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Chl a is present within both PS II and PS I. The FAST^tracka II defines the Chl a fluorescence signal using a narrow bandpass filter, centred at 685 nm, which minimises contamination of the PS II signal from PS I and free Chl (see figure above).

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The Multiple Turnover (MT) method

Fluorimeters that employ the multiple turnover method use a relatively long saturating pulse of high photon irradiance (PI) to drive the yield of photochemistry close to zero, through multiple turnovers of PS II: typically, a few hundred ms at several thousand µmol photons m^-2 s^-1. By comparing the fluorescence signal before the pulse is applied (F_o or F' with dark or light-adapted material, respectively) with the highest fluorescence signal achieved during the saturating pulse (F_m or F_m' with dark or light-adapted material, respectively) it is possible to estimate the yield of PS II photochemistry, as 1 - F_o/F_m or 1 – F'/F_m' (often written as F_v/F_m or F_q'/F_m', where F_v and F_q' are F_m – F_o and F_m' – F', respectively).

The multiple-turnover method has a number of weaknesses:

• A multiple-turnover measurement typically takes several hundred ms. When profiling or attached to a towed vehicle, this is very likely to mean that the multiple-turnover pulse is spread over a long trail of sample, such that F_m or F_m' is never reached. This could result in a very significant underestimate of PS II photochemical efficiency. 

•  Photosynthesis takes tens of seconds to 'recover' from the application of a multiple-turnover pulse. This limits the frequency at which measurements can be taken from a single sample .

• No information about the absorption cross-section of PS II can be derived from multiple-turnover data.
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Fluorimeters that employ the single-turnover method use a very short saturating pulse of very high PI to drive the yield of photochemistry close to zero, through near-simultaneous turnover of all PS II centres: typically, 100 µs at 20 000 µmol photons m^-2 s^-1. The yield of PS II photochemistry can then be calculated, in the same way as with the multiple-turnover method.
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The Fast Repetition Rate (FRR) technique

Sample Data

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Data fit to the mean of sequences 2 to 6 of a 6 sequence acquisition from dark-adapted material. A mechanistic model (currently under development), which incorporates the turnover of plastoquinone, semi-plastoquinone and plastoquinol at the Q_B site of PS II, was used to fit these data.

The interval between flashlets during the relaxation phase started at 50 µs, but was increased by 20% between consecutive flashlets. The model has generated a reasonable fit to the data, including the ‘kink’ in the relaxation phase.

Same as above except that the interval between flashlets during the relaxation phase was fixed at 199 µs. The mechanistic model has produced a reasonable fit to the data, including to the slow fluorescence increase during the latter part of the relaxation phase.

Analysis of individual sequences within an acquisition. To generate these data, six acquisitions of two sequences were made from dark-adapted cells, with a 30s intervals between acquisitions. The mean trace of the first sequences shows a lower value for F_o, but higher values for sPS _II and Fm than for the second sequence. The higher Fm value for the first sequence in an acquisition from dark-adapted material is a common feature of ST data. For example, Kolber et al. (1998) noted a 15 to 20% higher Fm after 10 s dark-adaptation.

Plot of a single MT data sequence. The interval between flashlets during the relaxation phase started at 800 µs, but was increased by 20% between consecutive flashlets.

The inset shows the relaxation phase in more detail. 

All of the examples shown above were collected from a mixed population of green algae, at a chlorophyll concentration of approximately 26 µg l^-1 (Chl a in acetone equivalent). A series of 9 concatenated protocols was used to collect all of the above data in one go. 

Reference: Kolber ZS, Prásîl O and Falkowski PG (1998) Measurements of variable chlorophyll fluorescence using fast repetition rate techniques: defining methodology and experimental protocols. Biochim. Biophys. Acta 1367: 88-106.

Specifications and Options

The FAST^tracka II profiling cage provides a high level of protection for the photomultiplier tube, against stray light.

The FAST^tracka II electro-optics assembly provides very even illumination within the sample zone. The filtering and optical arrangement of the LEDs and photomultiplier tube, which excite and detect Chl a fluorescence, respectively, minimise contamination by stray light and 'filter breakthrough' from the LEDs.  

The Fast^tracka II dark chamber can be combined with the profiling cage, with the bezel providing the point of attachment to the sensor for both items. The profiling adaptor kit, shown here, provides good flow through when the sensor is used within a towed vehicle, for example. If the sensor is being used in a static location, or in slow moving water, a pumped adaptor kit (not shown) can be used with the same dark chamber.

(top)

Sensor alone 

339.5 mm (excluding connector) 

With profiling cage

550.0 mm (excluding connector)

Sensor diameter Ti (Ac)*

112.5mm (130mm)

With profiling kit

170.5mm 

Pressure housing

Titanium or Acetal C

Dark chamber

Acetal C

Connector kits

Acetal C + Stainless Steel

Weight in air / water

60 N / 30 N approx.

*Ti = titanium pressure housing, Ac = Acetal C pressure housing

Range (standard)

0 - 600 µg l^-1

Excitation

470 nm peak, ± 20 nm

Detection

685 nm peak,  ± 10 nm

Sample volume

1 cm^-3

Internal storage

2 GBytes

Power in

9 to 72 VDC

Operating temperature

-10°C to +50°C

Storage temperature

-10°C to +40°C  

Max. operating depth Ti (Ac)*

500 m (200 m)

Basic Instrument: 

The FAST^tracka II is provided with a 3 m cable, Handbook and Calibration Certificate and fitting software

Available options:

Deck unit, profiling cage, dark chamber, profiling adaptor kit and pumped adaptor kit. PAR sensor and depth sensor

Chelsea Technologies Group Ltd
55 Central Avenue, West Molesey,
Surrey, KT8 2QZ, UK.
Tel: +44 (0)20 8481 9000    Fax: +44 (0)20 8941 9319
Email: sales@chelsea.co.uk

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