PGR5 and NDH pathways in photosynthetic cyclic electron transfer respond differently to sublethal treatment with photosystem-interfering herbicides.

Effects of sublethal levels of the photosystem-interfering herbicides atrazine (Atr) and methyl viologen (MV) on photosynthetic electron transport were investigated in Arabidopsis thaliana mutants with defects in cyclic electron transfer (CET) activity. Analysis based on chlorophyll fluorescence parameters showed that pgr5 mutant (a defect in the PGR5 pathway) was more sensitive to both Atr and MV than wild type (Wt) and pnsB3 mutant (a defect in the NDH pathway). Real-time PCR (polymerase chain reaction) analysis of transcripts indicated that Wt plants showed marked increases in transcripts in the PRG5 and NDH pathways under treatment with either Atr or MV. In contrast, Atr increased the gene transcripts in CET, but MV decreased them in pnsB3 mutant plants. Atr did not increase the transcripts, while MV down-regulated them in pgr5 mutant. Immunoblot analysis partially supported the changes in the transcripts; that is, the protein levels of PGRL1 and PGR5 were increased in pnsB3 mutant, while no protein level was increased in pgr5 mutant after the herbicide treatment. The present results suggest that cyclic electron transport is very sensitive to photosystem-interference induced by chemicals and that the PGR5 pathway is very critical for regulation. Thus, pgr5 mutants may be useful plants for monitoring photosystem-interfering herbicides.