Acute suppression of ripening and negation of a respiratory climacteric in midclimacteric tomato following short-term application of 1-MCP Under hypobaric hypoxia

Our previous studies have shown that midclimacteric tomato exposed to hypobaric hypoxia for 6 h show increased sensitivity to subsequent treatment with 1-methylcyclopropene (1-MCP), exhibiting an additional 2- to 3-d delay in the progression of ripening compared with fruit treated with 1-MCP without prior exposure to hypobaric hypoxia. In the present study, midclimacteric tomato were subjected to brief (1 h) combinatory treatment with 1-MCP (500 nL L^-1, 20.8 µmol m^-3) under hypobaric hypoxia (10 kPa, 2.1 kPa O₂) or normal atmospheric conditions. Treatment with 1-MCP for 1 h under atmospheric conditions had negligible effects on softening and timing and magnitude of peak ethylene production, and moderate effects on respiration and lycopene and PG accumulation compared with fruit treated under hypobaric hypoxia or atmospheric conditions without 1-MCP. By sharp contrast, fruit exposed to 1-MCP under hypobaric hypoxia for 1 h showed acute, long-term disturbance of ripening. Mid-climacteric trajectories for hue angle and firmness declines were arrested for 10 days and peak ethylene production delayed for 12 d compared with those for all other treatments. Fruit treated with 1-MCP/hypobaric hypoxia required nearly 10 to 12 d before lycopene, PG levels and hue angle reached values similar to those for the other treatments. 1-MCP/hypobaric hypoxia fruit eventually ripened as defined by development of full red-ripe color (hue angle ≤45^o); however, a delayed yet well-defined ethylene climacteric was not accompanied by a respiratory rise. Ingress and accumulation of internal gaseous 1-MCP were significantly enhanced under hypobaric conditions. Internal free 1-MCP in fruit exposed to 20 µL L^-1 1-MCP (831 µmol m^-3) under hypobaric hypoxia for 2 or 10 min  averaged 7.5 ± 0.5 and 8.7 ± 1.4 µL L^-1, respectively, compared with 0.8 ± 0.3 and 3.9 ± 0.7 µL L^-1 in fruit treated under atmospheric conditions. After 1-h exposure, internal 1-MCP averaged 10.8 ± 2.2 µL L^-1 under hypobaric hypoxia compared with 5.3 ± 1.4 µL L^-1 under atmospheric conditions. The hyper-response of mid-climacteric tomato to brief treatment with 1-MCP under hypobaric hypoxia is reminiscent of that of mature-green fruit treated with supraoptimal levels of 1-MCP under atmospheric conditions. The results indicate that tomato fruit at advanced ripening stage remain strongly ethylene responsive and also suggest that an ethylene-associated respiratory climacteric is not an obligatory requirement for completion of ripening.