Effects of nitrogen dioxide and nitrate nutrition on growth and nitrate assimilation in bean leaves

Abstract

The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO2 (0-0.5 parts per million) on growth, K, photosynthetic pigment, N contents, and the activities of enzymes of N assimilation was studied in bean (Phaseolus vulgaris L. cv Kinghorn Wax) leaves. Exposing 7-day old bean seedlings for 5 days continuously to 0.02 to 0.5 parts per million NO2 increased plant height, fresh weight, chlorophyll, carotenoid, organic N and nitrate contents, and nitrate reductase and glutamate synthase activities in the leaves of seedlings supplied with no external N. At 20 millimolar nitrate, most of the parameters examined were inhibited except for organic N and nitrate contents and glutamate synthase activity which increased in most cases. Generally, with an increase in NO2 concentration, the stimulatory effect declined and/or the inhibitory effect increased. A 3-hour exposure of 12-day-old bean seedlings to 0.1 to 2.0 parts per million NO2 increased nitrate content and nitrate reductase activity at each nutrient nitrate level except for a slight inhibition of enzyme activity during exposure to 2.0 parts per million NO2 at 20 millimolar nitrate. The experiments demonstrated that the effect of NO2 is strongly influenced by nutrient N level and that NO2 is assimilated into organic nitrogenous compounds to serve as a source of N, only to a limited extent.