Selected phytotoxins and organic extracts from endophytic fungus Edenia gomezpompae as light reaction of photosynthesis inhibitors

•Organic extracts from morphological variants of E. gomezpompae possess phytotoxic activity.•Naphthoquinone spiroketals tested inhibited the ATP synthesis from water to MV.•All naphthoquinone spiroketals tested act as Hill reaction inhibitors.•Naphthoquinone spiroketals tested exhibited an effect on the PSII electron.•Site of inhibition was corroborated by fluorescence of the chlorophyll a of PSII.

In a search for natural herbicides, we investigated the action mechanism of the naphthoquinone spiroketals, isolated from the endophytic fungus Edenia gomezpompae: preussomerins EG1 (1) and EG4 (2), and palmarumycins CP17 (3), and CP2 (4) on the photosynthesis light reactions. The naphthoquinone spiroketals 1–4 inhibited the ATP synthesis in freshly lysed spinach thylakoids from water to MV, and they also inhibited the non-cyclic electron transport in the basal, phosphorylating and uncoupled conditions from water to MV. Therefore, they act as Hill reaction inhibitors. The results suggested that naphthoquinone spiroketals 1–4 have two interactions and inhibition site on the PSII electron transport chain. The first one involves the water splitting enzyme inhibition; and, the second on the acceptor site of PSII in a similar way that herbicide Diuron, studied by polaroghaphy and corroborated by fluorescence of the chlorophyll a of PSII. The culture medium and mycelium organic extracts from four morphological variants of E. gomezpompae were phytotoxic, and the culture medium extracts were more potent than mycelium extracts. They also act as Hill reaction inhibitors.

Graphical abstractMorphological variants of Edenia gomezpompae. Colony appearance on potato dextrose agar after 14 days at 25 °C.Figure optionsDownload full-size imageDownload as PowerPoint slide