Two types of functionally distinct NAD(P)H dehydrogenases in Synechocystissp 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 muta nts were constructed by disrupting highly homologous ndhD genes in pairs. O nly the Delta ndhD1/Delta ndhD2 (Delta ndhD1/D2) mutant was unable to grow under photoheterotrophic conditions and exhibited low respiration rate, alt hough the mutant grew normally under photoautotrophic conditions in air. Th e Delta ndhD3/Delta ndhD4 (Delta ndhD3/D4) mutant grew very slowly in air a nd did not take up CO2. The results demonstrated the presence of two types of functionally distinct NAD(P)H dehydrogenases in Synechocystis PCC6803 ce lls. 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 capaci ty of Q(A) (tightly bound plastoquinone) reduction by plastoquinone pool, a s measured by the fluorescence increase in darkness upon addition of KCN, w as much less in Delta ndhD1/D2 and M55 than in Delta ndhD3/D4 and Delta ndh D5/D6. We conclude that electrons from NADPH are transferred to the plastoq uinone pool mainly by the NdhD1 . NdhD2 type of NAD(P)H dehydrogenases.