Relationship between the levels of ammonia and co-ordination of phenylalanine ammonia-lyase and phosphoenolpyruvate carboxylase in Annona cherimola stored under different conditions
2002
Maldonado, R. | Escribano, M.I. | Merodio, C.
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 CO2-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 CO2 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 CO2-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 phosphoenolpyruvate 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.
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