Extracts from cultures of Pseudomonas fluorescens induce defensive patterns of gene expression and enzyme activity while depressing visible injury and reactive oxygen species in Arabidopsis thaliana challenged with pathogenic Pseudomonas syringae

Abstract

We evaluated the ability of metabolic elicitors extracted from Pseudomonas fluorescens N21.4 to induce systemic resistance (ISR) in Arabidopsis thaliana against the pathogen Pseudomonas syringae DC3000. Metabolic elicitors were obtained from bacteria-free culture medium with n-hexane, ethyl acetate and n-butanol in three consecutive extractions. Each extract showed plant protection activity. The n-hexane fraction was the most effective and was used to study the signal transduction pathways involved by evaluating expression of marker genes of the salicylic acid (SA) signalling pathway ( NPR1, PR1, ICS and PR2) and the jasmonic acid/ethylene (JA/ET) signalling pathway ( PDF1, MYC2, LOX2 and PR3). In addition, the level of oxidative stress was tested by determining the activity of enzymes related to the ascorbate-glutathione cycle. N-hexane extracts stimulated both pathways based on overexpression of ICS, PR1, PR2, PDF1 and LOX2 genes. In addition, activity of the pathogenesis-related proteins glucanase (PR2) and chitinase (PR3), lipoxygenase and polyphenol oxidase was enhanced together with an increased capacity to remove reactive oxygen species (ROS). This was associated with less oxidative stress as indicated by a decrease in malondialdehyde (MDA), suggesting a causative link between defensive metabolism against P. syringae and ROS scavenging.

Abstract

With this study, and by using three different organic solvents, we extracted some molecules derived from the metabolism of the beneficial strain Pseudomonas fluorescens N21.4, which protected Arabidopsis thaliana plants from attack by the pathogen Pseudomonas syringae DC3000. The molecules extracted using the organic solvent n-hexane were the most efficient at protection. They were also capable of activating the two defensive pathways of the plant immune system and all the enzymes responsible for reducing the oxidative stress that plants experience when they are subjected to some kind of attack.