In situnitrate reductase activity in leaves of adult peach trees

Abstract

SummaryThe inducibility of nitrate reductase (NR) in the leaves of five year old orchard-grown peach trees was investigated using the in situ method for determination of NR activity (NRA) (Robin et al., 1983) The exogenous supply of NO3− to cut young shoots resulted in the induction of leaf in situ NRA. Full induction of the enzyme activity (i.e. increase to values of 2 µmoles NO2− h−1 g−1 FW) was obtained after 6 h on 50 mM exogenous NO3−. Under these conditions, leaf NO3− accumulation reached 30 to 50 µmoles g−1 FW. In leaves harvested from the adult trees in the orchard, and not subjected to the induction treatment, leaf NO3− accumulation was no longer detected, but the addition of 100 mM NO3− in the assay medium for in situ NRA (+NO3−NRA) led to an activity far from negligible (up to 1 µmol NO2− h−1 g−1 FW). These data reveal that although not accumulated in the tissues. NO3− was supplied through the xylem to the leaves of the adult trees, where it induced a noticeable level of NRA. This is interprete...