Auxin–light–position interactions affect organogenesis and somatic embryogenesis from the root explants in Angelica gigas

Angelica gigas Nakai is a Korean native medicinal plant containing coumarin-derived bioactive compounds such as decursin and decursinol angelate. Tissue culture–based clonal propagation is necessary to preserve genetic integrity and thereby ensure consistent, stable production of decursin and other functional metabolites. Establishment of an efficient in vitro propagation system is required for large-scale production of uniform plantlets and stable acquisition of functional metabolites. Here, we quantitatively evaluated organogenic responses of root explants derived from in vitro –grown plantlets according to explant position (A: 0–1.5 cm, B: 1.5–3.0 cm, C: ≥3.0 cm), and examined interactive effects of auxin (NAA; 5, 10, 15, and 20 µM) and LED spectral quality (control, white, green, red, and blue) using a three-factor full factorial design. A total of 60 treatment combinations (4 NAA × 5 LED × 3 positions; 48 explants per treatment) were cultured for 12 weeks. Three-way ANOVA revealed that NAA concentration, LED light quality, and explant position significantly affected callus formation, shoot and root induction, and somatic embryogenesis (p < 0.001). Significant NAA × LED × position interactions demonstrated that regeneration efficiency was regulated by multifactorial interactions rather than single-factor effects. Low NAA (5–10 µM) combined with red or blue LEDs promoted shoot induction and somatic embryogenesis (up to 52.1% and 50.0%, respectively), whereas high NAA (15–20 µM) under white LED induced excessive callus formation (85–100%) and suppressed organogenesis. Positional effects were evident, with basal explants (Position C) showing enhanced rooting capacity (maximum root length 2.35 cm and 2.94 roots per explant). Canonical correlation analysis identified a significant multivariate association between culture conditions and organogenic responses. The first canonical axis (ρ = 0.388, p < 0.001) represented a differentiation-efficiency gradient characterized by enhanced shoot induction, shoot elongation, and somatic embryogenesis coupled with reduced callus proliferation, mainly driven by low NAA and red LED treatments. Correlation analysis further revealed strong positive associations among shoot-related traits and somatic embryogenesis (r = 0.80–0.99, p < 0.001), while callus formation exhibited consistent negative correlations with organogenic traits. Collectively, regeneration efficiency in A. gigas root explants is determined by integrated effects of auxin concentration, LED spectral quality, and explant position. The combination of low NAA, red/blue LED, and high-competence basal explants provides a practical basis for standardized micropropagation and a technical foundation for future in vitro biofactory systems targeting sustainable production of high-value bioactive compounds.