Structural sensitivity analysis of the plant metabolism system.
(a) Metabolic pathway for sucrose synthesis from fructose in early plant development. Molecules that are supposed to be abundant in the cytoplasm, such as phosphate groups, are not described. The change in the concentration of each metabolite when the PPi-degrading enzyme was knocked down was determined by structural sensitivity analysis and shown by the color of each molecule [18]. Red: increase, blue: decrease, gray: no change. The dotted arrow indicates an example of modification of the newly added reaction. Adding this reaction does not change the qualitative response to PPi-degrading enzyme perturbations. (b) The effect on the sucrose response when various reactions are added to the plant metabolic pathway given in Figure 4a. Green: The addition of these reactions does not alter the sucrose concentration response to the disruption of PPi-degrading enzyme. An arrow with arrowheads at both ends means that the result does not depend on the reaction direction or whether it is reversible reaction or not. Blue: When any of these four reactions is added, the sucrose concentration decreases by the destruction of PPi-degrading enzyme. Red: When this reaction is added, the sucrose concentration rather increases with the destruction of PPi degrading enzyme.