ELEVATED CARBON-DIOXIDE EXPOSURE ALTERS INTRACELLULAR PH AND ENERGY-CHARGE IN AVOCADO FRUIT TISSUE

Changes in cytosolic and vacuolar pH, ATP, ADP, and the ATP : ADP rati o were measured in whole fruit or mesocarp disks of avocado [Persea am ericana (Mill.) cv, Hass] during brief exposures to elevated CO2. Inta ct climacteric fruit exposed to air (21% O-2), 20% CO2(17% O-2, balanc e N-2), or 40% CO2 (13% O-2, balance N-2) had cytosolic pH values of 7 .0, 6.6, and 6.4, respectively, while mesocarp disks had cytosolic pH values of 6.9, 6.7, and 6.4, respectively. The beta-ATP levels of inta ct climacteric fruit exposed to 20% CO2 or 40% CO2 for 2 h were reduce d by 25% or 43%, respectively, relative to air-exposed fruit. HPLC ana lysis of nucleotide phosphates from preclimacteric avocados revealed t hat ATP levels and the ATP : ADP ratio increased in 40% compared to th e air-stored fruit. However, 1 day after transfer to air, the effects of elevated CO2 had dissipated. These modifications in cellular state could alter the activity of respiratory enzymes in fruit exposed to el evated CO2 atmospheres.