Biomolecules (Jun 2023)

Probing the Influence of Novel Organometallic Copper(II) Complexes on Spinach PSII Photochemistry Using OJIP Fluorescence Transient Measurements

  • Sergei K. Zharmukhamedov,
  • Mehriban S. Shabanova,
  • Irada M. Huseynova,
  • Mehmet Sayım Karacan,
  • Nurcan Karacan,
  • Hande Akar,
  • Vladimir D. Kreslavski,
  • Hesham F. Alharby,
  • Barry D. Bruce,
  • Suleyman I. Allakhverdiev

DOI
https://doi.org/10.3390/biom13071058
Journal volume & issue
Vol. 13, no. 7
p. 1058

Abstract

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Modern agricultural cultivation relies heavily on genetically modified plants that survive after exposure to herbicides that kill weeds. Despite this biotechnology, there is a growing need for new sustainable, environmentally friendly, and biodegradable herbicides. We developed a novel [CuL2]Br2 complex (L = bis{4H-1,3,5-triazino[2,1-b]benzothiazole-2-amine,4-(2-imidazole) that is active on PSII by inhibiting photosynthetic oxygen evolution on the micromolar level. [CuL2]Br2 reduces the FV of PSII fluorescence. Artificial electron donors do not rescind the effect of [CuL2]Br2. The inhibitory mechanism of [CuL2]Br2 remains unclear. To explore this mechanism, we investigated the effect of [CuL2]Br2 in the presence/absence of the well-studied inhibitor DCMU on PSII-containing membranes by OJIP Chl fluorescence transient measurements. [CuL2]Br2 has two effects on Chl fluorescence transients: (1) a substantial decrease of the Chl fluorescence intensity throughout the entire kinetics, and (2) an auxiliary “diuron-like” effect. The initial decrease dominates and is observed both with and without DCMU. In contrast, the “diuron-like” effect is small and is observed only without DCMU. We propose that [CuL2]Br2 has two binding sites for PSII with different affinities. At the high-affinity site, [CuL2]Br2 produces effects similar to PSII reaction center inhibition, while at the low-affinity site, [CuL2]Br2 produces effects identical to those of DCMU. These results are compared with other PSII-specific classes of herbicides.

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