Formation & Elimination of Ethanol in Sugar Beet Roots

Abstract

Aquatic plants have a natural stem adaptation which permits gases from the atmosphere to be transported to the submerged root system. Sifton (9, 10) has cited various references establishing the role of highly developed intercellular spaces that permit the flow of oxygen from leaf to root. In the case of nonaquatic plants, however, the importance of soil-oxygen stress is not clear. James (2) has questioned the occurrence of oxygen stress in roots under field conditions. He has cited several examples of lysigenous duct formation in roots in association with flooded soil conditions. These data are supported by more recent findings with various upland crops grown in Japan (13). James suggested that under conditions of high water tables plants may not endure anaerobiosis but rather evade it. However, Russell (8) concluded, without quantitative verification, that the large volume of qualitative information seems to justify the thesis that soil aeration, in many instances, is a major factor in plant growth. The compounds which commonly accumulate in higher plants during anaerobiosis are ethanol and lactic acid (12). Ethanol appears to be the common indicator of anaerobiosis in sugar beet roots (2, 11). Ethanol was formed anaerobically in excised barley and rice roots and did not disappear upon return to aerobic conditions (6, 7). These conclusions were based primarily upon nonspecific chemical and physical determinations of ethanol. In the dichromate procedure for ethanol determination, the standard chemical method, substances such as methanol and acetaldehyde are also oxidized (1). These investigations were initiated to determine the feasibility of using an anaerobic end-product of carbohydrate metabolism as an indication of oxygen stress in roots of sugar beet plants. The study was aimed at: A. determining the principal anaerobic end-product in sugar beets, B. ascertaining the pattern of accumulation of an anaerobic end-product in sugar beet root tissue and its rate of elimination during an aerobic recovery period, and C. evaluating the role of foliage in the dissipation of this material from root tissue and as a source of oxygen during normal growth.