EFFECT OF HIGH CO2 LEVEL ON THE TITERS OF GAMMA-AMINOBUTYRIC-ACID, TOTAL POLYAMINES AND SOME PATHOGENESIS-RELATED PROTEINS IN CHERIMOYA FRUIT STORED AT LOW-TEMPERATURE

In this study the effect of treatment with 20% CO2 plus 20% O-2 for 3 d on gamma-aminobutyric acid (GABA) was analysed and total polyamine t itres and the production of some pathogenesis-related proteins (PR-pro teins) in cherimoya (Annona cherimola Mill,) fruit stored at low tempe rature. In immunoassays with anti-PR-Q and PR-2 protein sera, high CO2 levels were found to provoke the co-ordinated accumulation of a chiti nase-like protein and 1,3-beta-glucanase. Chitinase activity was highe r in treated than in untreated fruit. At the end of CO2 treatment, tot al polyamine and gamma-aminobutyric acid content and uptake of O-2 wer e observed to be higher in treated compared to untreated fruit, but th e accumulation of these compounds decreased when the fruit was transfe rred to air. Since this treatment effectively retains the fruit qualit y (Escribano ef al,, 1997), high CO2 levels may have a direct effect o n the activation of the above-mentioned specific responses that enable s cherimoya fruit to overcome chilling temperature. The relationship b etween the activation of the defence system and the capacity to regula te cytoplasmic pH in CO2-treated fruits was also addressed.