The onset of grapevine berry ripening is characterized by ROS accumulation and lipoxygenase-mediated membrane peroxidation in the skin

Abstract

BackgroundThe ripening of fleshy fruits is a complex developmental program characterized by extensive transcriptomic and metabolic remodeling in the pericarp tissues (pulp and skin) making unripe green fruits soft, tasteful and colored. The onset of ripening is regulated by a plethora of endogenous signals tuned to external stimuli. In grapevine and tomato, which are classified as non-climacteric and climacteric species respectively, the accumulation of hydrogen peroxide (H2O2) and extensive modulation of reactive oxygen species (ROS) scavenging enzymes at the onset of ripening has been reported, suggesting that ROS could participate to the regulatory network of fruit development. In order to investigate this hypothesis, a comprehensive biochemical study of the oxidative events occurring at the beginning of ripening in Vitis vinifera cv. Pinot Noir has been undertaken.ResultsROS-specific staining allowed to visualize not only H2O2 but also singlet oxygen (1O2) in berry skin cells just before color change in distinct subcellular locations, i.e. cytosol and plastids. H2O2 peak in sample skins at véraison was confirmed by in vitro quantification and was supported by the concomitant increase of catalase activity. Membrane peroxidation was also observed by HPLC-MS on galactolipid species at véraison. Mono- and digalactosyl diacylglycerols were found peroxidized on one or both α-linolenic fatty acid chains, with a 13(S) absolute configuration implying the action of a specific enzyme. A lipoxygenase (PnLOXA), expressed at véraison and localizing inside the chloroplasts, was indeed able to catalyze membrane galactolipid peroxidation when overexpressed in tobacco leaves.ConclusionsThe present work demonstrates the controlled, harmless accumulation of specific ROS in distinct cellular compartments, i.e. cytosol and chloroplasts, at a definite developmental stage, the onset of grape berry ripening. These features strongly candidate ROS as cellular signals in fruit ripening and encourage further studies to identify downstream elements of this cascade. This paper also reports the transient galactolipid peroxidation carried out by a véraison-specific chloroplastic lipoxygenase. The function of peroxidized membranes, likely distinct from that of free fatty acids due to their structural role and tight interaction with photosynthesis protein complexes, has to be ascertained.

Singlet Oxygen Plays an Essential Role in the Root’s Response to Osmotic Stress

“…The ubiquity of membrane substrate for lipoxygenases can explain the persistence of singlet oxygen production detected here even after cell death. Developmentally programmed singlet oxygen production that correlated with SOSG fluorescence was traced to lipoxygenase activity in grapevine berry skin ripening (Pilati et al, 2014). Indeed, in the case of ripening grape berry, over 10% of the side chains were oxidized to membrane bound 13-peroxy galactolipids.…”

Photo-Oxidative Stress during Leaf, Flower and Fruit Development

“…H 2 O 2 levels increase in the berry skin of grape (Vitis vinifera 'Pinot Noir') at the onset of ripening (veraison), when the most crucial events during berry ripening occur, including the change in color of the skin (Pilati et al, 2014). Studies on tomatoes also have revealed an elevation in H 2 O 2 levels during changes in color of the skin (Jimenez et al, 2002;Kumar et al, 2016).…”

Formação e maturação da uva e os efeitos sobre os vinhos: Revisão

“…Porém, interações diretas entre estas vias ainda carecem de evidências, impossibilitando ainda uma melhor compreensão da atuação dos hormônios durante o desenvolvimento das bagas (Fortes et al, 2015). Outros mecanismos de controle de desenvolvimento também podem estar envolvidos como sinalizadores do amadurecimento, como o acúmulo de algumas espécies reativas de oxigênio (ROS) em concentrações e compartimentos celulares específicos (Pilati et al, 2014 …”