SUPPRESSION OF RIPENING-ASSOCIATED GENE-EXPRESSION IN TOMATO FRUITS SUBJECTED TO A HIGH CO2 CONCENTRATION

High concentrations of CO2 block or delay the ripening of fruits. In t his study we investigated the effects of high CO2 on ripening and on t he expression of stress- and ripening-inducible genes in cherry tomato (Lycopersicon esculentum Mill.) fruit. Mature-green tomato fruits wer e submitted to a high CO2 concentration (20%) for 3 d and then transfe rred to air. These conditions effectively inhibited ripening-associate d color changes and ethylene production, and reduced the protein conte nt. No clear-cut effect was observed on the expression of two proteoly sis-related genes, encoding polyubiquitin and ubiquitin-conjugating en zyme E2, respectively. Exposure of fruit to high CO2 also resulted in the strong induction of two genes encoding stress-related proteins: a ripening-regulated heat-shock protein and glutamate decarboxylase. Ind uction of these two genes indicated that high CO2 had a stress effect, most likely through cytosolic acidification. In addition, high CO2 bl ocked the accumulation of mRNAs for genes involved in the main ripenin g-related changes: ethylene synthesis (1-aminocyclopropane-1-carboxyli c acid synthase and 1-aminocyclopropane-1-carboxylic acid oxidase), co lor (phytoene synthase), firmness (polygalacturonase), and sugar accum ulation (acid invertase). The expression of ripening-specific genes wa s affected by CO2 regardless of whether their induction was ethylene- or development-dependent. It is proposed that the inhibition of tomato fruit ripening by high CO2 is due, in part, to the suppression of the expression of ripening-associated genes, which is probably related to the stress effect exerted by high CO2.