Effects of Seasonal Nitrate Flush on Nitrogen Metabolism and Soluble Fractions Accumulation in Two Rice Varieties

ABSTRACT

Two rice varieties, ‘Piaui’ (a landrace) and ‘IAC-47’ (an improved variety), were grown in nutrient solution containing 20 mg nitrate (NO₃ ⁻)-nitrogen (N) L^{− 1} up to 32 days after germination (DAG). After this, a group of plants received 200 mg NO₃ ⁻NL^{− 1}, while the other was kept at 20 mg NO₃ ⁻NL^{− 1} up to 42 DAG. From 42 until 56 DAG, all plants received 5 mg NO₃ ⁻NL^{− 1}. Plants were collected at 42 and 56 DAG, soluble fractions, nitrate reductase (NR) and GS enzymatic activities were determined. The nutritional history of the plants affected significantly the uptake and use of nitrogen (N), and should be taken into consideration in the studies of N-use efficiency. The variety ‘Piaui’ was more efficient than ‘IAC-47’ in N-uptake use, accumulating more NO₃ ⁻ in its tissues at the initial phases of its cycle for subsequent utilization.

Keywords:

• amino-N
• nitrogen assimilation enzymes
• nitrate uptake
• nitrogen use efficiency
• Oryza sativa L.
• soluble sugars
• traditional varieties

ACKNOWLEDGMENT

The authors are grateful to CAPES, FAPERJ and CNPq for the financial support.

Notes

∗At 56 DAG, plants were submitted to 5 mg N.L^{− 1}, however, at the beginning of the experiment, plants were submitted to different doses of NO₃ ⁻-N (20; 200 mg N.L⁻¹) represented in the first column of the table.