Background: Light intensity and spectral quality are important abiotic factors that induce metabolic reprogramming in medicinal plants, thereby enabling adaptive responses to diverse radiation environments. This systematic review examines how different light conditions influence secondary metabolism, emphasizing that the observed differences can be interpreted as variations in response strategies and regulatory plasticity. Methods: Published transcriptomic and metabolomic studies on light-regulated secondary metabolism in medicinal plants were reviewed, with attention paid to light intensity, spectral quality, photoreceptor signaling, phytohormone interactions, and accumulation of major bioactive compounds. Results: Plants are often described as heliophytic or sciophytic; however, this classification primarily reflects ecological adaptations rather than inherent metabolic differences. Changes in metabolism are commonly associated with accumulation patterns of phenolic acids, terpenoids, alkaloids, and other bioactive compounds and are closely linked to dynamic regulation at the gene expression level. Based on transcriptomic and metabolomic evidence, we summarized signaling networks from photoreceptors, including phytochromes, cryptochromes, phototropins, and UV RESISTANCE LOCUS 8, to the Constitutive photomorphogenic 1–ELONGATED HYPOCOTYL 5 regulatory module and its interactions with JA, SA, and GA pathways. Variations in metabolic outcomes are mainly related to response thresholds, signaling intensity, and resource allocation, rather than exclusive production of specific metabolites. Conclusions: This review provides a framework for understanding light-regulated metabolic plasticity and offers insights into optimizing light environments and improving medicinal plant quality.
Xiao et al. (Wed,) studied this question.