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Robert L. Shewfelt and Albert C. Purvis

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Robert L. Shewfelt and Albert C. Purvis

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Darlene M. Cowart and Robert L. Shewfelt

-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.

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Brenda A. del Rosario, Robert L. Shewfelt, and Albert C. Purvis

Evidence is accumulating that mitochondria possess defense mechanisms which effectively protect component membranes from the attack by active oxygen species which are produced continuously within the organelle. This study compared the stability of microsomal (from bell pepper fruit pericarp and cauliflower florets) and mitochondrial (from bell pepper fruit pericarp) membranes against peroxidative challenge systems (cumene hydroperoxide and iron-ascorbate). Protein concentration, (i-tocopherol levels, and total lipids were observed to decrease for both membranes when challenged. The onset of peroxidation was observed to be earlier and at higher levels in microsomes than in mitochondria. These results demonstrate the increased stability of mitochondrial membrane fractions to peroxidative challenge and suggest that the level of antioxidants and not fatty acid composition is the critical factor in resistance to oxidative stress in plant mitochondria.

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Jeffrey K. Brecht, Robert L. Shewfelt, Joseph C. Garner, and E.W. Tollner

Cross-sectional X-ray-computed tomography (X-ray CT) images through the equator of tomato fruit (Lycopersicon esculentum Mill., cv. Sunny) ranging in maturity from immature (Ml) to advanced mature green (M4) revealed localized differences in X-ray absorption related to the formation of locular gel during maturation of the fruit. While maturity stage was poorly correlated with average X-ray absorbance and standard deviation or with average fruit density and water content, significant relationships' existed between maturity stage “and the number of image pixels with absorbance values >10 (Ml vs. M2 vs. M3) or 20 (M3 vs. M4) Hounsfield units. Using discriminant analysis, a relationship was developed that correctly identified the maturity class of 77% of the fruit and placed 96% of the tomatoes into the correct or an adjacent class.