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Theses and Dissertations

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Browsing Theses and Dissertations by Author "Abdel-Ghany, Salah, committee member"

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    The need for new inhibitors of photosynthesis in agricultural settings, and the novel herbicidal compound AS9057
    (Colorado State University. Libraries, 2024) Twitty, Alyssa, author; Dayan, Franck, advisor; Abdel-Ghany, Salah, committee member; Phillip, Yael, committee member
    Due to increased food demand, the need for use of herbicides is both necessary and on the rise. Several herbicide classes target photosynthetic electron transport: HRAC Groups 5, 6, and 22. These herbicides are used in large amounts in many different cropping systems to control several species of broadleaf and grass weeds. The first chapter provides a comprehensive review of what these photosynthesis inhibitors are, how they are used and their mode of action. Presently, commercial herbicides only inhibit electron flow at two different sites (PSII and PSI). Those which inhibit electron flow at PSII block the movement of electrons down the electron transport chain, while those which inhibit at PSI accept electrons. Necrosis developing on the leaves of plants treated with PSII and PSI inhibitors is due to the accumulation of reactive oxygen species. Evolution of resistance, toxicity concerns, and other limitations of these herbicides call for the exploration of new chemistries that can be used to target this pathway. One of these new chemistries has been identified as AS9057. AS9057 is a natural product identified as a novel herbicide with a potentially new mode of action using AI4AI, an AI platform for herbicide discovery developed by Agrematch. Greenhouse trials demonstrated that the herbicidal activity of AS9057 was light-dependent. The rapid burndown symptoms-developing on treated plants, combined with its chemical structure, suggested that AS9057 may target photosystem II. Measurements of photosynthetic electron transport rates in treated plants alongside data from oxygen evolution assays did not support this hypothesis. Further experiments suggested the AS9057 may instead act as an electron diverter. Oxygen consumption assays in isolated thylakoid membranes using a variety of electron transport inhibitors revealed that AS9057 likely acts on photosystem I in a similar manner to paraquat, but at a potentially new step between P700 and NADP+. This is consistent with other reports that AS9057 can act as an electron acceptor for flavoproteins. Ferredoxin-NAPD+ reductase is a flavoprotein with a redox potential similar to that of AS9057. Thus, it is currently hypothesized that AS9057 acts as an electron acceptor at or near the ferredoxin to form a radical and generate reactive oxygen species which causes the light-dependent herbicidal effect which is observed in treated plants from greenhouse trials.