Expression and activities of ethylene biosynthesis enzymes during ripening of banana fruits and effect of 1-MCP treatment

The respiratory climacteric, ethylene evolution and activities and expression of ethylene biosynthesis enzymes show a characteristic pattern in banana during ethylene induced ripening. A unique biphasic respiratory climacteric with a 10 and 6 fold increment in respiration rates on days 2 and 6 respectively after ethylene treatment is preceded by ethylene evolution on days 1 and 4 with 8.3 and 6.93 fold increments respectively. This represents a unique feature of ripening in banana. While ACC synthase transcript accumulation matched the respiratory climacteric, the ACC synthase activity and ACC oxidase transcript accumulation showed a different pattern. The most significant observation was the effect of 1-MCP on ACC content and in vitro ACC oxidase activity. Though 1-MCP treated fruit did not show any respiratory climacteric or burst in ethylene production, it did not inhibit completely ACC accumulation and in vitro ACC oxidase activity. No transcript accumulation of ACC synthase was observed at any time in 1-MCP treated fruits, whereas a basal level of ACC oxidase transcript was detected throughout. It is concluded that ethylene induced ripening of banana is characteristically different from that of other climacteric fruits and that ethylene biosynthesis may have more than one mechanisms operating during ripening which are tightly controlled at various levels.