Abstract
Respiration of bulky plant organs such as roots, tubers, stems, seeds, and fruit depends very much on oxygen (O2) availability and often follows a Michaelis-Menten-like response. A multiscale model is presented to calculate gas exchange in plants using the microscale geometry of the tissue, or vice versa, local concentrations in the cells from macroscopic gas concentration profiles. This approach provides a computationally feasible and accurate analysis of cell metabolism in any plant organ during hypoxia and anoxia. The predicted O2 and carbon dioxide (CO2) partial pressure profiles compared very well with experimental data, thereby validating the multiscale model. The important microscale geometrical features are the shape, size, and three-dimensional connectivity of cells and air spaces. It was demonstrated that the gas-exchange properties of the cell wall and cell membrane have little effect on the cellular gas exchange of apple (Malus×domestica) parenchyma tissue. The analysis clearly confirmed that cells are an additional route for CO2 transport, while for O2 the intercellular spaces are the main diffusion route. The simulation results also showed that the local gas concentration gradients were steeper in the cells than in the surrounding air spaces. Therefore, to analyze the cellular metabolism under hypoxic and anoxic conditions, the microscale model is required to calculate the correct intracellular concentrations. Understanding the O2 response of plants and plant organs thus not only requires knowledge of external conditions, dimensions, gas-exchange properties of the tissues, and cellular respiration kinetics but also of microstructure.
Highlights
Respiration of bulky plant organs such as roots, tubers, stems, seeds, and fruit depends very much on oxygen (O2) availability and often follows a Michaelis-Menten-like response
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, 2008, 2010). These models operate at the fruit scale and are based on Fick’s law, which assumes that the gas concentration gradient is the driving force for diffusion
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, 2008, 2010). Microstructural features such as pores, cell walls, membranes, and the cytoplasm are incorporated into a few apparent model parameters such as O2 and carbon dioxide (CO2) diffusivities that need to be determined experimentally (Lammertyn et al, 2003, Ho et al, 2008)
Summary
Respiration of bulky plant organs such as roots, tubers, stems, seeds, and fruit depends very much on oxygen (O2) availability and often follows a Michaelis-Menten-like response. 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 Microstructural features such as pores, cell walls, membranes, and the cytoplasm are incorporated into a few apparent model parameters such as O2 and carbon dioxide (CO2) diffusivities that need to be determined experimentally (Lammertyn et al, 2003, Ho et al, 2008). The model, predicted that considerable gas flow would occur through the cell walls, which is unlikely as their polysaccharide constituents would be completely hydrated in vivo and form a composite material with an even lower gas permeability than that of the cytosol This might be caused by the lack of connectivity of air spaces in the tissues when observed in two dimensions. Our understanding of gas exchange related to metabolic process and, would greatly benefit from a quantitative three-dimensional (3-D) analysis
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