New accessory for the DUAL-PAM-100: The P515/535 module and examples of its application

The P515/535 module has become available as a new accessory for the DUAL-PAM-100. It serves for si- multaneous measurements of the dual beam 550 - 515 nm difference signal, reflecting the electrochromic pigment shift (ECS, P515), and of the single beam 535 nm signal, reflecting energization (scattering changes). The technical features of the emitter and detector units of the new device are outlined and some typical examples of application are presented. A wide range of frequencies of the pulse modulated measuring light is provided, which can be rapidly altered under software control. In this way, the baseline can be assessed (at low frequency) and at the same time rapid induction kinetics can be measured (at high frequency). Due to an exceptionally high signal/noise ra- tio, the change induced by a single-turnover saturating flash can be reliably measured without averaging. Com- parison of the single beam responses at 550, 535 and 515 nm with the dual beam 550 - 515 nm difference signal sug- gests that the latter is essentially free of scattering changes. Besides (ECS), the 550 - 515 nm signal also con- tains information on the zeaxanthin content, which is reflected in changes of the dark baseline. Such changes can be reliably evaluated due to the high signal stability, as demonstrated by measurements using an inert sample (artificial leaf). Valuable information on the membrane potential (Δψ) and proton gradient (ΔpH) components of the proton motive force (pmf) can be obtained by analyzing light-dark responses of the signal, as previously demonstrated by David Kramer and co-workers (DIRK-analysis). The DUAL-PAM provides a special P515 Flux mode of opera- tion, with the actinic light being applied in form of light-dark pulses (1/1 modulation of light/dark). The P515 Flux signal provides valuable information on the steady-state rates of coupled electron and proton fluxes in vivo.