Two types of functionally distinct NAD(P)H dehydrogenases in Synechocystis 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 Delta ndhD1/Delta ndhD2 (Delta ndhD1/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 Delta ndhD3/Delta ndhD4 (Delta ndhD3/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. The Delta ndhD5/Delta ndhD6 (Delta ndhD5/D6) mutant grew like the wild-type strain. Under far-red light (>710 nm), the level of P700(+) was high in Delta ndhD1/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 darkness upon addition of KCN, was much less in Delta ndhD1/D2 and M55 than in Delta ndhD3/D4 and Delta ndhD5/D6. We conclude that electrons from NADPH are transferred to the plastoquinone pool mainly by the NdhD1 . NdhD2 type of NAD(P)H dehydrogenases.