Effects Of Short-Term Low Nitrogen Supply On Growth, AsA Content And Activity Of AsA Related Enzymes In Cucumber During Fruit Stage

Cucumber is the most widely cultivated vegetable following after tomato, cabbage and onions.Studying the relation aomong nitrogen fertilizer, plant growth, fruit qualtiy and yield, AsA metabolismallow us to provide the basis for nitrogen management research, with an important theory and practicalsignificance. This experiment was carried out with greenhouse cucumber (Cucumis sativus L.9930) innutrient solution. The plants were treated with different levels of nitrogen supplies for7days on the2ndof flowering. The nitrogen concentration of the treatments was: T1,3mmol/L; T2,6mmol/L; CK,12mmol/L. Plants transferred to CK solution after the7-days-treatment for recovery. Photosynthesis andplant growth, fruit quality and yield, activities and expressions of enzymes related to AsA synthesis andmetabolism were investigated. The main results are as follows:1. Moderately low nitrogen supply (T2) had no obvious suppression on net photosythetic rate andplant growth. The net photosythetic rate of T2was only3.6%lower than CK on the6thday of treatment,and yet it rised back to the level of CK after10days recovery. On the7thday of recovery, plant height ofT2was1.49%higher than CK. And its leaf area was12.64%higher than CK because of the fast growthduring revoery.2. Fruit quality had improved after low nitrogen supply during fruit stage, and moderatly lownitrogen supply (T2) had no significant effect on yield. Fruit AsA content increased after treatment. AsAcontent in T2fruit increased by13.61%than control. Nitrate content of T1and T2fruit decreased by50.93%and21.89%, respectively. Yield of per plant in T2was only0.8%lower than CK.3. Antioxidant ability of plant improved after the short term low nitrogen treatment. AsAconcentration and redox state, enzymes activities (SOD, CAT, POD) increased during treatment andrecovery. Reduction AsA concentration in fruit of T1and T2were22.57%and31.19%higher than CKon the7thday of treatment.. And the ratio of AsA/DHAwere as1.28and1.47times as control. Activitesof SOD, CAT and POD in fruit of T1and T2also improved. SOD activities in the fruit of T1and T2were increased by51.26%and56.95%comparing with CK on the7thday of treatment. CAT reached thehighest on the3rdday of treatment, T1, T2were respectively as1.73and1.63times high as control.POD activities of T1and T2were highest on the5thday of treatment, and T1, T2were respectively as1.24and1.18times high as control.5. Short term low nitrogen accelerate the synthesis and metabolism of AsA. Enzyme activities(AO，APX，MDHAR，DHAR，GR) increased during treatment and recovery. AsAsynthetases (GLDH,GMP) and metabolic enzymes (AO，APX，MDHAR，DHAR，GR) expression were affected in thestarting48h of the treatment and recovery, in different degrees. AO and MDHAR activities in fruitreached the highest on the5thday of treatment, when AO in T1and T2were68.72%and65.75%higherthan CK and MDHAR of T1and T2were respectively38.41%and39.68%higher than CK. Theexpression of APX and DHAR increased significantly on the12thhour of treatment, when APX in T1and T2fruit were3.4and4.4times higher than control, DHAR were as2.47and3.04times high ascontrol.To sum it up, short term moderately low nitrogen supply (T2) during fruit stage had no suppresstion on plant growth. Fruit quality improved and yield of per plant also showed no significantdifference between T2and control. Activities of antioxidase (SOD, CAT, POD) and enzymes related toAsA metabolism (AO, APX, MDHAR, DHAR, GR) in both fruit and leaf got improved duringtreatment and recovery. The expession of APX and DHAR improved significantly on the12thhour in thetreatment, while GMP, GLDH, MDHAR, AO and GR showed increasement comparing with CK in the48h in recovery.