Uptake and remobilization of NO3 - in rice (Oryza sativa L.): Proton pumps activity and dynamics of the process / Absorção e remobilização de NO3 - em arroz (Oryza sativa L.): Atividade das bombas de prótons e a dinâmica do processo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The nitrogen metabolism of rice (Caiapó variety) was studied under nitrate starvation in hidroponic culture. Thirty days after germination half of the plants continued to receive the nutrient solution, while the other group was maintained without solution change and monitored until the exhaustion of NO3 -. The depletion of NO3 - resulted in greater decrease of the nitrate redutase activity in the roots than in the leaves and sheaths. The largest reductions in the NO3 - tissue content was observed in the sheaths, indicating this compartment to be the preferential site for remobilization. Under 2mmol L-1 of NO3 - sheaths show great accumulation of this nutrient. After 72 h there is great decrease of the N-content in sheats. These results indicate clearly that the sheaths are the preferential site for accumulation, store and remobilização of NO3 - in this rice variety. The dynamics of NO3 - uptake was studied in Piauí and IAC-47 varieties. Thirty days after germination, plants were kept without N for 72 hours. After that nutrient solution was restored with 0.2 or 2 mmol L-1 of NO3 -. The harvests were made at 0, 6, 24 and 48 hours. The Piauí variety showed lower Cmin that IAC-47. At 2 mmol L-1, the apparent influx of NO3 - was higher than the proton extrusion, incrising the pH. Plants of the Piauí variety showed a greater NR and GS activity in the roots if compared with IAC-47 in the two NO3 - concentrations. Nitrate accumulation and reduction in the roots is a way to avoid waste of energy, sending this nutrient to leaves and sheaths. That would result in more efficient use of carbon. There were no great variations in the P-H+-ATPase activities in the roots and sheaths of the two varieties at this development stage, indicating that this protein should only participate in the citosolic pH control if affected by NO3 - uptake. Independent experiments with the varieties Piauí (Landrace), IAC-47 (Improved) and Caiapó (Bred for upland) were made to study the dynamics of nitrate remobilization. The supply of NO3 - was supresed 30 days after germination and harvests were made at 0, 24, 48 and 72 hours for the Piauí and Caiapó variety and 0 and 48 hours for the IAC-47 variety. N-NO3 -, N-NH4 + and N-amino decreased, but the content of soluble sugar did not show difference between 0 and 48 hours for the varieties Piauí and IAC-47. In the experiment with Piauí variety it was possible to see a negative correlation between V-ATPase activity and soluble sugars in roots and sheaths, suggesting that nitrate remobilization change the energy status of the plants. After suppression of N, there was an increase in the V-ATPase activity, preferentially in the roots of the Piauí variety, and in the sheath of the IAC-47, resulting in a great amount of NO3 - remobilization in the IAC-47 variety. The increase in the H+-PPase and P-H+- ATPase activities only observed in the Piauí variety may be a product of root growth metabolism as was showed in the experiment with the Caiapó variety. SDS-PAGE analysis of the tonoplast root fractions of the Piauí variety shows an incriase of proteins bands at 73 and 67 kDa agreeing with the observed activities of PPases and H+- ATPases.

ASSUNTO(S)

absorção de nitrato proton pumps. nitrate uptake remobilização de nitrato bombas de prótons ciencia do solo nitrate remobilization

ACESSO AO ARTIGO

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