Nitrite Uptake into Intact Pea Chloroplasts 1: I. Kinetics and Relationship with Nitrite Assimilation

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RESUMO

The uptake of nitrite into intact pea chloroplasts was observed and its relationship with internal nitrite reduction was assessed. Net nitrite uptake exhibited saturation kinetics and an alkaline pH preference. This evidence questioned the accepted major role for neutral HNO2 permeation and its reported influence on photosynthesis. The possible involvement of a nitrite permeation channel or transport protein is discussed. Net nitrite uptake curves were closely comparable with those for nitrite reduction within the chloroplast. Net nitrite uptake into chloroplasts was profoundly influenced by darkness, incubation temperature, and plant nitrate nutrition. Of several inorganic salts tested, sulfite was the only anion to exhibit a distinct inhibition of nitrite uptake. In contrast, nitrite uptake could be stimulated by the presence of certain cations, particularly at acidic pH values. It was concluded that nitrite uptake was closely related to stromal pH, internal nitrite accumulation, and nitrite reduction. The possible dependence of nitrite reduction on nitrite uptake rather than electron transport is discussed. External ATP and NAD(P)H did not significantly affect net nitrite uptake. This suggested that cytoplasmic ATP or reductant could not directly support nitrite uptake and, possibly, nitrite assimilation.

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