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Chlorophyll (Chi) fluorescence is anon-destructive intrinsic probe of several aspects of oxygenic photosynthesis. In this chapter, the goal is to bring to the readers the basics of Chi fluorescence, a bit of history, it’s potential in understanding primary photophysical events (excitation energy transfer; charge separation), and secondary reactions (electron transport). This chapter is an extension...
Oxygenic photosynthesis is the unique process (at least in the solar system) by which plants absorb fleeting sunlight photons and store their energy in three stable forms of chemical energy: (i) As non-autoxidizable reduced organic compounds (e.g., carbohydrates), (ii) as transmembrane electrochemical gradients (e.g., proton motive force difference), and (iii) as chemical bonds of high negative free...
Chlorophyll fluorescence is now widely employed to investigate electron transport and C02 assimilation in leaves and algae. A brief description of how the application of fluorescence parameters has developed for the investigation of electron transport, and C02 assimilation in situ, is initially presented and followed by a consideration of the current appropriate fluorescence terms for such studies...
The applications of Fluorescence Resonance Energy Transfer (FRET) have expanded tremendously in the last 25 years, and the technique has become a staple technique in many biological and biophysical fields. Our understanding of photosynthesis is tightly coupled to our understanding of the transfer of captured energy from the absorption of photons, and following the energy flow through the complex maize...
In this chapter we discuss the transfer and trapping of excitation energy by plant Photosystem I and Photo-system II. For both photosystems structural models are now available that allow detailed modeling of their spectroscopic and energy transfer properties. In the core of Photosystem I the energy transfer process is fast, and is characterized by a first passage time of less than 10 ps. On a similar...
This chapter gives an outline, quantitative description and a critical evaluation of the essentials of ‘classic’ single hit two-state trapping models of Photosystem II (PS II) and of a recently proposed extension of it. This double hit three-state trapping model (TSTM) suggests that closing of the photosynthetic reaction center of PS II requires at least two successive trapping events. It emphasizes...
Photosynthetic antenna systems of cyanobacteria and red algae are described at three levels: (1) pigments, pigment-protein complexes, and structures of those complexes, (2) processes of excitation energy transfer and the transfer mechanisms, and (3) diversity of photosynthetic antenna systems. A discussion of the above points has made full use of the availability of the crystal structures of Photosystem...
Photosystem II (PS II) is a light-dependent water: plastoquinone-oxidoreductase, an enzyme that uses light energy to oxidize water (with release of oxygen and protons) and to reduce plastoquinone (with uptake of protons). Complex multisubunit structure of PS II is needed to couple together the capture of light energy, oxidation of water, reduction of plastoquinone, formation of a transmembrane proton...
Fluorescence of chlorophylls in the Photosystem I (PS I) reaction center (RC) of plants and cyanobacteria in vivo and in vitro is reviewed. The purified PS I-RC has a structure with 90 antenna chlorophyll (Chi) a molecules surrounding the six core Chi a molecules that function in the fast electron transfer steps. The RC forms a system highly efficient for energy capture and charge separation. Measurements...
The remarkable productivity of the higher plant photosynthetic apparatus can often be matched by its sensitivity to photodestruction, particularly under environmental stress. Thus, plants have evolved mechanisms for down-regulation which safely dissipate excess solar energy. The most important of these processes, the ones that lead to non-photochemical quenching (NPQ) of antenna excitons, are triggered...
Chlorophyll (Chi) a fluorescence originates in close vicinity to the sites where light energy is transformed into chemically fixed energy. The same excitation states that give rise to fluorescence emission also participate in photochemical energy conversion. These features render Chi fluorescence aunique indicator of photosynthesis. During the past 15 years there has been remarkable progress in Chi...
This chapter deals with chlorophyll (Chi) a fluorescence signals and describes how fluorescence transients, known commonly as Kautsky curves, exhibited by photosynthetic organisms under different conditions can be analyzed to provide detailed information about the structure, conformation and function of the photosynthetic apparatus and especially of photosystem (PS) II. The emphasis in this chapter...
The photosynthetic machinery emits a fraction of absorbed light as a highly informative waste process. The emitted light can be observed as prompt fluorescence during illumination or as delayed luminescence after illumination is turned off. Luminescence is measured in the form of delayed light emission (DLE) as a function of time or in the form of thermoluminescence (TL) as a function of temperature...
Chlorophyll fluorescence imaging provides a powerful, non-invasive tool for investigating leaf photosynthesis under natural conditions. Applications of fluorescence imaging in plant research are increasing rapidly, ranging from basic discoveries to biotechnology. Fluorescence imaging reveals a wide range of internal leaf characteristics, including spatial variations due to differences in physiology,...
Chlorophyll (Chi) a fluorometry is now well established as a non-invasive technique for the investigation of photosynthesis in plants and algae. In recent years, the versatility of this technique has been increased significantly by the development of Chi a fluorescence imaging systems. For example, high resolution systems make it possible to compare Photosystem (PS) II photochemical efficiency from...
Recent developments of LIDAR (Light Detection and Ranging)-based fluorosensing techniques have provided efficient tools for ground truth monitoring of vegetation. In addition, there are reports of passive detection of chlorophyll fluorescence based on the FLD (Fraunhofer Line Discriminator) principle. Further, measurements of reflectance changes in the green part of the spectrum provides access to...
The machinery of oxygenic photosynthesis can move between two light-states. State 1 is induced by a light regime favoring Photosystem (PS) I, and favors light-harvesting by PS II. State 2 is induced by a light regime favoring PS II, and favors light-harvesting by PS I. Chlorophyll (Chi) fluorescence emission is an important and revealing signature of the modifications that occur to photosynthetic...
Chlorophyll (Chi) a fluorescence has become an important non-invasive tool to investigate the utilization and dissipation of absorbed light energy in photosynthesis. In particular, analysis of Chi fluorescence quenching serves as a convenient, widely applied method to obtain complex information on the response of the photosynthetic apparatus in green plants to environmental factors. Whereas ‘photochemical...
Photosynthetic organisms in natural environments are challenged by exposure to changing light intensities and stress conditions. The balance point between efficient light harvesting and potential photodamage is fine and dependent upon changing environmental conditions and metabolic demands. Plants appear to have developed numerous mechanisms that allow them to fine tune the absorption of light energy,...
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