Regulation of defense and cryoprotective proteins by high levels of CO2 in Annona fruit stored at chilling temperature

This study focuses on how the length of exposure to chilling temperature and atmosphere storage conditions regulate the hydrolytic activity and expression of chitinase (PR-Q) and 1,3-β-glucanase (PR-2) isoenzymes in cherimoyas (Annona cherimola Mill.). Storage at 6 °C modified the expression of constitutive isoenzymes and induced the appearance of novel acidic chitinases, AChi26 and AChi24, at the onset of the storage period, and of a basic chitinase, BChi33, after prolonged storage. The induction of this basic isoenzyme was concomitant with the accumulation of basic constitutive 1,3-β-glucanases. These low-temperature-induced chitinases modified the growth inhibition in vitro of Botrytis cinerea. Short-term high CO2 treatment activated a coordinated response of acidic chitinases and 1,3-β-glucanases after prolonged storage at chilling temperature. Moreover, the high in vitro cryoprotective activity of CO2-treated protein extracts was associated with the induction of two low molecular mass isoenzymes, AGlu19 and BChi14. Thus, exposure to high concentrations of CO2 modified the response of fruit to low temperature, inducing the synthesis of cryoprotectant proteins such as specific pathogenesis-related isoenzymes that could be functionally associated with an increase in chilling tolerance in vivo.