Hence, the presence of PsbS in the PsbO deficient population is mechanistically reasonable. This sub-population

of PSII monomers is probably similar to the lamellar PsbO-deficient PSII particles observed by Bassi et al. (1995) and to the inactive selleck chemical monomeric PSII present in the Y-100 domain reported by Danielsson et al. (2006). Finally, the other sub-population of PSIImM that contains PsbO, but lacks PsbS could originate from the stroma-lamellae domain. This assignment would agree with previous observations of a partially active PSII selleck chemicals llc monomer in this region of the membranes (Danielsson et al. 2006). Materials and methods Growth and cultivation of tobacco plants The transplastomic plants of N. tabacum, that carry a hexa-histidine tag sequence at the 5′ end of the gene coding for the PsbE subunit, were described by Fey et al. (2008). The plants were kept at a constant temperature of 25 °C at 50 % relative humidity and grown for 10–12 weeks under a light regime of 12 h/day, with a light intensity of 150–200 μmol photons/(s m2). Thylakoid preparation Thylakoid membranes were purified as reported previously by Fey et al. (2008) with only minimal modifications in the solubilization step. In brief, thylakoids were resuspended in 20 mM MES–NaOH, pH 6.5; 100 mM

NaCl; 5 mM MgCl2; 10 mM Selleck Go6983 NaHCO3; 12.5 % (v/v) glycerol prior solubilization. PSIImM core complexes were obtained from thylakoids membranes solubilized for 5′ at 4 °C at a final chlorophyll concentration of 3 mg/ml (protocol B). The PSII core complex lacking of PsbS (protocol A) was prepared starting from thylakoids membranes solubilized for 15′ at 4 °C at a final concentration of 1 mg/ml chlorophyll. In both cases solubilization was carried out using 20 mM β-dodecylmaltoside (β-DDM). PSII core complex purification by affinity chromatography Photosystem II

samples were prepared using Ni affinity chromatography. PSII isolated following the protocol A was prepared according to Piano et al. (2010); PSII isolated following the protocol B was prepared according to Fey et al. (2008) with minor changes. In brief, for the protocol A the washing buffer was free of glycerol (20 mM MES–NaOH, pH 6.5; 100 mM NaCl; 10 mM NaHCO3; 15 mM imidazole; 1 M betaine). For protocol Tobramycin B the washing buffer consisted of 20 mM MES–NaOH, pH 6.5, 100 mM NaCl, 10 mM NaHCO3, 15 mM imidazole, 1 M betaine, 12.5 % (v/v) glycerol. In both cases PSII cores were then eluted using 40 mM MES–NaOH, pH 6.5; 20 mM NaCl; 5 mM MgCl2; 1 mM CaCl2; 10 mM NaHCO3; 300 mM imidazole; 1 M betaine. In both preparations the washing and the elution buffers contained 0.02 % instead of 0.03 % (w/v) β-DDM. The volumes of washing were increased to 12 CV. Size exclusion chromatography Both preparations were concentrated using Vivaspin 20 ultrafiltration membranes with 100 kDa cutoff until a final volume of 500 μl.