Abstract
C(3) photosynthesis can be complemented with a C(4) carbon concentrating mechanism (CCM) to minimize photorespiratory losses. C(4) photosynthesis is often more efficient than C(3) under steady-state conditions. However, the C(4) CCM depends on inter-cellular metabolite concentration gradients, which must increase following increases in light intensity and could decrease rates of C(4) photosynthesis under fluctuating light. Additionally, incomplete flux through photorespiration could prove beneficial to C(4) assimilation during light induction of the CCM. Here, we compare metabolic profiles in the closely related C(3) Flaveria robusta and C(4) Flaveria bidentis during a light transient from low to high light to determine if these non-steady state accumulation patterns provide insight to the induction of the metabolite gradients needed to drive C4 intermediate transport and if there is incomplete cycling of photorespiratory intermediates. In these C(3) and C(4) species, metabolite steady-state pool sizes suggest that C(4) transport acids maintain concentration gradients across the bundle sheath and mesophyll cell types under these light fluctuations. However, there was incomplete flux through photorespiration in the C(4) F. bidentis, which could reduce photorespiratory CO(2) loss via glycine decarboxylation and help maintain higher rates of assimilation during following induction periods.