Evaluation of nitrate nutrition indexes in maize leaves: Metabolic nitrate, total nitrate content and nitrate reductase activity 1

Abstract The Metabolic Nitrate Pool (MNP) was measured in leaves by using the in situ nitrate reductase (NR) activity assay, as described Robin et al. [Physiol. Veg. 1983, 21:155–122]. Total nitrate (NCV) content and in vitro NR activity were also determined as indexes of the NO3 ‐ nutrition status of pure hydroponic grown maize plants. Two experiments were designed: i) increasing concentrations of NO3 ‐ in the nutrient solution, and ii) deprivation of NO3 ‐ in the nutrient solution. Although a time course accumulation of nitrite (NC2 ‐) occured after the incubation of maize leaves in anoxia and darkness in the in situ NR activity assay, the MNP determination was no consistent with the NC3 ‐ treatments. The MNP was small in excess of NO3 ‐ (30 mM), whereas the total NO3 ‐ content and the in vitro NR activity were the highest. Moreover, in the NO3 ‐ depletion experiment, the MNP increased after 6 h deprivation, while the total NO3 ‐concentration and the in vitro NR activity decreased. The Metabolic Nitrate...