Effects of NPK rates and ratios on activities of metabolism enzymes in leaves of cucumber in greenhouse

Using ratio of N∶P2O5∶K2O=1∶0.5∶1.2 as control,effects of different NPK rates and ratios on activities of metabolism enzymes in leaves of cucumber (Curcumas sativa L.) soilless-cultured in greenhouse were studied.The (results) showed that an increasing the rate and ratio of nitrogen caused plant height,stem diameter,and seedling dry weight,first to increase and then to fall;NR(nitrate reductase)activity in leaf rose significantly while SS(sucrose synthetase),SPS(sucrose phosphate synthetase)and Mg2+,(Ca2+ ATPase) activities first increased and then fell.When more phosphorus was applied,plant height,stem diameter and plant dry weight increased correspondingly,so did the(activities) of SS, SPS and Mg2+,Ca2+-ATPase,but the NR activity rose then fell.The NR,SPS and Mg2+、(Ca2+-ATPase) activities at higher nitrogen and phosphorus ratios were remarkably higher than those in CK,however SS activity(decreased) significantly at the same time.Increasing the rate and ratio of potassium had fewer influences on plant height,stem diameter,dry weight and leaf SPS activity;while NR,SS and Ca2+-ATPase activities remarkably increased when potassium rate was 2 times the control,Mg2+-ATPase activity rosed slightly;However,activities of enzymes mentioned above decreased when the rate and ratio of potassium increased to 4 times the control.