Thylakoid peroxidase activity responsible for oxidized chlorophyll accumulation during ripening of olive fruits (Olea europaea L.)

- Chlorophyll oxidative peroxidase activity (POX-chl) was studied in subcellular fractions.
- The 99.8% of POX-chl activity was in the soluble fraction.
- There are significant varietal differences in POX-chl activity subcellular distribution.
- POX-chl in thylakoid fraction is higher in Arbequina that in Hojiblanca variety.
- There is high correlation between POX-chl activity in thylakoid and oxidized chlorophylls.

Type III peroxidase (EC 1.11.1.7) (POX) is the enzyme direct responsible of the 132 OH chlorophyll formation on oxidative catabolism of chlorophylls (chls). Despite the higher content of oxidized derivatives of chlorophylls (ox-chls) in fruits of the Arbequina variety compared to Hojiblanca, the evolution of total chlorophyll oxidative peroxidase activity (POX-chl) showed that this activity levels were higher in fruits of Hojiblanca compared with Arbequina variety. Subsequently, a deepened study on the subcellular distribution of POX-chl activity from mesocarp and epicarp cells of olive fruit of both varieties was made, finding that the POX-chl activity located in thylakoid fraction (the only fraction in direct contact with chls in vivo) was in Arbequina fruits higher than in Hojiblanca ones and involved more than 50% of the membranous POX-Chl activity. It has been demonstrated also that the evolution of the POX-chl activity in thylakoid membranes enriched fraction throughout the whole life cycle was parallel with the formation and accumulation of ox-chls in olive fruits. Data allowed to conclude that the formation of ox-chls during the chl catabolism is mediated by a POX-chl activity localized in thylakoid fraction and allow to hypothesize that the high percentage of POX activity found in the soluble cell fraction, estimated at 99.8%, may be involved in the loss of pigmentation by oxidation occurring during fruit processing for obtaining olive oil.