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Additional index words. Malus domestics, physiological disorder, postharvest physiology Abstract. Ethylene biosynthesis and polyamine content were determined in normal and watercore-affected apple (Malus domestics Borkh. CV. Delicious). Fruit with watercore produced more ethylene and contained higher amounts of putrescine (PUT), spermidine (SPD), 1-aminocyclopropane-1-carboxylic acid (ACC), and 1-(malonylamino) cyclo- propane-1-carboxylic acid (MACC). The activities of ACC synthase and ethylene-forming enzyme (EFE) in watercore- affected fruit were also higher than in normal fruit. The EFE activity in severely affected flesh was inhibited, resulting in ACC accumulation and low ethylene production. S-adenosylmethionine (AdoMet) was maintained at a steady-state level even when C2H4 and polyamides were actively synthesized in normal and affected fruit. Watercore is a disorder that is usually associated with vas- cular bundles in apple fruit. Therefore, sorbitol, the major trans- locating carbohydrate in apple, cannot enter the cells; it remains in the intercellular spaces, where the higher osmoticum pro- motes water retention (Marlow and Loescher, 1984; Williams, 1966). As a consequence, the disorder appears as a translucent watersoaked area. In severe cases, the pitch adjacent to the core and all of the cortex may also be affected (Fisher, 1923; Marlow and Loescher, 1984; Olsen et al., 1962; Williams, 1966). The afflicted tissues have an elevated water content, decreased levels of reducing sugars and pectin, increased anaerobic products, and a higher sorbitol content (Atkinson, 1971; Faust et al., 1969; Marlow and Loescher, 1984; Williams, 1966) than nor- mal tissue. Watercore may disappear after harvest if the symp- toms are mild. However, a severe form of the disorder may cause internal breakdown during storage (Marlow and Loescher, 1984) and may result in severe economic losses. Watercore usually occurs at an advanced stage of maturity. Kato and Sato (1978) found that affected apples had a higher concentration of internal C 2H4 and higher rate of C2H4 evolution in whole fruit than unaffected fruit. The high C 2H4 content in the watercore-affected fruit could be a result of stress caused by high sorbitol concentration. Osmotic stress caused by a high concentration of sorbitol has been found to enhance polyamine levels (Flores and Galston, 1984). Ethylene and polyamine bio- synthesis use the same substrate, AdoMet, and produce the same by-product, methylthioadenosine (Adams and Yang, 1977). In general, C2H4 has multiple effects associated with senes- cence; it initiates fruit ripening, induces chlorophyll loss in leaves, and promotes senescence (Yang and Hoffman, 1984). On the contrary, polyamides are senescence inhibitors. They inhibit the rise in RNase (EC 3.1.27.5), protease (EC 3.4.24.4), and per- oxidase (EC 1.11.1.7); reduce the rate of senescence of leaf protoplasts; induce DNA synthesis and mitotic activity; promote the synthesis of macromolecule s; stabilize thylakoid mem- branes; maintain high protein content; and prevent the loss of chlorophyll in leaf disks (Galston, 1983). Since C 2H4 and poly- amides have opposing effects, the purpose of this study was to investigate the relation of these two types of compounds in

Ethylene Biosynthesis and Polyamine Accumulation in Apples with Watercore