Response Of Melatonin At Different Concentrations To Loquat Seedlings Under Cold Stress

In recent years,with the influence of extreme climate,the growth environment of plants has faced great challenges.In particular,the frequent occurrence of frost damage in southern crops.Loquat is an evergreen fruit tree that grows in southern China and blooms and sits in winter.It occurs when freezing damage occurs during the overwintering period of loquat,resulting in the death of loquat seedlings,fruit drop,and poor fruit development.Studies have found that melatonin can alleviate the damage of plants in stress to a certain extent,improve the cold resistance of plants,and make plants better respond to extreme low temperature climate stress.Therefore,in this study,the mechanism of melatonin response to loquat seedlings in response to cold stress is to improve the theoretical guidance for improving the ability of loquat seedlings to withstand low temperature and thus the survival rate.In this experiment,two-year-old Huabai No.1 loquat seedlings were selected.After setting pretreatments of different concentration gradients of melatonin to irrigate loquat seedlings,the loquat seedlings were subjected to a low temperature treatment of-5°C in an incubator,at 0h,12 h,24h,72 h,120h Observe and record the morphological changes of the plant leaves,determine the basic physiological indicators such as photosynthesis parameters,fluorescence parameters,relative conductivity,pigment content and other indicators,while measuring the endogenous hormones,antioxidant enzymes,MDA Content,clarify the physiological characteristics of melatonin treatment to improve the freezing resistance of loquat seedlings,on the basis of this,transcriptome sequencing screening was used to analyze the differential gene expression characteristics related to melatonin improving the freezing resistance of loquat seedlings;further cloning and plant cold resistance Related genes EjCBF1 and EjCBF2,and real-time fluorescence quantitative analysis of the expression differences of EjCBF1 and EjCBF2 at different time points in the samples.1.After two-year-old Huabai No.1 loquat seedlings were treated with melatonin at different concentration gradients,morphological observations revealed that 150 μM melatonin-treated loquat seedlings can effectively alleviate the damage caused by freezing damage and can effectively avoid plants caused by prolonged low temperature.The phenomenon of death.Observation by paraffin section revealed that the sponge tissue of loquat seedling leaves was severely damaged and degraded under low temperature stress,while the palisade tissue and sponge tissue of the leaves of loquat seedlings treated with 150μM melatonin remained basically normal.2.After treatment of two-year loquat seedlings with different concentration gradients of melatonin,the photosynthetic parameters were determined by measuring the photosynthetic parameters of 150 μM melatonin treated loquat seedlings.Rate,thereby reducing the concentration of intercellular carbon dioxide;after measuring the fluorescence parameters,it was found that with the prolongation of low temperature stress,Fv: Fm,Y(NPQ),ΦPSⅡ,ETR in the leaves of loquat seedlings treated with 150μM melatonin gradually increased,while Y(NO)decreased,Therefore 150μM melatonin treatment can effectively improve the photosynthetic capacity of loquat seedlings under low temperature stress.3.After treatment of two-year-old Huabai No.1 loquat seedlings with different concentration gradients of melatonin,phytohormones were determined by high-performance liquid chromatography(HPLC)using gradient elution.After analysis,it was found that 150μM melatonin treatment can significantly increase the content of Melatonin,SA,IAA,while the content of ABA,KT,GA did not change significantly.Determination of 150 μM melatonin-treated loquat seedlings by a microplate reader can effectively increase the content of SOD,POD,CAT,and APX in leaves,while the content of MDA decreases significantly.Therefore,150μM melatonin can increase the activity of plant antioxidant enzymes and reduce the content of MDA through hormone coordination,thereby reducing the damage caused by low temperature to loquat seedlings.4.Based on the above morphological observations and the determination of physiological indexes,transcriptome sequencing was performed on the leaves of loquat seedlings treated with 0μM and 150μM melatonin at 0h and the leaves of loquat seedlings treated with 0μM and 150μM melatonin at 120 h.Melatonin can regulate genes related to sugar metabolism pathways,photosynthetic pathways,and plant hormone signal transduction pathways in loquat seedlings under cold stress.5.Based on the analysis of transcriptome sequencing results,primers were designed for CDS sequence cloning,and the similarity between EjCBF1 and Apple Md CBF1 reached 92.38%.The similarity between EjCBF2 and Apple Md CBF2 reached96.19%.The sequence characteristics were as expected.