The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence

BIOPHYSICAL BASIS O F FLUORESCENCE EMISSION FROM CHLOROPLASTS . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 314 Fluorescence as a Reaction Competing in the Deactivation of Excited Chlorophyll . . . . . . . . . . ... . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Lifetimes of Fluorescence . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 317 Origin of Fluorescence Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1 Fluorescence of PS 11 and PS I at Ambient and Low Temperatures . . . . . . . . . . . . . . . . . . . 323 FLUORESCENCE INDUCTION AND PS II HETEROGENEITy 325 Fluorescence Transient from Fo to FM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 The FI Level and Inactive PS11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... .... . .. . . . .. . . . . . . . . . 326 Fluorescence Induction in High Ught .. . . . . . . . . 327 Rise in the Presence of DCMU and a/{3 Heterogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 FLUORESCENCE QUENCHING 329 Resolution of Quenching Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ........ . .. . . . . . . . . . . . . . . 330 Mechanism of Energy·Dependent Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 1 Quenching Related t o State Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . ......... . . .. .. . . . . . . . 334 Photoinhibitory Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 Further Quenching Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 Physiological Aspects of Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 338 CONCLUSIONS AND PERSPECTiVES 341

Chlorophyll Fluorescence and Photosynthesis: The Basics

The use of chlorophyll fluorescence to monitor photosynthetic performance in algae and plants is now widespread. This review examines how fluorescence parameters can be used to evaluate changes in photosystem II (PSII) photochemistry, linear electron flux, and CO(2) assimilation in vivo, and outlines the theoretical bases for the use of specific fluorescence parameters. Although fluorescence parameters can be measured easily, many potential problems may arise when they are applied to predict changes in photosynthetic performance. In particular, consideration is given to problems associated with accurate estimation of the PSII operating efficiency measured by fluorescence and its relationship with the rates of linear electron flux and CO(2) assimilation. The roles of photochemical and nonphotochemical quenching in the determination of changes in PSII operating efficiency are examined. Finally, applications of fluorescence imaging to studies of photosynthetic heterogeneity and the rapid screening of large numbers of plants for perturbations in photosynthesis and associated metabolism are considered.

Chlorophyll fluorescence: a probe of photosynthesis in vivo

O2- oxidizes the [4Fe-4S] clusters of dehydratases, such as aconitase, causing-inactivation and release of Fe(II), which may then reduce H2O2 to OH- +OH.. SODs inhibit such HO. production by scavengingO2-, but Cu, ZnSODs, by virtue of a nonspecific peroxidase activity, may peroxidize spin trapping agents and thus give the appearance of catalyzing OH. production from H2O2. There is a glycosylated, tetrameric Cu, ZnSOD in the extracellular space that binds to acidic glycosamino-glycans. It minimizes the reaction of O2- with NO. E. coli, and other gram negative microorganisms, contain a periplasmic Cu, ZnSOD that may serve to protect against extracellular O2-. Mn(III) complexes of multidentate macrocyclic nitrogenous ligands catalyze the dismutation of O2- and are being explored as potential pharmaceutical agents. SOD-null mutants have been prepared to reveal the biological effects of O2-. SodA, sodB E. coli exhibit dioxygen-dependent auxotrophies and enhanced mutagenesis, reflecting O2(-)-sensitive biosynthetic pathways and DNA damage. Yeast, lacking either Cu, ZnSOD or MnSOD, are oxygen intolerant, and the double mutant was hypermutable and defective in sporulation and exhibited requirements for methionine and lysine. A Cu, ZnSOD-null Drosophila exhibited a shortened lifespan.

Superoxide Radical and Superoxide Dismutases

Photon yields of oxygen evolution at saturating CO2 were determined for 44 species of vascular plants, representing widely diverse taxa, habitats, life forms and growth conditions. The photonyield values on the basis of absorbed light (φa) were remarkably constant among plants possessing the same pathway of photosynthetic CO2 fixation, provided the plants had not been subjected to environmental stress. The mean φa value ±SE for 37 C3 species was 0.106±0.001 O2·photon-1. The five C4 species exhibited lower photon yields and greater variation than the C3 species (φa=0.0692±0.004). The φa values for the two Crassulaceanacid-metabolism species were similar to those of C3 species. Leaf chlorophyll content had little influence on φa over the range found in normal, healthy leaves. Chlorophyll fluorescence characteristics at 77 K were determined for the same leaves as used for the photon-yield measurements. Considerable variation in fluorescence emission both at 692 nm and at 734 nm, was found 1) among the different species; 2) between the upper and lower surfaces of the same leaves; and 3) between sun and shade leaves of the same species. By contrast, the ratio of variable to maximum fluorescence emission at 692 nm (Fv/FM, 692) remained remarkably constant (The mean value for the C3 species was 0.832±0.004). High-light treatments of shade leaves resulted in a reduction in both φa and the Fv/FM, 692 ratio. The extent of the reductions increased with time of exposure to bright light. A linear relationship was obtained when φa was plotted against Fv/FM, 692. The results show that determinations of the photon yield of O2 evolution and the Fv/FM, 692 ratio can serve as excellent quantitative measures of photoinhibition of overall photosynthetic energy-conversion system and of photochemistry of photosystem II, respectively. This is especially valuable in field work where it is often impossible to obtain appropriate controls.

Photon yield of O2 evolution and chlorophyll fluorescence characteristics at 77 K among vascular plants of diverse origins.

Chloroplast and photosystem I particles were encapsulated in small spheres (about 20 mum diameter) with an artificial membrane built up by cross-linking amino groups of protamine with toluenediisocyanate. The artificial membrane was permeable to small substrate and product molecules but not to soluble proteins. Photosystem I activity was retained by the encapsulated chloroplast particles. Washed photosystem I particles were encapsulated with the soluble proteins, ferredoxin, and ferredoxin-NADP oxidoreductase, and the microcapsules photoreduced NADP using ascorbate plus dichlorophenolindophenol as the electron donor. The photosystem I particles were also encapsulated with hydrogenase from Chromatium and a very low rate of photoevolution of hydrogen was obtained. The results show that chloroplast membrane fragments can be encapsulated with soluble proteins that couple transfer reactions to the primary photochemical apparatus.

/pdf/microencapsulation-of-chloroplast-particles-338y2wfpzc.pdf

Microencapsulation of Chloroplast Particles

Energy transfer and the distribution of excitation energy in the photosynthetic apparatus of spinach chloroplasts

— In isolated spinach chloroplasts the light-induced electron paramagnetic resonance signal (signal II) associated with the oxygen evolving photosystem (photosystem II) decays slowly and incompletely in the dark. Tris-washing, hydroxylamine, or carbonylcyanide m-chlorophenylhydrazone (CCCP) enhance the decay of signal II, which can still be induced by red (645 nm) but not by far-red (735 nm) radiation. Although 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) alone has no effect on signal II, it blocks the induction of signal II in the presence of hydroxylamine or CCCP. These data suggest that signal II is an indicator of an oxidized intermediate on the water-splitting side of photosystem II.

Effects of photosystem ii inhibitors on electron paramagnetic resonance signal ii of spinach chloroplasts

Publisher Summary This chapter presents a historical background of fluorescence in relation to the development of the two-pigment-system concept of photosynthesis. It discusses the significance of fluorescence measurements in the study of photosynthesis. The indication that the two-pigment-system phenomenon is manifested in fluorescence as well as photosynthesis was reported in an experiment that was similar in design to those that revealed enhancement of photosynthesis. The experiment compared fluorescence obtained with 670 mμ, excitation, fluorescence obtained with 700 mμ excitation, and fluorescence obtained with simultaneous excitation with 670 mμ and 700 mμ light. The results showed a de-enhancement of fluorescence, that is, the intensity of fluorescence excited by simultaneous irradiation with both beams was less than the sum of the fluorescence intensities that were excited by the individual beams. The action spectrum for the effect of long-wavelength light in decreasing the fluorescence yield of leaves was determined by alternate irradiation of the sample with red light and with a monochromatic beam in the far-red region

Fluorescence Yield in Photosynthetic Systems and Its Relation to Electron Transport

— The mycelium of Neurospora crassa was ground and extracted with buffer and separated into a soluble supernatant fraction and a particulate fraction by centrifugation. Both fractions were examined for light-induced absorbance changes. Irradiation of the supernatant fraction caused a reversible photooxidation of cytochrome c which was inhibited by sodium azide or by dialysis. The action spectrum for the photooxidation showed that the response was mediated by an endogenous flavin. The photooxidation of cytochrome c, lost by dialysis, could be restored by adding flavin mononucleotide. Irradiation of the particulate fraction with blue light caused a reversible photoreduction of cytochrome c and cytochrome oxidase and, in some samples, of cytochrome b as well. The supernatant fraction showed photooxidation of cytochrome c rather than the more usual photoreductive changes because of the presence of super-oxide dismutase activity.

Warren L. Butler

Papers

Microencapsulation of Chloroplast Particles

Energy transfer and the distribution of excitation energy in the photosynthetic apparatus of spinach chloroplasts

Effects of photosystem ii inhibitors on electron paramagnetic resonance signal ii of spinach chloroplasts

Fluorescence Yield in Photosynthetic Systems and Its Relation to Electron Transport

Light-induced absorbance changes in cell-free extracts of Neurospora crassa.