In contrast to previous assumptions, the defense hormones salicylic acid and jasmonic acid do not always suppress each other in regulating plant chemical defenses against pests and pathogens. In trees, the interplay of both hormones can actually increase plant resistance. This is the conclusion researchers from the Max Planck Institute for Chemical Ecology draw in a new study on poplars. The scientists showed that higher levels of jasmonic acid were also detectable in poplars that had been modified to produce increased levels of salicylic acid or that had been treated with salicylic acid. Plants that had higher concentrations of both hormones were also more resistant to the rust fungus Melamspora larici-populina, with no negative effect on growth. Knowledge of the positive interaction of these hormones involved in plant resistance could help to better protect poplars and other trees against pathogens.
The function of plant hormones or phytohormones is to coordinate the growth and development of plants. Moreover, they also control plant immune responses to microbial pathogens such as pathogenic fungi. Until now, there has been a broad consensus in science that the signaling pathways of the defense hormones salicylic acid and jasmonic acid act in opposite directions. Thus, if plants produce more salicylic acid, this would inhibit the production of jasmonic acidand vice versa. Scientists have repeatedly shown this negative interplay in studies of the model plant Arabidopsis thaliana (thale cress) and many other annual herbs. "Contrary to the assumption that the salicylic acid and jasmonic acid hormone signaling pathways work in an opposite manner, we had already observed in our earlier studies on poplar trees that both of these hormones increase in response to infection by pathogenic fungi. Therefore, the main research question was to determine the interaction between these two defense hormones in poplar," Chhana Ullah, first author of the publication, explains the starting point of the current study.