Electrolyte Leakage, Firmness, and Scanning Electron Microscopic Studies of Watermelon Fruit Treated with Ethylene

Abstract

Studies were conducted to investigate the influence of 50 μl·liter −1 ethylene on the cell wall, polygalacturonase (PG) activity, and electrolyte leakage of harvested watermelon [ Citrullus lanatus (thunb) Matsum and Nakai] fruit. Electrolyte leakage was significantly increased in tissues from ethylene-treated fruit. The highest leakage occurred in distilled water, although the net effect of ethylene was less dramatic due to high leakage from control fruit. Leakage was greatly reduced but the ethylene effect more apparent compared to the control when tissues were incubated in an isotonic medium of mannitol or in isotonic medium containing CaCl 2 . Polygalacturonase activity increased markedly in ethylene-treated fruit, showing a > 10-fold rise during the first 6 days of treatment. Little change in PG activity occurred in melons stored in air, even in fruit stored for as long as 120 days. Cell walls of fruit exposed to ethylene exhibited acute ultrastructural damage. The decline in placental tissue firmness and the development of watersoaking symptoms observed by the third day of 50 μl·liter −1 ethylene treatment were apparently due, in part, to the PG-mediated cell wall breakdown resulting in cell rupture. Additionally, ethylene appeared to enhance membrane permeability.