Exogenous hexanoic acid induced primary defense responses in tomato (Solanum lycopersicum L.) plants infected with Alternaria solani

Abstract

The effect of exogenous hexanoic acid on Alternaria solani-infected tomato plants was investigated in the present study. Tomato seedlings treated with different doses of hexanoic acid were inoculated with A. solani and their antioxidative, biochemical and molecular responses were studied. Results indicated that hexanoic acid application increased hydrogen peroxide content by 49% and peroxidase activity by 408% in the infected plants, while ascorbate peroxidase and catalase activities and total polyphenol content were not significantly changed. It was revealed that the expression of NAM, ATAF1and 2, and CUC2 family multiple stress-responsive transcription factor (SlNAC1), Mitogen-activated protein kinase 3 (SlMAPK3), increased 13 and 4 folds, respectively, while the expression increase for pathogenesis related proteins type1) (SlPR1) was 57% in A. solani-infected plants. It was also revealed that SlPR1 expression in plants treated with 1 mM hexanoic acid reached its highest level 72 h post inoculation while highest superoxide dismutase (SlSOD) expression rate was recorded 24 h after inoculation. It seems that exogenous application of hexanoic acid increased reactive oxygen species (ROS) content in A. solani-infected plants and subsequently induced systemic acquired resistance (SAR) pathways which in turn enhanced expression of superoxide dismutase (SOD), NAC1 and MAPK3 genes. These findings indicated that hexanoic acid induced resistance in tomato plants against A. solani by enhanced SAR signaling network leading to enhanced defense responses. While Ja/Et pathway is believed to be the prevalent biochemical pathway involved in plant resistance to necrotrophic pathogens, our findings revealed that hexanoic acid-treated tomato plants activated defense responses though SAR which is mainly a salicylic acid-dependent signaling pathway.