Calcium and magnesium in ryegrass some differences in accumulation by roots and in translocation to shoots

Summary

Thirty-day old intact ryegrass plants (Lolium perenne) were exposed to solutions of Ca, Mg, or Ca+Mg. Each ion was present at 0.25 mM and each solution was labeled with an appropriate radioisotope (Ca⁴⁵ or Mg²⁸). Plants were harvested at various times over a 12-hour period and analyzed for incorporation of the radioisotopes and for the total quantities of Ca and Mg present. Uptake of the exogenous ions was calculated on the assumption that uptake of both carrier and isotopic species occurred in proportion to their concentrations in the ambient solution. Steady state rates of exogenous ion uptake by roots and translocation to shoots were observed for both ions during the 2–12 hour period. During this time the rate of exogenous Ca accumulation in the shoots substantially exceeded that in the roots, and the presence of ambient Mg had relatively little influence on either rate. However, ambient Mg did decrease the exogenous Ca taken up in the 0–2 hour period. The steady state rate of exogenous Mg accumulation in roots and shoots exceeded that of exogenous Ca, and the presence of ambient Ca suppressed both exogenous Mg rates about equally. Significant net accumulation of Ca occurred in the root tissue during the 2–12 hour period whereas with Mg there was little net accumulation. A constant rate of depletion of endogenous Mg, which was restricted by presence of ambient Ca, was observed. Evidence from the observed 2–12 hour y-intercept values for root accumulation of the two ions suggests the possibility of specific adsorption sites for Ca.