Effect of Glucose on the Induction of Nitrate Reductase in Corn Roots

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Abstract
In Zea mays L., addition of glucose to the induction medium has no effect on the induction of nitrate reductase during the initial 3 hours either in root tips (0-10 mm) or mature root sections (25-35 mm). With longer times, higher levels of enzyme activity are recovered from both root segments when glucose is present in the incubation medium. The induction in root tips is saturated by 10 mm NO3−. Higher concentrations of NO3− are required for saturation in mature root sections. The response to glucose is seen over a wide range of external NO3− concentrations. Nitrate reductase activity is lost rapidly when nitrate is withdrawn from the induction medium. Additions of glucose do not prevent this loss. Additions of glucose have no effect on total uptake of NO3− by the root segments but they increase the anaerobic NO2− production in both root tips and mature root segments. This latter measurement is considered to be an estimate of an active NO3− pool in the cytoplasm. Thus the results show that glucose alters the distribution of NO3− within the root sections. This may be an important factor in controlling the in vivo stability of the enzyme or its rate of synthesis.