Regulation of ethylene biosynthesis

Another hormone that can be affected by phenolics is ethylene. Coumaric acid is necessary as a cofactor for the biosynthesis of ethylene [33]. On the other hand, caffeic acid inhibits an enzyme (peroxidase type) for which the cofactor is /7-coumaric acid. Therefore, the balance between /7-coumaric and caffeic acid can in theory influence the regulation of ethylene biosynthesis [6]. 

Fig. 2. Pathway and regulation of ethylene biosynthesis. Dotted arrow represents the rate-limiting reaction solid heavy arrow indicates induction by auxin of synthesis of the enzyme hollow arrow indicates inhibition by AVG of the conversion (from Yu et al., 1979).

Yang SF (1980) Regulation of ethylene biosynthesis. Hortscience 15 238-243 Yeoman MM, Brown R (1971) Effects of mechanical stress on the plane of cell division in developing callus cultures. Ann Bot 35 1101-1112 Yu Y-B, Adams DO, Yang SF (1979) Regulation of auxin-induced ethylene production in mung bean hypocotyls role of 1-aminocyclopropane-l-carboxylic acid. Plant Physiol 63 589-590... 

Fig. 1. Ethylene biosynthesis. The numbered enzymes are (1) methionine adenosyltransferase, (2) ACC (l-aminocyclopropane-l-carboxylic acid) synthase, (3) ethylene forming enzyme (EFE), (4) 5 -methylthio-adenosine nucleosidase, (5) 5 -methylthioribose kinase. Regulation of the synthesis of ACC synthase and EFE are important steps in the control of ethylene production. ACC synthase requires pyridoxal phosphate and is inhibited by aminoethoxy vinyl glycine EFE requires 02 and is inhibited under anaerobic conditions. Synthesis of both ACC synthase and EFE is stimulated during ripening, senescence, abscission, following mechanical wounding, and treatment with auxins.

Production and Inhibition of Ethylene. Now I would like to illustrate how knowledge about a plant hormone can be used to control and regulate its action. Methionine is the precursor of ethylene in plant tissues (30). Therefore, any compound which blocks methionine metabolism might be expected to inhibit ethylene biosynthesis. Rhizobitoxine was recognized as an inhibitor of methionine biosynthesis (31) as were its analogues shown in Figure 6 (32). 9... 

The production of berberine in cell suspension cultures of T. minus was regulated by ethylene via the activation of berberine biosynthesis from (S)-reticuline. However, ethylene promoted the formation of bound polyphenolics that are associated with cell browning when added in the late stage of culture [157]. 

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