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

Author
item Lester, Gene
item Whitaker, Bruce

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Use of 1kGy of gamma irradiation is allowed by the U.S. Food and Drug Administration as a treatment to delay maturation and extend shelf-life of edible fruits, which after commercial irradiation are for sale in 25 countries. The plasma membrane, under the peel, is the tissue which regulates muskmelon fruit shelf-life, and it is this same tissue which is the most sensitive to irradiation treatments. Irradiation using a commercial irradiator of muskmelon fruits with 1kGy of gamma-rays, then storage of irradiated and non-irradiated fruits for 10 days (under commercial storage conditions), slowed the progress fo fruit senescence. Two key components of melon senescence most affected by irradiation were reduced loss of enzyme activity responsible for cellular function and reduced loss of plasma membrane phospholipids responsible for membrane structure and function. With 1 kGy of gamma irradiation to muskmelon fruit is initially stressful, it is useful for slowing melon senescence and extending postharvest shelf-life.

Technical Abstract: Gamma-irradiation (1.0 kGy) of intact, newly-harvested, mature muskmelon fruit appears to have an immediate deleterious effect, but also a long-term beneficial effect, on the integrity and function of the plasma membrane (PM) of hypodermal mesocarp tissue. The initial consequences of gamma-irradiation included an increase in the free sterol to phospholipid ratio, resulting at least in part from deglycosylation of steryl glycosides, a decrease in the spinasterol:7-stigmastenol ratio in each of the PM steryl lipids (free sterols, steryl glycosides, and acylated steryl glycosides), and a decrease in H+-ATPase activity. Irradiation did not increase protein loss, 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 of irradiation, observed following 10 days of commercial storage, included greater retention of total PM protein, a diminished decline in total PM phospholipids (PL) and in the PL:protein ratio, and maintenance of greater overall H+-ATPase activity (activity was the same as in controls on a per mg protein basis, but there was > 30% more protein in the PM of stored irradiated fruit). These results indicate that 1 kGy gamma irradiation administered prior to storage slowed the progression of two key parameters of senescence, PM protein loss and PL catabolism.