Priming for drought resistance: UV-C flashes triggered pipecolate accumulation and dehydration avoidance in Capsicum chinense Jacq. but induced no growth or metabolic costs

Ultraviolet (UV) radiation has been increasingly studied as an elicitor of plant defense against biotic and abiotic stress. The biological responses to these stimuli can be either beneficial or detrimental and are not yet fully understood. We treated chili pepper plants with UV-C flashes (1 kJ·m⁻², 2 s, 254 nm) three times for 1 week before imposing progressive drought stress for 2 weeks. In the absence of drought, plants treated with UV-C showed identical height, leaf number, water content, and stomatal conductance to those of the control plants. Analysis of leaf metabolic fingerprints covering large portions of central and secondary metabolism also revealed a limited effect of UV-C treatment on the metabolome, including the accumulation of pipecolate. In contrast, when subjected to drought, plants treated with UV-C exhibited enhanced water retention in leaves and significant changes in the metabolome. Further investigation of metabolic responses revealed that variations in major water stress markers were significantly mitigated by UV-C pretreatment. Overall, the results suggest that UV-C treatments induce priming based on the activation of systemic defense effectors and the absence of harmful symptoms, resulting in partial but significant avoidance of dehydration and reduced drought-related metabolic consequences. This paves the way for agricultural applications to concurrently manage multiple stresses and to study the specific mechanisms at work in UV-C-primed plants.