Abstract
The chloroplastic NAD(P)H:plastoquinone oxidoreductase complex (NDH) is homologue of respiratory complex I. Since NDH genes are encoded in plastid and possibly nucleus genome, we disrupted tobacco NDH genes in plastid. Their disruptants showed that NDH participates in cyclic electron flow around photosystem I and adjust ATP/NADPH ratio in chloroplast.
To examine the physiological function of NDH, we investigated the NDH activity among different plant species using 152 plants on the basis of chlorophyll fluorescence analysis. C4 plants tended to show high NDH activity, possibly reflecting the high ATP/NADPH ratio. Interestingly, the highest activity was shown in NAD-ME type plants in three types of C4 photosynthesis. Further comparison of NADP-ME type with NAD-ME type plants, suggested that the differences of energy requirement between mesophyll and bundle sheath cell is responsible for the difference between two types.
