Regulation of Fermentative Metabolism in Avocado Fruit under Oxygen and Carbon Dioxide Stresses

Abstract

`Hass' avocado (Persea americana Mill.) fruit were kept in air, 0.25% O 2 (balance N 2 ), 20 % O 2 + 80% CO 2 , or 0.25% O 2 + 80% CO 2 (balance N 2 ) at 20C for up to 3 days to study the regulation of fermentative metabolism. The 0.25% 0 2 and 0.25% 0 2 + 80% CO 2 treatments caused accumulations of acetaldehyde and ethanol and increased NADH concentration, but decreased NAD level. The 20% O 2 + 80% CO 2 treatment slightly increased acetaldehyde and ethanol concentrations without significant effects on NADH and NAD levels. Lactate accumulated in avocadoes kept in 0.25 % 0 2 . The 80% CO, (added to 0.25% O 2 ) did not increase lactate concentration and negated the 0.25% O 2 -induced lactate accumulation. Activities of PDC and LDH were slightly enhanced and a new isozyme of ADH was induced by 0.25% O 2 , 20% O 2 + 80% CO 2 , or 0.25 % O 2 + 80% CO 2 ; these treatments partly reduced the overall activity of the PDH complex. Fermentative metabolism can be regulated by changes in levels of PDC, ADH, LDH, and PDH enzymes and/or by metabolic control of the functions of these enzymes through changes in pH, ATP, pyruvate, acetaldehyde, NADH, or NAD. Chemical names used: alcohol dehydrogenase (ADH), adenosine triphosphate (ATP), lactate dehydrogenase (LDH), nicotinamide adenine dinucleotide (NAD), reduced NAD (NADH), pyruvate decarboxylase (PDC), pyruvate dehydrogenase (PDH).