Species differences in calcium and potassium distributions within plant roots

The Ca and K distributions in the roots of soybean, kidneybean and corn were investigated in relation to their lateral movement within the roots using an electronprobe X-ray microanalyzer. In the corn roots, the accumulation site of Ca was the wall of the cortical cells and little Ca was detected in the stele, suggesting that apoplasmic movement of Ca was blocked by the endodermis. In the legume roots, Ca was detected at the wall of the endodermal and stelar cells as well as the cortical cells, suggesting that the endodermis of the legume roots was permeable to the apoplasmic movement of Ca. K was mainly found within the cells of the roots, suggesting symplasmic movement of K. Neither accumulation nor depletion of the cations at the soil-root interface was observed, but the concentrations of the cations at the root surface appeared to be reduced when the roots were grown in the soil.