Hormone profile changes occur in roots and leaves of Micro-Tom tomato plants when exposing the aerial part to low doses of UV-B radiation

During the last decades, many studies investigated the effects of UV-B on the above-ground organs of plants, directly reached by the radiation but, to the best of our knowledges, the influence of mild UV-B doses on root hormones was not explored. Consequently, this research aimed at understanding whether low, not-stressful doses of UV-B radiation applied above-ground influenced the hormone concentrations in leaves and roots of Micro-Tom tomato (Solanum lycopersicum L.) plants during 11 days of treatment and after 3 days of recovery. In particular, ethylene, abscisic acid, jasmonic acid, salicylic acid and indoleacetic acid were investigated. The unchanged levels of chlorophyll a and b, lutein, total xanthophylls and carotenoids, as well as the similar H2O2 concentration between control and treated groups suggest that the UV-B dose applied was well tolerated by the plants. Leaf ethylene emission decreased after 8 and 11 days of irradiation, while no effect was found in roots. Conversely, indoleacetic acid underwent a significant reduction in both organs, though in the roots the decrease occurred only at the end of the recovery period. Salicylic acid increased transiently in both leaves and roots on day 8. Changes in leaf and root hormone levels induced by UV-B radiation were not accompanied by marked alterations of plant architecture. The results show that irradiation of above-ground organs with low UV-B doses can affect the hormone concentrations also in roots, with likely implications in stress and acclimation responses mediated by these signal molecules.