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DCMU‐INDUCED STIMULATION OF PHOTOSYSTEM I ELECTRON TRANSPORT. INVOLVEMENT OF MEMBRANE STRUCTURAL CHANGES
Author(s) -
Ramanujam P.,
Bose Salil
Publication year - 1983
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1983.tb04436.x
Subject(s) - dcmu , thylakoid , photosystem ii , photosystem i , chemistry , photochemistry , biophysics , photosynthesis , biology , biochemistry , chloroplast , gene
DCMU‐induced stimulation of the rate of photosystem I (PS I) electron transport in DCIPH 2 → MV photoreaction occurs through the action of DCMU on the rate‐limiting step which contains the site of electron donation of DCIPH 2 (Ramanujam et al. , 1981). The magnitude of stimulation of the rate by 50 μ M DCMU decreased with increasing concentration of chlorophyll (Chl), implying that DCMU is stoichiometrically related to Chl with respect to the stimulation of the PS I rate. DCMU‐induced stimulation was sensitive to the ionic condition of the thylakoids, the effect being reduced at low cation concentration. Cation‐induced scattering changes in thylakoid suspension were partially reversed by DCMU, and the percent Chl in the 10 K fraction of the thylakoid decreased upon addition of DCMU, indicating that grana structure is disrupted by DCMU. Hydroquinone‐mediated reduction of cytochrome f in thylakoids in the dark was accelerated in the presence of DCMU. The DCMU effect was not observed in isolated PS I particles. It is concluded that DCMU binds to the thylakoid membranes and brings about structural changes leading to unstacking of the thylakoids accompanied by an altered interaction of the electron transfer chain components with the added electron donor. This binding of DCMU must have an affinity lower than the well‐known binding of DCMU to photosystem II (PS II), because the concentration required is markedly higher.