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Abstract
Growth chamber studies were conducted to compare two procedures for measuring potassium influx kinetics by intact corn (Zea mays L.) seedlings. It was assumed in both procedures that K uptake by corn followed Michaelis‐Menten kinetics. In the first procedure (depletion method) corn seedlings were grown in complete nutrient solution for 7, 10, 14 and 28 days. The nutrient solution contained ≤ 500 μM K. Potassium influx kinetics were determined by transferring plants into nutrient solution containing 200 μM K and following the rate of K depletion from solution over time. In the second procedure (Hofstee method) six K concentrations ranging from 24 to 246 μM were established and maintained by daily additions of K. Corn seedlings were harvested from each of the six treatments at 7, 10, 14, 21 and 28 days and K was measured in the shoots and roots. Average net K influx rates were calculated for each treatment at each harvest date. The average influx rates were paired with the measured average K concentrations in solution and K influx kinetics were determined with Eadie‐Hofstee plots. Maximum K influx rates (Imax) determined by the Hofstee method were an average of 4.8 fold higher than Imax values determined by the depletion method. Michaelis‐Menten constants (Km) determined by the depletion method were 2.3 fold higher than Km values determined by the Hofstee method.
Notes
Contribution of Department of Agronomy and Soils, Alabama Agricultural Experiment Station, and USDA‐ARS, Soil and Water Research Unit, Auburn University, AL 36849–5412. Alabama Agric. Exp. Stn. Journal Series No. 3–871259.
Assistant Professor, Department of Agronomy and Soils, and Soil Scientist, U.S. Departmnet Agriculture, Agricultural Research Service, Soil and Water Research Unit.