Fe-chelatase (FeCh, EC 4.99.1.1) inserts Fe(2+) into
protoporphyrin IX (Proto IX) to form
heme, which influences the flux through the
tetrapyrrole biosynthetic pathway as well as fundamental cellular processes. In transgenic rice (Oryza sativa), the ectopic expression of Bradyrhizobium japonicum FeCh
protein in cytosol results in a substantial increase of FeCh activity compared to wild-type (WT) rice and an increasing level of
heme. Interestingly, the transgenic rice plants showed resistance to oxidative stress caused not only by the peroxidizing
herbicide acifluorfen (AF) as indicated by a reduced formation of leaf
necrosis, a lower conductivity, lower
malondialdehyde and H2O2 contents as well as sustained Fv/Fm compared to WT plants, but also by
norflurazon,
paraquat,
salt, and
polyethylene glycol. Moreover, the transgenic plants responded to AF treatment with markedly increasing FeCh activity. The accompanying increases in
heme content and
heme oxygenase activity demonstrate that increased
heme metabolism attenuates effects of oxidative stress caused by accumulating
porphyrins. These findings suggest that increases in
heme levels and
porphyrin scavenging capacity support a detoxification mechanism serving against
porphyrin-induced oxidative stress. This study also implicates
heme as possibly being a positive signal in plant stress responses.