Role of brassinosteroids, ethylene, abscisic acid, and indole-3-acetic acid in mango fruit ripening

Rapid ripening of mango fruit limits its distribution to distant markets. To better understand and perhaps manipulate this process, we investigated the role of plant hormones in modulating climacteric ripening of ‘Kensington Pride’ mango fruits. Changes in endogenous levels of brassinosteroids (BRs), abscisic acid (ABA), indole-3-acetic acid (IAA), and ethylene and the respiration rate, pulp firmness, and skin color were determined at 2-day intervals during an 8-day ripening period at ambient temperature (21 ± 1°C). We also investigated the effects of exogenously applied epibrassinolide (Epi-BL), (+)-cis, trans-abscisic acid (ABA), and an inhibitor of ABA biosynthesis, nordihydroguaiaretic acid (NDGA), on fruit-ripening parameters such as respiration, ethylene production, fruit softening, and color. Climacteric ethylene production and the respiration peak occurred on the fourth day of ripening. Castasterone and brassinolide were present in only trace amounts in fruit pulp throughout the ripening period. However, the exogenous application of Epi-BL (45 and 60 ng g−1 FW) advanced the onset of the climacteric peaks of ethylene production and respiration rate by 2 and 1 day, respectively, and accelerated fruit color development and softening during the fruit-ripening period. The endogenous level of ABA rose during the climacteric rise stage on the second day of ripening and peaked on the fourth day of ripening. Exogenous ABA promoted fruit color development and softening during ripening compared with the control and the trend was reversed in NDGA-treated fruit.The endogenous IAA level in the fruit pulp was higher during the preclimacteric minimum stage and declined during the climacteric and postclimacteric stages. We speculate that higher levels of endogenous IAA in fruit pulp during the preclimacteric stage and the accumulation of ABA prior to the climacteric stage might switch on ethylene production that triggers fruit ripening. Whilst exogenous Epi-BL promoted fruit ripening, endogenous measurements suggest that changes in BRs levels are unlikely to modulate mango fruit ripening

Role of 1-MCP in regulating 'Kensington Pride' mango fruit softening and ripening

Ripening of mango fruit is characterized by softening of flesh which limits its shelf life. 1-MCP is nontoxic gas that delays fruit softening and improves quality of several fruit. Therefore, the role of 1-MCP in regulating fruit softening and quality of ‘Kensington Pride’ mango was investigated. Physiological mature fruits treated with 1-MCP (1 mL L-1), ethylene (10 mL L-1) or 1-MCP + ethylene for 12 h at ambient condition (20 ± 1 C). Untreated (control) as well as treated fruits were allowed to ripe at ambient temperature (20 ± 1 C) for 10 days. Ethylene production, respiration rate and other fruit ripening parameters were determined periodically. Climacteric peaks of ethylene production and respiration rate were significantly supressed by 1-MCP application as compared to ethylene-treated and control fruit. Exogenous application of ethylene accelerated the development of fruit colour, fruit softening with increased activities of exo-PG, endo-PG and EGase enzymes in the pulp tissues. Whereas, activities of fruit softening enzymes were significantly delayed and/or suppressed in 1-MCP-treated fruit. 1-MCP-treated fruit showed improved rheological properties (i.e., firmness, springiness and stiffness), decreased level of citric acid, malic acid, succinic acid, total organic acids, total sugars and sucrose than other treatments. 1-MCP inhibited the activities of fruit softening enzymes which consequently delayed the ripening and ripening related changes in ‘Kensington Pride’ mango