Effects Of Abiotic Stress On Functional Components Of Barley Such As Melatonin And Metabonomics Analysis

Barley is an ancient cereal crop with higher nutritional value than most other grains,but there has been relatively little research on it.Abiotic stress refers to the adverse effects of abiotic factors in the environment on plant growth and development,which can lead to reduced seed germination rates and slowed seedling growth.Melatonin,an important plant hormone,also plays a crucial role in the growth and development of barley.Research has shown that melatonin can promote seed growth and development,and alleviate the adverse effects of non-biological stress on plant growth.However,there has been little research on the effects of abiotic stress on the germination of barley and other functional components,including melatonin.Therefore,this experiment focuses on barley as the raw material,and specifically studies the effects of different abiotic stress methods on the functional components of germinated barley,including melatonin,and analyzes the metabolomics of germinated barley under salt stress.The main research results are as follows:(1)Salt stress,low temperature stress,and low oxygen stress all affect the growth status of germinated barley,inhibit the growth of roots and the upper part of crops,and cause slow growth and development of plants.Different stress treatments induced the accumulation of melatonin content in germinated barley to varying degrees.Among them,0.8mmol/L zinc sulfate stress induced the maximum melatonin content on the 6th day of germination,which was(13.227 ± 0.119)ng/g,2.50 times that of the seed.(2)Three types of abiotic stress have different degrees of impact on the content of β-glucan,GABA,reducing sugar,and soluble sugar during barley germination.Among them,1.0 mmol/L zinc sulfate stress,low oxygen stress after vacuuming before germination,and low temperature stress at 10 and 15℃ all effectively inhibited the degradation of β-glucan.0.8 mmol/L zinc sulfate stress,low oxygen stress after germination and vacuuming,and low temperature stress at 15℃ all increased the content of GABA during barley germination.Salt stress and low temperature stress are not conducive to the accumulation of reducing sugars but increase the content of soluble sugars during barley germination,while vacuuming after germination has a positive effect on both the content of reducing sugar and soluble sugar.Salt stress,low temperature stress,and hypoxia stress have different effects on the total flavonoid and total phenolic contents of sprouted barley.Selecting appropriate stress conditions can increase their total flavonoid and total phenolic contents.Stress treatments such as 0.6-0.8 mmol/L zinc sulfate,short and moderate low-temperature stress,and hypoxia stress after sprouting have a promoting effect on the antioxidant capacity of sprouted barley.Correlation analysis shows that under different non-biological stress conditions,melatonin in sprouted barley can contribute to its antioxidant capacity.(3)The exposure to zinc sulfate with a concentration of 0.6～0.8mmol/L and low oxygen stress through post-germination vacuum have both been found to improve the total flavonoid and phenol contents,as well as the antioxidant capacity of germinated barley.Correlation analysis indicates that melatonin in germinated barley can contribute to the antioxidant capacity under various abiotic stress conditions.(4)This experiment utilized UPLC-Q-TOF MS untargeted metabolomics technology to identify 730 metabolites in both the barley seed sample and the barley seedling sample under 0,0.2,and 0.8 mmol/L zinc sulfate stress for 5 days,with a total of 380 differential metabolites,including carboxylic acids and their derivatives,organic oxidants,and flavonoids.Multivariate statistical analysis results showed that the differences in intragroup metabolites were smaller than those between groups,which could well explain whether barley was subjected to germination treatment and zinc sulfate stress.Combined with KEGG pathway analysis,metabolites were broadly divided into five categories.Further analysis revealed that the expression of precursors of melatonin synthesis increased in barley seedlings germinated under 0.8 mmol/L zinc sulfate stress,which may be the reason for the increase in melatonin content in plants caused by zinc sulfate stress.