ON THE EFFECTS OF DMSO IN CATION TRANSPORT BY EXCISED BARLEY ROOTS

Dimethyl sulfoxide (DMSO) in concentrations of up to 10% by volume stimulates the uptake of zinc by excised barley roots. In the same concentration it severely depresses uiptake of sodium and of rubidium. It does not seem to affect the permeability of the membrane since roots treated with desorption solutions which were 10% in DMSO did not lose more of the preferred ion than did roots desorbed in solutions not containing DMSO. Oxygen utilization (measured in the Warburg respirometer) was reduced when DMSO was present. It is suggested that DMSO is a poisoning agent which interferes with cation transport by attacking some aspect of metabolism and not by influencing the permeability of the membrane. IN RECENT YEARS a great deal of interest has been generated concerning the biological significance of dimethyl sulfoxide (DMSO) as it relates to many varied applications. In a symposium devoted to this subject (Leake, 1967) it has been pointed out that this material is a very good solvent, is capable of a high degree of penetrability, and is able to permeate cell membranes readily. Its clinical applications have been described extensively, but more recently much discussion has arisen concerning its usefulness as a drug. The many and varied sociopolitical aspects of this problem will not be within the scope of this report. Instead, the present investigation is addressed to a consideration of the membrane-influencing properties of DMSO because ion transport has been regarded as a membrane phenomenon and because the literature contains various references to the effect of DMSO in plant mineral nutrition. Leonard (1967) has reported that DMSO improves the ability of iron to enter citrus leaves. Anderson and Storey (1966) have employed DMSO in improving the zinc nutrition of pecans. Malo (1965) has noted that DMSO might be of value in enhancing corrective measures for alleviating iron chlorosis in avocados. The present investigation was carried out in an attempt to clarify the role of DMSO in the process of cation transport byr plant tissues. lReceived for publication 25 November 1967. Supported in part by a grant from the Office of Research and Projects, Southern Illinois University, and in part by a grant from the Atomic Energy Commission. The DMSO was obtained from a sample supplied to Dr. J. P. Vavra of the Plant Industries Department of Southern Illinois University by the Crown Zellerbach Corporation, Camas, Washington; this gift is gratefully acknowledged. Messrs. Robert M. Millaway and Charles E. Bare rendered technical assistance in the experimental portion of this work. MATERIALS AND METHODS-Barley roots (Hordeum vulgare L. 'Kenbar,' Sphar & Co., Mt. Carmel, Ill.) were grown and treated experimentally as described by Epstein (1961). All absorption solutions contained ZnCl2 at 5 Mm (labeled with Zn65); RbCl at 0.1 mm (labeled with Rb86); or NaCl at 0.1 mm (labeled with Na22). Calcium chloride always was added to a concentration of 0.5 mm (Epstein, 1961). All absorption times were 20 min except for those experiments in which the time-function of uptake was under examination. In those cases where total ion and absorbed ion in the tissue were distinguished, desorption times of 15 min were employed; the desorption solutions contained the preferred ion (in the chloride form) without radioactive label and in the same concentration employed in the corresponding absorption solution. The desorption solutions always contained CaCl2 in a concentration of 0.5 mM. In some cases length of desorption time varied. The experimental temperature was 22 C. All solutions were prepared with demineralized, distilled water. Radioactivity was determined either with a gas-flow detector or a gammacrystal detector mounted on a Picker automatic sample-changing system. Oxygen absorption by the roots was measured in an Aminco Warburg apparatus. In all cases 0.1-g batches of fresh barley roots were used. The bathing solution always contained CaCI2 in a concentration of 0.5 mm and DMSO was present, where required, in a concentration of 25 % by volume. In this case, too, the experimental temperature was 22 C. RESULTs-Initially the problem of a suitable DMSO concentration to be employed was examined. A series of experiments was set up in