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 ratio were measured in whole fruit or mesocarp disks of avocado [ Persea americana (Mill.) cv. Hass] during brief exposures to elevated CO 2 . Intact climacteric fruit exposed to air (21% O 2 ), 20% CO 2 (17% O 2 , balance N 2 ), or 40% CO 2 (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 ß-ATP levels of intact climacteric fruit exposed to 20% CO 2 or 40% CO 2 for 2 h were reduced by 25% or 43%, respectively, relative to air-exposed fruit. HPLC analysis of nucleotide phosphates from preclimacteric avocados revealed that ATP levels and the ATP : ADP ratio increased in 40% compared to the air-stored fruit. However, 1 day after transfer to air, the effects of elevated CO 2 had dissipated. These modifications in cellular state could alter the activity of respiratory enzymes in fruit exposed to elevated CO 2 atmospheres.