A mathematical model of the tetrapyrrole biosynthesis pathway

John Ward, Michael Moulin, Francois Feugier & Saul Hazeldine

The tetrapyrrole biosynthesis pathway is a key part in chlorophyll production and is essential for plant survival. It involves numerous interacting compounds and, crucially, light. The understanding of the complex regulation processes involved has been the focus of extensive experimental research providing a large source of data. A particular set of data, concerned with the modelling described in this report, involves 24 hour timecourse data from seedlings exposed to constant light, following a three day period of growth from seed in darkness. This data includes the levels of key components such as chlorophyll, ATP, chlorophyllide and proto-chlorophyllide. Amongst the questions posed in the study-group were: i) Can the timecoursedata be predicted by a model? ii) Can it predict the differences in levels of various components in found mutant strains.

To address these questions, we present in this report a model consisting of a coupled system of nonlinear ODEs that describes a simplified version of the tetrapyrrole pathway based on mass action laws. Model simulations produced results that agree qualitatively well with most, but not all, of the available timecourse data obtained from wild-type and mutant strains. Nearly all of the model’s parameters are not known, so the values used in these simulations are based on estimates of the relative timescales of the reactions. An attempt at improving these estimates using data fitting techniques is also discussed.

Proceedings of the Mathematics in the Plant Sciences Study Group