Mechanisms of acclimation regulation and stress response to UV-B in Dendrobium nobile Lindl

Ultraviolet-B radiation can enhance the accumulation of major chemical classes in medicinal plants but may simultaneously induce oxidative stress and cellular damage. Balancing these opposing effects is therefore critical for the effective application of UV-B in cultivation practices.

In this study, Dendrobium nobile Lindl. plants were exposed to five different UV-B intensities (0, 20, 40, 80, and 160 μW cm-2) for 21 days. We systematically evaluated physiological parameters, measured the contents of major chemical classes (polyphenols, flavonoids, alkaloids, and polysaccharides), and performed transcriptomic profiling to investigate the underlying regulatory mechanisms.

Plants exhibited strong acclimation to 20 μW cm-2 UV-B, with contents of polyphenols, flavonoids, alkaloids, and polysaccharides increasing by 41.0%, 16.3%, 33.1%, and 19.3%, respectively (P < 0.05), while maintaining relatively low stress levels. Transcriptomic analysis revealed that at 20 μW cm⁻², transcription factors including DnHY5, DnPCL1, DnMYBx1, DnBIM2, DnSCL9-l, DnMYBS3, DnBHLH66-l, DnWRKY2, DnPCF2, DnC3H2, and DnC3H14 may be involved in photomorphogenic acclimation, with key biosynthetic genes (DnC4H, DnCAD, DnCHI, DnCHS, DnPOD12, DnMVK, DnMVD) upregulated. In contrast, 80 μW cm-2 UV-B induced evident stress damage and activated stress-responsive genes (DnXTH, DnCYP77A6, DnCER1, DnCry-DASH, DnPHR, DnH64PHR), while suppressing several chemical biosynthesis-related genes.

These findings demonstrate that low-intensity UV-B (20 μW cm-2) promotes major chemical classes accumulation through photomorphogenic acclimation without significant stress damage, whereas high-intensity UV-B (80 μW cm-2) induces non-specific stress responses. This study provides a mechanistic framework for strategic UV-B application to improve medicinal plant quality and suggests optimized cultivation protocols for high-quality D. nobile production.