Fluorescence Of Chloroplasts Research Articles

Salt-induced changes in morpho-physiological and biochemical properties in chickpea (Cicer arietinum L.) seedlings

Salinity is one of the most severe abiotic stresses for crop production. The present study was conducted to evaluate the effect of NaCl on growth and some biochemical parameters in chickpea (Cicer arietinum L.) seedlings. Chickpeas were grown hydroponically for 14 days and then treated with 0 mM and 200 mM NaCl. Plants were harvested for the experiment 7 days after salt treatment. Salinity showed marked changes in growth parameters (fresh and dry weight of roots and shoots) and the amount of photosynthetic pigments. The study revealed that the activity of photosystems (PS I and PS II) under salt stress is lower than that of plants growing under normal conditions. The spectral characteristics of the chloroplasts isolated from chickpea leaves were studied by the fluorescence method at liquid nitrogen temperature (77K). Under salt stress, the chloroplast fluorescence emission spectrum decreased in the parts of the spectrum characterizing the PSII (maxima at 686 nm and 695 nm) and PSI complexes (maxima at 735 nm). Keywords: Photosynthetic pigments, chloroplasts, photosystems, fluorescence, chickpea

Effect of light stress on maximum photochemical efficiency of photosystem II and chloroplast structure in cryptogams Cladonia mitis and Pleurozium schreberi

Lichens and bryophytes are cosmopolitan organisms found in diverse environments with varying sunlight availability. However, excessive light can be a stress factor for both lichens and bryophytes, as it can damage their photosynthetic apparatus, particularly the chlorophyll a and b pigments located in the chloroplasts. The measurement of photosynthetic activity and the use of fluorescence microscopy allows the assessment of the influence of light as a stress factor on the preservation state of the thallus. The main goal of our research was to determine the changes that occur in the photosynthetic activity and structure of chloroplasts of selected species lichen Cladonia mitis (Sandst.) and moss Pleurozium schreberi (Willd. Ex Brid.) under the influence of different light intensity in laboratory conditions: FL - 100% light, RL - 30% maximum light, and NL - natural sunlight. The results of the two-factor analysis of variance (ANOVA) tests showed a variation in the activities of the selected species over time depending on the amount of light energy supplied. It was also demonstrated that soaking lichens increased their photosynthetic activity, whereas in bryophytes, it had the opposite effect, decreasing it. The microscopic results showed that Cladonia mitis showed the lowest level of chloroplast fluorescence in the strongest and reduced light, which coincides with its low level of photosynthetic activity. The mosses exhibited strong fluorescence activity of the chloroplasts, suggesting its significantly higher resistance to light radiation.

Lesion mimic mutant 8 balances disease resistance and growth in rice.

Lesion-mimic mutants (LMM) spontaneously produce necrotic spots, a process not affected by environmental stress or pathogen infection. In this study, we identified a LMM, lesion mimic mutant 8 (lmm8) in rice (Oryza sativa). The lmm8 mutant produces brown and off-white lesions on its leaves during the second- and third-leaf stages. The lesion mimic phenotype of the lmm8 mutant was enhanced by light. At the mature stage, lmm8 mutant are shorter and exhibit inferior agronomic traits than the wild type. Contents of photosynthetic pigments and chloroplast fluorescence were significantly reduced in lmm8 leaves, along with increased production of reactive oxygen species and programmed cell death compared to the wild type. The mutated gene was identified as LMM8 (LOC_Os01g18320) by map-based cloning. A point mutation occurred in LMM8, causing a Leu to Arg mutation of the 146th amino acid of LMM8. It is an allele of SPRL1, encoding a protoporphyrinogen IX oxidase (PPOX) located in chloroplasts and involved in the biosynthesis of tetrapyrrole in chloroplasts. The lmm8 mutant showed enhanced resistance and broad-spectrum resistance. Together, our results demonstrate the importance of rice LMM8 protein in defense responses and plant growth in rice, and provides theoretical support for resistance breeding to improve rice yield.

Influence of zinc and iron on population dynamics, morphology and fluorescent properties of <i>Prorocentrum foraminosum</i> (Dinophyta)

Influence of heavy metals as zinc and iron with concentrations of 50 and 100 mg/L on dynamics of the cells abundance, morphology, fluorescence of chlorophyll a, and green autofluorescence is examined for the microalgae Prorocentrum foraminosum. The impact was measured on the 3rd and 7th days of the experiment. Both elements in concentration above the maximum permissible levels reduce the cells number, with the higher impact for Fe3+. However, Fe3+ caused no changes in structure of cells. The impact of Zn2+ caused the cells deformation and excretion of the cellular content. The chloroplast fluorescence became less intensive under influence of Fe3+, but the green autofluorescence had increased under presence of Zn2+ and Fe3+ in the medium.

Влияние тяжелых металлов на динамику численности и фотосинтетический аппарат Alexandrium affine (Dinophyta)

The effect of heavy metals: cadmium, lead, nickel (in concentrations of 10 and 20 μg/l), zinc and iron (50 and 100 μg/l) on the dynamics of population, cell morphology and photosynthetic apparatus (according to the content of photosynthetic pigments – chlorophyll a and carotenoids, chloroplast fluorescence) of Alexandrium affine dinophyte algae during 7 days. It was shown that cadmium had the most depressing effect on the algae: the number of cells decreased and did not recover by the end of the experiment. There was also a decrease in the content of photosynthetic pigments. The addition of lead led to a slight increase in the number of cells, while the content of photosynthetic pigments increased. The presence of nickel, iron andzinc in the medium provoked an increase in the number of cells, but the content of chlorophyll a and carotenoids decreased. All metals led to changes in chloroplast fluorescence and morphological disorders of cells.

Press perturbations of microplastics and antibiotics on freshwater micro-ecosystem: Case study for the ecological restoration of submerged plants

Microplastics (MPs) can adsorb antibiotics to form complex pollutants, which seriously threatens the health of freshwater ecosystems. Few studies have examined the combined pollution characteristics of microplastics (MPs) and antibiotics in restored freshwater ecosystems and their effects on the growth traits of the aquatic primary producers. We studied both the ecotoxicological effects of polyethylene (PE) MPs and the antibiotics sulfanilamide (sulfa, SA) on the structural (diversity etc.,) and functional (nutrient cycling etc.,) properties of water–plant–sediment ecosystems. The synergistic toxic effects of PE and SA resulted in a reduction in the chlorophyll content and chloroplast fluorescence. Meanwhile, PE and SA single/combined pollution stress inhibits the radial oxygen loss in roots, and activates the antioxidant defense system in leaves. The change in the growth response characteristics of Vallisneria natans (V. natans) under oxidative stress induced by single/combined pollution showed a dosage effect. The microbial compositions of the overlying water and sediment were significantly changed by the pollution exposure, as evidenced by the increased microbial diversity and altered microbial taxa distribution. An increase in the total concentrations of sulfa in the overlying water was accompanied by an increase in the relative abundances of resistance genes. PE-MPs significantly affected the removal of total nitrogen and antibiotics from the overlying water. The interaction between PE and SA affects ammonia and nitrite nitrogen exchange in water–sediment systems. Thus, this study investigated the effects of combined MP and antibiotics pollution on the growth state, metabolic function, microbial community structure and microbial diversity of the freshwater ecosystems. The mechanism underlying of the combined polyethylene-sulfanilamide (PE–SA) effect on the V. natans was revealed. In addition, the correlation between different environmental factors was analyzed, and a structural equation model was constructed. This study provides primary data for evaluating the ecological and environmental effects of combined PE–SA pollution and its possible risks. Moreover, it provides a reference index for the study of ecological wetland environments and phytoremediation.

Changes in Chloroplast Fluorescence Related to Excitability and Metabolite Transport by Cytoplasmic Streaming in Chara Cells

Changes in Chloroplast Fluorescence Related to Excitability and Metabolite Transport by Cytoplasmic Streaming in Chara Cells

Growth-phase dependent morphological alteration in higher plant thylakoid is accompanied by changes in both photodamage and repair rates.

Thylakoid membranes of young leaves consist of grana and stroma lamellae (stroma-grana [SG] structure). The SG thylakoid is gradually converted into isolated grana (IG), almost lacking the stroma lamellae during growth. This morphological alteration was found to cause a reduction in maximum photosynthetic rate and an enhancement of photoinhibition in photosystem II (PSII). In situ microspectrometric measurements of chlorophyll fluorescence in individual chloroplasts suggested an increase of the PSII/PSI ratio in IG thylakoids of mature leaves. Western blot analysis of isolated IG thylakoids showed relative increases in some PSII components, including the core protein (D1) and light-harvesting components CP24 and Lhcb2. Notably, a nonphotochemical quenching-related factor in the PSII supercomplex, PsbS, decreased by 40%. Changes in the high light response of PSII were detected through parameters of pulse-amplitude modulation fluorometry. Chlorophyll fluorescence lifetime indicated an increase of fluorescence quantum yield in IG. A minimal photodamage-repair rate analysis on a lincomycin treatment of the leaves indicated that repair rate constant of IG is slower than that of SG, while photodamage rate of IG is higher than that of SG. These results suggest that IG thylakoids are relatively sensitive to high light, which is not only due to a higher photodamage rate caused by some rearrangements of PS complexes, but also to the retarded PSII repair that may result from the lack of stroma lamellae. The IG thylakoids found among many plant species thus seem to be an adaptive form to low light environments, although their physiological roles still remain unclear.

耐盐和盐敏感型小麦品种对NaCl胁迫的生理响应及耐盐性差异

为探究小麦品种类型对盐胁迫的生理响应及敏感性差异，以耐盐型品种济麦22和盐敏感型品种河农6425为材料，对幼苗期植株施以不同浓度的NaCl胁迫处理，比较分析了两个品种幼苗在胁迫条件下的生长、生理生化和叶绿体荧光特征等方面的差异。结果表明，NaCl胁迫对幼苗地上和地下部分的生长表现浓度依赖性的抑制效应，对耐盐型品种的抑制程度较小。在生理响应方面，幼苗体内的Na⁺含量随NaCl 浓度的增加而上升，K⁺和Ca²⁺含量则表现相反的变化趋势，耐盐型品种幼苗在胁迫处理前、后均具有较高的K⁺/Na⁺比和Ca²⁺/Na⁺比；NaCl胁迫导致幼苗的光系统Ⅱ受损，表现在Fv/Fm、Fv/Fo、qP 和YⅡ 等叶绿体荧光参数数值下降，降幅在耐盐性品种上相对较小。在氧化胁迫和抗氧化系统方面，NaCl胁迫导致幼苗体内活性氧水平的上升和过氧化物酶（POD）、过氧化氢酶（CAT）等抗氧化酶的响应；POD活性在处理后的0-12 d范围内呈先下降后上升的趋势，CAT活性则呈先上升后下降的趋势。耐盐品种的POD活性在胁迫早期受抑制时间较短，随后的响应更迅速且上升幅度更高；耐盐品种的CAT活性上升幅度更高，且在胁迫后期对高浓度NaCl和长时间胁迫导致的酶活性抑制的耐受性更强。耐盐品种抗氧化酶的这一响应特征与其较低的活性氧上升幅度一致，也与其较低水平的代表膜损伤程度的丙二醛（MDA）积累一致。耐盐型品种根部的MDA积累经200 mmol/L NaCl处理1 d后达到峰值，而盐敏感品种根部的MDA积累经150 mmol/L NaCl处理1 d后即达到峰值。以上研究结果表明，耐盐型小麦品种济麦22可分别通过其较强的K⁺/Na⁺、Ca²⁺/Na⁺调节能力和抗氧化酶体系缓解盐胁迫所导致的渗透胁迫和活性氧伤害，从而表现出耐盐的特征。;Soil salinity is a major abiotic stress inhibiting plant growth, development, and productivity, especially in case of crop. Wheat is an important cereal crop affected by high salinity. A better understanding of the physiological mechanisms underlying salt tolerance will facilitate efforts to improve crop performance under salinity. This study used two general wheat varieties as experimental materials to explore the growth physiological response and sensitivity difference of different cultivated wheat types to salt stress and their salt tolerance. Jimai 22 is salt-tolerant and Henong 6425 is salt-sensitive. In a hydroponic experiment, the effects of different concentrations (0, 50, 100, and 200 mmol/L) of NaCl stress on both Jimai 22 and Henong 6425 seedlings were investigated. The seedlings growth, salt tolerance index, main ion content, physiological and biochemical index, and chloroplast fluorescence parameters were compared. The results showed that NaCl stress inhibited the growth of aboveground and underground parts of wheat seedlings in a concentration dependent manner. The higher the concentration of NaCl was, the greater the toxicity on wheat seedlings would become. And the inhibition degree on Jimai 22 seedlings was smaller than that on Henong 6425 seedlings. In terms of physiological response, the Na⁺ contents in both Jimai 22 and Henong 6425 were increased with the increase of NaCl concentration, while the contents of both K⁺ and Ca²⁺ exhibited opposite trend of changing. The salt tolerance variety Jimai 22 had higher both K⁺/Na⁺ and Ca²⁺/Na⁺ before and after NaCl stress than those on salt sensitive Henong 6425. NaCl stress damaged the photosystem II of both Jimai 22 and Henong 6425 leaves. The concrete manifestation of damage effect was the decrease of chloroplast fluorescence parameters containing Fv/Fm, Fv/Fo, qP and YⅡ under different NaCl concentration. And the lowered range of these parameters in Jimai 22 induced by NaCl stress was lower than that in Henong 6425. In terms of oxidative stress and antioxidant system, the reactive oxygen species (ROS) level was increased with NaCl concentration stress increased. And the activities of peroxidase (POD) and catalase (CAT) were also changed. In 12 d after NaCl treatment, the POD activity was decreased firstly and then increased, while CAT activity was increased firstly and then decreased. The activities of both POD and CAT induced by NaCl stress in Jimai 22 were higher than those in Henong 6425. In the early stage of NaCl stress, the POD activity was temporally suppressed and the rising amplitude of POD activity was very large subsequently. The CAT activities induced by NaCl stress in Jimai 22 were higher than those in Henong 6425. In later days of NaCl stress, Jimai 22 had stronger tolerance to high NaCl concentration and inhibition of antioxidant system induced by long term NaCl stress. The rising range of antioxidant enzyme was consistent with lower ROS and lower malondialdehyde (MDA) which represents the degree of membrane damage in Jimai 22 under NaCl stress. The MDA content of salt tolerant Jimai 22 roots reached the peak after 200 mmol/L NaCl stress for 1 d. While the MDA content of salt sensitive Henong 6425 roots reached the peak after 150 mmol/L NaCl stress for 1 d. Overall, these results suggested that salt tolerant Jimai 22 had higher salt tolerance. Under NaCl stress, Jimai 22 can not only alleviate the damage of both active oxygen and osmotic stress due to the increasing activities of both POD and CAT, but also alleviate the ion stress by maintaining higher level of both K⁺/Na⁺ and Ca²⁺/Na⁺ after different concentrations of NaCl stress. Results from this study could be helpful for further understanding the physiological mechanism of severe NaCl stress in crop, and may be useful for elucidating the salt-tolerant mechanism of different cultivated crop types.

Terrestrial Plants Evolve Highly Assembled Photosystem Complexes in Adaptation to Light Shifts.

It has been known that PSI and PSII supercomplexes are involved in the linear and cyclic electron transfer, dynamics of light capture, and the repair cycle of PSII under environmental stresses. However, evolutions of photosystem (PS) complexes from evolutionarily divergent species are largely unknown. Here, we improved the blue native polyacrylamide gel electrophoresis (BN-PAGE) separation method and successfully separated PS complexes from all terrestrial plants. It is well known that reversible D1 protein phosphorylation is an important protective mechanism against oxidative damages to chloroplasts through the PSII photoinhibition-repair cycle. The results indicate that antibody-detectable phosphorylation of D1 protein is the latest event in the evolution of PS protein phosphorylation and occurs exclusively in seed plants. Compared to angiosperms, other terrestrial plant species presented much lower contents of PS supercomplexes. The amount of light-harvesting complexes II (LHCII) trimers was higher than that of LHCII monomers in angiosperms, whereas it was opposite in gymnosperms, pteridophytes, and bryophytes. LHCII assembly may be one of the evolutionary characteristics of vascular plants. In vivo chloroplast fluorescence measurements indicated that lower plants (bryophytes especially) showed slower changes in state transition and nonphotochemical quenching (NPQ) in response to light shifts. Therefore, the evolution of PS supercomplexes may be correlated with their acclimations to environments.

Modeling re-absorption of fluorescence from the leaf to the canopy level

Chlorophyll fluorescence is widely used as an indicator of photosynthesis and physiological state of plants. Remote acquisition of fluorescence allows the diagnosis of large field extensions, even from satellite measurements. Nevertheless, fluorescence emerging from chloroplasts, the one directly connected to plant physiology, undergoes re-absorption processes both within the leaf and the canopy. Therefore, corrections of the observed canopy fluorescence, taking into account these two re-absorption processes may help to draw accurate inferences about plant health. Here, we show the theoretical development and experimental validation of a model that allows to retrieve the spectral distribution of the leaf fluorescence spectrum from that on top of canopy (TOC) using a correction factor which is a function of both canopy and soil reflectance, and canopy transmittance. Canopy fluorescence spectra corrected by our theoretical approach and normalized shows 95% correlation with the normalized fluorescence spectrum at leaf-level, thus validating the model. Therefore, our results provide a physical explanation and quantification for fluorescence re-absorption within the canopy, a phenomenon which has only been mentioned but never measured up to the date. From a more general perspective, this new analytical tool together with the one previously developed by Ramos and Lagorio (2004) allows to obtain the spectral distribution of chloroplast fluorescence spectrum from that on top of canopy (TOC).

Effect of allelochemical tricin and its related benzothiazine derivative on photosynthetic performance of herbicide-resistant barnyardgrass

Despite increasing knowledge of allelochemicals as leads for new herbicides, relatively little is known about the mode of action of allelochemical-based herbicides on herbicide-resistant weeds. In this study, herbicidal activities of a series of allelochemical tricin-derived compounds were evaluated. Subsequently, a benzothiazine derivative 3-(2-chloro-4-methanesulfonyl)-benzoyl-hydroxy-2-methyl-2H-1,2-benzothiazine-1,1-dioxide with 4-hydroxyphenyl-pyruvate dioxygenase (HPPD) inhibiting activity was identified as a target compound on photosynthetic performance of penoxsulam-resistant versus -susceptible barnyardgrass (Echinochloa crus-galli). Regardless of barnyardgrass biotype, the benzothiazine derivative greatly affected chlorophyll fluorescence parameters (Fv/Fm, ETR1min and NPQ1min), reduced the chloroplast fluorescence levels and expression of HPPD gene. In particular, the benzothiazine derivative interfered with photosynthetic performance of resistant barnyardgrass more effectively than the allelochemical tricin itself. These results showed that the benzothiazine derivative effectively inhibited the growth of resistant barnyardgrass and its mode of action on photosynthesis system was similar to HPPD-inhibiting sulcotrione, making it an ideal lead compound for further development of allelochemical-based herbicide discovery.

Drought-induced changes in photosynthetic apparatus and antioxidant components of wheat (Triticum durum Desf.) varieties

Water deficit is a key factor influencing the yield and quality of crops. In the present study, the photosynthetic responses by means of chlorophyll fluorescence of chloroplasts, thylakoid membrane proteins, and antioxidant components were analyzed in wheat (Triticum durum Desf.) plants differing in their tolerance to drought. Two durum winter wheat varieties, Barakatli 95 (drought tolerant) and Garagylchyg 2 (drought sensitive) were grown under field well-watered and drought conditions. It was found that contents of the PS I core (CPI) with Mr of 123 kD and apoprotein P700 with Mr of 63 kD were relatively higher in Barakatli 95 variety under drought stress compared with the control plants. Synthesis of α- and β-subunits of CF1 ATP-synthase complex with Mr of 55 and 53.5 kD also slightly increased in the tolerant Barakatli 95 and decreased in the drought sensitive variety Garagylchyg 2. A decrease in the intensity of 30 kD band and a significant increase were found in the content of the 25-16 kD region in Garagylchyg 2 variety. The synthesis of 60 kD and content of low molecular mass polypeptides (21.5 and 12 kD) were increased in the tolerant genotype Barakatli 95. The intensity of peaks at 687, 695, and 742nm considerably increases in the fluorescence spectra (77K) of chloroplasts isolated from the sensitive variety Garagylchyg 2, and there is a stimulation of the ratio of fluorescence band intensity F687/F740. At the same time, higher level of glycine betaine was found in the drought tolerant variety compared with the control one throughout the different periods of growth.

Структурно-функціональні особливості фотосинтетичного апарату водяної папороті Salvinia natans (L.) All.

The characteristics of photosynthetic pigments and efficient use of light energy are analyzed fon the example of chloroplast ultrastructure of the photosynthetic apparatus of floating and submerged fronds of annual heterosporous of water fern Salvinia natans (L.) All. in ontogenesis. It is established that at the stage of intensive growth chloroplasts floating fronds had a well-developed system of thylakoid membranes with many faces and contain a lot of starch grains. Submerged fronds shaped chloroplasts are smaller with little starch in the stroma. Destructive changes in chloroplast photosynthetic membranes of both frond types are observed at the stage of sporocarp formation. Particularly, decomposition of gran tylakoiod membranes, disturbances in inter-gran connections, reduction of starch grain number in stroma were revealed. In the chloroplast stroma of floating wai numerous plastoglobules were fouond. In chloroplasts submerged fronds fewer plastoglobules education were noted. In addition, a certain portion of popu­lation hloroplastoa in both types fronds retains intact structures.The photosynthetic pigment content of floating fronds was found to exceed that of submerged two times, and at some stages of ontogenesis – three times. At the stage of sporocarp formation, the chloroplast and carotinoid content in fronds of the both types decreased. Floating fronds are characterized by an effective action of the chloroplast photosynthetic electron transport chain, and are adapted to an intensive natural lighting on a water surface. Submerged fronds affected by lighting whose intensity fits with a maximum level of natural characteristics were found to be at stress. That was confirmed by a decrease in quantum efficiency ФСІІ (Φ PSII ) and increase in dissipation of excessive light energy as heat in rise of the level of nonphotochemical quenching of chloroplast fluorescence (NPQ).

Purple chromoprotein gene serves as a new selection marker for transgenesis of the microalga Nannochloropsis oculata.

Among the methods used to screen transgenic microalgae, antibiotics selection has raised environmental and food safety concerns, while the observation of fluorescence proteins could be influenced by the endogenous fluorescence of host chloroplasts. As an alternative, this study isolated the purple chromoprotein (CP) from Stichodacyla haddoni (shCP). A plasmid in which shCP cDNA is driven by a heat-inducible promoter was linearized and electroporated into 2.5×108 protoplasts of Nannochloropsis oculata. Following regeneration and cultivation on an f/2 medium plate for two weeks, we observed 26 colonies that displayed a slightly dark green coloration. After individually subculturing and performing five hours of heat shock at 42°C, a dark brown color was mosaically displayed in five of these colonies, indicating that both untransformed and transformed cells were mixed together in each colony. To obtain a uniform expression of shCP throughout the whole colony, we continuously isolated each transformed cell that exhibited brown coloration and subcultured it on a fresh plate, resulting in the generation of five transgenic lines of N. oculata which stably harbored the shCP gene for at least 22 months, as confirmed by PCR detection and observation by the naked eye. As shown by Western blot, exogenous shCP protein was expressed in these transgenic microalgae. Since shCP protein is biodegradable and originates from a marine organism, both environmental and food safety concerns have been eliminated, making this novel shCP reporter gene a simple, but effective and ecologically safe, marker for screening and isolating transgenic microalgae.

Selenium Promotes the Growth and Photosynthesis of Tomato Seedlings Under Salt Stress by Enhancing Chloroplast Antioxidant Defense System

Tomato (Lycopersicon esculentum Miller) cv. Jiahe No. 9 (a salinity-resistant cultivar) and cv. Shuangfeng 87-5 (a salinity-sensitive cultivar) were used as experimental materials to investigate the effects of exogenous selenium (Na2SeO3 0.05 mM) on plant growth, chlorophyll fluorescence, photosynthetic rate, and antioxidative metabolism of chloroplasts in tomato seedlings under NaCl (100 mM) stress. Salt stress significantly inhibited plant growth, net photosynthetic rate (Pn), maximum quantum yield of PSII (Fv/Fm), actual photochemical efficiency of PSII (ΦPSII), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) of both cultivars, whereas application of Se reversed the negative effects of salt stress. Furthermore, application of Se significantly decreased the levels of hydrogen peroxide (H2O2) and malondialdehyde. Application of Se increased the activities of superoxidase dismutase, glutathione reductase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione peroxidase, and thioredoxin reductase, and the contents of ascorbate, glutathione (GSH) and NADPH, and the ratios of GSH/GSSH, AsA/DHA, and NADPH/ NADP+ in the salt-stressed chloroplasts of both cultivars. These results suggest that Se alleviates salt-induced oxidative stress through regulating the antioxidant defense systems in the chloroplasts of tomato seedlings, which is associated with the improvement of the photochemical efficiency of PSII, thereby maintaining higher photosynthetic rates. In addition, the salt tolerance of Jiahe No. 9 is closely related with high reactive oxygen species scavenging activity and reducing power levels in the chloroplasts.

Special issues on Photosynthesis Education honoring Govindjee

The special issues in volumes 116 and 117 of Photosynthesis Research are all dedicated to Photosynthesis Education. They honor Professor Govindjee, at his 80th birthday on October 24, 2013, for his contributions, dedication, and enthusiasm about photosynthesis, for which he has been called ‘‘Mr. Photosynthesis’’. He is a master educator of our time. The depth of his knowledge and understanding of all aspects of photosynthesis, ‘‘From Photons to a Leaf’’ is enormous. He is also the de facto Ambassador of Photosynthesis to the rest of the World. Govindjee, as he prefers to be called, is a renowned scientist who has made outstanding and significant contributions to photosynthesis research and education. Govindjee has authored or co-authored more than 400 publications which have brought understanding to many aspects of photosynthesis (for a list since 1994, see his webpage at: http://www.life.illinois.edu/govindjee/recent_ papers.html). This includes, most dramatically, his work on exploitation of light emission (chlorophyll fluorescence, delayed fluorescence and thermoluminescence) of plants and algae for understanding photosynthesis. In cooperation with his co-workers, he showed a unique role of bicarbonate in the electron and proton flow on the electron acceptor side of Photosystem II (PSII), and, in his early work on the minimum quantum requirement of oxygen evolution, he proved that Nobel-Laureate Otto Warburg was wrong and that his own professor Robert Emerson was right: i.e. a minimum of 8–12 photons, not 3–4, is required for the evolution of one oxygen molecule. His research, with many collaborators, included the discovery of a shortwavelength form of chlorophyll (Chl) a functioning in the Chl b-containing system, now called PS II, and of the twolight effects in Chl a fluorescence and NADP reduction in chloroplasts. Further, again, with his coworkers, he discovered the existence of different spectral fluorescing forms of Chl a, was the first to measure the temperature dependence of excitation energy transfer down to liquid helium temperature (4 K), the first to provide the current theory for thermoluminescence in plants, and the first to make picosecond measurements of the primary photochemistry of PSII. Equally important, Govindjee has played a key role in global dissemination of research through collaboration with scientists all over the world, and through his lucid lectures on the basics of photosynthesis, as well as on the history of ‘‘Photosynthesis Research’’. A major characteristic of Govindjee is his availability to help anyone and everyone who writes to him; always ready to respond to emails that he receives. In addition, we marvel at his tremendous accomplishments in terms of communication of ideas, and the unsurpassed marathon job he has done editing, which includes numerous books on Photosynthesis, S. I. Allakhverdiev Controlled Photobiosynthesis Laboratory, Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow 127276, Russia e-mail: suleyman.allakhverdiev@gmail.com

Propagation of photoinduced signals with the cytoplasmic flow along Characean internodes: evidence from changes in chloroplast fluorescence and surface pH

Emerging evidence suggests that cytoplasmic streaming can regulate the plasma-membrane H(+) transport and photosynthetic electron flow. Microfluorometric and surface pH measurements on Chara corallina internodes revealed the transmission of photoinduced signals by the cytoplasmic flow for a distance of few millimeters from the site of stimulus application. When a 30-s pulse of bright light was locally applied, the downstream cell regions responded with either release or enhancement of non-photochemical quenching of chlorophyll fluorescence, depending on the background irradiance of the analyzed cell area. Under dim background irradiance (<20 μmol m(-2) s(-1)), the arrival of the distant signal from the brightly illuminated 400-μm-wide zone elevated the maximal fluorescence F m (') in the analyzed downstream area, whereas at higher background irradiances it induced strong quenching of F m (') . At intermediate irradiances the increase and decrease in F m (') appeared as two successive waves. The transition between the F m (') responses of opposite polarities occurred at a narrow threshold range of irradiances. This indicates that inevitable slight variations in irradiance at the bottom chloroplast layer combined with the cyclosis-transmitted signals may contribute to the formation of a photosynthetic activity pattern. The rapid cyclosis-mediated release of non-photochemical quenching, unlike the delayed response of opposite polarity, was associated with opening of H(+) (OH(-))-conducting plasma membrane channels, as evidenced by the concurrent alkaline pH shift on the cell surface. It is proposed that the initial increase in F m (') after application of a distant photostimulus is determined, among other factors, by the wave of alkaline cytoplasmic pH.

Fluorescence transients in chloroplasts of Chara corallina cells during transmission of photoinduced signal with the streaming cytoplasm

Intracellular transport assisted by rotatory cytoplasmic movement in characean green algae exerts regulatory influence on plasmalemmal ion channels and photosynthetic activity of chloroplasts. In internodal cells of Chara corallina Klein ex Willd., the photoinduced signal transmitted with the flow of streaming cytoplasm for a distance of 1–3 mm from the site of its emergence was found to release or enhance non-photochemical quenching of chlorophyll fluorescence, depending on the intensity of background illumination in the analyzed area. Under dim background irradiance (10–30 μmol quanta/(m2s)), the distant signal transferred from brightly illuminated 0.4-mm-wide area elicited a transient increase in maximal (F′m) and actual (F) fluorescence. However, at higher background irradiances, the arrival of the same signal resulted in strong quenching of F′m and in transitory changes of F. The transformation of “low light response” to F′m changes of opposite polarity occurred at some threshold irradiance. Hence, even slight variations in irradiance at the chloroplast layer, attributed to structural features of characean internodes, might promote formation of uneven photosynthetic profile under the influence of signals transmitted along the cell with the cytoplasmic flow. Analysis of chloroplast fluorescence in situ as a function of pH in experiments with intracellular perfusion indicated that the initial response to a distant light stimulus is caused by the transient increase in cytoplasmic pH in the area of fluorescence measurements.

Effects of exogenous spermine on chlorophyll fluorescence, antioxidant system and ultrastructure of chloroplasts in Cucumis sativus L. under salt stress

The effects of exogenous spermine (Spm) on plant growth, chlorophyll fluorescence, ultrastructure and anti-oxidative metabolism of chloroplasts were investigated in Cucumis sativus L. under NaCl stress. Salt stress significantly reduced plant growth, chlorophylls content and F(v)/F(m). These changes could be alleviated by foliar spraying with Spm. Salt stress caused an increase in malondialdehyde (MDA) content and superoxide anion [Formula: see text] generation rate in chloroplasts. Application of Spm significantly increased activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), and ascorbate peroxidase (APX, EC 1.11.1.11) which decreased the levels of [Formula: see text] and MDA in the salt-stressed chloroplasts. Salt stress decreased the activities of dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) in the chloroplasts and reduced the contents of dehydroascorbate (DAsA) and glutathione (GSH), but increased monodehydroascorbate reductase (MDAR, EC 1.6.5.4) activity. On the other hand, Spm significantly increased the activities of antioxidant enzymes and levels of antioxidants in the salt-stressed chloroplasts. Further analysis of the ultrastructure of chloroplasts indicated that salinity induced destruction of the chloroplast envelope and increased the number of plastoglobuli with aberrations in thylakoid membranes. However, Spm application to salt-stressed plant leaves counteracted the adverse effects of salinity on the structure of the photosynthetic apparatus. These results suggest that Spm alleviates salt-induced oxidative stress through regulating antioxidant systems in chloroplasts of cucumber seedlings, which is associated with an improvement of the photochemical efficiency of PSII.