Phenylalanine ammonia‐lyase and phenolic compounds in leaves and fruits of <i>Olea europaea</i> L. cv. Picual during ripening

Abstract

Abstract BACKGROUND: The kinetic and molecular properties of phenylalanine ammonia‐lyase (PAL) in leaves and fruit of the olive tree (Picual variety) have been studied during the seasonal process of fruit maturation. The concentrations of total phenolic compounds, oleuropein, hydroxytyrosol and tyrosol, have also been determined. This study has been made in rainfed 30‐year‐old olive trees in Jaén, Spain, cultivated by the traditional method. RESULTS: PAL specific activity was assayed and hyperbolic kinetics were observed in both organs. The K m value for L ‐Phe was 0.22 mmol L −1 in leaf and 0.26 mmol L −1 in fruit. In leaf, the highest PAL specific activity was found in the stage prior to veraison. By immunoblot, a PAL‐immunoreactive 75 kDa polypeptide was detected in leaf and fruit. In leaf, the level of this protein progressively rose until the last stages of ripening at the same time that total phenols increased. In fruit, PAL activity and protein change as in two series coinciding with different fruit‐maturation period. By immunohistochemistry under light microscopy, PAL was located in the epidermis and parenchyma cells of leaf and fruit. CONCLUSION: These results demonstrate the involvement and regulation of PAL during fruit ripening of olive, cv. Picual. Copyright © 2008 Society of Chemical Industry