XVI International Botanical Congess

In maize, two ferredoxin (Fd) isoproteins, FdI and FdII, are expressed in mesophyll and bundle-sheath cells, respectively. The cyanobacterium, whose Fd gene had been disrupted, was transformed separately with genes for the two maize Fds to study their in vivo functions. The cyanobacterial cells with maize FdI grew photosynthetically whereas little growth was observed under a heterotorophic condition. The cells with maize FdII grew under both conditions, but showed a leaky phenotype of nitrogen deficiency under photoautotrophic condition. By measuring electron flow around photosystemI, FdII was found to be a superior molecule to mediate the cyclic electron flow. These functional differences of the two Fds will be discussed from the viewpoint of the metabolic compartmentation of two photosynthetic cells.