Evaluation of Vegetative Growth, Physiological Change and Nitrate Reductase Gene Expression in Spinach Treated by Urea Fertilizer

Spinach (Spinacea oleracea L.) is one of the most important vegetables of Chenopodiaceae. Excessive nitrogen fertilizers application increases plant nitrateaccumulation. A complete randomized block design greenhouse experiment was carried out to study the effects of nitrogen levels on growth, nitrate accumulation and nitrate reductase in ‘New persian’ variety of spinach in Gorgan University of Agricultural Sciences and Natural Resources. Treatments included 0, 100, 200, 300, 400 and 500 kg ha-1 urea. Measured traits included leaf number, leaf area, leaf dry weight, protein, nitrate content, chlorophyll a, b and nitrate reductase gene expression. Results showed that leaf number, leaf area, leaf dry weight and leaf protein content increased as urea level increased up to 300 kg ha-1 but there was no significant increase when urea increased to 400 and 500 kg ha-1. Chlorophyll content (a, b) and nitrate formation increased when more urea were used. Nitrate level was greater in petiol than leaf blade. Urea fertilizer up to 200 kg ha-1 increased nitrate reductase transcript significantly but at higher levels, the gene expression showed lower activity and caused higher accumulation of nitrate in the leaves.