Metabolomic analysis reveals stepwise metabolic adaptation to extended photoperiods in developing pea sprouts

Photoperiod strongly influences early seedling metabolism; however, its role during initial development remains unclear. We analysed 100 primary and secondary metabolites and phytohormones in pea sprouts grown under short-day (SD; 8 h light), long-day (LD; 16 h light), and all-day (AD; 24 h light) conditions. Principal component analysis revealed distinct photoperiod-dependent clustering, indicating stepwise metabolic reprogramming from SD to AD. SD enhanced amino acid accumulation and auxin conjugation by 1.01-6.50-fold and 0.99-2.66-fold over LD/AD, suggesting reduced carbon flux due to limited photosynthesis and a compensatory shift toward nitrogen metabolism to maintain metabolic homeostasis. Conversely, LD/AD increased sugars and stress-related hormones by 1.20-7.51-fold and 1.25-14.91-fold relative to SD. Notably, LD elevated abscisic acid (1.39-fold) and salicylic acid (14.91-fold) over SD, reflecting photooxidative stress. These findings highlight the significance of photoperiod in seedling metabolism and potential metabolic costs associated with prolonged light exposure.