Changes in total proteins related to chilling injury of nectarine

Low-temperature disorders in nectarines (Prunus persica) can be delayed by storage in atmospheres containing elevated CO₂; however, this benefit is limited to a few cultivars. The storage of produce at low temperatures itself leads to changes in protein synthesis; therefore, this study examined the applicability of 2-D electrophoresis to assess differences in protein production in cultivars of nectarine that either do ('Arctic Snow') or do not ('Red Gold') respond to elevated CO₂ levels during storage. In addition, the effect of harvest maturity and their response to added ethylene was assessed. Fruit of the two cultivars were either ripened immediately after harvest at 20°C before protein extraction or stored in air, air + CO₂, air + ethylene or air + CO₂ + ethylene then ripened at 20 °C before protein extraction. 2-D PAGE showed that the expression of approximately 30 proteins varied among cultivars and treatments. Two proteins showed clear differences in expression in both cultivars between fruit ripened immediately after harvest and those that had been stored. A second set of differences in protein expression was found in fruit of 'Red Gold' only and involved 12 proteins whose expression was either reduced or increased by storage: these proteins did not vary in expression in 'Arctic Snow'. A third set of differences in protein expression was observed in 'Arctic Snow' only in atmospheres containing ethylene. Several proteins were down-regulated by ethylene and this down-regulation was negated by the addition of CO₂ to the storage atmosphere. Thus, differences in protein expression can be found between cultivars of nectarines that do or do not respond to the addition of CO₂ to the storage atmosphere and in the cultivar that is known to respond to CO₂, this gas was able to antagonise protein changes mediated by ethylene.