Understanding of interlinked metabolism of guard cell (GC) and mesophyll cell (MC) and their 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 C ₃ MC, GC and Crassulacean Acid Metabolism (CAM) MC, detailed analysis of combined metabolism of GC and MC and their quantitative estimations in both C ₃ and CAM are still awaiting. We integrate stomatal opening, gaseous exchange and GC-MC metabolism in our constraint-based six-phase diel combined metabolic model and simulate this model to predict the temporal differential flux distributions 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 C ₄-like enzymes such as PEPC, MDH, ME etc., in GC compared to MC in C ₃, the possible storage patterns of the osmolytes like K ⁺, malate ^2-, sucrose etc., in CAM GC. Results also show temporally different patterns of starch synthesis and accumulation, ATP production and utilization in GC and MC of C ₃ and CAM. It is a significant step towards understanding and quantitative estimation of the whole leaf tissue metabolism linking gaseous exchange with environment.