The Inhibition of Photosynthetic Light Reactions by Halogenated Naphthoquinones

Abstract

Halogenated naphthoquinones act as inhibitors of photosynthetic electron flow. I50 concentra­ tion for inhibition of methylviologen reduction were found to range between 2 × 10-5 m to 2 × 10-6 M. Comparing their effects on several partial reactions of electron flow, the inhibition site of the naphthoquinones was found to be at the reducing site of PS II. Studies of fluorescence transients in presence of halogenated naphthoquinones give further evidence for a site action similar to that of diuron and different to that of DBMIB. All naphthoquinones act as quenchers of chlorophyll fluorescence with pure chlorophyll a, and with much higher efficiency in green algae and chloroplasts. It is concluded, that the halogenated naphthoquinones act similar to PS II-inhibitors like diuron, but do not share a common binding site at the PS II-complex. Implications of a possible involvement of phylloquinone K 1 in photosynthetic electron transport are discussed. The synthesis of 2-chloro-as well as 2-bromo-3-isopropyl-1,4-naphthoquinone is described.

Cyanobacteria-specific algicidal mechanism of bioinspired naphthoquinone derivative, NQ 2-0

“…and S. capricornutum ) organisms, following treatment with NQ 2-0. As a first step, differences in the algicidal activity of NQ 2-0 depending on the presence and absence of light were investigated, since evidence suggests that naphthoquinone can inhibit plant photosynthesis by disturbing the photosynthetic electron transport system 16 , 17 . Consequently, NQ 2-0 demonstrated a strong algicidal activity only against M. aeruginosa under light conditions (>90%) (Fig.…”

“…Based on previous studies, naphthoquinone-based materials, such as halogenated naphthoquinones, are known to inhibit photosynthesis by blocking electron transfer from the photosynthetic electron transport system 16 . In this study, to investigate whether NQ 2-0 can block electron transfer from the photosynthetic electron transport system, we examined changes in PSII efficiency ( Fv / Fm ) following the addition of NQ 2-0, and compared the results with those obtained following the addition of DCMU, which is capable of binding to the Q site of PSII and blocking energy transfer to the photosynthetic electron transport system to inhibit photosynthesis 19 .…”

“…Quinone-based compounds may have one or more of the following functions: electron transport chain inhibition, oxidative phosphorylation uncoupling, DNA intercalation, reductive alkylation, and free radical generation 15 . Thus, naphthoquinone inhibits photosynthesis by disturbing photosynthetic electron transport in plants 16 , 17 . However, to date, studies on the algicidal mechanisms of this naphthoquinone substance against phytoplankton species are lacking.…”

Interaction of electron acceptors with thylakoids from halophytic and non-halophytic species

“…Quinone supported O, evolution proved to be inhibited by DBMIB by 20-30% depending on the quinone. 9), there is a third site which can be inhibited by halogenated naphthoquinones (Pfister et al 1981). DBMIB at higher concentrations (20-30 #M) is able to accept electrons but does not do so as effectively as other quinones (Gould and Izawa 1973), and may have two sites of interaction with different affinities in much the same way as 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole, another PQ antagonist (Oettmeier et al 1981).…”

Herbicidal action of 2‐hydroxy‐3‐alkyl‐1,4‐naphthoquinones

“…They are well known as inhibitors of mitochondrial complex III (cytochrome b/c1), where they bind at the Qo site near the Rieske iron–sulfur protein 8. In plants they have been implicated as inhibiting PSII,9–11 although the majority of reports to date have been limited to in vitro measurements with the structurally related 5‐ n ‐undecyl‐6‐hydroxy‐4,7‐dioxo‐benzthiazole (UHDBT), which has been shown to act at the same site as the commercial herbicides diuron12 and metribuzin 13…”