The terpene limonene induced the green mold of citrus fruit through regulation of reactive oxygen species (ROS) homeostasis in Penicillium digitatum spores

Herein, the dosage effect of limonene on the P. digitatum spore germination and its regulatory mechanisms were investigated. Results showed that limonene only at low concentrations displayed a stimulatory role, with the optimal concentration being 0.25 mu L/mL. GC-MS and GC analysis revealed that limonene contents remained relative stable and no evidence of transformation was observed at stimulatory concentrations. Metabolomics analysis showed that 61 metabolites including organic acids, amino acids, sugars, nucleosides, fatty acids, and their derivatives, were significantly changed (P < 0.05), suggesting the transitions between soluble sugars and energy-related metabolisms. Proteomic analysis demonstrated that proteins in energy-related pathways and ROS homeostasis were also influenced. These were further confirmed by the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST), the contents of reactive oxygen species (ROS), hydrogen peroxide (H2O2), and glutathione (GSH). Our present research indicates that ROS homeostasis is involved in the limonene induced spore germination of P. digitatum.