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Plant Physiology 62:618-621 (1978)
© 1978 American Society of Plant Biologists

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Articles

Pathway for Nitrate Assimilation in Corn (Zea mays L.) Leaves

Cellular Distribution of Enzymes and Energy Sources for Nitrate Reduction 1

Carlos A. Neyra2 and Richard H. Hageman

Department of Agronomy, University of Illinois, Urbana, Illinois 61801

The localization of enzymes responsible for nitrate assimilation and the generation of NADH for nitrate reduction were studied in corn (Zea mays L.) leaf blades. The techniques used effectively separated mesophyll and bundle sheath cells as judged by microscopic observations, enzymic assays, chlorophyll a/b ratios and photochemical activities. Nitrate reductase, nitrite reductase, and the nitrate content of leaf blades were localized primarily in the mesophyll cells, although some nitrite reductase was found in the bundle sheath cells. Glutamine synthetase, NAD-malate dehydrogenase, NAD-glyceraldehyde-3-phosphate dehydrogenase, and NADP-glutamate dehydrogenase were found in both types of cells, however, more NADP-glutamate dehydrogenase was found in the bundle sheath cells than in the mesophyll cells. These data indicate that the mesophyll cells are the major site for nitrate assimilation in the leaf blade because they contained an ample supply of nitrate and the enzymes considered essential for the assimilation of nitrate into amino acids. Because the specific activity of nitrate reductase was severalfold lower than the other enzymes involved in nitrate assimilation, nitrate reduction is indicated as the rate-limiting step in situ. A sequence of reactions is proposed for nitrate assimilation in the mesophyll cells of corn leaves as related to the C-4 pathway of photosynthesis.

2 Present address: Biochemistry and Microbiology Department, Rutgers University, P.O. Box 231, New Brunswick, N.J. 08903.

1 Supported by a fellowship grant from MUCIA-Universidad Agraria, LaMolina, Peru to C. A. N., Hatch funds and a Frasch Foundation Grant. This work constitutes a portion of a Ph.D. thesis (C. A. N.) and was presented at the American Society of Plant Physiologists' Meeting in 1974.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1978 by the American Society of Plant Biologists