 0.05 mmol·L-1 SA can improve theheat resistance of Dahlia seedlings in vitro.2. Taking potted dahlia seedlings as test materials, explored the effects of high temperature stress and exogenous SA on the physiological and biochemical indexes of growth period of dahlia leaves. The experiment of concentration of SA showed that 0.5mmol·L-1 SA is best to induce the thermotolerance of potted dahlias in growth period.Besides, under the stress of high temperature(35 ℃ /30 ℃, day/night), MDA content increased all the time, soluble protein decreased, the contents of proline increased firstly and then decreased, the activity of SOD and CAT decreased, but the POD activity increased at first and then decreased; after stress relieved, three kinds of protective enzymes activity were increased in different degrees and MDA content decreased; in contrast, all physiological characters of dahlia induced by spouted SA before heat stress were outstanding than high temperature stress group(HT group), showed a physiological response to alleviate the effects of high temperature stress.3. Taking potted dahlia seedlings as test materials, the effects of high temperature and exogenous SA on the photosynthetic characteristics were determined. The results showed that under heat stress, SPAD value decreased and rebounded in some degree after relieving stress; Pn and Gs decreased, Ci increased all the time and Tr showed a down-up-down variation trend; in contrast, the SPAD value, Pn, Tr and Gs of dahlia in group with SA treatment maintained higher level than HT group, and Ci showed increased firstly and then decreased. It shows that SA could alleviate the inhibition of heat stress on the photosynthesis of dahlia.4. The effects of exogenous SA to the flower morphological characteristics, flowering habits and physiological characteristics of florescence dahlia under the high temperature in summer were studied. The results showed that different concentrations of SA have improvement on the leaf color, growth, flower amount, flower diameter and single flower florescence of dahlia in varying degree. And as the extension of stress time, MDA content increased, soluble protein content increased firstly and then decreased, the activity of SOD decreased, and the POD activity increased. Exogenous SA treatment reduced the content of MDA, and no significant difference among the different concentrations, besides different concentration of SA increased the activity of SOD and POD of florescence dahlia, and the effect of 0.5-1.0 mmol·L-1 SA is more significant. It shows that suitable concentration of SA can promote the flowering of dahlia under high temperature in summer.5. The expression changes of petals senescence related genes DpXTH1 and DpXTH2 of dahlia with heat stress and exogenous SA treatment were analyzed by real-time fluorescent quantitative PCR technology. The results showed the expression levels of DpXTH1 and DpXTH2 of dahlia petals declined significantly under heat stress during bloom stage. And the two genes expression levels of dahlia treated by SA before heat stress decreased less. This indicated that SA could alleviate the inhibition of high temperature on XTHs expression, thereby delaying the accelerated senescence of dahlia petals under high temperature stress.