Abstract
In this study we investigated the effect of exogenous ethylene treatment on ethylene production, 1-aminocyclopropane-1-carboxylate (ACC) oxidase activity and expression of an ACC oxidase (PP-ACO1) gene previously cloned (Mathooko et al., 2001) in peach (Prunus persica L.) fruit. We also investigated the mode of action of CO2 and 1-methycyclopropene (1-MCP) in the regulation of ethylene biosynthesis during peach fruit ripening. Fruits were treated with various concentrations of ethylene (0.1, 1, 10, 100, 500, 1000 ppm) and also with CO2 and 1-MCP in the presence or absence of 500 ppm ethylene. Ethylene stimulated ethylene production at concentrations of 100 ppm and above while ACC oxidase activity was stimulated in a concentration-dependent manner. PP-ACO1 was slightly constitutively expressed and exogenous ethylene stimulated accumulation of its mRNA transcript in a concentration-dependent manner up to 100 ppm after which the level remained constant. CO2 and 1-MCP inhibited the ethylene-stimulated ethylene production, ACC oxidase activity and accumulation of PP-ACO1 transcripts by about 50%. These results indicate that ethylene plays a key role in the regulation of ethylene production and ACC oxidase activity and its gene expression in peach fruit. Further the results indicate that CO2 and 1-MCP regulate ethylene biosynthesis in peach fruit during ripening, at least in part, by antagonizing ethylene action. Key words: ACC oxidase, carbon dioxide, ehylene, 1-methylcyclopropene, peach,Prunus persica.
Highlights
Fruit ripening is a genetically programmed event that is characterised by a number of biochemical and physiological processes that alter fruit colour, aroma, flavour, texture and its nutritional value
Callahan et al (1993) reported that treatment of preclimacteric peach fruit with ethylene had no effect on ACC synthase RNA accumulation this treatment caused accumulation of ACC oxidase RNA
Liu et al (1985) reported that when preclimacteric tomato and cantaloupe fruits were treated with ethylene, ACC oxidase activity increased without concomitant increase in ACC content or ethylene production indicating that the increase in ACC oxidase activity precedes that of ACC synthase
Summary
Fruit ripening is a genetically programmed event that is characterised by a number of biochemical and physiological processes that alter fruit colour, aroma, flavour, texture and its nutritional value. The increase in ethylene production that is induced by developmental stages such as fruit ripening is accompanied by increase in the activities of both ACC synthase and ACC oxidase (Yang and Hoffman, 1984; Mathooko, 1996). It is clear that ACC oxidase (Barry et al, 1996; Lasserre et al, 1996; Tang et al, 1994; Mathooko et al, 2001) is encoded by more than one gene and that the genes induced by different stimuli are differentially regulated (Huang et al, 1991; Kende, 1993; Zarembinski and Theologis, 1994; Fluhr and Mattoo, 1996; Bouquin et al, 1997; Ruperti et al, 2001)
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