Postharvest Gibberellin and Heat Treatment Effects on Polyamines, Abscisic Acid and Firmness in Lemons

Lemons at two ripening stages were vacuum‐infiltrated with 100 ppm of gibberellin A 3 (GA 3 ) or heat‐treated at 45°C, and then stored at 15°C for 3 wk. Both treatments increased fruit firmness either in stage 1 or in stage 2. Also, the levels of free putrescine and spermidine in the skin were higher in treated lemons than in controls but spermine concentration did not show significant differences, in fruits of either stage. GA 3 treatment was the most effective in retarding the color change during storage, especially in stage 1 fruits, which was related to the lowest levels of abscisic acid found.