Effeets Of Short-term Low Nitrogen Supply On Growth, AsA Content And Activity Of AsA Related Enzymes In Pepper During Fruit Stage

Pepper as a daily seasoning vegetable,It has important theoretical and practical significance to study the relationship between nitrogen nutrition and plant growth,fruit quality and yield,ascorbic acid metabolism,and to provide a basis for nitrogen fertilizer management in nutrient liquid cultivation.A pot experiment was conducted with the pepper variety"Longjiao No.5"as the test material,and a short-term?9d?nitrogen treatment at different levels was carried out during the pepper growing period?a total of 3 treatments:T1,0.83mmol·L-1;T2 5.83 mmol·L-1;CK,9.83 mmol·L-1?After low-nitrogen treatment for9 days,it returned to normal nitrogen?CK?supply level.The changes and expressions of pepper plant growth,photosynthetic characteristics,fruit yield and quality,antioxidant enzyme activity,and ascorbic acid-related anabolic enzyme activity under the conditions of low nitrogen treatment and normal nitrogen supply were studied.The main experimental results are as follows:1.Short-term moderate low nitrogen(5.83mmol·L^-1,T2)in the fruiting period had no significant effect on photosynthetic characteristics of pepper.The height of each plant treatment group decreased after low nitrogen treatment compared with the control lower than control,respectively.Yet However,after returning to normal nitrogen supply(9.83 mmol·L^-1)for 9 days,the plant height of moderately low nitrogen treatment increased compared with the control,but there was no significant difference.The leaf area of the plants was not significantly different during the treatment period.After recovering to normal nitrogen supply for 9 days,the leaf area of the plants treated with moderately low nitrogen treatment significantly increased compared with the control,while the yield was not significantly different from the control.2.Low nitrogen treatment improved the fruit quality.Compared with the control,the level of Vc,soluble protein,soluble sugar,capsaicin and dihydrocapsaicin in the fruits of moderately low nitrogen treatment significantly increased,and the nitrate level decreased significantly.Low nitrogen treatment increased plant biomass,and the dry and fresh weight of plants leaves supplied with moderately low nitrogen treatment higher than the control,respectively.3.Short-term low-nitrogen treatment significantly increased the activities of POD,SOD,and CAT in leaves and fruits of pepper compared with CK,and increased the plant's antioxidant capacity.Among pepper fruits and leaves,the largest change in SOD enzyme activity followed by POD,while the smallest change in CAT enzyme activity.4.After low nitrogen treatment,the ratio of redox state?AsA/DHA?in leaves and fruits increased and the concentrations of AsA and DHA also increased to varying degrees compared to CK.The leaves and fruits of peppers were treated with moderate low nitrogen(5.83mmol·L^-1,T2)The AsA,DHA and AsA/DHA ratios were significantly higher than CK levels during the treatment and recovery periods.Low nitrogen treatment has a positive effect on the increase of AO,APX,MDHAR,DHAR,and GR enzyme activities in pepper leaves and fruits,and it can maintain a higher enzyme activity during the recovery period.5.Gene expression levels of ascorbate oxidase?AO,APX?,ascorbate reductase?MDHAR,DHAR,GR?and ascorbate synthesis-related enzymes?GME,GaILDH?in leaves and fruits of peppers treated with T1 and T2 within 36 hours of low nitrogen treatment in the result period Compared with CK,it increased significantly,and the change in fruit was higher than that in leaves.Within 36 h of normal nitrogen levels,the expression of each gene was reduced,but still higher than the CK level.