Cell-free ethylene-forming systems lack stereochemical fidelity

In-vitro systems for the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene have been reported using pea supernatants, carnation petal microsomes, olive leaf protein and, most recently, pea mitochondria. It has also been shown, in intact tissues of apple, mung bean and pea, that the system responsible for conversion of ACC to ethylene can produce 1-butene from isomers of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC). This conversion shows a high degree of steroselectivity, and isomer discrimination is therefore a valuable criterion by which to judge the validity of subcellular systems. It is shown here that all in-vitro ethylene-forming systems so far described fail by a wide margin to match the AEC-isomer preference of the corresponding intact tissues with respect to 1-butene generation. This work supports and extends recent reports by McKeon and Yang (1984, Planta 160, 84-87) and by Guy and Kende (1984, Planta 160, 281-287) on the characteristics of ethylene formation by pea homogenates. The vacuolar conversion described by the latter authors is the simplest system yet described that retains appropriate sterochemical fidelity.