Looking for the Physiological Role of Anthocyanins in the Leaves of Coffea arabica

The aim of this study was to determine which anthocyanins are related to the purple coloration of young leaves in Coffea arabica var. Purpurascens and assess their impact on photosynthesis as compared to C. arabica var. Catuaí, with green leaves. Two delphinidin glicosides were identified and histological cross‐sections showed they were located throughout the adaxial epidermis in young leaves, disappearing as the leaves mature. Regardless the irradiance level, the photosynthetic performance of Purpurascens leaves did not differ from that observed in leaves of the Catuaí variety, providing no evidence that anthocyanins improve photosynthetic performance in coffee plants. To analyze the photoprotective action of anthocyanins, we evaluated the isomerization process for chlorogenic acids (CGAs) in coffee leaves exposed to UV‐B radiation. No differences were observed in the total concentration of phenolic compounds in either variety before or after the UV treatment; however, we observed less degradation of CGA isomers in the Purpurascens leaves and a relative increase of cis‐5‐caffeoylquinic acid, a positional isomer of one of the most abundant form of CQA in coffee leaves, trans‐5‐caffeoylquinic acid, suggesting a possible protective role for anthocyanins in this purple coffee variety. Purple young leaves of the cv. Purpurascens of Coffea arabica have lower reflectance for the light interval between 500 and 600 nm (green light) compared with green young leaves of cv. Catuai, but higher reflectance at the red light band (600 and 700 nm). Thus, it seems the anthocyanins in leaves of Purpurascens alter the quality and the amount of light reaching the cells beneath the adaxial epidermis layer, where anthocyanins are primarily located. In general, photons reaching mesophyll cells have more associated energy (lower wavelengths) in Catuai leaves than in Purpurascens.