Study On The Mechanisms Of Nitrate Accumulation In Pakchoi (Brassica Campestris L.ssp. Chinesis (L.))

Nitrate accumulated in vegetable plant tissues and vacuoles is known harmful to humanbeing health especially when people eat a lot of vegetables with high content of nitratre. Thus, increase of nitrate utilization efficiency could not only increase vegetable quality, but also increase nitrogen fertilizer use efficiency.Two pakchoi cultivars significantly different in nitrate content, Shanghaiqing with low nitrate content and Liangbaiye 1 with high nitrate content screened from twelve cultivars in previous experiments were used in this experiment. The biomass, photosynthesis capacity, carbon and nitrogen content, nitrate uptake amount of these two cultivars, tissue and vacuolar nitrate content, nitrate reductase activity (NRA) and nitrate reductase gene (Nia) relative expression amount in different organs (leaf blade, petiole and root) were measured. The time courses of tissue nitrate content of different organs, sub-cell (vacuolar and cytosolic) nitrate content and leaf blade NRA after these two cultivar plants were transferred to nutrient solution without nitrogen were also measured. Distribution, remobilization and metabolism of nitrate in different organs of the two cultivars were discussed to propose mechanisms of nitrate behave in vegetable plants.Results obtained were as followed.Biomass of Liangbaiye 1 per plant was only 2.8% higher than that of Shanghaiqing. Vacuolar nitrate activities in leaf blade, petiole and root were 4.6, 2.0 and 7.4 times of tissue nitrate contents in the respective organs, and vacuolar nitrate activity was much higher than cytosolic nitrate activity. Vacuolar nitrate activities of Liangbaiye 1 were 2.4, 1.7 and 4.3 times of those of Shanghaiqing in leaf blade, petiole and root. Tissue nitrate contents of...