Anthocyanin Accumulation and Chlorophyll Degradation Lead to the Formation of Colourful Leaves of Syringa oblata in Autumn

Abstract

Syringa oblata is an important garden plant whose leaf colour turns from green to red in autumn when air temperature and daylength decrease. This study explored the reasons for leaf reddening by detecting phenotypic characteristics and pigment types and contents. With leaf reddening, luminance L * increased and chrominance a * decreased significantly. Chlorophyll and carotenoid contents significantly decreased in accordance with the distribution change of green pigment in leaf cells. Conversely, the red pigment distribution increased and the total polyphenol, total flavonoid and total anthocyanin contents evidently increased. Anthocyanin accumulation was the important reason for leaf reddening. Of the anthocyanins detected in leaves, cyanidin and delphinidin-3-O-rutinoside contents gradually increased with leaf reddening and were negatively correlated with L * . They were considered key anthocyanins influencing leaf colour. Apigenin and syringic acid were correlated with delphinidin-3-O-rutinoside and cyanidin, and they could be the anthocyanin copigments. Cyanidin-3-O-arabinoside and taxifolin were more abundant polyphenols in leaves. In summary, anthocyanin accumulation and chlorophyll degradation occurred along with leaf reddening. Temperature, light, and other co-pigments influenced the anthocyanin and chlorophyll contents. This study provides evidence for applications of S. oblata as a coloured-leaf plant in gardens and as a source of active ingredients in the commercial market.