Exogenous abscisic acid regulates primary metabolism in postharvest cherry tomato fruit during ripening

Primary metabolites play crucial roles during fruit development and ripening. Phytohormone abscisic acid (ABA) has been reported to regulate postharvest tomato fruit ripening. However, knowledge about ABA in regulating primary metabolism in tomato fruit is obscure. In the present research, cherry tomato fruit were infiltrated with 1.0 mM ABA or deionized water under vacuum, and kept in darkness for 15 d. The changes of the relative contents of sugars, organic acids, and amino acids, as well as the expression levels of key genes involved in sugar and organic acid metabolisms, were analyzed. Results showed exogenous ABA accelerated tomato fruit ripening, accompanying with the enhanced changes of fruit color and firmness, the higher levels of respiration rate and ethylene production. Meanwhile, exogenous ABA enhanced the relative levels of some primary metabolites, such as glucose, lyxose and fructose; citric acid, citramalic acid, ascorbic acid and gluconic acid; also serine, pyroglutamic acid, GABA, glutamic acid, aspartic acid, asparagine and glutamine (1.69-3.25 folds). Furthermore, exogenous ABA stimulated the expression levels of most key genes (such as SPSs, SPP2, TIV1, Lins, SUSs, PPCs, MDH and CS ) (log 2 fold change ranged from 1.06 to 3.64). Results indicate ABA is systematically involved in the regulation of primary metabolism, which may provide valuable information for exploring technical means to improve tomato taste and flavor.