|Portis Jr, Archie|
Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2005
Publication Date: 5/1/2005
Citation: Zhu, X., Portis Jr, A.R., Ort, D.R., Long, S.P. 2005. Can Manipulation of The C2 Pathway Enzyme Activities Increase Photosynthetic Rate? An <i> In Silico </i> Analysis [abstract]. Plant Biology Annual Meeting. Paper No. 266. Available: http://abstracts.aspb.org/pb2005/public/P43/7516.html. Interpretive Summary:
Technical Abstract: Previous efforts to increase crop productivity have focused on modifying ribulose 1,5-bisphosphaste carboxylase/oxygenase (Rubisco) to improve its efficiency. This has been proved to be intractable. Can changes in enzymes of the photosyntheitc carbon oxygenation pathway (PCOP) lead to increased leaf photosynthetic CO<sub>2</sub> uptake (<i>A</i>) and correspondingly crop productivity? To address this question, a model of photosynthetic carbon metablolism was developed which includes the complete Calvin Cycle, PCOP pathway, starch synthesis and triose phosphate export. The whole model is simulated using a system of linked ordinary differential equations with each representing the rate of concentration change of a single metabolite. This system was numerically integrated with the <i>ode15s</i> algorithnm in MATLAB. Initial concentrations of metabolites and enzyme activities were collected from literature. The model is stable upon changes in O<sub>2</sub> concentration, achieves realistic photosynthetic rates and simulates the expected patterns of responses of metabolite concentrations to altered activites of enzymes in PCOP. Simulations using the model showed that the enzymes in PCOP exert negligible control over <i>A</i> and therefore engineering more efficient enzymes in PCOP will not lead to a substantial increase in <i>A</i>. Furthermore, simulations revealed that enzymes in PCOP are in excess of what is needed to maitain the flux of PCOP under current atmospheric conditions. This excess of enzyme activities may be an insurance against environmental conditions that promote photorespiration that could otherwise result in carbon accumulating within PCOP and slowing regeneration of ribulose 1,5-bisphosphate.