EFFECTS OF ELEVATED CARBON-DIOXIDE ON KEY MITOCHONDRIAL RESPIRATORY ENZYMES IN HASS AVOCADO FRUIT AND FRUIT DISKS

Preclimacteric avocado [Persea americana (Mill.) cv, Hass] fruit or fr uit disks as well as fruit harvested in either June (midseason) or Aug ust (late season) and partially ripened were kept in air (21% O-2 + 78 % N-2), 20% CO2 + 17% O-2 (63% N-2), or 40% CO2 + 13% O-2 (47% N-2) at either 10 or 20 degrees C. Ethylene production by preclimacteric frui t completely inhibited during CO2 exposure, whereas there was only par tial inhibition of ethylene production when partially ripened fruit we re exposed, Compared to the fruit stored in air, O-2 uptake of fruit s tored in 20% CO2 was decreased by 20%, whereas the fruit stored in 40% CO2 showed 25% more O-2 uptake than air-stored fruit, Fruit subjected to a storage regime of 40% CO2 at 10 degrees C followed by 2 d in air had the best visual quality, In general, climacteric fruit treated wi th 20% CO2 at 10 degrees C showed increased pyruvate dehydrogenase (PD H) activity and decreased cytochrome oxidase (CytOx) activity, Fruit s tored in 40% CO2 had reduced CytOx activity compared to air-stored fru it, and PDH activity was variable depending on the harvest season of t he fruit, Our results show that the effect of elevated CO2 on a given enzyme depends on concentration of CO2, duration of exposure, physiolo gical state of the fruit, and type of tissue exposed.