Diuron treatment reveals the different roles of two cyclic electron transfer pathways in photosystem II in Arabidopsis thaliana

Abstract Three ecotypes of Arabidopsis thaliana , ecotype Columbia (Wild type, Wt) and two mutants ( pgr 5 and ndf 4), were used to evaluate the effects of diuron on photosynthetic activity of A. thaliana . It was found that diuron adversely affected the fresh weight and chlorophyll content of the plants. Chlorophyll fluorescence studies determined that the pgr 5 mutant was more sensitive to diuron than Wt and the ndf 4 mutant. Gene expression analysis revealed different roles for the two cyclic electron transfer (CET) pathways, NAD(P)H dehydrogenase (NDH) and proton gradient regulation (PGR5) pathways, in the plant after diuron treatment. For example, a gene in the NDH pathway, lhca 5, was activated in the low dose (LD) group in the pgr 5 mutant, but was down-regulated in the moderate dose (MD) group, along with two other NDH-related genes ( ppl 2 and ndh H). In the PGR5 pathway, the pgr 5 gene was functional under conditions of increased stress (MD group), and was up-regulated to a greater extent in the ndf 4 mutant than that in the Wt and pgr 5 mutant. Our results suggest that the PGR5 pathway in plants is more important than the NDH pathway during resistance to environmental stress. Deficiencies in the PGR5 pathway could not be counteracted by the NDH pathway, but deficiencies in the NDH pathway could be overcome by stimulating PGR5.