Induction of water-soaking deterioration in watermelon fruit by ethylene.

Watermelon (Citrullus lanatus Thunb. Mansfeld) fruit were held in 50 microL/L of ethylene at 20 degrees C following 18 h application with 5 microL/L of 1-methylcyclopropene (1-MCP) to investigate the involvement of ethylene in the regulation of water-soaking. The early responses of watermelon fruit to ethylene were increased electrolyte leakage and free juice content, accompanying softening and water-soaking of placental tissue. Early evidence of water-soaking appeared in the inner pericarp near the calyx end after 2 d of ethylene treatment, and was accompanied by increased activities of ACC synthase (ACS) and ACC oxidase (ACO). While the application of 1-MCP showed no significant effects by itself, it completely suppressed water-soaking induced by exogenous ethylene. Water-soaking also developed in fruit stored over 10 d in air, and the affected fruit exhibited climacteric respiration and ethylene production peaks after 2 d of storage. These results, along with the observed prophylactic effects of 1-MCP, suggest that water-soaking in watermelon fruit is an ethylene-induced senescence phenomenon.