Alamethicin (AMT) is a linear antimicrobial peptide isolated from fungi Trichoderma viride. To date, the mode of action of AMT in plant cells remains unknown. Our experimental results indicate that AMT causes leaf lesion attributed to its multiple effects on PSII. AMT decreases the O2 evolution rate of PSII. Based on chlorophyll fluorescence data, similar to the classical herbicide diuron, AMT interrupts PSII electron transfer beyond QA at the acceptor side, leading to the inactivation of the PSII reaction centers. Additionally, AMT decreases chlorophyll content and destroys the architecture of PSII pigment assemblies. However, AMT does not affect the oxygen-evolving complex at the donor side of PSII. Thus, it is concluded that AMT is a natural photosynthetic inhibitor with several action sites in PSII.Additional key words: bioherbicide; chlorophyll a fluorescence; leaf lesion; natural product. transport rate; FV/FM -maximum quantum yield of PSII photochemistry; OEC -oxygen-evolving complex; qP -photochemistry quenching coefficient; RCs -reaction centers; ROSreactive oxygen species; TAP -Tris-acetate-phosphate; TR0 -trapping flux.
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