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 simultaneous 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 "membrane 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 dark 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 ratio, the P515 change induced by a single-turnover saturating flash can be reliably measured without averaging. Comparison of the single beam responses at 550, 535 and 515 nm with the dual beam 550 515 nm difference signal suggests that the latter is essentially free of "scattering" changes. Besides P515 (ECS), the 550 515 nm signal also contains 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 P515 signal, as previously demonstrated by David Kramer and co-workers (DIRK-analysis). The DUAL-PAM provides a special "P515 Flux" mode of operation, 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.