Pyridine 2,4-Dicarboxylate Downregulates Ethylene Production in Response to Mechanical Wounding in Excised Mature Green Tomato Pericarp Discs

Abstract

Pyridine 2,4-dicarboxylate (PDCA) is a structural analog of 2-oxoglutarate and a potent inhibitor of 2-oxoacid-dependent dioxygenases (2-ODDs), such as prolyl 4-hydroxylases (P4Hs). It has been reported that PDCA inhibited the in vitro activity of P4Hs in cut carnation flowers and delayed petal senescence due to suppression of climacteric ethylene production. In this study, the effect of PDCA on ethylene evolution in response to mechanical wounding due to excision of mature green tomato pericarp discs was investigated. Ethylene evolution was induced within 1 h of mechanical wounding in control discs and gradually increased throughout 24 h, whereas it was partially suppressed in PDCA-treated discs during the first 12 h of a 24-h experimental period. This transient, partial suppression of ethylene production can be attributed to the lack of induction and the downregulation of ethylene biosynthetic genes within 1 h and after 12 h of wounding, respectively. However, it cannot be attributed to the suppression of ACC oxidase, a well-known 2-ODD, because no significant change in enzymatic activity was observed in PDCA-treated discs. In addition, the transcript abundance of wound-induced and ethylene-regulated PIN1, PIN2, and E4 genes was also partially suppressed in PDCA-treated discs. PDCA was also shown to be involved in ethylene evolution and color development of mature green and turning fruit discs. Overall, these results indicate that PDCA downregulates ethylene production in response to mechanical wounding and during ripening of preclimacteric and climacteric tomato fruit discs.