Abstract
Nitrate uptake ability from low-concentration nitrate solution (below 1 mM) was evaluated based on Michaelis-Menten kinetics in 12 Japanese barley cultivars. Two kinetic parameters, Km and Vmax, were determined using 7-day-old seedlings that had been cultured with distilled water for 6 days and treated with induction medium (100 μM KNO3 plus 500 μM CaSO4) for 24h prior to the experiment. The uptake solution was composed of 25-1000 μM KNO3 and 500 μM CaSO4. At 25°C, Km and Vmax in the 12 cultivars used in this experiment ranged from 50.9 to 111.7 μM and from 2.24 to 4.99 μmol·g-1 f.w.·h-1, respectively. Km obtained in this experiment was roughly coincident with the values demonstrated by earlier studies in some plants including barley. A singnificantly high correlationship (r=0.896) was found between Km and Vmax. Km and Vmax decreased at low temperatures and the extent of the decrease in Km depended on the cultivars. The ratio of Km at 15°C to that at 25d°C ranged from about 1.00 to less than 0.50. Furthermore, it was observed that Vmax was not related to such morphological traits as plant fresh weight, first leaf length, and root length.
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