Jasmonoyl-L-Isoleucine Induces Systemic Photosynthetic Responses to Local Heat Stress by Contributing to Abscisic Acid Accumulation.

Systemic regulation of photosynthesis is crucial for plant survival in variable environments, yet the hormonal mechanisms coordinating photosynthetic responses to local stimuli are not fully elucidated. This study investigates the interplay between jasmonates (JAs) and abscisic acid (ABA) in systemic photosynthetic responses induced by local heat stress in Arabidopsis thaliana. Using phytohormone quantification, chlorophyll fluorescence and gas exchange measurements in wild-type and transgenic plants impaired in JA biosynthesis, this study showed that local heating-induced variation potential propagation triggers JA biosynthesis in systemic unstimulated leaves, followed by changes in ABA content, stomatal conductance and photosynthetic activity. Rapid systemic increases in jasmonoyl-L-isoleucine (JA-Ile) levels are essential for the systemic decreases in stomatal conductance and the consequent reduction in carbon assimilation. Systemic increases in JA-Ile levels also contribute to systemic accumulation of ABA, likely to maintain reduced stomatal conductance. Thus, the data support a model in which JA-Ile acts as a mediator of early stages of the systemic photosynthetic response, whereas ABA likely contributes to late stages of this response. These results highlight the complex integration of hormonal signals in the regulation of photosynthesis under stress conditions.