Study On The Mechanism Of Exogenous ALA Alleviating Pepper Seedling Growth Under Low Temperature And Weak Light

At present,Capsicum annuum L.has become an important vegetable and condiment in China,and has played an important role in ensuring the annual balanced supply of Chinese vegetables and enriching people’s lives.In order to ensure the annual balanced supply of fresh pepper,pepper cultivation techniques such as early spring and late autumn have been vigorously developed.However,in the process of early spring cultivation of pepper in Hunan,there are phenomena of low temperature in winter and spring,insufficient light time and light intensity.Under this low temperature and weak light environment,pepper growth and development is slow,resulting in flower and fruit drop,reduced fruit setting rate,reduced yield and poor quality,resulting in great losses to production.Studies have shown that 5-aminolevulinic acid（ALA）is a non protein amino acid widely existing in living cells such as plants,animals,fungi and bacteria.It is the key precursor of the biosynthesis of all porphyrin compounds（such as chlorophyll and heme）.It has an obvious effect on improving the photosynthetic efficiency,cold resistance and weak light resistance of plants.To explore the physiological and molecular response mechanism of ALA in alleviating low temperature and low light damage of pepper seedlings is of great significance to solve the practical production problems of pepper.In this paper,the best spraying concentration of ALA was selected under the condition of artificial low temperature and weak light,and the transcriptome sequencing of pepper seedlings was analyzed.The phenotypic changes,physiological,biochemical and metabolic pathway genes were studied in order to understand the mechanism of ALA regulating the growth of pepper seedlings.The research results are as follows:1.Pepper varieties"Bola Red Bull"and"xingvegetable 215"were used as test materials,which were cultivated in substrate,treated with low temperature and weak light stress,and set ala concentration gradients（0 mg/L,15 mg/L,30 mg/L,45 mg/L and 60 mg/L）.It was found that foliar spraying of exogenous ala could alleviate the inhibition of low temperature and weak light stress on the growth of pepper seedlings and improve the cold resistance of pepper seedlings.The best treatment was 30 mg/L ALA.2.The pepper variety"xingvegetable 215"was treated with low temperature and weak light stress.The effects of 5-aminolevulinic acid（30 mg/L ALA）treatment on osmotic regulation and antioxidant enzymes in pepper seedling leaves were studied.The results showed that spraying 30 mg/L ala under low temperature and weak light stress could significantly reduce O₂ production rate,MDA content and relative conductivity,reduce H₂O₂Content,significantly increase the activities of SOD,POD and CAT,APX and GR,and significantly increase the contents of proline,soluble sugar and soluble egg white.3.The effects of 5-aminolevulinic acid（30 mg/L ALA）treatment on chlorophyll content,gas exchange parameters and chlorophyll fluorescence of pepper seedlings were studied.It was found that spraying 30 mg/L ala could significantly increase F_v/F_m、q P、ETR、ABS/RC、TRo/RC、φRo andφEo,significantly reducing NPQ andφDo。4.The effects of 5-aminolevulinic acid（30 mg/L ALA）treatment on nitrogen metabolism of pepper seedlings were studied.After spraying 30 mg/L ala,the activities of NR,GOGAT,GDH and GS were higher than those of low temperature and low light treatment,which improved the antioxidant capacity of pepper seedlings.5.In this study,Xingshu 215 screened in the early stage was used as the material,and30 mg/L screened in the early stage was used as the spraying concentration of ALA.using high-throughput sequencing technology,transcriptome sequencing was carried out in 9samples of CK vs ALA0 and ALA30 vs ALA0 control groups.KEGG metabolic pathway analysis showed that the genes related to Ala alleviating the damage of pepper seedlings caused by low temperature and weak light were mainly enriched in photosynthesis,nitrogen metabolism,glutathione metabolism and plant hormone signal transduction metabolism.In this study,11 ala response genes such as photosynthesis（psb and psb27）,nitrogen metabolism（nii1 and GS2）,glutathione metabolism（APX and GPX）and plant hormone signal transduction（IAA32,SIGH3-2,PP2C,Sn RK2 and MYC2）were used as the key genes for ala to alleviate the damage of Pepper Seedlings under low temperature and weak light.