A simple model of the Calvin cycle has only one physiologically feasible steady state under the same external conditions

Most current photosynthesis research implicitly assumes that the photosynthetic process occurs only at one steady state. However, since the rate of each reaction in photosynthesis depends nonlinearly on its substrates and products, in theory, photosynthesis can have multiple steady states under given external conditions (i.e., in a given environment). The number of steady states of photosynthesis under the same external conditions has not been studied previously. Using the root finding program POLSYS_PLP [S.M. Wise, A.J. Sommese, L.T. Watson, Algorithm 801: POLSYS PLP: A partitioned linear product homotopy code for solving polynomial systems of equations, ACM Trans. Math. Software 26 (2000) 176–2000], we study the number of potential steady states of a simplified model of the Calvin cycle. Our results show that the simplified model of the Calvin cycle can reside in multiple steady states, but that only one of these is physiologically feasible. We discuss the results from an evolutionary perspective.