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.

Enzyme characterisation, isolation and cDNA cloning of polyphenol oxidase in the hearts of palm of three commercially important species.

Heart of palm (palmito) is the edible part of the apical meristem of palms and is considered a gourmet vegetable. Palmitos from the palms Euterpe edulis (Juçara) and Euterpe oleracea (Açaí) oxidise after harvesting, whereas almost no oxidation is observed in palmitos from Bactris gasipaes (Pupunha). Previous investigations showed that oxidation in Juçara and Açaí was mainly attributable to polyphenol oxidase (PPO; EC 1.14.18.1) activity. In this study, we partially purified PPOs from these three palmitos and analysed them for SDS activation, substrate specificity, inhibition by specific inhibitors, thermal stability, optimum pH and temperature conditions, Km and Ki. In addition, the total phenolic content and chlorogenic acid content were determined. Two partial cDNA sequences were isolated and sequenced from Açaí (EoPPO1) and Juçara (EePPO1). Semi-quantitative RT-PCR expression assays showed that Açaí and Juçara PPOs were strongly expressed in palmitos and weakly expressed in leaves. No amplification was observed for Pupunha samples. The lack of oxidation in the palmito Pupunha might be explained by the low PPO expression, low enzyme activity or the phenolic profile, particularly the low content of chlorogenic acid.

Polyphenoloxidase activity in coffee leaves and its role in resistance against the coffee leaf miner and coffee leaf rust.

In plants, PPO has been related to defense mechanism against pathogens and insects and this role was investigated in coffee trees regarding resistance against a leaf miner and coffee leaf rust disease. PPO activity was evaluated in different genotypes and in relation to methyl-jasmonate (Meja) treatment and mechanical damage. Evaluations were also performed using compatible and incompatible interactions of coffee with the fungus Hemileia vastatrix (causal agent of the leaf orange rust disease) and the insect Leucoptera coffeella (coffee leaf miner). The constitutive level of PPO activity observed for the 15 genotypes ranged from 3.8 to 88 units of activity/mg protein. However, no direct relationship was found with resistance of coffee to the fungus or insect. Chlorogenic acid (5-caffeoylquinic acid), the best substrate for coffee leaf PPO, was not related to resistance, suggesting that oxidation of other phenolics by PPO might play a role, as indicated by HPLC profiles. Mechanical damage, Meja treatment, H. vastatrix fungus inoculation and L. coffeella infestation caused different responses in PPO activity. These results suggest that coffee resistance may be related to the oxidative potential of the tissue regarding the phenolic composition rather than simply to a higher PPO activity.