Professor Govindjee | University of Illinois at Urbana-Champaign (original) (raw)

Papers by Professor Govindjee

This paper is concerned with relating thermoluminescence to the total free-energy change, EG, inv... more This paper is concerned with relating thermoluminescence to the total free-energy change, EG, involved in detrapping a particular electron-hole pair as a photosynthetic sample is warmed from an initial low temperature. It extends a mathematical discussion of four possible mechanisms introduced in an earlier paper [DeVault, Govindjee and Arnold, Proc Nat'l Acad Sci USA 80:983-987 (1983)]; here, particular attention is paid to the dependence of the absolute temperature of the maximum of a glow-peak, Tin, on the total free-energy change, EG. The conclusion from the cases studied is that Tm = EG/(kB W) where ZG is evaluated at Tm, W is a complicated function of temperature and of thermodynamic parameters in the steps of the mechanism, and kB is the Boltzmann constant. If the rate limiting step in the mechanism of detrapping is not preceded by any step in which AG is appreciably negative, Wis likely to have a value of about 33 and Tm is approximately proportional to EG. Otherwise W can become much smaller and more strongly dependent on temperature and Tm is no longer proportional to YG. These conclusions are of significance in lending theoretical support to the practice of inferring redox midpoint potential changes from shifts in Tin.

Chlorophyll a (Chl a) serves a dual role in oxygenic photosynthesis: in light harvesting as well ... more Chlorophyll a (Chl a) serves a dual role in oxygenic photosynthesis: in light harvesting as well as in converting energy of absorbed photons to chemical energy. No other Chl is as omnipresent in oxygenic photosynthesis as is Chl a, and this is particularly true if we include Chl a(2), (=[8-vinyl]-Chl a), which occurs in Prochlorococcus, as a type of Chl a. One exception to this near universal pattern is Chl d, which is found in some cyanobacteria that live in filtered light that is enriched in wavelengths >700 nm. They trap the long wavelength electronic excitation, and convert it into chemical energy. In this Viewpoint, we have traced the possible reasons for the near ubiquity of Chl a for its use in the primary photochemistry of Photosystem II (PS II) that leads to water oxidation and of Photosystem I (PS I) that leads to ferredoxin reduction. Chl a appears to be unique and irreplaceable, particularly if global scale oxygenic photosynthesis is considered. Its uniqueness is determined by its physicochemical properties, but there is more. Other contributing factors include specially tailored protein environments, and functional compatibility with neighboring electron transporting cofactors. Thus, the same molecule, Chl a in vivo, is capable of generating a radical cation at +1 V or higher (in PS II), a radical anion at -1 V or lower (in PS I), or of being completely redox silent (in antenna holochromes).

This review is dedicated to David Walker (1928-2012), a pioneer in the field of photosynthesis an... more This review is dedicated to David Walker (1928-2012), a pioneer in the field of photosynthesis and chlorophyll fluorescence. We begin this review by presenting the history of light emission studies, from the ancient times. Light emission from plants is of several kinds: prompt fluorescence (PF), delayed fluorescence (DF), thermoluminescence, and phosphorescence. In this article, we focus on PF and DF. Chlorophyll a fluorescence measurements have been used for more than 80 years to study photosynthesis, particularly photosystem II (PSII) since 1961. This technique has become a regular trusted probe in agricultural and biological research. Many measured and calculated parameters are good biomarkers or indicators of plant tolerance to different abiotic and biotic stressors. This would never have been possible without the rapid development of new fluorometers. To date, most of these instruments are based mainly on two different operational principles for measuring variable chlorophyll a fluorescence: (1) a PF signal produced following a pulseamplitude-modulated excitation and (2) a PF signal emitted during a strong continuous actinic excitation. In addition to fluorometers, other instruments have been developed to measure additional signals, such as DF, originating from PSII, and light-induced absorbance changes due to the photooxidation of P700, from PSI, measured as the absorption decrease (photobleaching) at about 705 nm, or

Optical Biopsy VII, 2010

A wheen o' mickles mak's a muckle "Like van Niels' concept of photochemical oxidoreduction, the i... more A wheen o' mickles mak's a muckle "Like van Niels' concept of photochemical oxidoreduction, the idea of the photosynthetic unit has become a cornerstone of current descriptions of photosynthesis." (Roderick K. Clayton, 1965

Photosynthesis research, Jan 8, 2015

The green alga Chlamydomonas (C.) reinhardtii is a model organism for photosynthesis research. St... more The green alga Chlamydomonas (C.) reinhardtii is a model organism for photosynthesis research. State transitions regulate redistribution of excitation energy between photosystem I (PS I) and photosystem II (PS II) to provide balanced photosynthesis. Chlorophyll (Chl) a fluorescence induction (the so-called OJIPSMT transient) is a signature of several photosynthetic reactions. Here, we show that the slow (seconds to minutes) S to M fluorescence rise is reduced or absent in the stt7 mutant (which is locked in state 1) in C. reinhardtii. This suggests that the SM rise in wild type C. reinhardtii may be due to state 2 (low fluorescence state; larger antenna in PS I) to state 1 (high fluorescence state; larger antenna in PS II) transition, and thus, it can be used as an efficient and quick method to monitor state transitions in algae, as has already been shown in cyanobacteria (Papageorgiou et al. 1999, 2007; Kaňa et al. 2012). We also discuss our results on the effects of (1) 3-(3,4-dic...

Frontiers in plant science, 2011

Cyanobacteria, or the blue-green algae as they used to be called until 1974, are the oldest oxyge... more Cyanobacteria, or the blue-green algae as they used to be called until 1974, are the oldest oxygenic photosynthesizers. We summarize here adventures with them since the early 1960s. This includes studies on light absorption by cyanobacteria, excitation energy transfer at room temperature down to liquid helium temperature, fluorescence (kinetics as well as spectra) and its relationship to photosynthesis, and afterglow (or thermoluminescence) from them. Further, we summarize experiments on their two-light reaction - two-pigment system, as well as the unique role of bicarbonate (hydrogen carbonate) on the electron-acceptor side of their photosystem II, PSII. This review, in addition, includes a discussion on the regulation of changes in phycobilins (mostly in PSII) and chlorophyll a (Chl a; mostly in photosystem I, PSI) under oscillating light, on the relationship of the slow fluorescence increase (the so-called S to M rise, especially in the presence of diuron) in minute time scale wi...

Biochemistry (Moscow), 2014

To honor Academician Alexander Abramovitch Krasnovsky, we present here an educational review on t... more To honor Academician Alexander Abramovitch Krasnovsky, we present here an educational review on the relation of chlorophyll a fluorescence transient to various processes in photosynthesis. The initial event in oxygenic photosynthesis is light absorption by chlorophylls (Chls), carotenoids, and, in some cases, phycobilins; these pigments form the antenna. Most of the energy is transferred to reaction centers where it is used for charge separation. The small part of energy that is not used in photochemistry is dissipated as heat or re-emitted as fluorescence. When a photosynthetic sample is transferred from dark to light, Chl a fluorescence (ChlF) intensity shows characteristic changes in time called fluorescence transient, the OJIPSMT transient, where O (the origin) is for the first measured minimum fluorescence level; J and I for intermediate inflections; P for peak; S for semi-steady state level; M for maximum; and T for terminal steady state level. This transient is a real signature of photosynthesis, since diverse events can be related to it, such as: changes in redox states of components of the linear electron transport flow, involvement of alternative electron routes, the build-up of a transmembrane pH gradient and membrane potential, activation of different nonphotochemical quenching processes, activation of the Calvin-Benson cycle, and other processes. In this review, we present our views on how different segments of the OJIPSMT transient are influenced by various photosynthetic processes, and discuss a number of studies involving mathematical modeling and simulation of the ChlF transient. A special emphasis is given to the slower PSMT phase, for which many studies have been recently published, but they are less known than on the faster OJIP phase.

Photosynthesis Research, 2014

Prasanna K. Mohanty, a great scientist, a great teacher and above all a great human being, left u... more Prasanna K. Mohanty, a great scientist, a great teacher and above all a great human being, left us more than a year ago (on March 9, 2013). He was a pioneer in the field of photosynthesis research; his contributions are many and wide-ranging. In the words of Jack Myers, he would be a ''photosynthetiker'' par excellence. He remained deeply engaged with research almost to the end of his life; we believe that generations of researchers still to come will benefit from his thorough and enormous work. We present here his life and some of his contributions to the field of Photosynthesis Research. The response to this tribute was overwhelming and we have included most of the tributes, which we received from all over the world. Prasanna Mohanty was a pioneer in the field of ''Light Regulation of Photosynthesis'', a loving and dedicated teacher-unpretentious, idealistic, and an honest human being.

Photosynthesis Research, 2014

Investigations were carried to unravel mechanism(s) for higher tolerance of floating over submerg... more Investigations were carried to unravel mechanism(s) for higher tolerance of floating over submerged leaves of long leaf pondweed (Potamogeton nodosus Poir) against photoinhibition. Chloroplasts from floating leaves showed *5and *6.4-fold higher Photosystem (PS) I (reduced dichlorophenol-indophenol ? methyl viologen ? O 2) and PS II (H 2 O ? parabenzoquine) activities over those from submerged leaves. The saturating rate (V max) of PS II activity of chloroplasts from floating and submerged leaves reached at *600 and *230 lmol photons m-2 s-1 , respectively. Photosynthetic electron transport rate in floating leaves was over 5-fold higher than in submerged leaves. Further, floating leaves, as compared to submerged leaves, showed higher F v /F m (variable to maximum chlorophyll fluorescence, a reflection of PS II efficiency), as well as a higher potential to withstand photoinhibitory damage by high light (1,200 lmol photons m-2 s-1). Cells of floating leaves had not only higher mitochondria to chloroplast ratio, but also showed many mitochondria in close vicinity of chloroplasts. Electron transport (NADH ? O 2 ; succinate ? O 2) in isolated mitochondria of floating leaves was sensitive to both cyanide (CN-) and salicylhydroxamic acid (SHAM), whereas those in submerged leaves were sensitive to CN-, but virtually insensitive to SHAM, revealing the presence of alternative oxidase in mitochondria of floating, but not of submerged, leaves. Further, the potential of floating leaves to withstand photoinhibitory damage was significantly reduced in the presence of CNand SHAM, individually and in combination. Our experimental results establish that floating leaves possess better photosynthetic efficiency and capacity to withstand photoinhibition compared to submerged leaves; and mitochondria play a pivotal role in protecting photosynthetic machinery of floating leaves against photoinhibition, most likely by oxidation of NAD(P)H and reduction of O 2. Keywords Chlorophyll a fluorescence Á CN-resistant alternative oxidase pathway Á CN-sensitive cytochrome oxidase pathway Á Chloroplast-mitochondria interaction Á Photoinhibition Á Potamogeton nodosus Abbreviations Chl Chlorophyll CN Cyanide

Photosynthesis Research, 2014

and Taiwan. In fact, more than 20 countries were represented at this conference. Fig. 2 shows a g... more and Taiwan. In fact, more than 20 countries were represented at this conference. Fig. 2 shows a group photograph of most of the participants.

Photosynthesis Research, 2012

In this brief report, we provide a perspective on an international conference &am... more In this brief report, we provide a perspective on an international conference "Photosynthesis Research for Sustainability-2011", held in Baku, Azerbaijan, during July 24-30, 2011 ( http://www.photosynthesis2011.cellreg.org/ ). At this conference, awards were given to nine young investigators; they are recognized in this Report. We have also included here some photographs to show the pleasant ambiance at this conference. (See http://www.photosynthesis2011.cellreg.org/Photos.php and http://www.life.illinois.edu/govindjee/g/Photo/Baku.html for more photographs taken by the authors as well as by others.) We invite the readers to the next conference on "Photosynthesis Research for Sustainability-2013" to be held in May or June 2013, in Baku, Azerbaijan. Information will be posted at: http://www.photosynthesis2013.cellreg.org/ .

Photosynthesis Research, 2013

Online access to the Internet and the World Wide Web has become important for public awareness an... more Online access to the Internet and the World Wide Web has become important for public awareness and for educating the world's population, including its political leaders, students, researchers, teachers, and ordinary citizens seeking information. After a brief Introduction, relevant information found on photosynthesis-related Web sites and other online locations is presented under five categories: (a) group sites, (b) sites by subject, (c) individual researcher's sites, (d) sites for educators and students, and (e) other useful sites.

Photosynthesis Research, 2012

We provide a News Report on the 2012 Gordon Research Conference on Photosynthesis held at Davidso... more We provide a News Report on the 2012 Gordon Research Conference on Photosynthesis held at Davidson College, North Carolina during July 8-13 that focuses on four young investigators who were presented awards during the conference.

Photosynthesis Research, 2010

We celebrate Andy Benson's 93rd birthday on September 24, 2010 through this Editorial. Th... more We celebrate Andy Benson's 93rd birthday on September 24, 2010 through this Editorial. This short account about Andy Benson should serve as a prelude to the short article that Andy has written for the entire photosynthesis community, which gives a glimpse of why he left the field of the "path of carbon in photosynthesis," when he had already discovered, together with Melvin Calvin, James Alan Bassham, and others, most of the major steps in what we now call the Calvin-Benson cycle.

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2013

Nonphotochemical quenching (NPQ) of Photosystem II fluorescence is one of the most important phot... more Nonphotochemical quenching (NPQ) of Photosystem II fluorescence is one of the most important photoprotection responses of phototropic organisms. NPQ in Macrocystis pyrifera is unique since the fast induction of this response, the energy dependent quenching (qE), is not present in this alga. In contrast to higher plants, NPQ in this organism is much more strongly related to xanthophyll cycle (XC) pigment interconversion. Characterization of how NPQ is controlled when qE is not present is important as this might represent an ancient response to light stress. Here, we describe the influence of the XC pigment pool (ΣXC) size on NPQ induction in M. pyrifera. The sum of violaxanthin (Vx) plus antheraxanthin and zeaxanthin (Zx) represents the ΣXC. This pool was three-fold larger in blades collected at the surface of the water column (19molmol(-1) Chl a×100) than in blades collected at 6m depth. Maximum NPQ was not different in samples with a ΣXC higher than 12molmol(-1) Chl a×100; however, NPQ induction was faster in blades with a large ΣXC. The increase in the NPQ induction rate was associated with a faster Vx to Zx conversion. Further, we found that NPQ depends on the de-epoxidation state of the ΣXC, not on the absolute concentration of Zx and antheraxanthin. Thus, there was an antagonist effect between Vx and de-epoxidated xanthophylls for NPQ. These results indicate that in the absence of qE, a large ΣXC is needed in M. pyrifera to respond faster to light stress conditions.

Astrobiology, 2007

Why do plants reflect in the green and have a “red edge” in the red, and should extrasolar photos... more Why do plants reflect in the green and have a “red edge” in the red, and should extrasolar photosynthesis be the same? We provide (1) a brief review of how photosynthesis works, (2) an overview of the diversity of photosynthetic organisms, their light harvesting systems, and ...

This News Report is a brief description of the 2010 Lifetime Achievement Award received by Willia... more This News Report is a brief description of the 2010 Lifetime Achievement Award received by William (Bill) L. Ogren from the Rebeiz Foundation for Basic Research, at Champaign, Illinois, on Sep 10, 2011. It focuses mainly on the presentations by two of us (ARP and Gov), Christoph Benning (on behalf of Chris Somerville), David Krogmann and Jack Widholm, at this ceremony. It is enriched by the testimonial received from George Bowes at the time of the preparation of this report.

There are several types of light emission in plants: prompt fluorescence, delayed fluorescence, t... more There are several types of light emission in plants: prompt fluorescence, delayed fluorescence, thermoluminescence, and phosphorescence. This chapter focuses on two of them: prompt and delayed fluorescence. Chlorophyll a fluorescence measurements have been used for more than 80 years to study photosynthesis; since 1961, it has been used, particularly, for the analysis of PhotosystemII (PS II). Fluorescence is now used routinely in agricultural and biological research where many measured and calculated parameters are used as biomarkers or indicators of plant tolerance to different abiotic and biotic stress. This has been made possible by the rapid development of new fluorometers. Most of these instruments are mainly based on two different operational principles for the measurement of variable chlorophyll a fluorescence: (1) pulse-amplitude-modulated (PAM) excitation followed by measurement of prompt fluorescence and (2) a strong continuous actinic excitation leading to prompt fluorescence. In addition to fluorometers, other instruments have been developed to measure other signals, such as delayed fluorescence, originating mainly from PS II, and light-induced absorbance changes due to the photo-oxidation of the reaction center P700 of PS I, measured as absorption decrease (photobleaching) at about 705 nm, or increase at 820 nm. This chapter includes technical and theoretical basis of newly developed instruments that allow for simultaneous measurement of the prompt fluorescence (PF) and the delayed fluorescence (DF) as well as some other In vivo MEASUREMENTS OF LIGHT EMISSION IN PLANTS 3 parameters. Special emphasis is given here to a description of comparativemeasurements on PF and DF. Since DF is much less used and less known than PF, it is discussed in greater details; it has great potential to provide useful, and qualitatively new information on the back reactions of PS II electron transfer. This chapter, which also deals with the history of fluorometers, is dedicated to David Walker (1928–2012), who was a pioneer in the field of photosynthesis and chlorophyll fluorescence.

We provide here insights on the life and work of Berger C. Mayne (1920-2011). We remember and hon... more We provide here insights on the life and work of Berger C. Mayne (1920-2011). We remember and honor Berger, whose study of photosynthesis began with the most basic processes of intersystem electron transport and oxygen evolution, continued with application of fluorescence techniques to the study of photophosphorylation and the unique features of photosystems in specialized cells, and concluded with collaborative study of photosynthesis in certain nitrogen fixing symbioses. Berger loved the outdoors and was dedicated to preserving the environment and to social justice, and was a wonderful friend. Keywords C 4 plants Á Chlorophyll Á Prompt and delayed fluorescence Á Hill reaction Á Emerson enhancement effect Á Nitrogen fixation Á Photophosphorylation Á Photosystem I Á Photosystem II Early life Berger Mayne was born on July 10, 1920, in the small settlement of Towner, in eastern Colorado, USA. His love of nature found expression in hunting and fishing, and sometimes even in adopting local wildlife. During World War II, he served at an army hospital in Hawaii. In 1947, Berger graduated from Western State College in Gunnison, Colorado, with an A. B. degree in Biology. A formative experience occurred while he was dissecting a shark during a biology laboratory, when he accidentally dragged his necktie through a puddle of blood. Subsequently, he only wore bow ties (Fig. 1). Berger attended graduate school at the University of Utah, and received his Ph.D. in Experimental Biology in 1958. Working with John Spikes and Rufus Lumry, he examined the relationship between chlorophyll a fluorescence yield and Hill reaction velocities in chloroplasts and the green alga Chlorella (Mayne 1958; Lumry et al. 1959; Spikes and Mayne 1960). Throughout his career, Berger would continue to use his expertise with chlorophyll fluorescence measurement to address a diversity of questions. Darrell Fleischman was invited to contribute a Tribute to Berger C. Mayne by Govindjee, Founding Historical Corner Editor of Photosynthesis Research. Several others joined Fleischman in honoring Berger Mayne.

This paper is concerned with relating thermoluminescence to the total free-energy change, EG, inv... more This paper is concerned with relating thermoluminescence to the total free-energy change, EG, involved in detrapping a particular electron-hole pair as a photosynthetic sample is warmed from an initial low temperature. It extends a mathematical discussion of four possible mechanisms introduced in an earlier paper [DeVault, Govindjee and Arnold, Proc Nat'l Acad Sci USA 80:983-987 (1983)]; here, particular attention is paid to the dependence of the absolute temperature of the maximum of a glow-peak, Tin, on the total free-energy change, EG. The conclusion from the cases studied is that Tm = EG/(kB W) where ZG is evaluated at Tm, W is a complicated function of temperature and of thermodynamic parameters in the steps of the mechanism, and kB is the Boltzmann constant. If the rate limiting step in the mechanism of detrapping is not preceded by any step in which AG is appreciably negative, Wis likely to have a value of about 33 and Tm is approximately proportional to EG. Otherwise W can become much smaller and more strongly dependent on temperature and Tm is no longer proportional to YG. These conclusions are of significance in lending theoretical support to the practice of inferring redox midpoint potential changes from shifts in Tin.

Chlorophyll a (Chl a) serves a dual role in oxygenic photosynthesis: in light harvesting as well ... more Chlorophyll a (Chl a) serves a dual role in oxygenic photosynthesis: in light harvesting as well as in converting energy of absorbed photons to chemical energy. No other Chl is as omnipresent in oxygenic photosynthesis as is Chl a, and this is particularly true if we include Chl a(2), (=[8-vinyl]-Chl a), which occurs in Prochlorococcus, as a type of Chl a. One exception to this near universal pattern is Chl d, which is found in some cyanobacteria that live in filtered light that is enriched in wavelengths >700 nm. They trap the long wavelength electronic excitation, and convert it into chemical energy. In this Viewpoint, we have traced the possible reasons for the near ubiquity of Chl a for its use in the primary photochemistry of Photosystem II (PS II) that leads to water oxidation and of Photosystem I (PS I) that leads to ferredoxin reduction. Chl a appears to be unique and irreplaceable, particularly if global scale oxygenic photosynthesis is considered. Its uniqueness is determined by its physicochemical properties, but there is more. Other contributing factors include specially tailored protein environments, and functional compatibility with neighboring electron transporting cofactors. Thus, the same molecule, Chl a in vivo, is capable of generating a radical cation at +1 V or higher (in PS II), a radical anion at -1 V or lower (in PS I), or of being completely redox silent (in antenna holochromes).

This review is dedicated to David Walker (1928-2012), a pioneer in the field of photosynthesis an... more This review is dedicated to David Walker (1928-2012), a pioneer in the field of photosynthesis and chlorophyll fluorescence. We begin this review by presenting the history of light emission studies, from the ancient times. Light emission from plants is of several kinds: prompt fluorescence (PF), delayed fluorescence (DF), thermoluminescence, and phosphorescence. In this article, we focus on PF and DF. Chlorophyll a fluorescence measurements have been used for more than 80 years to study photosynthesis, particularly photosystem II (PSII) since 1961. This technique has become a regular trusted probe in agricultural and biological research. Many measured and calculated parameters are good biomarkers or indicators of plant tolerance to different abiotic and biotic stressors. This would never have been possible without the rapid development of new fluorometers. To date, most of these instruments are based mainly on two different operational principles for measuring variable chlorophyll a fluorescence: (1) a PF signal produced following a pulseamplitude-modulated excitation and (2) a PF signal emitted during a strong continuous actinic excitation. In addition to fluorometers, other instruments have been developed to measure additional signals, such as DF, originating from PSII, and light-induced absorbance changes due to the photooxidation of P700, from PSI, measured as the absorption decrease (photobleaching) at about 705 nm, or

Optical Biopsy VII, 2010

A wheen o' mickles mak's a muckle "Like van Niels' concept of photochemical oxidoreduction, the i... more A wheen o' mickles mak's a muckle "Like van Niels' concept of photochemical oxidoreduction, the idea of the photosynthetic unit has become a cornerstone of current descriptions of photosynthesis." (Roderick K. Clayton, 1965

Photosynthesis research, Jan 8, 2015

The green alga Chlamydomonas (C.) reinhardtii is a model organism for photosynthesis research. St... more The green alga Chlamydomonas (C.) reinhardtii is a model organism for photosynthesis research. State transitions regulate redistribution of excitation energy between photosystem I (PS I) and photosystem II (PS II) to provide balanced photosynthesis. Chlorophyll (Chl) a fluorescence induction (the so-called OJIPSMT transient) is a signature of several photosynthetic reactions. Here, we show that the slow (seconds to minutes) S to M fluorescence rise is reduced or absent in the stt7 mutant (which is locked in state 1) in C. reinhardtii. This suggests that the SM rise in wild type C. reinhardtii may be due to state 2 (low fluorescence state; larger antenna in PS I) to state 1 (high fluorescence state; larger antenna in PS II) transition, and thus, it can be used as an efficient and quick method to monitor state transitions in algae, as has already been shown in cyanobacteria (Papageorgiou et al. 1999, 2007; Kaňa et al. 2012). We also discuss our results on the effects of (1) 3-(3,4-dic...

Frontiers in plant science, 2011

Cyanobacteria, or the blue-green algae as they used to be called until 1974, are the oldest oxyge... more Cyanobacteria, or the blue-green algae as they used to be called until 1974, are the oldest oxygenic photosynthesizers. We summarize here adventures with them since the early 1960s. This includes studies on light absorption by cyanobacteria, excitation energy transfer at room temperature down to liquid helium temperature, fluorescence (kinetics as well as spectra) and its relationship to photosynthesis, and afterglow (or thermoluminescence) from them. Further, we summarize experiments on their two-light reaction - two-pigment system, as well as the unique role of bicarbonate (hydrogen carbonate) on the electron-acceptor side of their photosystem II, PSII. This review, in addition, includes a discussion on the regulation of changes in phycobilins (mostly in PSII) and chlorophyll a (Chl a; mostly in photosystem I, PSI) under oscillating light, on the relationship of the slow fluorescence increase (the so-called S to M rise, especially in the presence of diuron) in minute time scale wi...

Biochemistry (Moscow), 2014

To honor Academician Alexander Abramovitch Krasnovsky, we present here an educational review on t... more To honor Academician Alexander Abramovitch Krasnovsky, we present here an educational review on the relation of chlorophyll a fluorescence transient to various processes in photosynthesis. The initial event in oxygenic photosynthesis is light absorption by chlorophylls (Chls), carotenoids, and, in some cases, phycobilins; these pigments form the antenna. Most of the energy is transferred to reaction centers where it is used for charge separation. The small part of energy that is not used in photochemistry is dissipated as heat or re-emitted as fluorescence. When a photosynthetic sample is transferred from dark to light, Chl a fluorescence (ChlF) intensity shows characteristic changes in time called fluorescence transient, the OJIPSMT transient, where O (the origin) is for the first measured minimum fluorescence level; J and I for intermediate inflections; P for peak; S for semi-steady state level; M for maximum; and T for terminal steady state level. This transient is a real signature of photosynthesis, since diverse events can be related to it, such as: changes in redox states of components of the linear electron transport flow, involvement of alternative electron routes, the build-up of a transmembrane pH gradient and membrane potential, activation of different nonphotochemical quenching processes, activation of the Calvin-Benson cycle, and other processes. In this review, we present our views on how different segments of the OJIPSMT transient are influenced by various photosynthetic processes, and discuss a number of studies involving mathematical modeling and simulation of the ChlF transient. A special emphasis is given to the slower PSMT phase, for which many studies have been recently published, but they are less known than on the faster OJIP phase.

Photosynthesis Research, 2014

Prasanna K. Mohanty, a great scientist, a great teacher and above all a great human being, left u... more Prasanna K. Mohanty, a great scientist, a great teacher and above all a great human being, left us more than a year ago (on March 9, 2013). He was a pioneer in the field of photosynthesis research; his contributions are many and wide-ranging. In the words of Jack Myers, he would be a ''photosynthetiker'' par excellence. He remained deeply engaged with research almost to the end of his life; we believe that generations of researchers still to come will benefit from his thorough and enormous work. We present here his life and some of his contributions to the field of Photosynthesis Research. The response to this tribute was overwhelming and we have included most of the tributes, which we received from all over the world. Prasanna Mohanty was a pioneer in the field of ''Light Regulation of Photosynthesis'', a loving and dedicated teacher-unpretentious, idealistic, and an honest human being.

Photosynthesis Research, 2014

Investigations were carried to unravel mechanism(s) for higher tolerance of floating over submerg... more Investigations were carried to unravel mechanism(s) for higher tolerance of floating over submerged leaves of long leaf pondweed (Potamogeton nodosus Poir) against photoinhibition. Chloroplasts from floating leaves showed *5and *6.4-fold higher Photosystem (PS) I (reduced dichlorophenol-indophenol ? methyl viologen ? O 2) and PS II (H 2 O ? parabenzoquine) activities over those from submerged leaves. The saturating rate (V max) of PS II activity of chloroplasts from floating and submerged leaves reached at *600 and *230 lmol photons m-2 s-1 , respectively. Photosynthetic electron transport rate in floating leaves was over 5-fold higher than in submerged leaves. Further, floating leaves, as compared to submerged leaves, showed higher F v /F m (variable to maximum chlorophyll fluorescence, a reflection of PS II efficiency), as well as a higher potential to withstand photoinhibitory damage by high light (1,200 lmol photons m-2 s-1). Cells of floating leaves had not only higher mitochondria to chloroplast ratio, but also showed many mitochondria in close vicinity of chloroplasts. Electron transport (NADH ? O 2 ; succinate ? O 2) in isolated mitochondria of floating leaves was sensitive to both cyanide (CN-) and salicylhydroxamic acid (SHAM), whereas those in submerged leaves were sensitive to CN-, but virtually insensitive to SHAM, revealing the presence of alternative oxidase in mitochondria of floating, but not of submerged, leaves. Further, the potential of floating leaves to withstand photoinhibitory damage was significantly reduced in the presence of CNand SHAM, individually and in combination. Our experimental results establish that floating leaves possess better photosynthetic efficiency and capacity to withstand photoinhibition compared to submerged leaves; and mitochondria play a pivotal role in protecting photosynthetic machinery of floating leaves against photoinhibition, most likely by oxidation of NAD(P)H and reduction of O 2. Keywords Chlorophyll a fluorescence Á CN-resistant alternative oxidase pathway Á CN-sensitive cytochrome oxidase pathway Á Chloroplast-mitochondria interaction Á Photoinhibition Á Potamogeton nodosus Abbreviations Chl Chlorophyll CN Cyanide

Photosynthesis Research, 2014

and Taiwan. In fact, more than 20 countries were represented at this conference. Fig. 2 shows a g... more and Taiwan. In fact, more than 20 countries were represented at this conference. Fig. 2 shows a group photograph of most of the participants.

Photosynthesis Research, 2012

In this brief report, we provide a perspective on an international conference &am... more In this brief report, we provide a perspective on an international conference "Photosynthesis Research for Sustainability-2011", held in Baku, Azerbaijan, during July 24-30, 2011 ( http://www.photosynthesis2011.cellreg.org/ ). At this conference, awards were given to nine young investigators; they are recognized in this Report. We have also included here some photographs to show the pleasant ambiance at this conference. (See http://www.photosynthesis2011.cellreg.org/Photos.php and http://www.life.illinois.edu/govindjee/g/Photo/Baku.html for more photographs taken by the authors as well as by others.) We invite the readers to the next conference on "Photosynthesis Research for Sustainability-2013" to be held in May or June 2013, in Baku, Azerbaijan. Information will be posted at: http://www.photosynthesis2013.cellreg.org/ .

Photosynthesis Research, 2013

Online access to the Internet and the World Wide Web has become important for public awareness an... more Online access to the Internet and the World Wide Web has become important for public awareness and for educating the world's population, including its political leaders, students, researchers, teachers, and ordinary citizens seeking information. After a brief Introduction, relevant information found on photosynthesis-related Web sites and other online locations is presented under five categories: (a) group sites, (b) sites by subject, (c) individual researcher's sites, (d) sites for educators and students, and (e) other useful sites.

Photosynthesis Research, 2012

We provide a News Report on the 2012 Gordon Research Conference on Photosynthesis held at Davidso... more We provide a News Report on the 2012 Gordon Research Conference on Photosynthesis held at Davidson College, North Carolina during July 8-13 that focuses on four young investigators who were presented awards during the conference.

Photosynthesis Research, 2010

We celebrate Andy Benson's 93rd birthday on September 24, 2010 through this Editorial. Th... more We celebrate Andy Benson's 93rd birthday on September 24, 2010 through this Editorial. This short account about Andy Benson should serve as a prelude to the short article that Andy has written for the entire photosynthesis community, which gives a glimpse of why he left the field of the "path of carbon in photosynthesis," when he had already discovered, together with Melvin Calvin, James Alan Bassham, and others, most of the major steps in what we now call the Calvin-Benson cycle.

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2013

Nonphotochemical quenching (NPQ) of Photosystem II fluorescence is one of the most important phot... more Nonphotochemical quenching (NPQ) of Photosystem II fluorescence is one of the most important photoprotection responses of phototropic organisms. NPQ in Macrocystis pyrifera is unique since the fast induction of this response, the energy dependent quenching (qE), is not present in this alga. In contrast to higher plants, NPQ in this organism is much more strongly related to xanthophyll cycle (XC) pigment interconversion. Characterization of how NPQ is controlled when qE is not present is important as this might represent an ancient response to light stress. Here, we describe the influence of the XC pigment pool (ΣXC) size on NPQ induction in M. pyrifera. The sum of violaxanthin (Vx) plus antheraxanthin and zeaxanthin (Zx) represents the ΣXC. This pool was three-fold larger in blades collected at the surface of the water column (19molmol(-1) Chl a×100) than in blades collected at 6m depth. Maximum NPQ was not different in samples with a ΣXC higher than 12molmol(-1) Chl a×100; however, NPQ induction was faster in blades with a large ΣXC. The increase in the NPQ induction rate was associated with a faster Vx to Zx conversion. Further, we found that NPQ depends on the de-epoxidation state of the ΣXC, not on the absolute concentration of Zx and antheraxanthin. Thus, there was an antagonist effect between Vx and de-epoxidated xanthophylls for NPQ. These results indicate that in the absence of qE, a large ΣXC is needed in M. pyrifera to respond faster to light stress conditions.

Astrobiology, 2007

Why do plants reflect in the green and have a “red edge” in the red, and should extrasolar photos... more Why do plants reflect in the green and have a “red edge” in the red, and should extrasolar photosynthesis be the same? We provide (1) a brief review of how photosynthesis works, (2) an overview of the diversity of photosynthetic organisms, their light harvesting systems, and ...

This News Report is a brief description of the 2010 Lifetime Achievement Award received by Willia... more This News Report is a brief description of the 2010 Lifetime Achievement Award received by William (Bill) L. Ogren from the Rebeiz Foundation for Basic Research, at Champaign, Illinois, on Sep 10, 2011. It focuses mainly on the presentations by two of us (ARP and Gov), Christoph Benning (on behalf of Chris Somerville), David Krogmann and Jack Widholm, at this ceremony. It is enriched by the testimonial received from George Bowes at the time of the preparation of this report.

There are several types of light emission in plants: prompt fluorescence, delayed fluorescence, t... more There are several types of light emission in plants: prompt fluorescence, delayed fluorescence, thermoluminescence, and phosphorescence. This chapter focuses on two of them: prompt and delayed fluorescence. Chlorophyll a fluorescence measurements have been used for more than 80 years to study photosynthesis; since 1961, it has been used, particularly, for the analysis of PhotosystemII (PS II). Fluorescence is now used routinely in agricultural and biological research where many measured and calculated parameters are used as biomarkers or indicators of plant tolerance to different abiotic and biotic stress. This has been made possible by the rapid development of new fluorometers. Most of these instruments are mainly based on two different operational principles for the measurement of variable chlorophyll a fluorescence: (1) pulse-amplitude-modulated (PAM) excitation followed by measurement of prompt fluorescence and (2) a strong continuous actinic excitation leading to prompt fluorescence. In addition to fluorometers, other instruments have been developed to measure other signals, such as delayed fluorescence, originating mainly from PS II, and light-induced absorbance changes due to the photo-oxidation of the reaction center P700 of PS I, measured as absorption decrease (photobleaching) at about 705 nm, or increase at 820 nm. This chapter includes technical and theoretical basis of newly developed instruments that allow for simultaneous measurement of the prompt fluorescence (PF) and the delayed fluorescence (DF) as well as some other In vivo MEASUREMENTS OF LIGHT EMISSION IN PLANTS 3 parameters. Special emphasis is given here to a description of comparativemeasurements on PF and DF. Since DF is much less used and less known than PF, it is discussed in greater details; it has great potential to provide useful, and qualitatively new information on the back reactions of PS II electron transfer. This chapter, which also deals with the history of fluorometers, is dedicated to David Walker (1928–2012), who was a pioneer in the field of photosynthesis and chlorophyll fluorescence.

We provide here insights on the life and work of Berger C. Mayne (1920-2011). We remember and hon... more We provide here insights on the life and work of Berger C. Mayne (1920-2011). We remember and honor Berger, whose study of photosynthesis began with the most basic processes of intersystem electron transport and oxygen evolution, continued with application of fluorescence techniques to the study of photophosphorylation and the unique features of photosystems in specialized cells, and concluded with collaborative study of photosynthesis in certain nitrogen fixing symbioses. Berger loved the outdoors and was dedicated to preserving the environment and to social justice, and was a wonderful friend. Keywords C 4 plants Á Chlorophyll Á Prompt and delayed fluorescence Á Hill reaction Á Emerson enhancement effect Á Nitrogen fixation Á Photophosphorylation Á Photosystem I Á Photosystem II Early life Berger Mayne was born on July 10, 1920, in the small settlement of Towner, in eastern Colorado, USA. His love of nature found expression in hunting and fishing, and sometimes even in adopting local wildlife. During World War II, he served at an army hospital in Hawaii. In 1947, Berger graduated from Western State College in Gunnison, Colorado, with an A. B. degree in Biology. A formative experience occurred while he was dissecting a shark during a biology laboratory, when he accidentally dragged his necktie through a puddle of blood. Subsequently, he only wore bow ties (Fig. 1). Berger attended graduate school at the University of Utah, and received his Ph.D. in Experimental Biology in 1958. Working with John Spikes and Rufus Lumry, he examined the relationship between chlorophyll a fluorescence yield and Hill reaction velocities in chloroplasts and the green alga Chlorella (Mayne 1958; Lumry et al. 1959; Spikes and Mayne 1960). Throughout his career, Berger would continue to use his expertise with chlorophyll fluorescence measurement to address a diversity of questions. Darrell Fleischman was invited to contribute a Tribute to Berger C. Mayne by Govindjee, Founding Historical Corner Editor of Photosynthesis Research. Several others joined Fleischman in honoring Berger Mayne.