Oleuropein, the main phenolic compound of olive fruit, has important antioxidant properties that are responsible for some of the nutritional properties of fruits and the defence mechanism of leaves. Polyphenol oxidase (PPO) activity changes during fruit ripening in many plants. We studied the kinetics and molecular properties of PPO in fruits and leaves of olive (Olea europaea L.) cv. 'Picual' trees and the relationship between PPO and oleuropein concentration during fruit ripening. Polyphenol oxidase showed hyperbolic kinetics in fruits and leaves. Significant increases in PPO specific activity, V(max), K(m )and catalytic efficiency occurred during fruit ripening. Based on SDS-PAGE under partially denaturing conditions and in-gel staining with DL-3,4-dihydroxyphenylalanine, PPO activity was found in one major protein of 55 and 50 kDA in fruits and leaves, respectively. During the last stages of fruit maturation, a second 36 kDa protein was observed in fruits but not in leaves, indicating that this protein could serve as a marker of the final phase of fruit maturation. Under fully denaturing conditions, only one 27.7 kDa immunoreactive band was detected in fruits. Both the amount of PPO activity and the amount of PPO protein increased significantly during fruit maturation. Immunohistochemical studies indicated that PPO is located in the epidermis, parenchyma and companion vascular cells of leaves as well as in the epidermis of fruit. During fruit maturation, oleuropein concentration measured by HPLC significantly decreased in fruits and increased in leaves.

BACKGROUND: In this study the activities of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) and the concentrations of hydroxytyrosol, tyrosol and oleuropein in olive tree (Olea europaea L. cv. Picual) leaves were investigated before and after cold stress by freezing. The air temperature fell to below −7• C and, according to the specific field conditions, four categories of orchard were selected: not cold stressed (NS), lightly cold stressed (LS), moderately cold stressed (MS) and heavily cold stressed (HS).

Ole, Htyr, and Tyr are present in the stems and roots of the olive tree and significantly change in concentration during ripening, demonstrating the involvement of these compounds in the metabolism of both organs during this phase.

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.

The kinetics and protein-expression level of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) in fruits of olive trees (Olea europaea) cv. Picual, Verdial, Arbequina, and Frantoio have been studied in relation to the concentration of total phenolic compounds, oleuropein, hydroxytyrosol, and tyrosol during fruit ripening. Frantoio was the variety that showed the highest total phenol concentration, the highest PAL activity, the lowest PPO activity, and the lowest protein levels. In contrast, Verdial was the variety that showed the lowest total phenol concentration, the least PAL activity, the greatest PPO activity, and the highest protein levels. Arbequina and Picual showed intermediate levels. These results suggest the existence of a coordinated response between PAL, PPO, and the concentration of total phenols over ripening in the four varieties. The concentration of total and specific phenols differed between varieties and specifically changed over ripening.