The new MINI-PAM-II fluorometer combines the merits of its predecessor “MINI-PAM” with most modern LED and computer technology.
Sensitivity, small dimensions, reliability under rugged conditions, and simple execution of fluorescence analysis makes the MINI-PAM-II the new standard for PAM fluorometry in field research.
Well-tested fiberoptics with 5.5 mm or 2 mm active diameter reaches even hidden samples.
Measurements under field conditions are easily controlled and monitored by a transflective touchscreen.
Energy-efficient LED sources, storage capacity of 27,000 data sets, and easy replaceable off-the-shelf batteries permit long term research campaigns at remote places.
A new fully digital leaf clip combines fluorescence analysis with measurements of photosynthetically active radiation (PAR), leaf temperature and relative humidity.
Expandable through accessories such as external multicolor lamp, optical oxygen sensor and barcode scanner.
Microsecond timing enables the MINI-PAM-II fluorometer to use the same LED as source for PAM measuring light, actinic light and saturation pulses. Measuring light corresponds to μs flashes of constant amplitude, actinic light is quasi-constant light employed to drive photosynthesis, and saturation pulses temporarily saturate primary photosynthesis so that all photosystem II reaction centers are “closed”.
Being a PAM fluorometer, the MINI-PAM-II device records only the fluorescence elicited by measuring light. Fluorescence excited by internal actinic light, saturation pulses or constant external light, like sun radiation, is not measured. Therefore, the MINI-PAM-II determines how environmental factors modulate the efficiency of conversion of measuring light into fluorescence. These “PAM fluorescence data” are required to retrieve information on primary photosynthesis like the photosynthetic efficiency of photosystem II, Y(II).
A second LED in the MINI-PAM-II emits far red light. This LED preferably excites photosystem I but is negligibly absorbed by photosystem II. A special measuring routine uses this far red LED to determine the F0’ fluorescence level which is important to correctly assess the reduction state of photosystem II reaction centers.
In experiments using internal actinic light, the light intensity at sample level can be monitored online using an internal light sensor. This internal sensor must be calibrated against an external light sensor.
The color of light emitted by the primary LED distinguishes the BLUE from the RED version of the MINI-PAM-II fluorometer (Fig. 1). The BLUE version (MINI-PAM-II/B) possesses a blue LED emitting maximally around 475 nm which is replaced by a red LED emitting maximally around 655 nm in the RED version (MINI-PAM-II/R). Both versions have a second LED providing far red light for specific excitation of photosystem I.
Figure 1: Typical LED emission spectra normalized to their maxima. The blue curve corresponds to the spectrum of the blue LED of the MINI-PAM-II/B, the orange curve represents the red LED in the MINI-PAM-II/R. Both MINI-PAM-II versions possess a far red LED which emits maximally above 700 nm (rightmost curve). Max, peak wavelength in nm. FWHM, full width at half maximum in nm.
The second difference between the two versions is the spectral window for fluorescence detection. The BLUE version detects fluorescence at wavelengths > 630 nm but the RED version detects fluorescence at wavelengths > 700 nm (Fig. 2).
Figure 2: Transmittance spectra of detection filters in the MINI-PAM-II-B (blue line) and MINI-PAM-II/R (orange line).
The detection window for fluorescence of the BLUE version extends to 640 nm but the RED version detects only fluorescence at wavelengths longer than 700 nm (Fig. 2). In principle, its extended range for fluorescence detection makes the BLUE version more sensitive than the RED version because photosystem II fluoresces at wavelength between 650 and 700 nm. In fully green leaves, however, a large part of this short wavelength fluorescence (650 - 700 nm) is reabsorbed by chlorophyll so that the gain in sensitivity of the BLUE version is moderate. When reabsorption (and also the fluorescence signal) is low, like in extremely bleached leaves, the increased sensitivity of the BLUE version can be advantageous.
The MINI-PAM-II can be used to investigate lichens or photosynthetic microbial mats. Cyanobacteria present in these mats often absorb poorly in the blue. Therefore, the RED version is normally preferred in studies of cyanobacteria.
Blue actinic light of the MINI-PAM-II/B excites the broad short wavelength band of the major light-harvesting complex of photosystem II in higher plants (LHC II). Red light of the MINI-PAM-II/R excites the comparably minor long-wavelength band of the LHC II. Hence, if LHC II excitation is important, the BLUE version is recommended.
Blue is absorbed by blue light photoreceptors which can stimulate plant responses like chloroplast relocation and stomatal movements. Therefore, the BLUE version can be advantageous when blue light responses are of interest. Blue light-driven chloroplast relocation, however, can affect the fluorescence signal by changing the efficiency of light absorption which is difficult to distinguish from the effects of high-energy fluorescence quenching on fluorescence.