Effects Of Ⅲ Simulated Drought Stress On Physiological And GlAT Gene Expression Of Cultivated And Wild Glehnia Littoralis

Drought is one of the most important abiotic stresses affecting plant growth and development.Drought usually causes a series of changes in plant growth and development,morphological structure,physiology and biochemistry,gene expression and so on.Its effects on plant growth are much higher than those of other abiotic stresses such as salt and high temperature.The Glehnia littoralis Fr.Schmidt ex Miq.is a perennial herbaceous plants of the Glehnia in Apiaceae.Its dry root is a traditional Chinese medicinal material called Beisha ginseng.In China,G.littoralis is mainly distributed in Shandong,Inner Mongolia,Hebei and other places.Although it has high medicinal value,its wild resources are depleted.It has been listed as a national second-class protected plant.At present,the studies on the stress tolerance of G.littoralis are mainly focused on the mechanism of salt tolerance,but the mechanism of drought resistance is still lacking.It is of great significance to explore the regulation mechanism of drought resistance at physiological and molecular level for accelerating the molecular breeding process of drought resistance germplasm of G.littoralis.Therefore,cultivated species from Laiyang and wild species from Rizhao have been used as experimental materials.Under simulated drought stress with different concentrations of PEG（Polyethylene glycol）,the anatomical structure,physiological indexes and gene expression were determined.By comparing the difference of indexes between the drought treatment group and the normal control group,the drought resistance of G.littoralis was analyzed and the possible mechanism of drought resistance was discussed.The main research contents are as follows:（1）Different concentrations of PEG stress（20%、25%、30%）were applied to cultivated species and wild species,respectively,and the changes of phenotype and anatomical structure were observed.The results showed that:with the increase of the degree of drought,the leaves of the two species became soft,bent and even withered under high PEG concentration.Wild species were wilter than cultivated species.The thickness of leaf,upper and lower epidermis,palisade tissue and spongy tissue decreased,and 30%PEG stress had the most obvious effect on the two species.（2）Physiological and biochemical indexes were determined,including soluble protein content,SOD activity,POD activity,CAT activity,MDA content,chlorophyll content and chlorophyll fluorescence parameters.According to the physiological indexes,the drought resistance ability of the two kinds of G.littoralis was comprehensively analyzed.It showed that:the responses of cultivated and wild species to the increase of PEG concentration were different.On the one hand,the chlorophyll content of cultivated species changed less than that of wild species;on the other hand,the content of soluble protein was higher in cultivated species than that in wild species,and it increased significantly compared with the control group.The SOD activity of cultivated species increased significantly under stress,while the wild species showed a fluctuating change.The POD activity decreased in general,but increased in wild species under high PEG stress.The CAT activity of cultivated species increased and reached the highest under30%PEG stress.However,there was no significant difference in CAT activity of wild species between the treatment groups and the control.The accumulation of MDA in cultivated species was the highest under 25%PEG stress,and that in wild species was the highest under 30%PEG stress.The blades F_v/F_m,the photochemical fluorescence quenching coefficient（q_p）,and the actual photochemical efficiency of PSII（Y（II））in the two G.littoralis species decrease compared with the control,and the decrease of cultivated species was less than that of wild species.Based on the analysis of the above physiological indexes,the cultivated species of G.littoralis suffer less damage to PSII under drought stress,and the efficiency of protecting enzyme system is higher.Compared with the wild species,the stress response of cultivated species is more significant,while the wild species suffer more serious damage under drought stress,and the drought resistance ability is lower than the cultivated species.（3）The AT protein encoded by GlAT gene forms a series of secondary metabolites catalyzed by coenzyme A thioester and plays a key role in the resistance of G.littoralis.The expression of GlAT gene was analyzed by real-time fluorescence quantitative PCR under severe drought stress of 30%PEG to cultivated and wild species.It suggested that:the GlAT genes of the two species were up-regulated and then down-regulated to normal,and the cultivated species were up-regulated more rapidly and expressed more stably than the wild species.