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.

A far red absorbing form of chlorophyll.

Redox titration of the primary electron acceptor of Photosystem I in spinach chloroplasts

The effects of lipase on spinach and Chlamydomonas chloroplasts

ESCULETIN was found in an extract of plant tissue which contained caffeic acid. The esculetin was not a natural product but was formed from caffeic acid during the paper-chromatographic purification procedures. This conversion was confirmed by two-dimensional chromatography of authentic caffeic acid.

Warren L. Butler

Papers

A far red absorbing form of chlorophyll.

Redox titration of the primary electron acceptor of Photosystem I in spinach chloroplasts

The effects of lipase on spinach and Chlamydomonas chloroplasts

Conversion of caffeic acid to esculetin during paper chromatography.

The back reaction in the primary electron transfer couple of photosystem II of photosynthesis.