Regulation of ethylene and polyamine synthesis by elevated carbon dioxide in cherimoya fruit stored at ripening and chilling temperatures

In this study we focused on the effect of high CO2 level (20%) on ethylene and polyamine biosynthesis in cherimoya (Annona cherimola Mill.) fruits sto red at ripening (20 degrees C) and chilling (6 degrees C) temperatures. At ripening temperature, CO2 inhibited ethylene production, but 1-aminocyclopr opane-1-carboxylate (ACC) oxidase activity was similar to that in ripe cont rol fruits. CO2 treatment led to a decline in putrescine (Put) and a major accumulation of spermidine (Spd) and spermine (Spm) without any effect on a rginine decarboxylase (ADC) activity. These results confirm the preferentia l transformation of Put to Spd and Spm in CO2-treated fruits. At chilling t emperature, the increase in ACC oxidase activity was inhibited and the V-ma x of ADC increased. A combination of chilling temperature storage and high CO2 level led to suppression of basal ethylene production while ACC oxidase activity remained unchanged. In addition, fruits held at these conditions had higher polyamine titres than the untreated control. We propose that, in CO2-treated fruits, the absence of autocatalytic or basal ethylene product ion, depending on the temperature, may be due to deviation of the S-adenosy lmethionine (SAM) pool towards polyamine synthesis, primarily Spd and Spm.