Saturday, 15 July 2006

Changes of Nitrate Assimilation and Ascorbic Acid Content in Artificially Wilted Spinach by Nutrient Solution of High Nitrogen and Low Potassium.

Yang Ho Park, National Institute of Agricultural Science and Technology, RDA, Seodun-Dong 249, Gwonseon-Gu, Suwon-Shi, 441-707, South Korea

Introduction: Nitrate in the plant leaf cells is reduced to nitrite at the cytoplasm by Nitrate Reductase (NR) and nitrite is reduced to ammonia at the chloroplast by Nitrite Reductase (NiR). Also much of the ascorbic acid synthesized at the cytoplasm and mitochondria, exists at the cytoplasm and chloroplast. The concentrations of ascorbic acid are 2-4 mM in leaf cells usually, but much higher at the chloroplast. There are three forms of ascorbic acid in the plant mainly L-ascorbic acid (AsA), monodehydroascorbic acid (MDHA) and dehydroascorbic acid (DHA). AsA in plant cell performs antioxidants by changing those three forms. Purpose of this study was to compare physiological differences of healthy plant and wilted plant against differences in nitrate assimilation and ascorbic acid, which is the main nutrient absorbed from vegetables for mankind based on content. But comparing healthy plant with wilted plant is difficult at the actual place of a farmhouse due to differences in cultivation method and spatial and temporal dimensions. So we have to make artificially wilted plants to compare with healthy plants. Method of inducing artificial plant was by treatment of nutrient solution which contained high nitrogen and low potassium. Nutrient solution was based on Robinson solution and we established 4 different plots, 1N-1P-1K (control), 6N-1P-0K (0K), 6N-1P-0.5K (0.5K), 6N-1P-2K (2K). The rates of wilted plants: control was 0%, 2K was 10%, 0.5K was 40% and 0K was 70%. Namely, the lower the potassium treatment, the higher the rate of wilted plants under high nitrogen condition. There were no differences in leaf number, leaf width, leaf length and root length among different K levels under high nitrogen condition, but they were decreased compare to the control plot. Nitrate content of high nitrogen treated plots were higher than that of control plot both in leaf and root. Also nitrate content was decreased by increasing K levels. Nitrite patterns were the same, also was observed that nitrite content of root was increased remarkably at 0K plot which had highly wilted plants. Activities of nitrate reductase(NR) and nitrite reductase(NiR) followed the same pattern as above for nitrate and nitrite. There were high NR activities under high nitrogen nutrient solution compared to the control plot. Content of ascorbic acid of plot under high nitrogen nutrient solution was lower than control plot. Rate of K/N in 0K level, which had highly wilted plants, was lower than those of other plots. This study shows that plants can be artificially wilted, a finding that should expand the range of study about wilted plants.

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