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Ethylene Biosynthesis in Soil: I. Method of Assay in Conversion of 1-aminocyclopropane-1-carboxylic Acid to Ethylene¹

ABSTRACT

Ethylene (C₂H₄) is a common biologically active secondary metabolite produced by soil microorganisms which can have a tremendous potential impact on crop yield. Methionine (MET) has been shown to be the major substrate for C₂H₄ biosynthesis in higher plants and soil microorganisms. Although 1-aminocyclopropane-1-carboxylic acid (ACC) is an intermediate in the conversion of MET to C₂H₄ in plant tissues, the immediate precursor of C₂H₄ and its biosynthetic pathway in soils has yet to be established. The primary objective of this study is to develop a method of assay to characterize the microbial conversion of ACC to C₂H₄ in soil. Results showed that the rate of C₂H₄ released from soil was enhanced with increasing pH (up to pH 9.0). The reaction rates of this transformation approached zero-order kinetics when 9.9 mM ACC was added to soils. Under standard conditions, the accumulation of C₂H₄ was linear with time of incubation for at least 7 d. Maximum reaction rates in the conversion of ACC to C₂H₄ were observed at 50°C with enzyme denaturation occurring at 55°C. ACC derived-C₂H₄ production in soils was enhanced under highly oxidized conditions and severely inhibited under anaerobiosis. Among various pretreatments that affected the conversion of ACC to C₂H₄, toluene, CoCl, and oscillation enhanced C₂H₄ biosynthesis, whereas, DMSO, formaldehyde, EDTA, 2-mercaptoethanol, 2,4-dinitrophenol, NaF, KCN, KNO₂, and KNO₃ inhibited this reaction.

¹ Contribution of the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521. Presented before Div. S-3, Soil Sci. Soc. Am., Las Vegas, Nevada, 27 Nov. 1984.

² Assistant Professor of Soil Science and Research Assistant, Univ. of California, Riverside, Riverside, CA 92521.

Received for publication February 4, 1985. Accepted for publication June 14, 1985.