DUAL-KLAS-NIR

The photosynthetic electron transport chain passes electrons from water through photosystem II, plastoquinone, the cytochrome b6f complex, plastocyanin, P700 (the photosystem I reaction center), and ferredoxin to NADP⁺. Understanding how electrons flow through this chain and where bottlenecks occur is key to understanding photosynthetic regulation, stress responses, and the coordination between the two photosystems. The DUAL-KLAS-NIR is the only instrument that can monitor the redox state of P700, plastocyanin, and ferredoxin simultaneously and in real time. By adding chlorophyll fluorescence data from the integrated PAM fluorometer, the system provides a comprehensive picture of the entire electron transport chain in a single measurement - from PSII to the acceptor side of PSI.

The DUAL-PAM-100 employs one pair of wavelengths in the near-infrared (NIR) to measure absorbance changes related to redox changes of the photosystem I reaction center. Using four wavelength pairs in the NIR (780/820, 820/870, 870/965 and 840/965 nm), the DUAL-KLAS-NIR is capable of unequivocally discriminating redox changes of plastocyanin, P700, and ferredoxin. The software of the DUAL-KLAS-NIR shares many features with that of the DUAL-PAM-100, making the transition straightforward for existing users. Using automated measuring routines, even complex measuring protocols can be easily performed.

The redox changes of P700, plastocyanin, and ferredoxin all produce overlapping absorbance changes in the near-infrared. By applying an innovative analytical approach, the DUAL-KLAS-NIR acquires the in vivo spectral characteristics of pure PC, P700, and Fd. This spectral information allows the system to monitor online the redox changes of all three components and to determine PC/P700 and Fd/P700 ratios, thereby providing direct estimates of the relative pool sizes of these electron carriers.

The DUAL-KLAS-NIR includes a full PAM chlorophyll fluorometer with both green and blue measuring light. Green light penetrates deeper into the leaf than blue light - thus, green-excited fluorescence includes information from deeper leaf layers and provides the best match with the NIR absorbance measurements, which always probe the entire leaf. The blue measuring light gives more specific information on the upper or lower leaf side and produces a fluorescence signal that is one order of magnitude larger than the green-excited signal.

The system measures in 1, 2, or 6 channel mode with time resolutions of 35 µs, 150 µs, and 1 ms respectively. The pulse modulation technique developed for the DUAL-PAM-100, in which channels are measured as blocks of 50 µs, has been extended for the DUAL-KLAS-NIR to accommodate 6-channel measurements. An extremely wide range of measuring light frequencies (1 Hz to 400 kHz) supports both continuous F₀ assessment and high-resolution recording of fast kinetic transients such as the polyphasic fluorescence rise or flash relaxation kinetics.

Integrated red (635 nm), blue (460 nm), and far-red actinic LEDs provide continuous actinic illumination, multiple turnover pulses, and single turnover flashes. The red LED array serves as the main actinic light source, while the blue LED in the detector unit allows continuous illumination with up to 300 µmol m⁻² s⁻¹ from the detector side of the sample. Both sides of the leaf can be illuminated for homogeneous light distribution or, by removing the LED array cable of the DKN-E emitter unit, only one side. All light sources switch with 2.5 µs time resolution under software control.

When single-channel measurements are made, a dedicated script allows the different signals to be measured consecutively at high time resolution combining the speed of single-channel mode with the information content of multi-channel measurements.

The software supports automated slow kinetics recordings, pre-programmed triggered runs, online and offline averaging, and operation via automated measuring routines through script file programming. This enables reproducible, multi-step experiments without manual intervention.