Two types of functionally distinct NAD(P)H dehydrogenases in Synechoeystis sp. strain PCC6803

The ndhD gene encodes a membrane protein component of NAD(P)H dehydrogenase. The genome of Synechocystis sp. PCC6803 contains 6 ndhD genes. Three mutants were constructed by disrupting highly homologous ndhD genes in pairs. Only the ΔndhD1/ΔndhD2 (ΔndhD1/D2) mutant was unable to grow under photoheterotrophic conditions and exhibited low respiration rate, although the mutant grew normally under photoautotrophic conditions in air. The ΔndhD3/ΔndhD4 (ΔndhD3/D4) mutant grew very slowly in air and did not take up CO₂. The results demonstrated the presence of two types of functionally distinct NAD(P)H dehydrogenases in Synechocystis PCC6803 cells. TheΔndhD5/ΔndhD6 (ΔndhD5/D6) mutant grew like the wild-type strain. Under far-red light (>710 nm), the level of P700⁺ was high in ΔndhD1/D2 and M55 (ndhB-less mutant) at low intensities. The capacity of Q(A) (tightly bound plastoquinone) reduction by plastoquinone pool, as measured by the fluorescence increase in darkrness upon addition of KCN, was much less in ΔndhD1/D2 and M55 than in ΔndhD3/D4 and ΔndhD5/D6. We conclude that electrons from NADPH are transferred to the plastoquinone pool mainly by the NdhD1·NdhD2 type of NAD(P)H dehydrogenases.