Effects of N-acyl-homoserine lactones on growth and host-pathogen interactions in cucumber (Cucumis sativus L.)

Pathogen or symbiotic bacteria interact with eukaryotes to regulate group activities by a mechanism called quorum sensing. Many gram negative bacteria use N-acyl-homoserine lactone molecules as chemical signals for communication. It is shown here that Cucumis sativus is able to sense AHLs and response depending on the length of acyl chain. N-hexanoyl-L-homoserine lactone (C6-HSL) increased primary root elongation, and N-3-oxo-decanoyl-L-homoserine lactone (oxo-C10-HSL) enhanced plant root growth by promoting lateral root and root hair density. Treatment with long chain oxo-C14-HSL induced systemic resistance to Pseudoperonospora cubensis and Pseudomonas syringae pv. lachrymans. AHL molecules did not effect plant metabolism until the occurrence of secondary stress. Oxo-C14-HSL pre-treated plants accumulated more callose, lignin and cell wall-associated phenolic compounds than that of untreated control plants when inoculated with P. cubensis. Moreover, AHL primed plants showed enhanced H2O2, O2- accumulation and defense related enzyme activity. The data shown here suggest that chemical factors such as accumulation of defense related enzymes and physical factors such as reinforcement of cell walls are involved in AHL-related plant defense. Gene expression data indicated that AHL-related defense might depend on both SA and JA metabolic routes.