Abstract
Abstract Autocatalytic (System II) C 2 H 4 biosynthesis in climacteric ‘Golden Delicious’ apples ( Malus domestica Borkh) was effectively inhibited at 20°C by atmospheres of 20% CO 2 -enriched air (17% O 2 + 63% N 2 ) or 0.25% O 2 (balance N 2 ). In vitro 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACC-S) activity of apples held in atmospheres of air + 20% CO 2 or 0.25% O 2 was significantly inhibited when compared to apples kept in air, and correlated well with fruit C 2 H 4 production rates. In vivo and in vitro ACC oxidase (ACC-O) activity of fruit held in atmospheres of air, air + 20% CO 2 or 0.25% O 2 were similar when the assays were performed under standard assay conditions (i.e., in vivo assay performed in air, in vitro assay performed in air + 6% CO 2 ). However, if the in vivo or in vitro ACC-O enzyme activity assays were performed in an atmosphere of 0.25% O 2 , ACC-O catalytic competency and activity were significantly reduced. When the in vivo or in vitro ACC-O enzyme activity assays were performed in an atmosphere of air + 20% CO 2 , ACC-O enzyme activity was actually stimulated. These data indicate that elevated levels of CO 2 do not inhibit ACC-O catalytic competency. Western blot analysis revealed that ACC-O protein abundance was not significantly affected by any of the treatments tested, and only the 0.25% O 2 atmosphere significantly inhibited ACC-O activity. ACC-S activity was significantly reduced by atmospheres of air + 20% CO 2 or 0.25% O 2 but not via direct inhibition of ACC-S catalytic competency.
Published Version
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