Figure 8. (A) The light-minus-dark CO₂ assimilation rates in the PSI deleted ΔAB and the WT cells in the presence of glucose and in the WT cells in the absence of glucose.

Each experiment is represented by one open circle. The mean, the standard error, the p-value, and the number of independent experiments are indicated. The light-minus-dark CO₂ assimilation rates were calculated as the difference between the light and the dark CO₂ assimilation rates. Despite the high variation in the dark CO₂ assimilation rates, the light-minus-dark CO₂ assimilation rates are statistically highly significant, as evaluated by the paired t-test. (B) The working model for the O₂ evolving electron transport (thin solid-line arrows) and light-minus-dark CO₂ assimilation (thick dotted-line arrows) in the ΔPSI cells. The PQ pool serves as the “hub” of the electron flows, with the incoming electrons from H₂O (via PSII) as well as succinate (via succinate dehydrogenase) and/or NADPH (via type 1 NAD(P)H dehydrogenase) and with the outgoing electrons to O₂ (via cytochrome c oxidases) and CO₂ (via Rubisco-dependent mechanisms and/or a glycolysis-dependent mechanism). The glycolysis-dependent CO₂ assimilation may involve PEP carboxylase and/or malic enzyme, which generate malate and/or oxaloacetate via carboxylation reactions, followed by a succinate dehydrogenase working in reverse as a fumarate reductase to reduce fumarate to succinate. All abbreviations used in this model are defined as follows: PSII – photosystem II, PQ – the plastoquinol pool, SDH – succinate dehydrogenase, SDH* – succinate dehydrogenase working in reverse as fumerate reductase, NDH-1 – type 1 NAD(P)H dehydrogenase, Cyt c oxidase – cytochrome c oxidase, OAA – oxaloacetate, PEPC – PEP carboxylase, ME – malic enzyme.