A single UV-C pulse modulates Gibberellin homeostasis and Plant Development in Arabidopsis.

Plants are rarely exposed to ultraviolet C (UV-C) radiation because it is absorbed by the ozone layer. Nevertheless, low doses of UV-C can induce physiological and developmental responses, although the underlying hormonal mechanisms are not well understood. We show that a single one-minute UV-C pulse (20 W/m2) is associated with temporally distinct differences in gibberellin (GA) homeostasis in Arabidopsis. At early sampling times, levels of GA12, a precursor of bioactive GAs, are lower in UV-C-treated plants compared with controls. This is accompanied by lower transcript levels of KS and KAO2. Similarly, bioactive GA4 levels are lower in UV-C-treated plants. These results suggest that UV-C suppresses the early stages of GA-biosynthesis. At later time points, however, the GA4 levels are higher in UV-C-treated plants than in controls, coinciding with earlier flowering, enhanced growth, and increased fertility. The GA-signalling mutant gdella and the early GA-biosynthesis mutants kao1 and kao2 do not show wild-type developmental responses to UV-C, indicating that GA biosynthesis and signalling contribute to this response. In contrast, the C19-GA 2-oxidase quintuple mutant (C19-2oxq) retained wild-type-like responses, suggesting a limited role for C19-GA 2-oxidation. These results highlight the importance of GA-homeostasis in UV-C-mediated regulation of plant development.