Nitrogen metabolism in rice cultivated under seasonal flush of nitrate

Two rice varieties, a land race (Pia ui) and an improved variety (IAC-47), were Cultivated in pots in a system that simulates the seasonal nitrate (NO3-) flushes in tropical soils. Piaui plants did accumulate more NO3- in the shoots than IAC-47. especially in the sheaths. Piaui plants have also shown a low nitrate reductase activity (NRA) at the early stages of growth, what may be and advantage for the accumulation of NO3-. Piaui plants showed a higher NO3- content and a lower NRA in the flag leaves at anthesis, while IAC-47 on the contrary showed lower NO3- content and higher NRA at anthesis. The data indicated that Piaui plants have apparently a higher N-use efficiency than IAC-47 plants do. This ability results in higher content of grain protein, even when g-rowing in poor soils. These results suggest this to be related to a superior capacity of Piaui plants to take up NO3- from low nutrient soils, and store it in the reserve pools during the early stages of growth and development.