Anaerobic stress in germinating castor bean, ethanol metabolism, and effects on subcellular organelles

Abstract

Endosperms from castor beans (Ricinus communis) germinated for 0 to 6 days were exposed to anoxia for 0 to 15 hours. Ethanol, the only alcohol detected by gas chromatography in the tissue, accumulates to a concentration of 15 millimolar during the first 2 to 4 hours of anoxia and subsequently decreases. The absolute amount of ethanol varies from 10 micromoles per 5-day endosperm after 4 hours anoxia to less than 1 micromole in 2-day endosperm after 4 hours. Lactate content is 2 micromoles or less per endosperm. Alcohol dehydrogenase and pyruvate decarboxylase activities, which are localized in cytosolic fractions, are not greatly affected by anoxia. The recoveries of the marker enzymes and protein in endoplasmic reticulum (ER) and mitochondrial fractions decrease during anoxia. After 15 hours, the recovery of NADPH cytochrome c reductase is 15% of that in controls, fumarase is 50%, and catalase is 75%.Glyoxysomes and ER are capable of converting ethanol to acetaldehyde which was measured using the fluorogenic reagent, 5,5-dimethyl-1,3-cyclohexanedione. The glyoxysomal activity is dependent on a hydrogen peroxide-generating substrate and the ER is dependent on NADPH. However, these activities are less than 3% of the alcohol dehydrogenase activity.