Crop Science Journal of Natural Resources and Life Sciences Education
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Published in Crop Sci 16:775-779 (1976)
© 1976 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Nitrate Reductase Activity in Heat (Drought) Tolerant and Intolerant Maize Genotypes1

U. R. Pal, R. R. Johnson and R. H. Hageman2

The objective of this work was to determine if stability of enzyme activity under heat stress might be associated with differences in heat or drought tolerance in corn (Zea mays L.) inbreds in the seedling stage. Three heat (drought) tolerant and three intolerant inbreds that had been field evaluated were obtained from Pioneer Hi-Bred International, Inc. and were used to test the effect of assay temperature on three cytoplasmic enzymes [nitrate reductase (NR), glyceraldehyde-phosphate dehyrogenase (NAD), and ribonuclease] and two chloroplastic enzymes [nitrite reductase and glyceraldehyde-phosphate dehydrogenase (NADP+) (phosphorylating)]. Only NR and trite reductase exhibited a differential genotypic temperature response. NR (in vivo and in vitro) from three tolerant and one intolerant inbreds was inhibited less at 40 to 45 C than the other two intolerant inbreds. This is consistent with field evaluation of these genotypes during vegetative development. When all inbreds were grown at 40/21 C day/night temperature for 19 days, four inbreds (three tolerant and one intolerant with anomalous NR sensitivity to high temperature) accumulated proportionately more dry weight than the two intolerant inbreds. In vitro and in vivo (with NO3- in the infiltration medium) assays of the temperature-treated seedlings showed no differential genotypic effect. However, the in vivo (without NO3- in the infiltration medium) activity declined in a manner consistent with growth response, suggesting involvement of a "metabolic" NO3- pool. Although maintenance of NR activity under temperature stress is associated with heat or drought tolerance during the vegetative stage, the simplest selection criterion may be plant growth rate in response to temperature stress.

Key Words: Enzyme activity • Temperature stress • Zea mays L.

1 Contribution from the Dep. of Agronomy, Univ. of Illinois, Urbana, IL 61801, and supported by Hatch Funds and a grant from the Frasch Foundation. The senior author gratefully acknowledges a National Fellowship from the Indian Government.

2 Postdoctoral research associate (present address: assistant professor, Dep. of Agronomy, G.B. Pantnagar Univ., Nanital, India 263145), assistant professor of crop production and professor of plant physiology, respectively.

Received for publication February 28, 1976.




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Copyright © 1976 by the Crop Science Society of America.