Influence of High Day and Variable Night Temperatures on Nitrate Reductase Activity of Young Corn (Zea mays L.) Plants1

Abstract

Sixteen corn (Zea mays L.) genotypes (a four‐parent diallel cross) were grown from seed for a month in controlled‐environment rooms in the University of Wisconsin Biotron. A high day (35 C) and three night temperatures (24, 16, and 7 C) were provided to study the influence of high day and variable night temperatures on nitrate reductase (E.C. 1.6.6.1) activity (NRA) in these genotypes. A 15‐hour photoperiod at 35 klux was provided. Plants were grown in vermiculite with nutrient solution.Growth was fastest at a high night temperature of 24 C and slowest at 7 C, but NRA per g fresh wt (gfw) of leaf blades declined more rapidly at the high night temperature of 24 C than at 16 or 7 C and the decline was least rapid at 7 C. NRA per plant changed little at the 24 C night temperature during the first 21 days, but increased markedly thereafter. At 16 C, NRA per plant increased from 11 to 17 days, but decreased thereafter, whereas it increased at 7 C from 13 to 30 days in most genotypes.Significant genotypic differences were observed at all night temperatures and at 9 of 10 samplings. At 24 C, levels of NRA of each reciprocal cross generally were intermediate with respect to levels of NRA in the two parental inbreds. However, in a few cases, one or both reciprocal crosses were higher than the midparent with respect to NRA. At 16 C, additional crosses were higher than the midparent with respect to NRA per gfw and per plant, though a few were intermediate in NRA as compared with their parents. At 7 C, NRA per plant generally was higher in the hybrids than in either parent.Reciprocal effects were statistically significant in only 2 out of 10 samplings. General combining ability (GCA) effects were significant in eight samplings. In all samplings and at all temperature regimes, inbred ‘A632’ was the parent with most positive GCA effects.