Ge. Lester et Bd. Whitaker, GAMMA-RAY-INDUCED CHANGES IN HYPODERMAL MESOCARP TISSUE-PLASMA MEMBRANE OF PRE-STORAGE AND POST-STORAGE MUSKMELON, Physiologia Plantarum, 98(2), 1996, pp. 265-270
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
.