Metabolic Flux Balance Analysis with Plant Cell Compartmentallization

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Abstract

The aim of this research was the development of both a homogeneous and a heterogeneous metabolic model for Nicotiana tabacum cell suspension cultures using computational metabolic flux balance analysis (MFBA) approach as well as experimentation. Batch experiments were performed using Murashige-Skoog medium with 30 g/L initial sucrose under continuous light or dark conditions as well as cycled light with 16 h light/8 h dark photo-regime and photosynthetic growth with zero initial sucrose level. A kinetic model was developed for the growth, sucrose conversion to glucose and fructose and their simultaneous uptake. The maximum specific growth rates ranged 0.0014-0.0095 hâ€Â“1 in the batch experiments. The homogeneous MFBA model consisted of 180 reactions with 176 metabolites and was constructed in GAMS software. This was then integrated with the kinetic model using Excel for dynamic representation of the batch cultures. In the heterogeneous model, 81 reactions with 69 metabolites were used for the chloroplast, 50 reactions with 42 metabolites for the mitochondria and 121 reactions with 109 metabolites for the cytosol. When the maximised specific growth rates were compared with the experimental values, the homogeneous model results were 4-5 times and the heterogeneous values were 2-3 times higher than the experimental values. This indicated that the heterogeneous model gave a more realistic representation of the plant cell metabolism. The MFBA was also used in order to investigate the effect of inter-compartment metabolite fluxes on the cellâ€Â™s metabolism. Sensitivity analyses also indicated that fatty acid synthesis influenced the cell growth rate the most.

Keyword(s)

Compartmentalization; Heterogeneous; Homogeneous; MFBA; Metabolism; Model

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