| Maize is the main food crop in Heilongjiang Province,and its planting area has accounted for more than 50% of the total planted area.Low temperature is a type of disaster that is common in Heilongjiang Province,and it occurs mostly in the early spring.Low temperature stress can affect the growth and physiological balance of crops,which in turn affects the yield and quality of crops.5-Aminolevulinic acid is a novel growth regulator and is widely used in horticultural crops,but research on field crops has rarely been reported.Therefore,in order to explore the mitigating effect and physiological mechanism of 5-aminolevulinic acid(ALA)to improve the cold resistance of maize seedlings,the experiment was conducted in 2016-2017 at the maize cultivation physiology laboratory and potting test site of the agricultural college of northeast agricultural university.Maize variety Zhengdan 958 was used as experimental material,low temperature stress was applied at seed germination and seedling stage,and different concentrations of ALA(0,10,15,20 and 25 mg/L)were applied toinvestigate the optimal concentration.The effects of 15 mg/L ALA(optimal concentration)on the growth and physiological characteristics of maize seedlings under low temperature stress for 2,4,6 and 8 days were investigated.In this study,seed germination,seedling growth,antioxidant enzyme activity,osmotic adjustment substance content,photosynthetic system,key enzymes of nitrogen metabolism and endogenous hormones were measured.The aim of this study was to explore the physiological mechanism of ALA improving cold tolerance of maize seedlings and to prov ide a theoretical basis for the wide application of such exogenous substances.The main findings are as follows:(1)Applying a certain concentration of 5-aminolevulinic acid(ALA)can effectively alleviate the inhibition of maize seed germination under lo w temperature stress.Under low temperature stress,the germination potential,germination rate,germination index,vigor index and storage material transport rate of maize seeds treated with exogenous 15 mg/L ALA were significantly higher than those of maize seeds treated with low temperature.At the same time,exogenous 15 mg/L ALA treatment could effectively alleviate the inhibition of bud and root biomass under low temperature stress;compared with low temperature stress,the root length,bud length and root number of seedlings treated with ALA increased by 48.33%,19.21% and 35.71%,respectively.Low temperature stress significantly inhibited the bud promotion rate and root promotion rate of seedlings.The application of ALA treatment increased the bud promotion rate and root promotion rate of seedlings,and the treatment effect of 15 mg/L ALA was the best.(2)Applying a certain concentration of 5-aminolevulinic acid(ALA)could promote biomass accumulation and morphogenesis of maize seedlings under low temperature stress,and alleviate the inhibition of low temperature stress on maize seedlings.Compared with the low temperature treatment,the seedling height,biomass and leaf area of different concentrations of ALA treatment were higher than the low temperature treatment in different degrees,and the treatment of ALA concentration of 15 mg/L was the best.At the same time,15 mg/L ALA treatment could significantly promote the growth of root length,root surface area and root volume of maize seedlings,and ultimately alleviate the adverse effects of low temperature stress on seedlings.(3)Applying a certain concentration of 5-aminolevulinic acid(ALA)could improve the activity of antioxidant enzymes and scavenge the accumulation of reactive oxygen speci es in seedlings under low temperature stress.ALA treatment significantly inhibited the increase of O2-production rate,H2O2 content and malondialdehyde(MDA)content in leaves and roots of seedlings,and maintained the stability of cell membrane system.Application of 15 mg/L ALA also significantly increased the activity of SOD,CAT,POD and APX in leaves and roots of seedlings.The toxic substances such as MDA,H2O2 and O2-in the seedlings were completely removed,the ROS metabolic balance was maintained,and the membrane lipid peroxidation was alleviated,thereby enhancing the cold resistance of the seedlings.(4)Applying a certain concentration of 5-aminolevulinic acid(ALA)can promote the synthesis of osmotic regulators,increase the cell water pote ntial and improve the cold resistance of seedlings under low temperature stress.The contents of proline,soluble protein and soluble sugar in leaves and roots of seedlings increased significantly under low temperature stress.The content of proline,soluble protein and soluble sugar in leaves and roots of seedlings was further increased by applying 15 mg/L ALA,and the content of three osmotic adjustment substances increased gradually with the application of low temperature stress.It can effectively regul ate intracellular osmotic regulators,reduce cell water potential,maintain functional protein structure and functional integrity,and then alleviate seedling osmotic damage caused by low temperature stress.(5)Applying a certain concentration of 5-aminolevulinic acid(ALA)can alleviate the damage of low temperature stress on photosynthetic system of seedlings and improve the photosynthetic capacity of seedling leaves.The photosynthetic system of seedling leaves was damaged by low temperature stress,which showed that the value of SPAD decreased.The activities of Pn,Tr,Gs,Ru BP carboxylase and PEPc carboxylase were also decreased,and the intercellular CO2 concentration(Ci)was decreased first and then increased by applying 15 mg/L ALA to the leaves of seedlings.The gas exchange parameters,Ru BP and PEPC carboxylase activities of seedling leaves were significantly increased by applying 15 mg/L ALA.The photosynthetic capacity and CO2 utilization efficiency of seedling leaves were improved.(6)Applying a certain concentration of 5-aminolevulinic acid(ALA)could regulate the activities of nitrogen metabolism-related enzymes in seedlings under low temperature stress.Under low temperature stress,the activity of nitrate reductase(NR)in leaves and root s of maize seedlings was significantly decreased,and the activity of glutamine synthetase(GS)was significantly increased.Application of 15 mg/L ALA can reduce the water dissipation and promote the synthesis of penetrating substances in seedlings under low temperature stress,thereby increasing the NR and GS activities in leaves and roots of seedlings.(7)Applying a certain concentration of 5-aminolevulinic acid(ALA)can regulate the content of endogenous hormones in seedlings and alleviate the effect of low temperature stress on endogenous hormone metabolism in seedlings.Low temperature stress resulted in a significant increase in ABA content in leaves and roots of seedlings,and a significant decrease in ZR and GA content,after exogenous application of 15 mg/L ALA,the ABA content in leaves and roots of seedlings was decreased,ZR and GA contents were increased,and various metabolic regulation in seedlings was improved,and the adverse effects of low temperature stress on seedlings were alleviated. |
PDF Full Text Request