GAMMA-RAY-INDUCED CHANGES IN HYPODERMAL MESOCARP TISSUE-PLASMA MEMBRANE OF PRE-STORAGE AND POST-STORAGE MUSKMELON

Gamma irradiation (1.0 kGy) of intact, newly harvested, mature muskmel on fruit (Cucumis melo L. var. reticulatus Naud.) appears to have an i mmediate deleterious effect, but also a long-term beneficial effect, o n the integrity and function of the plasma membrane (PM) of hypodermal mesocarp tissue. The initial consequences of gamma irradiation includ ed an increase in the free sterol:phospholipid ratio, resulting at lea st in part from deglycosylation of steryl glycosides, a decrease in th e spinasterol:7-stigmastenol ratio in each of the PM steryl lipids (fr ee sterols, steryl glycosides, and acylated steryl glycosides), and a decrease in H+-ATPase activity. Irradiation did not increase protein l oss, suggesting that the decrease in H+-ATPase activity resulted from either direct inactivation of the enzyme or altered PM ordering caused by the steryl lipid modifications. The long-term beneficial effects o f irradiation, observed following 10 days of commercial storage, inclu ded greater retention of total PM protein, a diminished decline in tot al PM phospholipids (PL) and in the PL:protein ratio, and maintenance of greater overall H+-ATPase activity (activity was the same as in con trols on a per mg protein basis, but there was > 30% more protein in t he PM of stored irradiated fruit). These results indicate that 1 kGy g amma irradiation administered prior to storage slowes the progression of two key parameters of senescence, PM protein loss and PL catabolism .