| Summary: | In rice plants, it is important to recognize N metabolism efficiency parameters in order to design strategies for improvements, increasing grain protein and enhancing people nutrition quality. Two rice varieties grown under humid tropic conditions were evaluated: Piaui, a landrace adapted to low N availability, and reduced light supply, and IAC-47, an improved variety. The assay was carried out in controlled conditions of 24oC and 12/12 hour light/dark periods (200 µE.m-2.s-1) using a growth chamber, simulating humid tropic environment. Rice plants were grown under 0.1 and 1.0 mM NH4+-N, in a Hoagland & Arnon nutrient solution, pH 5.5, up to 26 days after germination. The activity of PM H+-ATPases in the plasma membrane, vacuole VH+-ATPases, H+-PPases as well as GS, GOGAT, and GDH were determined. PM H+-ATPase presented higher activity in IAC-47 roots. On the other hand, Piaui roots showed an enhanced microsomal protein content and VH+-ATPases activity, which apparently allows this variety to absorb N as well as the improved one. Increases in the cytosolic ammonium would result in high GDH deamination in Piaui variety at 1.0 mM NH4+-N. Meanwhile, GS increases were observed in IAC-47 shoots, together with GOGAT increases at same treatment.
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