FMS 1+

Lab-based pulse-modulated chlorophyll fluorometer

  • Upgraded model with LED light sources replacing older halogen bulbs
  • USB connectivity replacing older RS232 communications
  • Pulse-modulated system
  • Integral LED light sources for modulation bean, actinic & saturating pulses
  • Digital external device control interface
  • Programmable by user-friendly iconised script editor
  • Optional leafclip with integral PAR/temperature sensor
  • Fibre-optic cable suitable for incorporation into O2 electrode chambers & legacy IRGA systems
  • Windows® data acquisition & data analysis software

FMS 1 Overview

FMS 1 Pulse-Modulated Chlorophyll Fluorescence Monitoring System | Hansatech Instruments | Oxygen electrode and chlorophyll fluorescence measurement systems for cellular respiration and photosynthesis research

The FMS 1+ modulated chlorophyll fluorimeter is a versatile pulse-modulated instrument with mains power supply for laboratory/near-field use. It is suitable for non-invasive sampling of chlorophyll fluorescence under natural or artificial light conditions and may be interfaced with our range of oxygen electrode chambers for simultaneous oxygen measurements.

The FMS 1+ modulated chlorophyll fluorimeter consists of a control unit housing all of the electronics, optics and light sources necessary to derive most common chlorophyll fluorescence parameters. These are optically linked to the sample by a statistically randomised fibre-optic cable that is suitable for insertion into a range of sample containers such as oxygen electrode chambers, older infra-red gas analysis (IRGAS) chambers, Petri dishes and microtitre plates.

The system may be operated in several different modes: serial connection to a Windows® PC enables real-time instrument control and data presentation.

Captured data is simultaneously presented as a real-time chart recorder emulation and parameters-only format for easy identification of key experimental events. This PC mode of operation is suitable for development of complex protocols which may be programmed into the instrument using the simple drag and drop editor to generate user-defined scripts. These scripts automate the execution of experiments, allowing complex protocols involving many control events to be operated with the same ease as single control event measurement such as Fv/Fm. Once programmed, the FMS 1+ chlorophyll fluorimeter can be operated as a stand-alone fluorimeter inside the laboratory or outside (via connection to an optional external battery). All measurement data and calculated parameters are saved to integral protected memory. The unit can store up to six experimental protocols, any one of which may be accessed and executed using the built-in menu system. When data collection is complete the results can be downloaded to the Windows® software for full analysis.

All of the light sources required for modulated measurement of common chlorophyll fluorescence parameters are self-contained within the instrument.

  • 594nm amber modulating beam with 4-step frequency control. (Optional 470 nm blue LED)
  • Dual-purpose ultra-bright LED light source providing actinic light (0 µmol m-2 s-1 – >4,000 µmol m-2 s-1 in 50 steps) and saturating pulse (0 µmol m-2 s-1 – >13,000 µmol m-2 s-1 at the sample surface in 100 steps)
  • 735nm far-red LED source for preferential PSI excitation allowing accurate determination of the Fo' parameter.


FMS Dark Adaptation Leafclips

FMS Pulse-Modulated Chlorophyll Fluorescence Monitoring System Dark Adaptation Leafclips | Hansatech Instruments | Oxygen electrode and chlorophyll fluorescence measurement systems for cellular respiration and photosynthesis researchA leafclip system has been developed for situations where ambient light is to be excluded from the sample during measurement using the FMS 1+ or FMS 2+ chlorophyll fluorimeter. This is suitable for experiments requiring dark adapted measurements e.g. screening applications measuring Fv/Fm or situations which require adaptation of tissue to standardised doses of actinic light.

The system consists of small, lightweight leafclips and 2 different types of fibre-optic cable adapter. The leafclip itself has a small shutter-plate which should be closed over the leaf when the clip is attached so that light is excluded and dark adaptation takes place. The body of the clips are constructed from white plastic to minimise the effects of heat build-up on the leaf during the period when the clip is in place.

The locating ring section of the clip which interfaces with the fibre-optic adapter is also constructed from white plastic.

The sample rests on a foam pad whilst in the clip in order to minimise damage to the structure of the sample. The shutter-plate should be closed to exclude light from the sample during dark adaptation.

During dark adaptation, all the reaction centers are fully oxidised and available for photochemistry and any chlorophyll fluorescence yield is quenched. This process takes a variable amount of time and depends upon plant species, light history prior to the dark transition and whether or not the plant is stressed. Typically, 15 – 20 minutes may be required to dark adapt effectively. In order to reduce waiting time before measurement, a number of leaves may be dark adapted simultaneously using several leafclips.

FMS Pulse-Modulated Chlorophyll Fluorescence Monitoring System Open Leafclip Adapter | Hansatech Instruments | Oxygen electrode and chlorophyll fluorescence measurement systems for cellular respiration and photosynthesis research

The fibre-optic cable is inserted into either one of the adapters which in turn, fits over the locating ring of the leafclip. The closed fibre-optic adapter is suitable for applications where ambient light must be excluded whilst the open adapter is suitable for studies under ambient conditions.

Modfluor32 & Parview32 Software

PC control from Modfluor32 Windows® software allows real-time trace plotting as a chart-recorder emulation with calculated parameters written to a text parameters window. Instrument features and parameter measurement routines are selected from a toolbar with drop-down menus to control file handling and instrument configuration.

Modfluor32 Software for FMS Pulse-Modulated Chlorophyll Fluorescence Monitoring System | Hansatech Instruments | Oxygen electrode and chlorophyll fluorescence measurement systems for cellular respiration and photosynthesis researchComplex experimental protocols may be automated to reduce repetitive work by developing scripts using an iconised script editor which allows a sequence of control functions and measurements to be developed into a protocol. Once created, scripts may be executed directly from the Modfluor32 program and data viewed while the instrument automatically completes a user-defined experiment. A maximum of six scripts can be downloaded to the instrument’s internal memory for operation without a computer.

The connection of an optional external battery to FMS 1+ (FMS 2+ is supplied with batteries) enables portable operation with data stored to instrument memory for subsequent upload and full graphical presentation on the computer.

A further application is also included with the FMS 1 and FMS 2+ chlorophyll fluorimeters. Parview32 is a stand-alone utility designed to allow easy upload and transfer of multiple parameter files to a spreadsheet type program.

FMS Parameters Measured

Dark adapted parameters measured

Dark adaptation inhibits all light-dependent reactions. The resulting absence of photochemistry for a sufficient length of time allows complete re-oxidation of PSII electron acceptor molecules, opening PSII reaction centers and thus maximising the probability that absorbed light can be used for photochemistry. Commonly measured parameters from tissue in this state are used to calculate the maximum quantum efficiency of PSII and are usually used to reference measurements made on light adapted samples.

Fo – The fluorescence origin (Fo) is defined as the chlorophyll fluorescence yield following dark adaptation when all of the PSII reaction centers and electron acceptor molecules are fully oxidised and hence available for photochemistry. As a result, Fo is often measured at the beginning of an experiment when only the modulating beam is illuminated.

Fm – The maximum fluorescence yield (Fm) is attained when the dark adapted sample is exposed to an intense saturating pulse of light from the chlorophyll fluorometer. This temporarily reduces all PSII electron acceptors preventing PSII photochemistry. The temporary absence of competition from photochemistry for absorbed energy ensures maximum chlorophyll fluorescence emission from the sample.

Fv – The difference between the Fo and Fm chlorophyll fluorescence yield relates the maximum capacity for photochemical energy quenching by the sample and is defined as variable fluorescence (Fv).

Fv/Fm – Calculation of the rate constants for competing energy dissipation pathways in tissue under dark-adapted (Fo) and light-saturated (Fm) conditions have shown that the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) is directly proportional to the quantum efficiency of PSII photochemistry (Butler 1977, 19781). Close correlation with other measures of quantum efficiency of photochemistry in a wide range of species (Björkman and Demmig 19872) has resulted in widespread use of Fv/Fm as a screening parameter for stress response.

Light adapted parameters

In the case of light adapted tissue, a proportion of PSII electron acceptors are reduced, closing some PSII reaction centers. Hence the probability that absorbed energy is used for photochemistry is not maximal as competing non-photochemical processes are operating. The measurement of the light adapted ratio of variable to maximal chlorophyll fluorescence ratio permits the estimation of PS II quantum efficiency (\Phi PSII) using the model of Genty et al. 19893.

Fs, Fm' and \Phi PSII – Several measurements of fluorescence yield from the sample in different defined states are required to estimate \Phi PSII. Initially, the fluorescence yield of the sample under the ambient light regime is required. Such measurements are often made after a sample has adapted to a particular light regime or environment and is operating at steady state. Consequently, the measurement is often referred to as the steady-state fluorescence yield or Fs.

A fully saturating pulse from the chlorophyll fluorimeter is then required to close all of the PSII reaction centers; the temporary inhibition of PSII photochemistry ensures that the maximal fluorescence yield (Fm') is achieved. If a previous dark adapted measurement of Fv/Fm has been made the extent of photochemical and non-photochemical quenching processes can be determined from the equations of Schreiber et al 19864.

Fo' and \Phi PSIIR – Adaptation to high irradiance can involve significant changes in the confirmation of the photosynthetic apparatus which result in non-photochemical energy dissipation in the PSII antennae, before energy reaches the reaction centers (Horton et al. 19915, Horton and Ruban 19946). Failure to account for this effect can lead to inaccuracies in calculation of the relative contributions of photochemical and non-photochemical energy dissipation. This problem can be overcome by transiently shading the sample and using a far-red light source to preferentially excite PSI relative to PSII (electrons are drawn through the electron transport chain effectively opening PSII reaction centers and allowing measurement of a light adapted Fo, usually given the notation Fo'.

Other parameters measured

PAR – Takes a reading of the current incident photosynthetically active radiation value in µmol m-2 s-1 from the on-board PAR sensor of the FMS/PTL if connected to the chlorophyll fluorometer. Please note that the FMS/PTL leafclip is supplied as standard with FMS 2 but must be purchased as an option for FMS 1.

Temp – Takes a reading of the current temperature in °C from the on-board thermocouple of the FMS/PTL if connected to the chlorophyll fluorometer. Please note that the FMS/PTL leafclip is supplied as standard with FMS 2 but must be purchased as an option for FMS 1.

qP – A measure of the photochemical quenching coefficient calculated as:

(Fm'-Fs) / (Fm'- Fo)

qNP – A measure of the non-photochemical quenching coefficient calculated as:

(Fm-Fm') / (Fm-Fo)

NPQ – An alternative definition of non-photochemical quenching calculated as:

(Fm-Fm') / Fm'

ETR – A measure of the electron transport rate calculated as:

PAR \times 0.5 \times \Phi PSII \times  0.84

Measurement of ETR requires the FMS/PTL leafclip which is supplied as standard with FMS 2+ but must be purchased as an option for FMS 1+.

1 Butler, W. L., (1977).
Chlorophyll fluorescence: a probe for electron transfer and energy transfer.
In Encyclopaedia of Plant Physiology, ed. A. Trebst, M. Avron, 5, 149-167. Berlin: Springer-Verlag.

Butler, W. L., (1978).
Energy distribution in the photochemical apparatus of photosynthesis.
Annual Review of Plant Physiology, 29, 345-378.

2 Björkman, O. and B. Demmig (1987).
Photon yield of O2 evolution and chlorophyll fluorescence characteristics at 77K among vascular plants of diverse origins.
Planta, 170, 489-504.

3 Genty, B., Briantais, J-M. and N.R. Baker (1989).
The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence.
Biochimica et Biophysica Acta, 990, 87-92.

4 Schreiber, U., Schliwa, W. and U. Bilger (1986).
Continuous recording of photochemical and non-photochemical chlorophyll fluorescence quenching with a new type of modulation fluorimeter.
Photosynthesis Research, 10, 51-62.

5 Horton, P., Ruban, A.V., Rees, D., Pascal, A. A., Noctor, G. and A. J. Young (1991).
Control of the light-harvesting function of chloroplast membranes by aggregation of the LHCII chlorophyll-protein complexes.
FEBS Lett., 292,1-4.

6 Horton, P. and A. Ruban (1994).
The role of light-harvesting complex II in energy quenching. In Photoinhibition of photosynthesis from molecular mechanisms to the field
ed. N. R. Baker and J. R. Bowyer pp. 111-128. Oxford: BIOS, Scientific Publishers Ltd.

System Components

FMS 1+ is supplied with the following components:

  • FMS 1+ control unit
  • FMS/SFO: 1m fibre-optic cable with short ferule
    (optional FMS/LFO 1.5m long fibre-optic cable with long ferule suitable for interface with LD2/3 Leafdisc electrode chamber may be supplied at point-of-purchase for no additional cost)
  • FMS/LC: 10 x dark adaptation leafclips
  • 2 x leafclip adapters – closed and open-faced
  • Mains power supply
  • USB connection cable
  • USB drive containing ModFluor32 and Parview32 software and manuals.


Technical Specifications

  • Suitability: Lab-based measurement assays
  • Light sources:
    • Modulation beam: Temperature compensated 594nm amber LED with 4-step frequency control (Optional 470nm blue LED)
    • Ultra-bright white LED: Actinic >3,500 μmol m-2 s-1, saturating >13,000 μmol m-2 s-1 at sample surface
    • Far-red: 735nm LED
  • Detector: PIN photodiode with >700 nm filter
  • Detection method: Rapid peak-pulse tracking
  • Sampling rate: Variable 10 Hz – 20 kHz depending upon instrument mode
  • Electronics:
    • 16-bit 165 microprocessor
    • 8 A/D channels 12-bit resolution
    • 4 external digital I/O lines
    • Single 12-bit buffered DAC (0mV – 4095mV)
  • Storage: 256 Kb backed up RAM storing up to 2,430 full trace or 12,850 parameter only Fv/Fm data sets
  • Display: 20 x 4 LCD display
  • User-interface: 4-button keypad
  • Power supply: 95V – 260V universal input mains supply
  • Leafclips:
    • FMS/LC: 10 x dark adaptation leafclips
    • 2 x leafclip adapters (closed and open-faced)
    • Optional PAR/temperature leafclip (required for measurement of Electron Transport Rate (ETR) featuring:
      • Cosine corrected PAR sensor (0 μmol m-2 s-1 – 20,000 μmol m-2 s-1)
      • Leaf temperature thermocouple (-10°C – 90°C)
      • Remote trigger button and tripod mount
  • Dimensions: 260mm (L) x 235mm (D) x 83mm (H)
  • Weight: 2.8 kg.


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