IMAGING-PAM

Chlorophyll fluorescence is a very sensitive indicator of photosynthesis. Quantitative information on the quantum yield of photosynthetic energy conversion is obtained by PAM fluorometry and the saturation pulse method (Schreiber U (2004) Pulse-Amplitude-Modulation (PAM) Fluorometry and Saturation Pulse Method: An Overview, pp. 279-319. Kluwer Academic Publishers, Dordrecht, The Netherlands).

A wide range of photosynthetic parameters can be derived from fluorescence measurements, giving insight into the physiological state of all photosynthetically active organisms, including higher plants, mosses and ferns as well as various types of algae, phytoplankton and biofilms.

With the advance of highly sensitive CCD cameras and extremely powerful light-emitting diodes (LEDs), the development of IMAGING-PAM fluorometers has become possible systems that not only record images of chlorophyll fluorescence but are also fully capable of delivering all relevant chlorophyll fluorescence parameters using the saturation pulse method. This enables researchers to obtain detailed images of photosynthetic activity and to track its spatio-temporal variations with high precision. The newest addition to this technology platform, the HEXAGON-IMAGING system, is equipped with far-red (FR) LEDs that open up advanced experimental capabilities, including state-shift experiments and accurate Fo′ determinations.

All IMAGING-PAM fluorometers provide images for 17 different parameters. The fluorescence parameter Ft is monitored continuously, while Fo and Fm are determined after dark adaptation and serve as key references for fluorescence quenching analysis using the saturation pulse method. In addition to Fv/Fm, the maximum quantum yield of PS II after dark acclimation, the systems also deliver images of the effective PS II quantum yield during illumination (Y(II)), the quantum yields of regulated and non-regulated energy dissipation (Y(NPQ) and Y(NO)), as well as the apparent electron transport rate (ETR and PS).

A dedicated routine for measuring a PAR-absorptivity image is available for both the MAXI and MINI versions of the IMAGING-PAM. This “Abs.-image,” based on NIR and red-light remission, allows for direct calculation of the apparent rate of photosynthesis for each pixel—eliminating the need to rely on the commonly used universal PAR-absorptivity mean value of 0.84 (ETR). In addition, the parameter PS/50 is displayed to visualize apparent photosynthesis using the same intuitive false-color coding employed for all other photosynthesis parameters.