Effects of the Combined Application of 1-MCP + Low O2 on Ripening of Apple Fruits

For the past two years we have been studying the effects of the combined application of 2 ppm 1-MCP + 1.5% O-2 on apple (Malus (x)domestica Borkh.) fruit ripening at 1 degrees C and 6.5 degrees C. In fruits stored at 6.5 degrees C, the onset of the C2H4 climacteric occurred 10, 55, and 95 days. For the controls, 1.5% O-2, and 2 ppm 1-MCP, respectively, whereas in fruits treated with 1-MCP and kept under 1.5% O-2, the onset of the ethylene climacteric did not occur for 200 d, the duration of the experiment. The retardation of the climacteric rise was attended by a complete suppression of the ACC synthase 1 (ACS1) and ethylene response sensor 1 (ERS1) genes. The promoters of both genes contain C2H4-responsive elements. Thus, once ACS1 is induced, it can sustain the auto-catalytic increase in C2H4 evolution. The dependence of mRNA accumulation in both genes on C2H4 was also demonstrated by treating climacteric fruits with 1.5% O-2, 2 ppm 1-MCP, and 2 ppm 1-MCP + low O-2. The degree of decrease in C2H4 evolution differed with the treatments, being stronger in the combined 1-MCP + low O-2 treatment. This was reflected in the amounts of the accumulated transcripts. At present the developmental changes that precede the induction of ACS1 are unknown. At 1 degrees C, the climacteric rise in C2H4 evolution was also retarded by the combined treatment for 250 days. However, when the fruits were transferred after 250 d to 18 degrees C, ripening occurred normally, as could be judged by the rise in C2H4 evolution, softening and induction of the expression of C2H4-dependent genes, e.g., polygalacturonase. The data thus show that apples treated with 1-MCP + 1.5% O-2 can be successfully stored at relatively high temperatures. The expression of the alcohol dehydrogenase (ADH) gene that is induced by 1.5% O-2 is not affected by 1-MCP.