CHANGES IN ALTERNATIVE PATHWAY AND MITOCHONDRIAL RESPIRATION IN AVOCADO IN RESPONSE TO ELEVATED CARBON-DIOXIDE LEVELS

Partially ripened avocado [Persea americana (Mill.) cv, Hass] fruit ha rvested in either June or Aug, 1994 were kept at 10 degrees C in air ( 21% O-2), 20% CO2 (17% O-2, balance N-2), or 40% CO2 (13% O-2, balance N-2) for 7 to 12 days and then were transferred to air at 10 degrees C for 2 to 3 days, Mitochondrial respiration was stimulated in respons e to elevated CO, treatments at 10 degrees C. A shift to alternative p athway (Alt) respiration occurred on day 4 in experiments using avocad os from both harvest dates, with a return to initial levels in only th e 20% CO2-treated fruit (June-harvested fruit after return to air), El evated CO2 at 20 degrees C decreased the in vitro O-2 consumption of i solated mitochondria compared to mitochondria kept in air, The Alt pat hway contributed less to the total O-2 uptake of CO2-treated mitochond ria compared to mitochondria kept in air, The respiratory control rati os of the CO2-treated fruit and mitochondria were higher and lower, re spectively, than the air controls. Induction of 33 to 37 kD proteins ( corresponding to the size of the alternative oxidase proteins) occurre d in avocados after 4 days in 40% CO2. These results indicate that ele vated CO2 has various effects depending on concentration, duration and temperature of exposure, and mitochondrial function of avocado fruit, such as increased and altered respiratory oxidation and up-regulation of alternative oxidase proteins.