Roberto Maldonado

Effect of high carbon dioxide concentration on PAL activity and phenolic contents in ripening cherimoya fruit

Abstract Cherimoya fruit ( Annona cherimola , Mill.) were kept at 20°C in air or in 20% CO 2 for 3 days and then transferred to air, to study the effect of a high CO 2 treatment on phenolic metabolism and ripening-related changes. Total polyphenol levels remained constant while a rapid decline in lignin content was observed in cherimoyas stored in air. However, a sharp increase in PAL activity up to the second day at 20°C was observed. The maximum ethylene production was observed 2 days later. At the end of the CO 2 treatment, ethylene production was inhibited and PAL activity was similar to that found in air-treated fruit. These data suggest that the increase in PAL activity at 20°C was not affected by high CO 2 and does not relate to ethylene. The CO 2 treatment inhibited flesh softening and maintained lignin at levels found in freshly harvested fruit. Exposure to 20% CO 2 also improved internal colour and increased the non-tannin polyphenol fraction, but prevented the decline in the tannin fraction otherwise observed upon ripening in air. We concluded that high CO 2 treatment at 20°C did not enhance PAL activity and lignin deposition although treated fruits retained more lignin after transfer to air. The possible involvement of PAL activity in the supply of important metabolic compounds for early events of ripening will be discussed.

Relationship between the levels of ammonia and co-ordination of phenylalanine ammonia-lyase and phosphoenolpyruvate carboxylase in Annona cherimola stored under different conditions

Abstract The levels of ammonia in cherimoya ( Annona cherimola , Mill) fruit changed in response to different storage conditions. The highest amount of ammonia was observed in fruit stored at a chilling temperature, and the lowest ammonia level was found in CO 2 -treated fruit at ambient temperature. These fruit presented the highest amount of nitrogen incorporated in polyamines, mainly in spermidine and spermine. Moreover, the fact that the trend in polyamines and ammonia content reverted when treated fruit were transferred to air would appear to confirm preferential reassimilation of ammonia under high CO 2 treatment. The increase in phenylalanine ammonia-lyase (PAL) activity observed in ripening fruit at ambient temperature was substantially reduced in fruit stored at a chilling temperature. Our results suggest that PAL activity increases in fruit with a high demand of ammonia for further assimilation processes, and that this activity decreases in fruit where ammonia reassimilation does not take place. Additionally, in the case of CO 2 -treated fruit, ammonia availability is apparently promoted by the deamination of amino acids, which is reflected in a significant decrease in free amino acid content without a concomitant rise in total protein levels. We observed that the patterns of change in phospho enol pyruvate carboxylase (PEPC) and PAL activities were opposite. Moreover, coordination between these enzymes was related to the metabolic endogenous levels of ammonia. The role of ammonia levels as a significant metabolic signal for controlling carbon and nitrogen metabolism is discussed.