LAUSR

Acclimation of plants to water deficit involves biochemical and physiological adjustments. Here, we studied how UV-B exposure and exogenously applied hydrogen peroxide (H2 O2 ) potentiates drought tolerance in tobacco (Nicotiana tabacum L. cv. xanthi nc). Separate and combined applications for 14 days of 1.75 kJ m-2 day-1 UV-B radiation and 0.2 mM H2 O2 were assessed. Both factors, individually and combined, resulted in inhibition of growth. Furthermore, the combined treatment led to the most compacted plants. UV-B- and UV-B+H2 O2 -treated plants increased total antioxidant capacity and foliar epidermal flavonol index. H2 O2 - and UV-B+H2 O2 -pre-treated plants showed cross-tolerance to a subsequent 7-day moderate drought treatment, which was assessed as the absence of negative impact on growth, leaf wilting, and leaf relative water content (RWC). Plant responses to the pre-treatment were notably different: (1) H2 O2 increased the activity of catalase (CAT, EC 1.11.1.6), phenylalanine ammonia lyase (PAL; EC 4.3.1.5) and peroxidase activities (POD, EC 1.11.1.7), and (2) the combined treatment induced epidermal flavonols which were key to drought tolerance. We report synergistic effects of UV-B and H2 O2 on transcription accumulation of UV RESISTANCE LOCUS 8, NAC DOMAIN PROTEIN 13 (NAC13), and BRI1-EMS-SUPPRESSOR 1 (BES1). Our data demonstrate a pre-treatment-dependent response to drought for NAC13, BES1 and CHALCONE SYNTHASE transcript accumulation. This study highlights the potential of combining UV-B and H2 O2 to improve drought tolerance which could become a useful tool to reduce water use.