REGULATION OF FERMENTATIVE METABOLISM IN AVOCADO FRUIT UNDER OXYGEN AND CARBON-DIOXIDE STRESSES

'Hass' avocado (Persea americana Mill.) fruit were kept in air, 0.25 % O-2 (balance N-2), 20% O-2 + 80% CO2, or 0.25% O-2 + 80% CO2 (balance N-2) at 20C for up to 3 days to study the regulation of fermentative metabolism, The 0.25 % O-2, and 0.25% O-2 + 80% CO2 treatments caused accumulations of acetaldehyde and ethanol and increased NADH concentration, but decreased NAD level. The 20% O-2 + 80% CO2 treatment slightly increased acetaldehyde and ethanol concentrations without significant effects on NADH and NAD levels. Lactate accumulated in avocadoes kept in 0.25% O-2. The 80% CO2 (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% CO2, or 0.25 % O-2 + 80% CO2; 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).