Nitrate Uptake and Assimilation and Associated Metabolism Among Maize Genotypes
Mueller, Elaine Cowan
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https://hdl.handle.net/2142/71611
Description
Title
Nitrate Uptake and Assimilation and Associated Metabolism Among Maize Genotypes
Author(s)
Mueller, Elaine Cowan
Issue Date
1985
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Abstract
Five maize hybrids (B73 x Mo17, B84 x Mo17, B73 x B77, FS 854, P3382) and four maize strains (IHP, ILP, IRHP, and IRLP) were evaluated for nitrate assimilation, nitrate uptake, rate of depletion of nitrate from solution, and associated metabolic parameters.
Plants were grown in 1/2 strength Hoagland's solution containing 7.5 mM nitrate. Nitrate uptake was followed by measuring depletion from the nutrient medium during the experimental period. At harvest, composite leaf sample for each genotype was assayed for in vivo nitrate reductase activity. Plants were then divided into leaves, stalk, and root. The plant parts were dried, ground, and assayed for total and reduced nitrogen, nitrate, carbohydrate, free sugars, and phosphorus.
B73 x B77 and IRLP had the greatest dry weight (g part('-1) or g plant('-1)) of the hybrids and strains, respectively. FS 854 and IHP had the highest concentration of nitrate in leaves and highest level of "minus nitrate" in vivo nitrate reductase activity of the hybrids and strains. B73 x B77 had the highest level of "plus nitrate" in vivo nitrate reductase activity among the hybrids, and there were no differences among the strains. There were no differences in reduced nitrogen concentration among the hybrids. IHP had the highest concentration of reduced nitrogen in the stalk among the strains.
Cumulative nitrate uptake during the experimental periods was highly correlated (r = 0.99) with total plant dry weight at harvest in both hybrids and strains. Despite measurable root growth, daily rates of nitrate uptake were constant from 17 or 18 DAP to harvest. During this time interval rate of nitrate uptake was independent of root growth. There was no difference in daily rate of nitrate uptake among the hybrids. IRLP had the highest rate of nitrate uptake among the strains.
In depletion experiments with the hybrids, the hourly rates of uptake were constant as the external nitrate concentrations were depleted from 0.85 mM to near zero. Because of the lack of any observable change in uptake rate with concentration, no kinetic parameters of nitrate uptake were calculated.
There were no differences in carbohydrate or free sugar concentrations among the hybrids nor was there any difference in carbohydrate concentration among the strains. However, IRLP maintained the highest concentration of free sugars in all plant parts.
The four strains ranked ILP, IRHP, IHP, IRLP in phosphorus concentration in all plant parts.
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