The Differences of Subcellular Ca2+ Distribution in Root Meristem Region ofCucumber Seedling Under Different NO3- Concentrations Stress The Differences of Subcellular Ca2+ Distribution in Root Meristem Region ofCucumber Seedling Under Different NO3- Concentrations Stress Effects of exogenous NO on the growth and antioxidant enzyme activities of cucumber seedlings under NO3- stress. Effects of exogenous spermine on activities of antioxidant enzymes and photosynthesis in cucumber seedlings under NO-3 stress