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Dernière mise à jour : Mai 2018

Menu Institutions

SPS - Saclay Plant Sciences

In vivo real-time measurements of photosynthetic processes

The team «Regulatory mechanisms in photosynthetic organisms» of the Institute of Integrative Biology of the Cell (I2BC) is equipped with different spectrophotometers for the in vivo study of  photosynthetic processes, one of which was partially funded by the Saclay Plant Sciences LabEx. Most of this equipment is relatively easy to use, even if automatic data analysis should be used with caution. Various fluorescence and absorption signals can be measured, sometimes simultaneously:

Setif1

Types of measurements currently available in the laboratory (WALZ spectrophotometers, http://www.walz.com/). The minus sign (--) indicates that the measurement is not possible with the corresponding biological material. Orange and green frames indicate measurements that can be performed simultaneously with some of the instruments. It is also possible to measure the transmembrane ΔpH with the use of 9-aminoacridine (simultaneously with chlorophyll fluorescence).

 

Whereas chlorophyll fluorescence arising mostly from photosystem II has long been studied in the field of photosynthesis, measurements of P700 (the primary electron donor of photosystem I) oxidation are now of wide use. Later developments concerned chlorophyll fluorescence imaging (see below), NAD(P)H fluorescence and DpH measurements.

Setif2

Chlorophyll fluorescence of wild type tobacco and of a mutant expressing the protein PTOX from a green alga. Images reveal the degradation of photosystem II in the mutant whereas kinetics show the efficiency of PTOX in oxidizing the plastoquinone pool.

More recently, it has become possible to detect, together with P700 photooxidation, the redox transitions of the photosystem I partners, plastocyanin and ferredoxin:

Setif3

Kinetics of near infrared absorption changes measured on a tobacco leaf during a sequence of different illuminations. Data were deconvoluted to provide the individual kinetics of P700, plastocyanin and ferredoxin.

These techniques, some of these being of recent availability, allows non-invasive real-time measurements of photosynthetic processes with a time resolution of less than 100 µs (except for chlorophyll fluorescence imaging). In addition to the processes mentioned in the above table, these measurements, especially when used in combination, help us identify limiting step(s) during linear electron transfer, in the evaluation of the relative contributions of different modes of electron transfer (linear, cyclic, pseudo-cyclic), in the characterization of activation/deactivation kinetics of the Calvin cycle, and more generally in studying regulations involved in photosynthetic (and in some cases respiratory) electron transfer.

SPS LabEx members wishing to use this equipment may contact the team for more information.