Pu 830

Chlorophyll fluorescence emission spectra were determined at 77 K with a fluorescence spectrometer (FP-8500, JASCO, Japan) with a low temperature attachment (PU-830, JASCO, Japan)18 (link). Cell suspensions were adjusted to a concentration of 2 μg chlorophyll ml⁻¹ in growth medium. Chlorophyll concentration was determined by extraction with 100% methanol83 (link). Prior to the measurements, the cells were dark-adapted for 15 min with or without KCN (1 mM) (Fig. 1A,B), illuminated by while light (30, 200 and 500 μmol m⁻² s⁻¹) for 4 min (Fig. 3), or illuminated by white light at 500 μmol m⁻² s⁻¹ for 180 min, at 1200 μmol m⁻² s⁻¹ for 4, 30, 60 and 180 min or at 2000 μmol m⁻² s⁻¹ for 180 min (Fig. 5) from a light source (PICL-NRX, NIPPON P-I). The effect of 10 μM DCMU was also tested for the measurements of cells illuminated at 500 μmol m⁻² s⁻¹ (Fig. 1A,B). The samples were excited by 625 nm light for phycocyanin excitation and 435 nm for chlorophyll excitation with excitation slit width at 10 nm. The fluorescence spectra were recorded with fluorescence slit width at 2.5 nm and resolution of 0.2 nm. The spectra were corrected for the sensitivity of photomultiplier and spectrum of light source using a secondary standard light source (ESC-842, JASCO, Japan). Chlorophyll fluorescence emission spectra were normalized at their respective maxima at around 725 nm.

Chlorophyll fluorescence emission spectra were measured at 77 K with a fluorescence spectrometer (FP-8500, JASCO) with a low temperature attachment (PU-830, JASCO) as described in Ogawa et al. (2013) (link). Cell suspensions were adjusted to a chlorophyll concentration of 2 μg ml⁻¹. Prior to the measurements, the cells were incubated for 10 min at room temperature either in the dark, or in the dark in the presence of 0.2 mM KCN, or under growth light, or under high light at 550 μmol m⁻² s⁻¹ in the presence of 10 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU).