Conditions affecting in vivo nitrate reductase activity in chlorophyllous tissues

Abstract

Nitrite production during darkness by vacuum-infiltrated strips of foliar material was investigated in 6-day-old corn, field peas, wheat, barley, and marrow and in 10-week-old Gomphrena globosa. Inclusion of n-propanol enhanced nitrite production by 10 to 40%, at a species-specific optimum concentration of 0.5 to 1.0% v/v, in all plants except Gomphrena. Triton X-100 (0.1% v/v) caused additional enhancement in corn only. Substantial nitrite production (59 to 94% of maximum) occurred in plants grown with moderate (5 mM) and high (20 mM) nitrate concentrations without exogenous assay nitrate; optimum exogenous nitrate concentration was 50 to 100 mM. The patterns of response towards nitrate and propanol were highly species specific. In contrast, all species responded analogously to pH of the incubating medium, yielding a maximum plateau of activity at pH 7 to 8. Nitrite production was not enhanced by substitution of nitrogen for air during vacuum infiltration and incubation. Assay conditions yielding maximum rates of nitrite production were not affected by growth conditions which yielded higher in vivo activity at high vs. low irradiance and at high vs. low nutrient nitrate. Plants grown with moderate irradiance and nitrate exhibited 1.2- to 6-fold higher in vitro than in vivo nitrate reductase (EC 1.6.6.1) activities. In plants grown at high irradiance and low nutrient nitrate, in vivo nitrite production without exogenous nitrate was severely limited by in situ nitrate, indicating that nitrate reduction can be regulated by the rate of supply of substrate to foliar tissues under certain conditions.