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Nitrate Reductase Activity of Maize Hybrids and Their Parental Inbred¹

Field experiments were conducted over a 4-year period to compare the level of nitrate reductase (NR) activity of corn hybrids with their respective inbred parents. From previous experiments, two groups of inbreds, ranked "high" and "low" with respect to seasonal mean NR activity were selected and used to obtain FI hybrids representing the following categories: "high x high", "high x low", and "low x low".

The level of NR activity in the lq hybrid appeared to differ from category to category. In the "high x high" category, the level of NR activity of the hybrids of all three sets of material was lower than the mean of the respective parental inbreds. In the "high x low" category, the hybrids were essentially intermediate in NR activity with respect to their parental inbreds and lower, in all cases, than the higher inbred parent. Two hybrids of the "low x low" category exhibited heterosis for this character. That is, the level of NR activity of the hybrids was significantly higher than the level of the higher inbred parent. Other hybrids of this category were not significantly different in NR activity than the mean of their respective inbred parents or the higher inbred.

Since it is accepted that the mechanism of gene action is at the biochemical level through the control of protein synthesis, this work provides some insight into the mode of gene action and outlines an approach to the knowledgeable synthesis of hybrids with specified metabolic characteristics.

² Research Assistants (L.E.S. and D.M.P.), Professors of Plant Breeding and Genetics and Plant Physiology, respectively. Current Address of D. M. Peterson: Biological Laboratories, Harvard University, Cambridge 38, Mass.

Received for publication October 2, 1965.