Inhibition of a Photosystem II Electron Transfer Reaction by the Natural Product Sorgoleone

Abstract

Effects of the alleochemical sorgoleone on photosynthetic electron transport by oxygen-evolving chloroplast thylakoids and Triton X-100-prepared Photosystem II (PSII) membranes were analyzed. The Hill activity of the thylakoids proved to be at least as sensitive to inhibition by sorgoleone as it was to DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea], a potent herbicidal inhibitor of PSII. However, a Photosystem I (PSI) partial reaction was not affected by a 10-fold greater concentration of sorgoleone than is required for complete inhibition of Hill activity. Measurements of flash-induced chlorophyll a variable fluorescence showed that sorgoleone neither dissipated excitation energy nor diminished the amplitude of chlorophyll a variable fluorescence. However, it inhibited the decay of variable fluorescence as effectively as DCMU, which blocks the oxidation of the PSII-reduced primary electron acceptor, Q- A, by the PSII secondary electron acceptor, QB, by displacing QB from the D1 protein. Additionally, sorgoleone competitively inhibited the binding of [14C]atrazine to the QB locus. Increasing durations of trypsin proteolysis of the PSII membranes or thylakoids and of the QB-binding niche itself caused parallel losses of inhibition of O2 evolution from sorgoleone and DCMU, as well as from bromoxynil, a phenol-type herbicide also binding to the QB locus. Keywords: Allelopathy; sorgoleone; photosystem II; electron transfer; herbicide

Challenges, achievements and opportunities in allelopathy research

“…It affects chloroplastic, mitochondrial, and cell replication functions of higher plant cells. It binds the D1 protein coupled with electron transfer between Q A and Q B within photosystem II (PSII), thus inhibiting PSII (Gonzalez et al 1997, Rimando et al 1998. It inhibits respiration (Rasmussen et al 1992) and root membrane H ' -ATPase (Hejl & Koster 2004).…”

Natural Compounds as Next-Generation Herbicides

“…A key step in this process that is sensitive to inhibition is the transfer of electrons from the secondary electron-acceptor (Qb) binding site to plastoquinone. Sorgoleone, a plastoquinone analog produced by sorghum roots, is a very potent inhibitor of photosynthesis (Gonzalez et al, 1997;Rimando et al, 1998;Dayan et al, , 2007bDayan, 2006). Several microbial metabolites, such as cyanobacterin from S. hofmanni (Lee and Gleason, 1994), fischerellin A from F. muscicola (Hagmann and Juettner, 1996;Srivastava et al, 1998), and stigmatellin from S. aurantica (Oettmeier et al, 1985), also inhibit PSII.…”

Functional Characterization of Desaturases Involved in the Formation of the Terminal Double Bond of an Unusual 16:3Δ9, 12, 15 Fatty Acid Isolated from Sorghum bicolor Root Hairs

“…One of the key steps is the formation of hexadecatrienoic acid (16:3⌬ 9,12,15 ), an unsaturated fatty acid proposed to serve as a precursor for the associated PKS in the pathway. To examine the presence and distribution of 16:2⌬ 9,12 and 16:3⌬ 9,12,15 in S. bicolor, the fatty acid compositions of various tissues (mature and immature leaves, stems, shoot apices, panicles, and whole root systems) were analyzed ( Fig.…”

“…BAA28358 and BAA11397 - Fig. 5 6,9,12 ). As a control, strains harboring the empty pYES2 vector were cultured in parallel.…”

“…4 In this report, we describe the cloning and functional characterization of two fatty acid desaturases, designated SbDES2 and SbDES3, which consecutively convert 16:1 fatty acid to 16:3 fatty acid having a terminal double bond, identified from mining of the sorghum root hair EST data base. 5 Yeast cells overexpressing the SbDES3 cDNA were able to convert 16:3⌬ 9,12 fatty acid substrate to its 16:3⌬ 9,12,15 trienoic form, which is considered to be the substrate used by polyketide synthases in the sorgoleone biosynthetic pathway (15,16). To our knowledge, this is the first plant fatty acid desaturase described to date exhibiting terminal desaturase activity.…”