Repeated UV-C exposure alters gibberellin homeostasis and inhibits growth in Arabidopsis thaliana

Ultraviolet-C (UV-C) radiation can be highly damaging to plants, yet its effects on gibberellin (GA) homeostasis are not well understood. In this study, we show that short daily UV-C pulse treatments (12 s, 1,200 J m ^-2 ) applied for seven days reduce plant height and delay flowering in Arabidopsis thaliana . Endogenous levels of the GA biosynthesis precursors GA ₁₂ , GA ₅₃ , GA ₁₅ , and GA ₂₄ , the bioactive GA ₄ , and the GA catabolites GA ₃₄ and GA ₁₁₀ are all lower in UV-C treated plants than in untreated controls. These changes were accompanied by lower transcript levels of the GA biosynthesis genes KS, GA13ox1, GA20ox1 , and GA3ox1 , together with opposing changes in the expression of GA2ox genes. Exogenous GA ₄ restores growth in UV-C-treated plants, suggesting that reduced GA availability contributes to UV-C-induced growth inhibition. Consistent with this finding, the GA-signalling mutant gdella and the GA-biosynthesis mutants kao1 and kao2 show strongly reduced UV-C responses. Together, these findings highlight the importance of GA metabolism and signalling in the developmental response to repeated UV-C exposure, and suggest that exposure regimen influences the dynamics of UV-C-induced hormonal responses.