Effect of Metabolic Inhibitors and Temperature on Uptake and Translocation of 45Ca and 42K by Intact Bean Plants

The dependence of Ca uptake and translocation by intact roots of Phaseolus vulgaris on concurrent root metabolism was investigated using (45)Ca-labeled Hoagland solutions at one-half and one-twentieth strength (2.5 and 0.25 mM Ca(2+)). Adsorbed and absorbed (45)Ca fractions in the roots were distinguished on the basis of the time course of exchange with the outer solution. Uptake of (42)K, of which the characteristics are better known, was measured for comparison. The absorbed (45)Ca fraction showed a markedly nonlinear increase with time in contrast to the near linear increase in (42)K. Exposure of roots to cyanide, arsenate, 2,4-dinitrophenol, or low temperatures caused only slight reductions in (45)Ca absorption by roots, but significant reductions of (42)K. In all treatments involving inhibitors and low temperatures, the translocation to shoots of both (45)Ca and (42)K was strongly inhibited. The conclusion that much of the absorbed (45)Ca fraction in the root tissue is taken up by processes which are not rate-limited by metabolism is discussed.