Ion Absorption by Shoot Tissue: Kinetics of Potassium and Rubidium Absorption by Corn Leaf Tissue

Abstract

By means of a technique recently described, the absorption of K and Rb by excised leaf tissue of corn (Zea mays) was studied in short-term experiments (30-minute absorption periods). Kinetics and selectivity of the absorption of these ions were found to resemble closely the characteristics of the absorption of these ions by barley root tissue in every feature examined. Over the concentration range 0.002 to 0.2 m[image] K or Rb, a single Michaelis-Menten term describes the relation Between the external concentrations of the ions and the rates of their absorption. The Michaelis constants for these 2 ions are on the order of 0.02 m[image]. There is mutual competition between K and Rb on essentially equal terms. The following ions compete with Rb absorption, in order of decreasing effectiveness: K, Cs, NH4, Li, Na. The affinity of the K-Rb transport mechanism for Na is on the order of 1-2% of its affinity for K-Rb. Rates of absorption and degree of interference are nearly the same, whether Cl or SO4 is the counterion. The close correspondence between the observations on the K absorption mechanism in leaf tissue of corn and roots of barley leads to the conclusion that the carriers effecting the K transport and their mode of operation are identical in the 2 tissues.