Cell-free ethylene-forming systems lack stereochemical fidelity

Area of Science:

• Biochemistry
• Plant Physiology
• Molecular Biology

Background:

• In-vitro systems converting 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene are established using various plant subcellular fractions.
• Intact plant tissues demonstrate stereoselective conversion of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC) isomers to 1-butene.
• This stereoselectivity serves as a critical benchmark for evaluating the fidelity of in-vitro ethylene-forming systems.

Purpose of the Study:

• To assess the stereochemical fidelity of previously reported in-vitro ethylene-forming systems.
• To compare the isomer discrimination of in-vitro systems with that of intact plant tissues using AEC conversion.
• To identify in-vitro systems that accurately reflect the natural biochemical pathways of ethylene biosynthesis.

Main Methods:

• Evaluation of ethylene-forming activity in various in-vitro systems, including pea supernatants, carnation petal microsomes, olive leaf protein, and pea mitochondria.
• Testing the conversion of specific 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC) isomers to 1-butene in these in-vitro systems.
• Comparison of the substrate stereoselectivity observed in vitro with established data from intact apple, mung bean, and pea tissues.

Main Results:

• All tested in-vitro ethylene-forming systems exhibited significant deficiencies in discriminating between AEC isomers for 1-butene generation.
• The observed isomer preference in vitro widely deviated from the stereoselectivity documented in intact plant tissues.
• The vacuolar conversion system, as described by Guy and Kende (1984), demonstrated the highest degree of sterochemical fidelity among the evaluated in-vitro methods.

Conclusions:

• Existing in-vitro systems for ethylene formation lack the necessary stereoselectivity to accurately model the conversion of AEC isomers.
• The findings support previous research highlighting the limitations of current subcellular models for ethylene biosynthesis.
• The vacuolar system represents the most promising in-vitro model for studying ethylene formation with appropriate stereochemical accuracy.