Involvements of dicyclohexylcarbodiimide and adenosine diphosphate-mediated respiration and organic acid metabolisms in pulp acidification of Phomopsis longanae Chi-infected longan fruit.

Effects of dicyclohexylcarbodiimide (DCC) and adenosine diphosphate (ADP) on energy state and pulp acidification in P. longanae-infected longans were investigated. Compared to P. longanae-infected group, DCC + P. longanae-infected group demonstrated higher TA content and respiration rate but lower energy levels. Moreover, DCC + P. longanae-infected group showed lower values of NADK and NADP(H), but higher levels of PGI, SDH, CCO, NAD(H), and organic acids (lactic-acid, oxaloacetic-acid, fumaric-acid, succinic-acid, isocitric-acid, α-ketoglutaric-acid), higher activities of OAMREs (IDH, SCS, MDH, LDH), and upregulated expression of OAMREs-related genes (DlACO, DlIDH, DlSCS, DlSDH, DlMDH, DlLDH). However, ADP + P. longanae-infected group exhibited opposite trends. Therefore, DCC-disrupted energy synthase expedited organic acid accumulation by boosting EMP-TCA cycle and CCP, inhibiting PPP, and upregulating the levels of OAMREs and their corresponding gene expression, eventually promoting acidification in P. longanae-treated longans. Conversely, ADP-supplemented energy level negatively regulated this process, thereby delaying pulp acidification caused by pathogen inoculation.