A proteomics approach to study core breakdown disorder in stored 'Conference' pears

Consumers demand fresh fruits and vegetables throughout the whole year. Horticultural crops are very perishable. Thus, strategies to control and extend their storage life are mandatory. Commonly, controlled atmospher e (CA) conditions are applied to retard respiration, ethylene production , ripening and senescence. The temperature is reduced and the air atmosp here composition is modified by reducing the oxygen content and by incre asing the carbon dioxide composition. This CA strategy is commodity spec ific; inappropriate conditions may cause physiological disorders. When improperly stored, pears of the variety Conference are very susce ptible to develop core breakdown which is characterized by flesh brownin g and cavities. This disorder is supposed to be the consequence of an im paired respiration triggering a cascade of metabolic events. Previous st udies have mainly focused on understanding this disorder by gas transpor t and antioxidant system studies, thereby ignoring many biochemical aspe cts. In this dissertation, core breakdown has been studied in a broader perspective by using a holistic proteomics approach. The main objective of this work was to understand the physiological background of core brea kdown disorder by using proteomics tools. To start the study of core breakdown in Conference pears it was necess ary to fine tune protein extraction, two-dimensional electrophoresis (2- DE) and data analysis protocols. Subsequently a complete 2-DE study aimi ng at characterizing tissue either or not affected by core breakdown rev ealed impairment of respiration, protein synthesis and antioxidant and e thylene biosynthesis pathways. Cell death was also evident in brown tiss ue. One common problem associated to gel based proteomics data is the presen ce of missing values. Missing values present a challenge not only in ter ms of how to deal with them but also in the interpretation of the data. It was shown that missing values in gel-based proteomics data can be tre ated satisfactorily by means of the Bayesian Principal Component imputat ion method. The effect of long term exposure to different CA conditions on the metab olism of stored pears was studied. Different combinations of oxygen and carbon dioxide concentrations induced differences at the level of respir ation, protein synthesis, antioxidant and ethylene pathways. Finally, the short term effect of extreme CA conditions on the metabolis m of pear slices was studied. Results partially confirmed the findings f or the long term exposure of pears. Only subtle changes in respiration p athways were observed except for the pentose phosphate pathway which was activated under anoxia. Similarly to long term exposure of intact pears to anoxia, allergens and other defense related enzymes were regulated. No significant changes in the glutathione-ascorbate pathway were found l eading us to suspect that browning development appears as soon as this p athway collapses. This proteomic approach allowed the selection of poten tial candidate markers for the early-stage detection and tracking of cor e breakdown during storage of pears.status: publishe