Lessons from combined metabolic model of mesophyll and guard cells

Understanding of overall metabolisms of guard cell (GC) and mesophyll cell (MC), their possible interactions and roles in stomatal movement will help in designing crop plants with higher water use efficiencies. Although, previous constraint based modelling and analyses correctly predicted some known metabolic patterns of isolated C3 MC, GC and Crassulacean Acid Metabolism (CAM) MC, quantitative estimations of combined metabolism of GC and MC and detailed analysis of GC metabolism in CAM are still awaiting. A six phase diel combined model of GC and MC is constructed integrating existing models of two different cell types with necessary modifications guided by known physiology. It is used to predict the similarities and dissimilarities of GC and MC metabolisms. In addition to previously predicted results, analysis of this new two-cell model successfully shows higher activities of some experimentally observed C4 like enzymes in GC than MC in C3, the possible storage patterns of the osmolytes like K+, malate2-, sucrose etc., in CAM GC. Results also show different patterns of starch synthesis and accumulation, ATP production and utilization in GC and MC of C3 and CAM. This combined model integrates stomatal opening, gaseous exchange and GC-MC metabolisms. It is a significant step towards understanding and quantitative estimation of the whole leaf tissue metabolism linking gaseous exchange with environment. Significance statementOur time-resolved combined metabolic model of guard and mesophyll cells integrates stomatal opening, gaseous exchange and cellular metabolisms in C3, CAM and partial CAM conditions; their analyses provide quantitative estimations of metabolic fluxes, ATP production and utilization, and different metabolic patterns of starch synthesis and accumulation of both the cells. It is a significant step towards understanding and quantitative estimation of the whole leaf tissue metabolism linking gaseous exchange with environment and phloem loading.