Autocatalytic C 2 H 4 biosynthesis in preclimacteric apple fruit ( Malus domestica Borkh. `Golden Delicious') was prevented by storage in atmospheres of 20% CO 2 -enriched air (17% O 2 + 63% N 2 ) or 0.25% O 2 (balance N 2 ). In preclimacteric fruit, both treatments inhibited C 2 H 2 biosynthesis by suppressing expression of ACC synthase (ACC-S) at the mRNA level. ACC oxidase (ACC-O) mRNA abundance and in vitro enzyme activity also were impaired by these treatments. However, the conversion of ACC to C 2 H 4 never became the rate limiting step in C 2 H 4 biosynthesis. C 2 H 4 biosynthesis also was effectively inhibited in climacteric apple fruit kept in air + 20% CO 2 or 0.25% O 2 . Climacteric apples also exhibited suppressed expression of ACC-S at the mRNA level, while ACC-O transcript abundance, enzyme activity, and protein abundance were reduced only slightly. ACC-S is the key regulatory enzyme of C 2 H 4 biosynthesis and is the major site at which elevated CO 2 and reduced O 2 atmospheres inhibit C 2 H 4 biosynthesis, irrespective of fruit physiological maturity. Chemical names used: 1-aminocyclopropane-1-carboxcylic acid (ACC).
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Gorny et al. (1997) studied this question.