Anaerobic Stress in Germinating Castor Bean, Ethanol Metabolism, and Effects on Subcellular Organelles

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Abstract
Endosperms from castor beans germinated for 0-6 days were exposed to anoxia for 0-15 h. Ethanol, the only alcohol detected by gas chromatography in the tissue, accumulates to a concentration of 15 mM during the first 2-4 h of anoxia and subsequently decreases. The absolute amount of ethanol varies from 10 .mu.mol/5-day endosperm after 4 h anoxia to < 1 .mu.mol in 2-day endosperm after 4 h. Lactate content is 2 .mu.mol 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 h, 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. These activities are < 3% of the alcohol dehydrogenase activity.