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Apparent Induction of Nitrate Uptake in Nitrate-depleted Plants¹

Previous investigations revealed that nitrogen-depleted wheat absorbed nitrate slowly on first exposure to nitrate solutions. Subsequently, however, the rate of nitrate uptake increased. The present studies were initiated to more thoroughly characterize this response in wheat, and to determine if other species responded similarly. Nitrate uptake of various species was determined from changes in the amount of nitrate in the external solution. Both chemical and isotopic procedures were employed. With nitrogen-depleted wheat, the characteristic two-phase pattern was observed even when nitrate uptake was severely restricted by presence of ammonium. Chloride uptake differed from nitrate uptake in two ways; the initial slow phase was not observed and the tissue reached chloride flux equilibrium at about six hours. Corn seedlings previously grown with ammonium showed the two phase pattern of nitrate uptake whereas linear rates were observed when they were previously grown with nitrate. After being deprived of nitrate, cotton and tobacco both exhibited the two-phase pattern of nitrate uptake.

Key Words: Chloride uptake • Ammonium uptake • Triticum vulgare • Zea mays • Gossypium hirsutum • Nicotiana rustica

² Department of Soil Science (Present address of T. C. Tucker is Department of Soils and Agricultural Chemistry, University of Arizona, Tucson). We thank Mrs. Clara Blackwood, Mrs. Ann Matrone, T. A. Terry and A. D. Pendasulo for their assistance with these experiments. Results shown in Figure 4 were obtained by the senior author in R. H. Hageman's laboratory at the University of Illinois. His interest and encouragement are sincerely appreciated.

Received for publication December 9, 1971.