ANOXIA TOLERANCE AND ANAEROBIC CATABOLISM OF AGED BEETROOT STORAGE TISSUES

The relationship between anoxia tolerance and rates of anaerobic catab olism was studied using aged storage tissues of red beetroot. This tis sue has substantial experimental advantages over most other tissues fo r studies on response to anoxia; even the aerated tissues do not grow, thus allowing assesment of any possible Pasteur effect. Furthermore, loss of the endogeneous dye, betacyanin, serves as a marker for death of individual cells. A high tolerance to anoxia was achieved by adding glucose and by applying a hypoxic pretreatment for 48 h (O-2 at 0.003 -0.015 mol m(-3)). Such tissues survived anoxia for at least 150 h. Al coholic fermentation was the principal catabolic pathway in anoxic bee troot tissue; ethanol synthesized over 88.5 h of anoxia accounted for about 86% of the decrease in endogenous sugar content in hypoxically p retreated tissues. During the first 24 h of anoxia, rates of alcoholic fermentation were stimulated by high concentrations of endogenous glu cose, supplying exogenous glucose and also by hypoxic pretreatment. In aerobically pretreated tissues, alcoholic fermentation increased with time over the first 24 h of anoxia and these increases were correlate d with increases in activity of pyruvate decarboxylase (PDC). The most rapid rates of glycolysis under anoxia were observed in the presence of glucose, c. 50% above the rate in aerated tissues. When anoxia last ed longer than 24 h, the rate of alcoholic fermentation declined with time, in all treatments. Furthermore, decreases in content of endogeno us substrates (sugars + starch), between 0 and 88.5 h anoxia, indicate d that, in hypoxically pretreated tissues, glycolysis was 30% lower un der anoxia than in air. These decreases in rate of alcoholic fermentat ion were not due to injury, or decreases in activity of PDC. Reduced a vailability of endogenous sugar can not be excluded as a cause for the decrease in rate of glycolysis. However, we favour fine control, whic h would regulate glycolysis once requirements for ATP are reduced, aft er adaptation to anoxia has been completed. We also estimate that main tenance requirement for ATP is 10-25 times lower in anoxic than in aer ated tissues.