Simultaneous Recording

The oxidized minus reduced difference spectrum of the photosystem I reaction center shows a distinct minimum at 700 nm and a broad positive range peaking at 830 nm in the near infrared (NIR) spectral region. The standard configuration of the DUAL-PAM-100 system determines the photosystem I redox state by quantifying NIR absorption changes in the dual wavelength mode with 830 nm as the sample wavelength and 870 nm as the reference wavelength.

Redox changes in plastocyanin, which is the natural electron donor to photosystem I, also result in NIR absorption changes. The plastocyanin-associated difference spectrum is rather broad and featureless and affects both, absorption changes at 830 and at 870 nm.

Being interested in both, P700 and plastocyanin redox kinetics, Mark A. Schöttler from the Max-Planck-Institut für Molekulare Pflanzenphysiologie in Potsdam, Germany, developed in collaboration with Christof Klughammer and Ulrich Schreiber of the Walz Company a novel instrument, the DUALPAM-S.

The DUAL-PAM-S measures simultaneously the difference absorption changes at 830–870 nm (predominantly P700 changes) and 870–950 nm (predominantly plastocyanin changes). The plastocyanin and P700 redox kinetics were obtained from the two difference signal using a special deconvolution procedure (Kirchhoff H, Schöttler MA, Maurer J, Weis, E. (2004) Biochim Biophys Acta 1659: 63–72).