David H. Picha

Atmospheric oxygen level influences alcohol dehydrogenase and pyruvate decarboxylase activities in sweetpotato roots

Summary Alcoholic fermentation enzyme activities in sweetpotato ( Ipomoea batatas L. Lam, cv. Beauregard) roots varied with atmospheric O 2 content (0, 1, 1.5, 5, and 21 % O 2 ) at 22 ± 2 °C. Pyruvate decarboxylase (PDC) activity and alcohol dehydrogenase (ADH) activity were assayed at their experimentally determined pH optima and increased significantly when roots were placed under anoxic atmospheres (generally ≤1.5 % O 2 ). PDC activity increased more than ADH activity in response to anoxia. PDC activity was 21- to 28-fold less than ADH activity under aerobic conditions, but was 6- to 8-fold less under anoxic atmospheres. Both PDC and ADH activities significantly decreased after transfer from anoxic atmospheres to air. However, PDC activity decreased more rapidly and reached a level similar to aerobic conditions, indicating PDC was more sensitive to oxygen availability than ADH. Generally, PDC and ADH activities continued to increase during the first 4.5 d of low oxygen exposure. PDC activity was strongly correlated to ADH activity during the entire 14.5 d exposure period to low oxygen atmospheres. A strong correlation existed between PDC activity and acetaldehyde concentration (R 2 = 0.95), but a weak correlation existed between ADH activity and ethanol concentration (R 2 = 0.52). Our results explicitly suggest that PDC is likely to be the rate-limiting enzyme in alcoholic fermentation of sweetpotatoes under low oxygen atmospheres.