Low UV-B radiation induces acclimation in Micro-Tom tomato plants. Do hormones and their interaction play a role in leaves and roots?

During the last decades a lot of studies investigated the effects of the UV-B wavelength on the above-ground organs of plants directly reached by the radiation, while less is known about UV-B-induced root modifications, although also this organ expresses the specific UV-B photoreceptor, UVR8 (UV RESISTANCE LOCUS 8), and several regulators needed for signal transduction. From this perspective, this work aimed at deepening the knowledge on the photomorphogenic responses to low UV-B radiation (1.19 kJ m-2 day-1) on various physiological aspects of Micro-Tom tomato (Solanum lycopersicum L.) leaves and roots at different times of treatment (8 and 11 days) and after a recovery period of 3 days. After checking the acclimation of plants, foliar and root hormones were quantified. The results showed a lower ethylene emission in treated plants which was associated to changes in the gene expression of the two enzymes involved in its biosynthesis. The transiently increased salicylic and abscisic acid concentrations in treated plants were accompanied by a lower stomatal conductance and a transient increase iWUE. The expression of genes involved in stomata control was also investigated. Finally a metabolomic approach was performed on leaves and roots with a particular focus on phenolomics, that was associated with modification in the expression of genes involved in UVR8 signalling pathway and the first steps of phenols biosynthesis, which showed a different modulation of phenolic compounds between leaves directly reached by the UV-B radiation and roots not directly exposed.