THE INFLUENCE OF SOME RESPIRATORY INHIBITORS AND INTERMEDIATES ON RESPIRATION AND SALT ACCUMULATION OF EXCISED BARLEY ROOTS

Abstract

THE ACCUMULATION of salts by barley roots is dependent on a concomitant aerobic respiration. This has been demonstrated by the use of reduced oxygen concentrations (Hoagland and Broyer, 1936). A logical next step, as suggested by Hoagland and Broyer (1942), is an attempt to analyze the nature of the linkage between salt accumulation and respiration through the use of respiratory inhibitors. This report consists of a preliminary survey of the effects of the oxidase inhibitors, cyanide and azide, and of the dehydrogenase inhibitors, iodoacetate and malonate, on the respiration and the accumulation of the bromide ion by excised barley roots. When the latter two reagents were found to be strong inhibitors of both processes concerned, the problem was extended to include the effects of malic, succinic, fumaric, and citric acids, since these compounds are considered to be both intermediates and catalysts in a cycle whereby pyruvate is oxidized (Elliott, 1941; Evans, 1941; Barron, 1943; Krebs, 1943; and references listed). The experimental data are preceded by a detailed discussion of the method of growth and preparation of barley roots as well as those characteristics of the roots which have a bearing on subsequent experiments. GROWTH AND PREPARATION OF THE BARLEY ROOTS FOR STUDY BY MICROSPIROMETER METHODS.-Growing the plants.-Prevot and Steward (1936) and Ulrich ( 1941 ) demonstrated that under certain conditions barley produces long, unbranched roots with a high capacity for absorbing and accumulating salts. By combining and modifying their methods, unbranched roots, 12-15 cm. long, relatively free of root hairs, and of a uniform diameter slightly under 0.5 mm. were grown in five days. The grain used was the Sacramento strain of barley from the 1939 crop grown at Davis, California. Approximately twice as many grains as plants to be needed are soaked for twenty-four hours in a cheesecloth sack suspended in well-aerated distilled water inside a thoroughly darkened, circulating air type incubator at 240 ? 0.050C. The air, before passing through the water, is brought to the proper temperature by passing it through a series of copper coils within the incubator. After washing the soaked grains with distilled water, twenty of those with