Genotype effects on internal gas gradients in apple fruit

Abstract

A permeation-diffusion-reaction model was applied to study gas exchange of apple fruit (Kanzi, Jonagold, and Braeburn) as effected by morphology and respiratory metabolism. The gas exchange properties and respiration parameters of the fruit organ tissues were measured. The actual internal tissue geometry of the fruit was reconstructed from digital fruit images and the model was solved over this geometry using the finite element method. The model was validated based on measurements of internal gas concentrations and the gas flux of the fruit to its environment. Both measurements and an in silico study revealed that gradients of metabolic gases exist in apple fruit, depending on diffusion properties and respiration of the different cultivars. Macroscale simulation confirmed that Jonagold has large potential for controlled atmosphere (CA) storage while low diffusion properties of cortex tissue in Braeburn indicated a risk of storage disorder development. Kanzi had less O(2) anoxia at CA storage compared with Braeburn.

A Three-Dimensional Multiscale Model for Gas Exchange in Fruit

“…This would imply that both O 2 and CO 2 would be transported mostly through the intercellular space rather than through the cells and that the apparent diffusivity of CO 2 in tissue would also be smaller than that of O 2 . Yet, in previous research, we found the opposite (Ho et al, 2010). A possible explanation of this paradox would be that the larger solubility of CO 2 in water would mean that the cells would provide an additional transport route for CO 2 .…”

“…While microscale sensors are available for O 2 (Rolletschek et al, 2004;Ho et al, 2010), for various practical reasons it was not feasible to carry out local O 2 measurements at well-specified positions in the same samples that were used for 3-D synchrotron imaging. Also, such invasive measurements would most likely have an effect on the local gas transport itself.…”

“…As we earlier validated the macroscale model (Ho et al, 2010), we only needed to investigate whether the homogenization procedure would yield reliable results. We decided to follow a similar procedure as in the validation of the microscale model: rather than comparing local O 2 and CO 2 concentrations, we used the multiscale model to predict gas exchange of an entire fruit in a contained environment and compared this with actual measured values.…”

“…While these theories are not mutually exclusive, the diffusion hypothesis has been questioned by authors such as Geigenberger (2003) and Gupta et al (2009). Indeed, even in the center of bulky plant organs, the measured or simulated local O 2 concentration is often above the K m value of cytochrome c oxidase (van Dongen et al, 2003;Ho et al, 2010), indicating that O 2 would not be a rate-limiting substrate. Yet, the K m value of respiration of plant organs where the diffusion path is short is generally smaller than when it is long; this suggests that diffusion does play a role, as the diffusion rate is known to be inversely proportional to the diffusion path length (Nobel, 1991).…”

“…Continuum gas-exchange models have been developed to describe the gas exchange of fruit (Mannapperuma et al, 1991;Lammertyn et al, 2003;Ho et al, 2008Ho et al, , 2010. These models operate at the fruit scale (macroscale) and are based on Fick's law, which assumes that the gas concentration gradient is the driving force for diffusion.…”