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

Abstract

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 W_IP 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 P₇₀₀⁺. 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 P₇₀₀⁺, showing a smaller slow phase and PC⁺ and P₇₀₀⁺ re-reduction rate. Additionally, TeA and DBMIB also somewhat declined the fast phase and PC and P₇₀₀ oxidation rate (V_ox).

Keywords: Ageratina adenophora; Chlorophyll a fluorescence rise kinetics; JIP-Test; Modulated 820 nm reflection Signal; Photosynthetic inhibitors.