Short-term experiments on ion transport by seedlings and excised roots : technique and validity

The absorption of K(+) by excised roots of barley (Hordeum vulgare L. cv California Mariout) has been systematically compared with that of entire, undisturbed seedlings. Some experiments have also been done with wheat (Triticum aestivum L.) and an amphiploid obtained from a cross between it and salt-tolerant tall wheatgrass (Lophopyrum elongatum Host Löve [syn. Agropyron elongatum Host]). For all three genotypes, the rate of K(+) absorption measured in a 20-min period was identical for entire 8-d-old seedlings and their excised roots within the experimental error. Manipulation gentler than root excision, viz. careful transfer of seedlings from one experimental solution to another, was also without effect on the rate of K(+) absorption. Absorption of K(+) measured by assay of its (86)Rb label in the tissue was identical with that measured by K(+) depletion of the experimental solutions assayed chemically. For the plant materials and conditions of these experiments, the excised root technique for studying ion transport into roots is validated. The advantages of the technique, and findings differing from the present ones, are discussed.