Pigment distribution and physicochemical characteristics of petals during flowering of Camellia pitardii var. compressa (Hung T. Chang & X. K. Wen) T. L. Ming ‘Hongling’

Dynamic variation in flower color phenotype, anatomical structure, pigment distribution, and related physiological indices was examined across five flowering stages of Camellia pitardii var. compressa ‘Hongling’. The relationship between flower color and these characteristics was analyzed. Results showed that during floral development, petal lightness (L*) progressively increased, whereas red-green chromaticity (a*), chroma (C*), and hue angle (h°) generally declined and yellow-blue chromaticity (b*) increased initially and subsequently decreased. Pigments were concentrated on both adaxial and abaxial petal surfaces, with progressive degradation in mesophyll tissues following anthesis. Flavonoid and anthocyanin contents decreased sharply during the early stages, and their rate of decline slowed after full bloom, while carotenoid and chlorophyll levels remained consistently low. Concurrently, cellular pH and water content rose rapidly during early development, with a reduced rate post-initial bloom, whereas soluble sugars declined and soluble protein initially decreased followed by recovery. Phenylalanine ammonia-lyase (PAL) activity diminished gradually, in contrast to the continuous rise in peroxidase (POD) activity. Flavonoid and anthocyanin concentrations exhibited strong negative correlations with L* value, cellular pH, water content, and POD activity but strong positive correlations with a*, soluble sugar, soluble protein, and PAL activity. These findings indicate that anthocyanin accumulation serves as the primary determinant of petal coloration in ‘Hongling’, modulated by complex biochemical and physiological interactions. Temporal and spatial regulation of pigment distribution underlies the distinct chromatic differentiation between adaxial and abaxial petal surfaces and drives the overall trajectory of color change during flowering.