The onset of grapevine berry ripening is characterized by reactive oxygen species accumulation and 13-lipoxygenase-derived galactolipid peroxides in the chloroplasts

The ripening of fleshy fruits is a complex developmental program characterized by extensive transcriptomic and metabolic re-modelling in the pericarp tissues (pulp and skin). The onset of ripening is triggered by a network of external and endogenous signals. Previous studies reported the accumulation of hydrogen peroxide (H2O2), proposing reactive oxygen species (ROS) may be involved in the regulatory mechanisms. We therefore carried out a detailed investigation of their accumulation during seven weeks of Vitis vinifera 'Pinot Noir' berry ripening centred on véraison. We demonstrated that both H2O2 and singlet oxygen (1O2) accumulated in berry skin cells during softening, in the cytosol and plastids, respectively. H2O2 peak at véraison was followed immediately by a peak of catalase activity. The analysis of lipid extracts by HPLC-mass spectrometry showed that only membrane galactolipids accumulate oxidized species at véraison, namely monogalactodiacylglicerols (MGDGs) and digalactodiacylglicerols (DGDGs) peroxidized on one or both α-linolenic fatty acid chains, with a 13(S) absolute configuration implying the participation of an enzymatic activity. We identified a lipoxygenase (PnLOXA) which is expressed at véraison and localized at the plastid thylakoid membranes. This enzyme was able to catalyze membrane galactolipid peroxidation in tobacco leaves overexpressing PnLOXA, strongly supporting its role in berry lipid peroxidation and possibly oxylipins synthesis. We provide evidence that H2O2, 1O2 and the peroxy-galactolipids are candidate signaling molecules during grape berry ripening.