Ethylene synthesis in mango fruit following heat treatment

Mango fruits (Mangifera indica L. cv. Nam Dokmai) were held for 3 days at 38 degrees C and then transferred to 20 degrees C. Fruits placed directly at 25 degrees C after harvest reached their peak ethylene production after 4 days, while the heated fruit took 9 days (6 days after the end of the heat treatment). The 1-aminocyclopropane-1-carboxylic acid (ACC) content paralleled that of ethylene production in unheated fruits, with highest content occurring on day 4. In heated fruit, ACC content continued to increase for 8 days following the heat treatment. The 1-aminocyclopropane-1-carboxylic acid synthase (ACS) activity in unheated fruit was also highest on day 4. In heated fruit the activity was undetectable following heat treatment, but recovered partially during the ripening period. Initial ethylene production from discs with peel was B-fold higher in unheated fruit than heated, although after 6 h of incubation the production from both was similar. Activity of 1-aminocyclopropane-carboxylic acid oxidase (ACO) in the discs also showed an 8-fold difference in initial activity in heated versus unheated discs with peel. This difference disappeared during incubation of the discs. In heated discs without peel, both ethylene and ACO activity remained lower than in discs with peel, and the differences between heated and unheated fruit discs were more pronounced. We conclude that the inhibition of ethylene production found during heat treatment is due to inhibition of both ACS and ACO. ACO recovers full activity following heat, while ACS activity recovers only partially, but enough to allow the heated fruit to achieve an ethylene peak. (C) 1999 Elsevier Science B.V. All rights reserved.