METABOLISM OF ORGANIC ACIDS IN EXCISED BARLEY ROOTS AS INFLUENCED BY TEMPERATURE, OXYGEN TENSION AND SALT CONCENTRATION

Abstract

IN A previous paper (Ulrich, 1941) data were reported on the relationship between cation and anion accumulation and organic acid metabolism in excised barley roots. The general conclusion was that when cations were absorbed in excess of anions from the external culture solution, the ionic balance in the root cells was adjusted by the formation of organic acids and that conversely, when anions were absorbed in excess of cations, the organic acid content of the roots decreased. In the present paper the effects of temperature, oxygen tension and salt concentration of the external culture solution upon the organic acid content of excised barley roots will be presented. The technique employed for studying the metabolism of organic acids in excised barley roots has been reported (loc. cit.), and will be summarized only briefly. Under a carefully standardized procedure barley seeds were germinated and grown in darkness for five days and sixteen hours. At the end of this period, the excised barley roots were placed into the desired culture solution maintained at a definite temperature and constant oxygen tension (Ulrich, 1940). Following the removal of the roots after treatment in the culture solution, they were centrifuged to remove excess solution and stored at -180 C. until chemical analyses could be made on the expressed sap. EFFECT OF TEMPERATURE ON ORGANIC ACID CONTENT OF EXCISED ROOTS.-The organic acid content of plants has generally been reported to be inverselv related to changes in temperature (Bennet-Clark, 1933b; Wolf, 1931, 1938). Wolf (1931) considers that the rate of formation of organic acids is decreased at low temperatures, but that at the same time their rate of decomposition is decreased to an even greater extent. At higher temperatures the rate of decomposition is increased faster than the rate of formation and consequently the quantity of organic acids decreases. Bennet-Clark (1933b) believes the formation of organic acids has the following schematic relationship, and accordingly, should follow the Le Chatelier principle. Carbohydrate :? Malic acid + energy