Systemic induction of peroxidase and phenolic responses to UV radiation in Nicotiana tabacum

Abstract Key message Systemic changes in isoperoxidase profile and phenolic composition mirror those in leaves exposed to ultraviolet radiation, underscoring the essential role of systemic responses in plant health and development. Abstract Plants respond to direct exposure to broadband ultraviolet (UV) light (280–400 nm) through localized protective and regulatory mechanisms. In our recent study using Nicotiana tabacum as a model plant, we showed that protective responses triggered by moderate, non-harmful UV doses could spread from directly treated leaves to UV-unexposed leaves situated above (systemic leaves). This study aimed to broaden the understanding of previous findings by investigating the similarities between direct and systemic plant responses, concentrating on two main aspects: class III peroxidase (POD) isozymes and the phenolic profiles of leaves. We compared the responses of directly UV-exposed and systemic leaves from the same plant with those of negative (completely UV-unexposed) and positive control (fully UV-exposed) plants. Native gel electrophoresis confirmed a general increase in POD activity in both direct and systemic UV responses, demonstrating similar rearrangements in POD isozyme patterns, which is a novel finding. Furthermore, high-performance liquid chromatography analyses of leaf extracts showed similar quantitative and qualitative alterations in phenolic profiles between UV-exposed leaves and systemic leaves. These changes included increased levels of potential POD substrates, such as chlorogenic acids and flavonoids, particularly quercetin-3-O-rutinoside, which serves as an excellent UV-absorbing compound and antioxidant. In general, our findings indicate that the extent and nature of the systemic UV response are similar to those triggered by direct exposure to UV radiation. These results highlight the potential of applying localized low-dose UV treatment to activate systemic antioxidant responses that affect plant health and their growth.