In grape berries, the signal that triggers fruit ripening and their transduction pathway still remain largely unknown. Fruits which display a respiration peak and an ethylene increase at the beginning of ripening are classified as climacteric but grape, which does not accumulate ethylene and lacks a respiration peak, classifies as non-climacteric fruit (Coombe and Hale 1973). However, fruit ripening and especially berry development is considered to involve both ethylene-dependent and ethylene-independent processes (Lelievre et al. 1997, Chervin et al. 2004).
Experiments have been performed to evaluate whether the ethylene signal transduction pathway could be involved in the control of ADH expression in grapevine (Tesniere et al. 2004). The effect of 1-methycyclopropene (1-MCP), an inhibitor of the ethylene receptors, and of 2-chloroethylphosphonic acid (CEPA), a chemical that releases ethylene when applied to plants, was evaluated on the ADH enzyme activity and VvADH transcript levels in a series of berry development and in suspension cells of Vitis vinifera (Fig. 4). For berries, a single treatment with 1-MCP had only an effect on enzyme activity treated 10 WPF (data not shown), whereas repeated treatments resulted in a significant reduction of enzyme activity at 9 WPF (Fig. 4A). Concerning expression at the transcript levels, no significant changes in VvADHl and VvADH3 levels were observed by specific Northern blotting in MCP-treated berries (data not shown). By contrast, increase in VvADH2 expression after veraison and during ripening was significantly reduced after 1- MCP treatment (Fig. 4B). For suspension cells 24 h CEPA-treated samples exhibited a significant increase of ADH activity and VvADH2 transcript level (data not shown). ADH activity, but not VvADH2 expression, was also enhanced when associated with a nitrogen treatment. Conversely 1-MCP-treated cells had significantly reduced ADH activity and VvADH2 transcript expression level. All these results indicated that VvADH2 transcription is, at least partially, responsive to ethylene. In berries, ethylene effect was development- and dose-dependent, suggesting some changes in the regulation of ethylene signalling during fruit development. In cells, ethylene signalling was more efficient by increasing VvADH2 transcription, when associated with low oxygen treatment. In fact ethylene appears to be implicated in the triggering of a number of responses to oxygen deficiency (Morgan and Drew 1997), and is required, although not solely responsible, for the induction of ADH during hypoxia (Peng et al. 2001). In conclusion, ADH could be regulated by ethylene in non-climacteric fruit, as this has also been shown in climacteric fruits, such as melon (Manriquez et al. 2006).
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