Effects Of Simulated Acid Rain On Physiological Characteristics And Related Gene Expression Of Tea Plants

Acid rain is one of the most serious environmental problems in the last century.Since the 21 st century,with the improvement of the environment,the problem of acid rain has been alleviated,but it cannot be ignored.Acid rain can cause normal growth and development of plants to be affected,and tea plant is a cash crop widely cultivated on a global scale.Therefore,it is of practical significance to study the impact of simulated acid rain on tea.In order to explore the effects of simulated acid rain on physiological characteristics and related gene expression of tea plants,potted tea plants cultured in greenhouse after simulated acid rain treatment were used as research materials.Three simulated acid rain gradients were set in this experiment: pH 2.5,pH 3.5 and pH 4.5,and CK(pH 7.0)in a control group.The effects of simulated acid rain with different concentration gradients on the morphological,physiological and biochemical characteristics and gene expression of tea plants were studied.Key findings are reported below:(1)In order to explore the effects of simulated acid rain on the morphological structure of tea plants,the changes of the whole plant and leaves after simulated acid rain treatment were observed,the changes of plant height and root length were measured,and the changes of leaf epidermis and ultrastructure were observed by scanning electron microscopy and transmission electron microscopy.The results showed that the simulated acid rain treatment at pH4.5 had no obvious damage to the phenotype of tea plants and promoted the growth of tea plants.At pH 3.5 simulated acid rain treatment,some tea leaves showed visible lesions,growth was inhibited,stomatal density of epidermis waxy layer was damaged and osmiophilic granules increased in chloroplasts.PH 2.5 simulated acid rain treatment had the most serious effect on the phenotype of tea plant,the growth was severely inhibited,and the structure of chloroplast and mitochondria was severely damaged.(2)The effects of simulated acid rain on Photosynthetic Physiology of tea leaves were studied by measuring the content of photosynthetic pigments,photosynthetic parameters and chlorophyll fluorescence parameters.The results showed that pH 4.5 simulated acid rain treatment had no significant effect on the photosynthetic physiology of tea plants.However,the simulated acid rain at pH 3.5 and pH 2.5 had some effects on the photosynthetic physiology of tea plants.Compared with the control group,the content of photosynthetic pigments decreased significantly,the light compensation point increased significantly,the light saturation point decreased significantly,and the dark respiration rate increased significantly.The chlorophyll fluorescence parameters showed that the simulated acid rain treatment at pH 3.5 and pH 2.5 had harmful effects on PS II,which resulted in obvious stress effects on tea plants.However,the effect of simulated acid rain at p H 2.5 on the photosynthetic physiology of tea plants is more significant.It can be concluded that light acid rain has no effect on the photosynthetic physiology of tea plants,but when the acidity of acid rain exceeds a certain threshold,the greater the intensity of acid rain,the greater the impact on the photosynthetic physiology of tea plants.(3)In order to further study the effects of simulated acid rain on stress physiology of tea plants,the antioxidant enzymes activities and the contents of PRO and MDA in different parts of tea plants after simulated acid rain treatment were measured.The activities of SOD,POD,CAT,APX and PRO increased with the increase of acid rain concentration,except that there was no significant change in SOD and CAT activities and POD activity showed a trend of “first rising and then decreasing” in the tender stems of tea plants.Although the activities of antioxidant enzymes and osmotic regulators in various organs of tea plant increased to alleviate the damage caused by reactive oxygen species(ROS),MDA,a membrane lipid peroxidation product,still accumulated in the cells of different parts of tea plant treated with simulated acid rain at pH 2.5 and pH 3.5.It can be concluded that the simulated acid rain of pH 2.5 and 3.5 still exerts strong stress on tea plants.(4)In addition,tea as a plant whose leaves are used by human beings,the effect of acid rain on the contents of tea leaves cannot be ignored.In order to explore the effect of simulated acid rain on the formation of tea quality,the main chemical components of tea tender leaves(one bud and two leaves)treated with simulated acid rain were determined.The results showed that simulated acid rain had no significant effect on the water extract of tea leaves.The content of tea polyphenols increased first and then decreased with the increase of simulated acid rain acidity,while the content of amino acid caffeine decreased first and then increased.(5)In order to further understand the molecular mechanism of the effects of simulated acid rain on tea plants,high-throughput sequencing technology was used to RNA-seq of mature leaves of control group and pH 2.5 simulated acid rain treatment group.A total of 363 differentially expressed genes were screened.By predicting the transcription factors of differentially expressed genes,29 differentially expressed transcription factors were screened out,belonging to 14 different transcription factor families.The functions of MYB,AP2-EREBP,NAC,bZIP,G2-like and other transcription factor families in their transcription factor families were all related to plant stress resistance.Carbon fixation in photosynthetic organisms,carbon metabolism,biosynthesis of amino acids,photosynthesis-antenna proteins,cysteine and methionine metabolism,glyoxylate and dicarboxylate metabolism were up-regulated(p<0.05).ABC transporter and lysine degradation were down-regulated(p<0.05)by KEGG enrichment analysis.In addition,HemE2 gene is up-regulated in porphyrin and chlorophyll synthesis pathway,presumably due to negative feedback regulation.PAL2 gene was significantly down-regulated in phenylpropane biosynthetic pathway,which was related to the synthesis of flavonoids in tea.PR-1 gene is up-regulated in plant signal transduction pathway,which is related to plant disease resistance.It is concluded that tea plants can resist acid rain stress through various metabolic pathways.