Absorption kinetics of Ca, Mg, Na and P by intact corn and onion roots

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Abstract
The influence of Ca on the influx kinetics of Mg and Na, and Mg effects on Ca influx kinetics were evaluated in intact corn roots. Increasing levels of Mg (25 to 75 μM) reduced the Imax for Ca. However, in absence of Mg, increasing levels of Ca (10 to 30 μM) increased the Imax and Km for Ca. Higher levels of Mg interfered with Ca influx. Increasing levels of Ca promoted the Mg influx rates and increased Km as well. Absence of Ca reduced the magnitude of Imax and Km for Mg. At an initial level of 50 μM Ca, increasing Na levels from 50 to 100 μM enhanced the Imax and Km for Na. In the absence of Ca, higher Imax were recorded for Na. Calcium reduced the Na influx rates. Ion influx kinetics for Ca, Mg, Na and P were determined with the two morphologically differing intact root systems of corn and onion. The rate of influx for Ca, Mg and Na in corn were lower than onion roots. The Imax for P in corn were slightly higher than in onion. The Km vaues for Ca, Mg and Na in corn were also higher than onion indicating a lower affinity by the carrier sites for these ions in corn roots.