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Theo Solomos, Bruce Whitaker and Changwen Lu

Exposure of `Gala' and `Granny Smith' apples to pure oxygen resulted in inhibition of the rise in ethylene evolution and development of visual symptoms of extensive injury akin to that which occurs under the condition of very low oxygen. Analytical data showed that fruit kept under pure O2 accumulated ethanol. In `Granny Smith' apples, the accumulation of ethanol was associated with increases in pyruvate and citrate concentration, and a sharp decrease in isocitrate concentration. These data indicate that an atmosphere of pure O2 inhibited cis-aconitase activity in the fruit, thereby disrupting the TCA cycle. This, in turn, caused an increase in production of ethanol. The possible mechanism by which pure O2 inhibits cis-aconitase will be discussed.

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Peter M.A. Toivonen, Jared Stoochnoff, Kevin Usher, Changwen Lu, Paul A. Wiersma and Chunhua Zhou

The market value of the apple (Malus ×domestica Borkh.) cultivar Ambrosia is closely linked to the characteristic blush on the skin surface. For ‘Ambrosia’ orchards that produce consistently low levels of surface blush, the implementation of reflective rowcovering has improved surface coloration, but the reflected wavebands responsible for this enhanced color production have not been confirmed. This study consisted of two separate experiments: one conducted in the field to confirm reflective rowcovering efficacy and the other in a controlled environment cabinet to determine which waveband was enhancing red blush production. The red blush production in orchards with and without reflective rowcovering was then directly compared with the red blush produced on the surface of apples that were poorly colored at harvest and then exposed to visible, fluorescent, ultraviolet A (UVA), or ultraviolet B (UVB) light sources within the controlled environment chamber. Consequent analysis of the red blush color within the Commission Internationale de l’Eclairage a* and b* color space was conducted to evaluate the quality of the red blush pigment under each treatment in the field and the controlled environment chamber. The analysis revealed that the red blush that developed on apples from the reflective rowcover treatment most closely matched the red blush that developed in response to UVB exposure in the controlled environment cabinet. Further analysis of gene expression and anthocyanin contents in the ‘Ambrosia’ apples support the hypothesis that the primary driver for the characteristic red blush development, when reflective rowcovers are used, is increased exposure to UVB light.