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- Author or Editor: Darlene M. Cowart x
-Lipid peroxidation has been proposed as an important factor in chilling injury of susceptible fruits and vegetables. The effect of in vitro peroxidative challenge on H+ATPase activity in intact plasma membrane vesicles and solubilized enzyme was determined by incubation with (1) deionized water (control), (2) Fe3+-ascorbate, and (3) lipoxygenase (LOX) + phospholipase A2(PLA2) for 0, 30, and 60 min. Enzyme activity increased throughout the incubation period with no accumulation of thiobarbituric acid-reactive substances (TBA-RS) in the control, but vesicles challenged by the peroxidative systems showed significant increases in TBA-RS and decreases in membrane-bound H+ATPase activity. Greater losses in H+ATPase activity were observed in solubilized enzyme than in intact vesicles. The results indicate that loss of H+ATPase activity due to chemical modification of the protein rather than changes in membrane fluidity and suggest that modification is away from the active site.
Temperature stress resulting in membrane-associated disorders has been linked to lipid peroxidation through free radicals, but the susceptibility of membrane lipids in microsomal fractions to chilling stress has not been clearly delineated. Microsomal membranes isolated from bell peppers were subjected to five oxidative conditions (iron-ascorbate, xanthine oxidase, cumene hydroperoxide, and lipoxygenase (LOX) with and without PLA2) at three temperatures (6, 21, and 37C) and measured at 30 min. intervals during a 2 hour incubation to determine the effect of temperature on peroxidation as measured by TBA-RS. During the first 30 min., the rate of peroxidation was greater at 6C than at 21C or 37C in four of the five systems tested. Preincubation with PLA2 followed by addition of LOX produced the highest amount of peroxidative products when compared with all other systems demonstrating the importance of free fatty acids in lipoxygenase-catalyzed peroxidation. The results demonstrate an increased susceptibility of microsomal membranes isolated from a chilling-susceptible fruit to peroxidative challenge at chilling temperatures than at higher temperatures.