Primary Reactions Of Photosynthesis Research Articles

Evaluation of the primary reactions of photosynthesis in microalgae single cell by microfluorimetric method

Evaluation of the primary reactions of photosynthesis in microalgae single cell by microfluorimetric method

Dynamic Regulation of the Light-Harvesting System through State Transitions in Land Plants and Green Algae.

Photosynthesis constitutes the only known natural process that captures the solar energy to convert carbon dioxide and water into biomass. The primary reactions of photosynthesis are catalyzed by the photosystem II (PSII) and photosystem I (PSI) complexes. Both photosystems associate with antennae complexes whose main function is to increase the light-harvesting capability of the core. In order to maintain optimal photosynthetic activity under a constantly changing natural light environment, plants and green algae regulate the absorbed photo-excitation energy between PSI and PSII through processes known as state transitions. State transitions represent a short-term light adaptation mechanism for balancing the energy distribution between the two photosystems by relocating light-harvesting complex II (LHCII) proteins. The preferential excitation of PSII (state 2) results in the activation of a chloroplast kinase which in turn phosphorylates LHCII, a process followed by the release of phosphorylated LHCII from PSII and its migration to PSI, thus forming the PSI-LHCI-LHCII supercomplex. The process is reversible, as LHCII is dephosphorylated and returns to PSII under the preferential excitation of PSI. In recent years, high-resolution structures of the PSI-LHCI-LHCII supercomplex from plants and green algae were reported. These structural data provide detailed information on the interacting patterns of phosphorylated LHCII with PSI and on the pigment arrangement in the supercomplex, which is critical for constructing the excitation energy transfer pathways and for a deeper understanding of the molecular mechanism of state transitions progress. In this review, we focus on the structural data of the state 2 supercomplex from plants and green algae and discuss the current state of knowledge concerning the interactions between antenna and the PSI core and the potential energy transfer pathways in these supercomplexes.

From Soil Amendments to Controlling Autophagy: Supporting Plant Metabolism under Conditions of Water Shortage and Salinity.

Crop resistance to environmental stress is a major issue. The globally increasing land degradation and desertification enhance the demand on management practices to balance both food and environmental objectives, including strategies that tighten nutrient cycles and maintain yields. Agriculture needs to provide, among other things, future additional ecosystem services, such as water quantity and quality, runoff control, soil fertility maintenance, carbon storage, climate regulation, and biodiversity. Numerous research projects have focused on the food–soil–climate nexus, and results were summarized in several reviews during the last decades. Based on this impressive piece of information, we have selected only a few aspects with the intention of studying plant–soil interactions and methods for optimization. In the short term, the use of soil amendments is currently attracting great interest to cover the current demand in agriculture. We will discuss the impact of biochar at water shortage, and plant growth promoting bacteria (PGPB) at improving nutrient supply to plants. In this review, our focus is on the interplay of both soil amendments on primary reactions of photosynthesis, plant growth conditions, and signaling during adaptation to environmental stress. Moreover, we aim at providing a general overview of how dehydration and salinity affect signaling in cells. With the use of the example of abscisic acid (ABA) and ethylene, we discuss the effects that can be observed when biochar and PGPB are used in the presence of stress. The stress response of plants is a multifactorial trait. Nevertheless, we will show that plants follow a general concept to adapt to unfavorable environmental conditions in the short and long term. However, plant species differ in the upper and lower regulatory limits of gene expression. Therefore, the presented data may help in the identification of traits for future breeding of stress-resistant crops. One target for breeding could be the removal and efficient recycling of damaged as well as needless compounds and structures. Furthermore, in this context, we will show that autophagy can be a useful goal of breeding measures, since the recycling of building blocks helps the cells to overcome a period of imbalanced substrate supply during stress adjustment.

Structural basis for the assembly and quinone transport mechanisms of the dimeric photosynthetic RC\u2013LH1 supercomplex

The reaction center (RC) and light-harvesting complex 1 (LH1) form a RC–LH1 core supercomplex that is vital for the primary reactions of photosynthesis in purple phototrophic bacteria. Some species possess the dimeric RC–LH1 complex with a transmembrane polypeptide PufX, representing the largest photosynthetic complex in anoxygenic phototrophs. However, the details of the architecture and assembly mechanism of the RC–LH1 dimer are unclear. Here we report seven cryo-electron microscopy (cryo-EM) structures of RC–LH1 supercomplexes from Rhodobacter sphaeroides. Our structures reveal that two PufX polypeptides are positioned in the center of the S-shaped RC–LH1 dimer, interlocking association between the components and mediating RC–LH1 dimerization. Moreover, we identify another transmembrane peptide, designated PufY, which is located between the RC and LH1 subunits near the LH1 opening. PufY binds a quinone molecule and prevents LH1 subunits from completely encircling the RC, creating a channel for quinone/quinol exchange. Genetic mutagenesis, cryo-EM structures, and computational simulations provide a mechanistic understanding of the assembly and electron transport pathways of the RC–LH1 dimer and elucidate the roles of individual components in ensuring the structural and functional integrity of the photosynthetic supercomplex.

D‐Band EPR and ENDOR Spectroscopy of 15N‐Labeled Photosystem I

For billions of years, nature has optimized the photosynthetic machinery that converts light energy into chemical energy. Key primary reactions of photosynthesis occur in large membrane protein–cofactor complexes. The light-induced sequential electron transfer reactions occur through a chain of donor/acceptor cofactors embedded in the protein matrix resulting in a long-lived transmembrane charge-separated state. EPR is the method of choice to study electron transfer and the interaction of protein environment with redox-active cofactors. However, the spectra of organic cofactor radicals typically are not fully resolved and severely overlap at conventional X-band EPR. Even at Q-band EPR, this overlap is present and often a serious problem. As a result, there is a large variation of the reported EPR data and limited understanding of electronic structures of several redox-active cofactors. These serious problems can often be overcome by the excellent spectral resolution provided by high-frequency EPR (HF EPR). Here, we study the electronic structure of the primary electron donor P700 and the secondary electron acceptor A1 of Photosystem I (PSI) using 130 GHz (D-band) EPR and Electron–Nuclear-Double-Resonance (ENDOR) spectroscopy. PSI was isotopically labeled with 15N (I = ½) to avoid quadrupolar interactions in the most abundant nitrogen isotope 14N (I = 1) and simplify the ENDOR spectra. ENDOR spectroscopy is central for determining the hyperfine coupling of nitrogen atoms of the two chlorophyll molecules comprising oxidized P700 and the involvement of protein nitrogen atoms with reduced A1. While HF ENDOR of A1− allows identification of two nitrogen atoms, HF ENDOR of P700+ still does not permit unique assignment of the recorded hyperfine couplings.

Cadmium toxicity reduction in rice (Oryza sativa L.) through iron addition during primary reaction of photosynthesis.

Cadmium (Cd) pollution is a worldwide concern due to its biotoxicity. Because Cd and Fe are closely associated during plant photosynthesis, this study aims at investigating the mechanism governing Cd toxicity during photosynthetic primary reaction in rice by adjusting Fe concentration. The results show that moderate Fe concentration (1.0gkg-1) added to soil can increase the stomatal conductance (Gs) and SPAD value by stimulating the stomatal opening and chlorophyll synthesis. Moderate Fe concentration can also improve the maximum fluorescence (Fm) and the maximal photochemical efficiency (Fv/Fm) to keep the high reaction center activity and electronic transfer efficiency in photosystems I and II. Thus, moderate Fe can eliminate Cd-induced decrease in Gs, intercellular CO2 concentration (Ci) and net photosynthetic rate (Pn) as well as the disorder of antioxidative system under Cd concentration of 2.0mgkg-1 in the soil. When its application is increased to 2.0gkg-1, Fe can notably decrease Pn, and result in remarkable decrease in the biomass of shoots and grains. Decrease in Pn can be mainly attributed to high Fe concentration which can greatly destroy chloroplast structure and, meanwhile, inhibit the electron transfer between acceptor and donator in photosynthetic chain especially from quinone A (QA) to quinone B (QB). Unlike the situation under moderate Fe concentration, the high Fe application cannot mitigate the Cd-induced decrease in photosynthetic index. Our results indicate that the moderate Fe application is necessary to promote rice performance and production and, in the meantime, to inhibit Cd toxicity in the extensively polluted soils.

Enzyme functioning: Along the lines of nonequilibrium phase transitions

In recent decades the mechanisms of regulation of enzyme activity attract growing attention. Even the cornerstone schemes and notions of enzymology, such as the Michaelis-Menten scheme or cooperativity, undergo permanent refinements and revisions. Theoretical interpretations of new data, however, remain within the standard chemical kinetics framework. Although this admits qualitative explanations of some significant regulation phenomena like performance of ‘hysteretic’ enzymes, many characteristic features of enzymatic reactions (essentially nonexponential kinetics, dependence of rate constants on substrate concentration, and others) can hardly be accommodated. On the other hand, the inherent factors of enzyme functioning – flux conditions, slow structural changeability, nonlinear feedback between fast reaction acts and slow conformational rearrangements – provide a natural basis for self-organization phenomena. While their typical manifestations are related to macroscopic systems, the enzyme functioning can serve as an example of self-organization on the lowest possible level, down to single molecules. We put forward this concept of dynamical molecular self-organization in early 90’s and then developed its theoretical and experimental substantiations with the example of primary reactions of photosynthesis. In this work, I apply it to the Michaelis-Menten scheme. Within this paradigm, suitable for either ensemble or single molecule conditions, the stable functional regimes of enzyme operation emerge and interchange/coexist due to analogues of nonequilibrium phase transitions determined by the strength of substrate-conformation interaction and controlled by substrate concentration. In particular, the phenomena like ‘monomeric cooperativity’ or self-inhibition naturally follow from even the simplest two-state model of an enzyme with an only binding site.

Nitric Oxide Enhancing Resistance to PEG-Induced Water Deficiency is Associated with the Primary Photosynthesis Reaction in Triticum aestivum L.

Photosynthesis is affected by water-deficiency (WD) stress, and nitric oxide (NO) is a free radical that participates in the photosynthesis process. Previous studies have suggested that NO regulates excitation-energy distribution of photosynthesis under WD stress. Here, quantitative phosphoproteomic profiling was conducted using iTRAQ. Differentially phosphorylated protein species (DEPs) were identified in leaves of NO- or polyethylene glycol (PEG)-treated wheat seedlings (D), and in control seedlings. From 1396 unique phosphoproteins, 2257 unique phosphorylated peptides and 2416 phosphorylation sites were identified. Of these, 96 DEPs displayed significant changes (≥1.50-fold, p < 0.01). These DEPs are involved in photosynthesis, signal transduction, etc. Furthermore, phosphorylation of several DEPs was upregulated by both D and NO treatments, but downregulated only in NO treatment. These differences affected the chlorophyll A–B binding protein, chloroplast post-illumination chlorophyll-fluorescence-increase protein, and SNT7, implying that NO indirectly regulated the absorption and transport of light energy in photosynthesis in response to WD stress. The significant difference of chlorophyll (Chl) content, Chl a fluorescence-transient, photosynthesis index, and trapping and transport of light energy further indicated that exogenous NO under D stress enhanced the primary photosynthesis reaction compared to D treatment. A putative pathway is proposed to elucidate NO regulation of the primary reaction of photosynthesis under WD.

COMPARATIVE CHARACTERISTICS OF PHOTOSYNTHETIC ACTIVITY OF NECTARINE CULTIVARS AND FORMS WITH DIFFERENT COLORED LEAF PLATE

Genotypes of nectarine with red leaves were created in Nikita botanical gardens.They have commercially valuable properties and biological characteristics (resistanceto powdery mildew, large-fruited, the ability of transmitting the trait of redleaves with constant result to progeny seed, etc. ). The aim of our researches was tostudy the main indicators of photoactivity of leaf apparatus of nectarine with greenand anthocyanin leaves coloration. Investigations have been carried out in 2010-2015 on intact leaf plates for three cultivars and forms of nectarine with greenleaves – Rubinoviy-8 (control), Chemus, Krymtsuht 53-85 and 2 forms withanthocyanin coloration of leaf plate (NektadianaKrasnolistnaya 996-88, Krasnola495-86). Photosynthetic activity was characterized by chlorophyll fluorescenceparameters (Kautsky effect). The content of chlorophyll a and b were determinedby spectrophotometry. The cultivar Rubinoviy-8 and the form - Krasnola 495-86were selected according to intensity indicators of the primary reactions ofphotosynthesis. Anthocyanin forms concede cultivar Rubinoviy-8 in efficiency ofthe primary reactions of photosynthesis an average of 48-50%; but they exceednectarines Chemus and Krymtsuht 53-85 with green color of leaves of 23-25%.The efficiency of energy supply in the "dark" reactions of photosynthesis in allvarieties and forms of nectarine maintained within 41-46%. But the further abilityto utilize received energy is most efficiently implemented at the nectarine cultivarRubinoviy-8 and form Krasnola 495-86. The forms of red-leaved nectarine incomparison with traditional cultivars are distinguished by a great potential forretaining the stability and productivity of the functioning of the photosyntheticapparatus.

Structure of photosynthetic LH1-RC supercomplex at 1.9 Å resolution.

Light-harvesting complex 1 (LH1) and the reaction centre (RC) form a membrane-protein supercomplex that performs the primary reactions of photosynthesis in purple photosynthetic bacteria. The structure of the LH1-RC complex can provide information on the arrangement of protein subunits and cofactors; however, so far it has been resolved only at a relatively low resolution. Here we report the crystal structure of the calcium-ion-bound LH1-RC supercomplex of Thermochromatium tepidum at a resolution of 1.9 Å. This atomic-resolution structure revealed several new features about the organization of protein subunits and cofactors. We describe the loop regions of RC in their intact states, the interaction of these loop regions with the LH1 subunits, the exchange route for the bound quinone QB with free quinone molecules, the transport of free quinones between the inside and outside of the LH1 ring structure, and the detailed calcium-ion-binding environment. This structure provides a solid basis for the detailed examination of the light reactions that occur during bacterial photosynthesis.

Effect of ionic liquids with different cations and anions on photosystem and cell structure of Scenedesmus obliquus

The rapid increase in the production and practical application of ionic liquids (ILs) could pose potential threats to aquatic systems. In this study, we investigated the effects of four ILs with different cations and anions, including 1-hexyl-3-methylimidazolium nitrate ([HMIM]NO3), 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl), N-hexyl-3-metylpyridinium chloride ([HMPy]Cl), and N-hexyl-3-metylpyridinium bromide ([HMPy]Br), on photosystem and cellular structure of Scenedesmus obliquus. The results indicated that ILs are phytotoxic to S. obliquus. The contents of chlorophyll a, chlorophyll b and total chlorophyll decreased with increasing ILs concentrations. The chlorophyll fluorescence parameters of photosynthetic system II (PSII), including minimal fluorescence yield (F0), potential efficiency of PSII (Fv/Fo), maximum quantum efficiency of PSII photochemistry (Fv/Fm), yield of photochemical quantum [Y(II)], and non-photochemical quenching coefficient without measuring F0′ (NPQ), were all affected. This indicates that ILs could damage PSII, inhibit the primary reaction of photosynthesis, interdict the process of electron-transfer and lead to loss of heat-dissipating ability. ILs also increased cell membrane permeability of S. obliquus, influenced the cellular ultrastructure, changed the morphology of algae cells and destroyed the cell wall, cell membrane and organelles. The results indicated that imidazolium ILs had greater effect than pyridinium ILs, NO3−-IL and Br−-IL had greater effect than Cl−-IL. To minimize threats to the environment, the structure of ILs should be taken into consideration.

Subunit and chlorophyll organization of the plant photosystem II supercomplex.

Photosystem II (PSII) is a light-driven protein, involved in the primary reactions of photosynthesis. In plant photosynthetic membranes PSII forms large multisubunit supercomplexes, containing a dimeric core and up to four light-harvesting complexes (LHCs), which act as antenna proteins. Here we solved a three-dimensional (3D) structure of the C2S2M2 supercomplex from Arabidopsis thaliana using cryo-transmission electron microscopy (cryo-EM) and single-particle analysis at an overall resolution of 5.3 Å. Using a combination of homology modelling and restrained refinement against the cryo-EM map, it was possible to model atomic structures for all antenna complexes and almost all core subunits. We located all 35 chlorophylls of the core region based on the cyanobacterial PSII structure, whose positioning is highly conserved, as well as all the chlorophylls of the LHCII S and M trimers. A total of 13 and 9 chlorophylls were identified in CP26 and CP24, respectively. Energy flow from LHC complexes to the PSII reaction centre is proposed to follow preferential pathways: CP26 and CP29 directly transfer to the core using several routes for efficient transfer; the S trimer is directly connected to CP43 and the M trimer can efficiently transfer energy to the core through CP29 and the S trimer.

Endophytic infection alleviates Pb2+ stress effects on photosystem II functioning of Oryza sativa leaves

The aims of this study were to examine the effect of Pb2+ stress on the primary reaction of photosynthesis and to assess the potential benefits of endophytic infection on the Pb2+ tolerance of rice seedlings. Rice inoculated with an endophytic fungus (E+) and non-inoculated (E−) were subjected to 0, 50, 100, 150 and 200μM Pb2+. The responses to Pb2+ stress were characterized by the analysis of Chl a fluorescence. A comparison of E− with E+ rice seedlings, as evaluated by their performance index (PIABS and PItot), revealed the inhibitory effects of Pb2+ on photosystem II (PSII) connectivity, the oxygen evolving complex (OEC), and on the J step of the induction curves, which is associated with an inhibition of electron transport from the quinone acceptor QA to QB. Furthermore, the changes of the donor and the acceptor parameters of PSII were greater in E− than in E+ under Pb2+ stress. These observations suggest that the efficiency and stability of PSII are markedly affected by Pb2+ stress, and the photosynthetic energy conservation in E+ was more effective than in E−. We showed that endophytic infection plays an important role in enhancing the photosynthetic mechanism of rice seedlings exposed to Pb2+ stress.

Assembly of the Photosynthetic Apparatus

The primary reactions of photosynthesis are mediated by three protein complexes embedded in the thylakoid membranes of chloroplasts. These complexes are PSII, the cytochrome b 6f complex (Cyt b 6f), and PSI, which are connected in series through the photosynthetic electron transport chain. Light

Cytokinin-induced photosynthetic adaptability of Zea mays L. to drought stress associated with nitric oxide signal: Probed by ESR spectroscopy and fast OJIP fluorescence rise

Nitric oxide (NO), as a diffusible molecule, performs important roles in diverse physiological processes. Interestingly, NO signaling is based on interactions with plant hormones. The aim of this study was, first, to test the effect of cytokinin (CTK) on the primary reaction of photosynthesis under drought stress, and then to examine whether NO is involved in CTK-induced photosynthetic resistance due to its role as a second messenger in stress response. Under drought stress, plants were treated with CTK, or CTK plus the NO scavenger (Hemoglobin [Hb]) for 6h. The effects of CTK and Hb on fast OJIP fluorescence rise were then examined. At the same time, NO and reactive oxygen species (ROS) signals in all the treatments were detected by electron spin resonance (ESR) spectroscopy. The results showed that CTK-regulated fluorescence transient rise under drought stress and increased the electron donation capacity of photosynthesis system (PS) II. The plant photosynthetic performance index (PI) on an absorption basis and corresponding three PI components (RC/ABS, P(TR,) and P(ET)) also increased. High NO signal intensity alleviated drought-induced ROS damage to plants; thus, the signal probably played a direct role in eliciting CTK regulation to energy absorption (RC/ABS) and excitation energy trapped (P(TR)) in response to drought. Although CTK stimulated more excitation energy conversion to electron transfer (P(ET)), because NO was probably bound to the plastoquinone pool (PQ) of the electron transport chain, CTK decreased electron transport to the acceptor side of PSII (see V(I), Sm and N). Furthermore, CTK stimulated more NO signal formation, probably mainly via a nitrate reductase (NR) source under the conditions of the study, and Hb prevented stimulation from CTK. However, these results will require confirmation from future studies.

Introduction to optical methods in photosynthesis

Optical spectroscopy is widely used to study structure and function of photosynthetic systems. Due to the large variety of different methods, these studies have contributed a lot to the identification of the cofactors involved in the primary reactions of photosynthesis and to the elucidation of the kinetics of the light-induced energy and electron transfer reactions. Within other aspects of photosynthesis research as e.g. photoinhibition, these techniques play an important role as well. In this brief introduction, I will focus on the basic principles of the different methods and the information obtained by applying these various techniques. In the reviews that follow, under the section "Optical Methods", these methods are discussed in detail.

Effects of High Temperature on Chlorophyll Fluorescence, Active Oxygen Resistance Activity, and Grain Quality in Grain-Filling Periods in Rice Plants

The synthesis of assimilate such as starch,protein and lipid depends on the photosynthesis. Under stresses,the pigments,primary reaction and electronic transport chain which have relations with photosynthesis are hurt or inhibited. The effect of high temperature caused by "Greenhouse Effects" becomes more and more frequent. To elucidate the injury mechanism under high temperature in rice plants,the dynamic changes of chlorophyll content,chlorophyll fluorescence parameters and active oxygen resistance activity were measured and the grain quality indices including starch,protein,and chalkiness were also analyzed in rice plants of cultivars Xinongyou 30 and Fuyou 1 during grain-filling period under high temperature treatment in climatic cabinets. The results showed that under high temperature(33℃ ),chlorophyll content of leaves decreased,initial fluorescence(Fo) increased obviously,maximal photochemical efficiency of PS II(Fv/Fm) and the potential photochemical efficiency of PS II(Fv/Fo) decreased,Fv/Fo and Fv/Fm declined faster during the whole grain-filling period,especially in late period. Meanwhile,active oxygen resistance activity(AORA) lowered by 45.16 and 35.99% as compared with the control in the late grain-filling period;under high temperature condition,the total starch and amylose contents of grains were lower than those of control,the protein contents increased to a different degree,and chalkiness and 1000-grain weight changed significantly in two cultivars. The main reason of degeneration of grain quality under high temperature stress is related to the inhibition of primary reaction of photosynthesis,drop of active oxygen resistance activity and contraction of functional period in leaves of rice plants.

30-year progress of membrane transport in plants

In the past 30 years enormous progress was made in plant membrane biology and transport physiology, a fact reflected in the appearance of textbooks. The first book dedicated to 'Membrane Transport in Plants' was published on the occasion of the 'International Workshop on Membrane Transport in Plants' held at the Nuclear Research Center, Jülich, Germany [Zimmermann and Dainty (eds) 1974] and was followed in 1976 by a related volume 'Transport in plants II' in the 'Encyclopedia of plant physiology' [Lüttge and Pitman (eds) 1976]. A broad spectrum of topics including thermodynamics of transport processes, water relations, primary reactions of photosynthesis, as well as more conventional aspects of membrane transport was presented. The aim of the editors of the first book was to bring advanced thermodynamical concepts to the attention of biologists and to show physical chemists and biophysicist what the more complex biological systems were like. To bundle known data on membrane transport in plants and relevant fields for mutual understanding, interdisciplinary research and clarification of problems were considered highly important for further progress in this scientific area of plant physiology. The present review will critically evaluate the progress in research in membrane transport in plants that was achieved during the past. How did 'Membrane Transport in Plants' progress within the 30 years between the publication of the first book about this topic (Zimmermann and Dainty 1974), a recent one with the same title (Blatt 2004), and today?

Chlorophyll Fluorescence as a Tool in Cereal Crop Research

Chlorophyll (Chl) fluorescence is a subtle reflection of primary reactions of photosynthesis. Intricate relationships between fluorescence kinetics and photosynthesis help our understanding of photosynthetic biophysical processes. Chl fluorescence technique is useful as a non-invasive tool in eco-physiological studies, and has extensively been used in assessing plant responses to environmental stress. The review gives a summary of some Chl fluorescence parameters currently used in studies of stress physiology of selected cereal crops, namely water stress, heat stress, salt stress, and chilling stress.

Loading beans with sublethal levels of copper enhances conditioning to oxidative stress

The relationship between Cu2+-overloading and oxidative stress in plant cells was studied. The involvement of Cu2+ in the reduction of superoxide O2− and hydrogen peroxide (H2O2) to hydroxyl radical (OH.), suggest that excess Cu in plants leads to oxidative stress. Cu excess was induced in Phaseolus vulgaris (cv. Pinto) plants by soaking the roots in a 1 mmol/L Cu(NO3)2 solution for 24 hours. As a result, Cu content in bean leaves increased from 12 to 23 mg Cu kg−1 DW. Indications for oxidative stress response were detected by monitoring changes in the activities and contents of some components of the antioxidative mechanism. The Cu treatment resulted in doubled activity of ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (EC 1.11.1.6). Excess of copper inhibited glutathione reductase (GR, EC 1.6.4.2) to 60 % of control activity. No differences were found in CuZn-SOD (SOD, EC 1.15.11) and Mn-SOD activity, and glutathione and ascorbate content. Copper overloading affected also, primary reactions of photosynthesis and electron transport as probed by the photochemical energy storage in far-red light. Cu treatment of bean plants resulted in enhanced conditioning to successive methyl viologen and SO2 treatments as compared to non-treated control.