Y. Kimata-ariga et al., Differential electron flow around photosystem I by two C-4-photosynthetic-cell-specific ferredoxins, EMBO J, 19(19), 2000, pp. 5041-5050
In the C-4 plant maize (Zea mays L.), two ferredoxin isoproteins, Fd I and
Fd II, are expressed specifically in mesophyll and bundle-sheath cells, res
pectively. cDNAs for these ferredoxins were introduced separately into the
cyanobacterium Plectonema boryanum with a disrupted endogenous ferredoxin g
ene, yielding TM202 and KM2-9 strains expressing Fd I and Fd II. The growth
of TM202 was retarded under high light (130 mu mol/m(2)/s), whereas KM2-9
grew at a normal rate but exhibited a nitrogen-deficient phenotype, Measure
ment of photosynthetic O-2 evolution revealed that the reducing power was n
ot efficiently partitioned into nitrogen assimilation in KM2-9, After starv
ation of the cells in darkness, the P700 oxidation level under far-red illu
mination increased significantly in TM202, However, it remained low in KM2-
9, indicating an active cyclic electron flow. In accordance with this, the
cellular ratio of ATP/ADP increased and that of NADPH/NADP(+) decreased in
KM2-9 as compared with TM202. These results demonstrated that the two cell
type-specific ferredoxins differentially modulate electron flow around phot
osystem I.