External 1 cm cuvette holder

Analysis of the effects of herbicides or inhibitors on the kinetics of charge recombination was performed using a Cary60 spectrophotometer connected to an external 1 cm cuvette holder (Ocean Optics) via a fibre-optic coupler. A white light pulse of 50 ms duration was applied to the sample cuvette at 90° to the pulsed measuring beam by an HL-2000-FHSA white light source with a fast shutter (Ocean Optics) delivering approximately 25 W m⁻² illumination at the cuvette surface. The actinic pulse was triggered by a TGP110 pulse generator (Thurlby Thandur Instruments). Solutions of 13.2 µM reaction centres in 20 mM Tris (pH 8.0)/ 30 µM UQ₀ were prepared with and without the addition of 500 µM atrazine, terbutryn, stigmatellin, bromoxynil, bentazon, capsaicin or DCMU. Test samples were loaded into to a 3×3 mm fluorescence cuvette (Hellma) aligned to the measuring and excitation pulses and absorbance at 865 nm was measured for 20 s after delivery of the light pulse, with a further period of at least 60 s to allow full dark adaptation of the reaction centres before re-excitation. A set of eight kinetic traces were recorded for each sample, averaged, and fitted using a single or double exponential function in Origin 8 (OriginLab).

Analysis of the effects of herbicides or inhibitors on the kinetics of charge recombination was performed using a Cary60 spectrophotometer connected to an external 1 cm cuvette holder (Ocean Optics) via a fibre-optic coupler. A white light pulse of 50 ms duration was applied to the sample cuvette at 90° to the pulsed measuring beam by an HL-2000-FHSA white light source with a fast shutter (Ocean Optics) delivering approximately 25 W m⁻² illumination at the cuvette surface. The actinic pulse was triggered by a TGP110 pulse generator (Thurlby Thandur Instruments). Solutions of 13.2 µM reaction centres in 20 mM Tris (pH 8.0)/ 30 µM UQ₀ were prepared with and without the addition of 500 µM atrazine, terbutryn, stigmatellin, bromoxynil, bentazon, capsaicin or DCMU. Test samples were loaded into to a 3×3 mm fluorescence cuvette (Hellma) aligned to the measuring and excitation pulses and absorbance at 865 nm was measured for 20 s after delivery of the light pulse, with a further period of at least 60 s to allow full dark adaptation of the reaction centres before re-excitation. A set of eight kinetic traces were recorded for each sample, averaged, and fitted using a single or double exponential function in Origin 8 (OriginLab).