Induction of defense response against Alternaria rot in Zaosu pear fruit by exogenous L-lysine through regulating ROS metabolism and activating defense-related proteins

L-lysine, an important basic amino acid, its catabolic pathway is activated upon microbial pathogen attack in plants and has a central role in plant immunity. The control effects of exogenous L-lysine treatment on Alternaria rot in postharvest ‘Zaosu’ pear fruit and possible mechanisms involved were studied. The results showed that L-lysine treatment inhibited Alternaria rot development and the effect was negatively correlated with the treatment concentration, lesion diameter of 0.1 mM L-lysine treated fruit was 43.7 % lower than that of the control 15 d after treatment. Further studies showed that L-lysine treatment significantly suppressed O2−, H2O2, Malondialdehyde (MDA) content, and enhanced catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities and gene expression in pear fruit. β-1,3-glucanase (GLU), and chitinase (CHI) activities and PbrGLU, PbrCHI, and PbrPR-1 gene expression were also induced by exogenous L-lysine. The findings suggest that postharvest L-lysine treatment effectively enhanced disease resistance through inhibiting reactive oxygen species (ROS) production and activating defense-related protein in pear fruit.