EFFECT OF EXTERNAL NITRATE CONCENTRATIONS ON NITRATE EFFLUX FROM ROOTS AND ACCUMULATION IN TWO BRASSICA NAPUS L. CULTIVARS

The nutrient solution was replaced on day 72 after sowing, and then the relationship between nitrate (NO(3))-nitrogen(N) concentration in plants and nitrate efflux from roots of two oilseed rape cultivars (Brassica napus L. cv. 'Zhongyou 821' ('ZY821') and D89) was compared on days 73, 74, and 75, respectively. Nitrate-N concentration in petioles of ZY821 was significantly greater than in D89. Nitrate-N concentrations in the nutrient solution and petioles were high on day 73 and nitrate efflux from roots of D89 was greater than from ZY821. On day 75, as nitrate-N concentrations in the nutrient solution declined, both the maximum cumulative efflux and efflux rate of ZY821 was higher than D89. We hypothesized that ZY821 could remobilize more nitrate-N from the petioles to meet its N needs. This would result in a decline in translocation of nitrate from roots to shoots and an increase in root cytoplasm nitrate concentrations and root efflux.