Comparative effect of tenuazonic acid, diuron, bentazone, dibromothymoquinone and methyl viologen on the kinetics of Chl a fluorescence rise OJIP and the MR₈₂₀ signal

In this study, the comparative effect of TeA, DCMU, bentazone, DBMIB and MV on prompt fluorescence and the MR820 signal was simultaneously analyzed to provide an insight into how to elucidate their precise influence on Ageratina adenophora photosystems. The herbicides that interrupt electron transport beyond Q(A), such as TeA, DCMU and bentazone, mainly increased the J-step level of fluorescence rise kinetics as a result of accumulation of Q(A)(-), but showed differences in detail. The IP phase disappeared in the presence of DCMU and bentazone with a significant increase in F-O value. TeA treatment retained the IP phase with lowering F-M. As an inhibitor of plastoquinone re-oxidation, DBMIB increased the I-step (IP phase almost unnoticable) without changing F-O and F-M values. MV blocking PSI electron transfer through intercepting electrons from the FeS clusters suppressed the IP phase by decreasing the P level. Considering the WIP kinetics, TeA and DBMIB also affected PSI activity. After DCMU and MV treatment, the major change in the MR820 kinetics was the loss of the slow phase due to the complete prevention of electron movement from PSII to re-reduce PC+ and P-700(+). TeA, bentazone and DBMIB clearly suppressed the MR820 slow phase and decreased the re-reduction rate of PC+ and P700 + (V-red), significantly. However, there were still parts of electrons being donated to PC+ and P-700(+), showing a smaller slow phase and PC+ and P-700(+) re-reduction rate. Additionally, TeA and DBMIB also somewhat declined the fast phase and PC and P700 oxidation rate (V-ox).