FACTORS AFFECTING THE INVIVO NITRATE REDUCTASE ASSAY FOR MM-106 APPLE-TREES

Factors affecting the in vivo nitrate reductase (NR) assay were investigated in order to optimize the assay conditions for various tissues of MM 106 apple trees. The addition of nitrate and phosphate to the assay medium significantly increased nitrate reductase activity (NRA), but high concentrations of nitrate and phosphate inhibited the NRA. The optimum concentrations of nitrate and phosphate for in vivo NRA ranged from 50 to 100 mM and were tissue-specific. The optimum pH of the assay medium was 7.5. The addition of 2% (v/v) n-propanol to the assay medium stimulated NRA, but concentrations of n-propanol greater than 2% significantly decreased the NRA. Vacuum infiltration was effective in stimulating NRA. The in vivo NR assays for leaves and stems were linear for at least 60 minutes following an initial 30 minute lag, whereas there was no lag phase in root tissues.