Synthesis, phloem mobility and induced plant resistance of synthetic salicylic acid amino acid or glucose conjugates.

Abstract

The growing demand for food, combined with a strong social expectation for a diet produced with fewer conventional agrochemical inputs, has led to the development of new alternatives in plant protection worldwide. Among different possibilities, the stimulation of the plant innate immune system by chemicals represents a novel and promising way. The vectorization strategy of an active ingredient that we previously developed with fungicides can potentially extend to salicylic acid (SA) or its halogenated analogues. Using the click chemistry method, six new conjugates combining SA or two mono- or di-halogenated analogues with L-glutamic acid or β-D-glucose via a 1,2,3-triazole nucleus have been synthesized. Conjugate 8a, which is derived from SA and glutamic acid, showed high phloem mobility in the Ricinus model, similar to that of SA alone despite a much higher steric hindrance. In vivo bioassays of the six conjugates against two maize pathogenic fungi Bipolaris maydis and Fusarium graminearum revealed that, unlike SA, the amino acid conjugate 8a with good phloem mobility exerted a protective effect not only locally at the application site, but also in distant stem tissues after foliar application. Moreover, compounds 8a and 8b induced up-regulation of both defense-related genes ZmNPR1 and ZmPR1 similar to their parent compounds upon challenge inoculation with B. maydis. The vectorization of salicylic acid or its halogenated derivatives by coupling them with an α-amino acid can be a promising strategy to stimulate SA-mediated plant defenses responses against pathogens outside the application site. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.