A 3-D multiscale model for gas exchange in fruit

31 Respiration of bulky plant organs such as roots, tubers, stems, seeds and fruit depends very much 32 on the O 2 availability and often follows a Michaelis-Menten-like response . A multiscale model is 33 presented to calculate gas exchange in plants using the microscale geometry of the tissue, or vice 34 versa, local concentrations in the cells from macroscopic gas concentration profiles. This 35 approach provides a computationally feasible and accurate analysis of the cell metabolism in any 36 plant organ during hypoxia and anoxia. The predicted O 2 and CO 2 partial pressure profiles 37 compared very well to experimental data, thereby validating the multiscale model. The important 38 microscale geometrical features are the shape, size and three-dimensional connectivity of cells 39 and air spaces. It was demonstrated that the gas exchange properties of the cell wall and cell 40 membrane have little effect on the cellular gas exchange of apple parenchyma tissue. The analysis 41 clearly confirmed that cells are an additional route for CO 2 transport, while for O 2 the 42 intercellular spaces are the main diffusion route. The simulation results also showed that the local 43 gas concentration gradients were steeper in the cells than in the surrounding airspaces. Therefore, 44 to analyse the cellular metabolism under hypoxic and anoxic conditions, the microscale model is 45 required to calculate the correct intracellular concentrations. Understanding oxygen response of 46 plants and plant organs thus not only requires knowledge of external conditions, dimensions, gas 47 exchange properties of the tissues and cellular respiration kinetics, but also of microstructure. 48