INVIVO NITRATE REDUCTASE-ACTIVITY IN CAREX-PSEUDOCYPERUS L - THE INFLUENCE OF NITRATE AMMONIUM CONCENTRATION RATIOS AND CORRELATION WITH GROWTH

The influence of the nitrate nutritional status and increasing ammonium concentrations on the nitrate reductase activity of shoots and roots of Carex pseudocyperus L. was investigated. The activity of this enzyme was correlated with the relative growth rates of the plant. Nitrate reductase activity was determined by a modified in vivo test (1). A specially developed test system allowed a large amount of samples to be handled easily. The optimization procedure of the incubation buffers led to different assay conditions for the shoot and the root, respectively. Enzyme activity in the shoot was dependent on the length of the incubated leaf pieces. Incubation had to take place under dark, anaerobic conditions. Enzyme activity was influenced by an evident diurnal rhythm with an optimum six hours after starting illumination, so that harvesting occurred always at that day time. Increasing nitrate concentrations of up to 2.5mM NO3- in the nutrient solution induced an increasing nitrate reductase activity in the shoot. Tle The nutrient solutions were renewed every third day. Last renewal was 12h before harvesting. All experiments lasted 3 weeks. Experiments concerning the diurnal changes of NRA were run under constant environmental conditions in a growth chamber (BBC). The day/night regime was 16/8h, 22/16-degrees-C, 70% relative humidity, with an illuminance of 100uE m-2 s-1.