Nitrate Reductase Activity in Corn Seedlings as Affected by Light and Nitrate Content of Nutrient Media.

The requirement of light for the reduction of nitrate by higher plants has been under investigation for sonme time. Burstronm (2) obtained evidence that wheat leaves would reduce nitrate in the light but not in the dark. He concluded that nitrate reduction was directly linked to a photochemical reaction, or that it occurred concomitantly with the fixation and reduction of carbon dioxide. In contrast, Delwiche (5) used isotopic nitrogen to demonstrate that tobacco plants metabolize nitrate or ammonia in the dark as well as in the light. Other workers (7, 13) have (demonstrated that nitrate and hyponitrite are metabolized both in dark and light but that in light the rate is accelerated. The extraction, purification, and characterization of a pyridine nucleotide-nitrate reductase from soybean leaves and the occurrence of this enzyme in other higher plant species was reported in 1953 (6). Other aspects of nitrate reductase metabolism and characteristics have been published by Nason (14), Nicholas and Stevens (15), and Cheniae and Evans (4). In 1956 experiments were initiated on the Agronomy South Farm, Urbana, to determine the effect of shade, both artificial and self(competitive plant) shading on the nitrate metabolism of corn plants. It was concluded from these experiments (12) that nitrate accumulated in plants grown under conditions of low light intensity and that nitrate metabolism in two lines of corn (Hy2 x Oh7 and WF9 X C103) were differentially affected by the shade treatments. Candella et al (3) demonstrated that cauliflower plants slowly lost their nitrate reductase activity when placed in the dark. The nitrate reductase activity returned rapidly when the plants were returned to light. The experinments described in this report were carried out to determine effects of light and nitrate supply on the activity of nitrate reductase in young corn plants.