Showing papers on "Photosynthesis published in 2018"

Functioning of potassium and magnesium in photosynthesis, photosynthate translocation and photoprotection.

Abstract: Potassium (K) and magnesium (Mg) are mineral nutrients that are required in large quantities by plants. Both elements critically contribute to the process of photosynthesis and the subsequent long-distance transport of photoassimilates. If K or Mg is not present in sufficient quantities in photosynthetic tissues, complex interactions of anatomical, physiological and biochemical responses result in a reduction of photosynthetic carbon assimilation. As a consequence, excessive production of reactive oxygen species causes photo-oxidation of the photosynthetic apparatus and causes an up-regulation of photoprotective mechanisms. In this article, we review the functioning of K and Mg in processes directly or indirectly associated with photosynthesis. Focus is given to chloroplast ultrastructure, light-dependent and -independent reactions of photosynthesis and the diffusion of CO2 - a major substrate for photosynthesis - into chloroplasts. We further emphasize their contribution to phloem-loading and long-distance transport of photoassimilates and to the photoprotection of the photosynthetic apparatus.

Effects of Different Metals on Photosynthesis: Cadmium and Zinc Affect Chlorophyll Fluorescence in Durum Wheat.

Abstract: A comparative study of the effects of exposure to high Cd2+ (50 µM) and excess Zn2+ (600 µM) on photosynthetic performance of hydroponically-grown durum wheat seedlings was performed. At day 8, Cd and Zn were added to the nutrient solution. After 7-days exposure, the chosen concentrations of both metals resulted in similar relative growth rate (RGR) inhibitions of about 50% and comparable retardations of the CO2 assimilation rates (about 30%) in the second developed leaf of wheat seedlings. Analysis of chlorophyll a fluorescence indicated that both metals disturbed photosynthetic electron transport processes which led to a 4- to 5-fold suppression of the efficiency of energy transformation in Photosystem II. Non-specific toxic effects of Cd and Zn, which prevailed, were an inactivation of part of Photosystem II reaction centres and their transformation into excitation quenching forms as well as disturbed electron transport in the oxygen-evolving complex. The specificity of the Cd and Zn modes of action was mainly expressed in the intensity of the toxicity effects: despite the similar inhibitions of the CO2 assimilation rates, the wheat photochemistry showed much more sensitivity to Cd than to Zn exposure.

Photochemistry beyond the red limit in chlorophyll f–containing photosystems

Abstract: Photosystems I and II convert solar energy into the chemical energy that powers life. Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal and is considered to define the energy "red limit" of oxygenic photosynthesis. We present biophysical studies on the photosystems from a cyanobacterium grown in far-red light (750 nm). The few long-wavelength chlorophylls present are well resolved from each other and from the majority pigment, chlorophyll a. Charge separation in photosystem I and II uses chlorophyll f at 745 nm and chlorophyll f (or d) at 727 nm, respectively. Each photosystem has a few even longer-wavelength chlorophylls f that collect light and pass excitation energy uphill to the photochemically active pigments. These photosystems function beyond the red limit using far-red pigments in only a few key positions.

Zinc oxide nanoparticle-mediated changes in photosynthetic efficiency and antioxidant system of tomato plants

Abstract: The present study was carried out to assess the role of zinc oxide nanoparticles (ZnO-NPs) in tomato plants on growth, photosynthetic efficiency, and antioxidant system. At 20-d stage of growth, roots of tomato plants were dipped into 0, 2, 4, 8, or 16 mg(ZnO-NPs) L–1 for 15, 30, and 45 min and then seedlings were transplanted in their respective cups and allowed to grow under natural environmental conditions. At 45-d stage of growth, the ZnO-NPs treatments significantly increased growth, photosynthetic efficiency together with activities of carbonic anhydrase and antioxidant systems in a concentration- and duration-dependent manner. Moreover, the treatment by 8 mg(ZnO-NPs) L–1 for 30 min proved to be the most effective and resulted in maximum activities of antioxidant enzymes, proline accumulation and the photosynthetic rate. We concluded that presence of ZnO-NPs improved the antioxidant systems and speeded up proline accumulation that could provide stability to plants and improved photosynthetic efficiency.

Photosystem II Subunit S overexpression increases the efficiency of water use in a field-grown crop.

Abstract: Insufficient water availability for crop production is a mounting barrier to achieving the 70% increase in food production that will be needed by 2050. One solution is to develop crops that require less water per unit mass of production. Water vapor transpires from leaves through stomata, which also facilitate the influx of CO2 during photosynthetic assimilation. Here, we hypothesize that Photosystem II Subunit S (PsbS) expression affects a chloroplast-derived signal for stomatal opening in response to light, which can be used to improve water-use efficiency. Transgenic tobacco plants with a range of PsbS expression, from undetectable to 3.7 times wild-type are generated. Plants with increased PsbS expression show less stomatal opening in response to light, resulting in a 25% reduction in water loss per CO2 assimilated under field conditions. Since the role of PsbS is universal across higher plants, this manipulation should be effective across all crops.

Effects of drought stress on photosynthesis and photosynthetic electron transport chain in young apple tree leaves.

Abstract: In our study, the effects of water stress on photosynthesis and photosynthetic electron transport chain (PETC) were studied in several ways, including monitoring the change of gas exchange parameters, modulated chlorophyll fluorescence, rapid fluorescence induction kinetics, reactive oxygen species (ROS), antioxidant enzyme activities and D1 protein levels in apple leaves. Our results show that when leaf water potential ( ψ w ) is above –1.5 MPa, the stomatal limitation should be the main reason for a drop of photosynthesis. In this period, photosynthetic rate ( P N ), stomatal conductance ( G s ), transpiration rate ( E ) and intercellular CO 2 concentration ( C i ) all showed a strong positive correlation with ψ w . Modulated chlorophyll fluorescence parameters related to photosynthetic biochemistry activity including maximum photochemical efficiency (F v /F m ), actual photochemical efficiency of PSII (Φ PSII ), photochemical quenching coefficient ( q P ) and coefficient of photochemical fluorescence quenching assuming interconnected PSII antennae ( q L ) also showed a strong positive correlation as ψ w gradually decreased. On the other hand, in this period, Stern-Volmer type non-photochemical quenching coefficient (NPQ) and quantum yield of light-induced non-photochemical fluorescence quenching [ Y (NPQ) ] kept going up, which shows an attempt to dissipate excess energy to avoid damage to plants. When ψ w was below –1.5 MPa, P N continued to decrease linearly, while C i increased and a ‘V’ model presents the correlation between C i and ψ w by polynomial regression. This implies that, in this period, the drop in photosynthesis activity might be caused by non-stomatal limitation. F v /F m , Φ PSII , q P and q L in apple leaves treated with water stress were much lower than in control, while NPQ and Y (NPQ) started to go down. This demonstrates that excess energy might exceed the tolerance ability of apple leaves. Consistent with changes of these parameters, excess energy led to an increase in the production of ROS including H 2 O 2 and O 2 • − . Although the activities of antioxidant enzymes like catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) increased dramatically and ascorbate peroxidase (APX) decreased in apple leaves with drought stress, it was still not sufficient to scavenge ROS. Consequently, the accumulation of ROS triggered a reduction of net D1 protein content, a core protein in the PSII reaction center. As D1 is responsible for the photosynthetic electron transport from plastoquinone A (Q A ) to plastoquinone B (Q B ), the capacity of PETC between Q A and Q B was considerably downregulated. The decline of photosynthesis and activity of PETC may result in the shortage of adenosine triphosphate (ATP) and limitation the regeneration of RuBP ( J max ), a key enzyme in CO 2 assimilation. These are all non-stomatal factors and together contributed to decreased CO 2 assimilation under severe water stress.

Enhanced Biological Photosynthetic Efficiency Using Light-Harvesting Engineering with Dual-Emissive Carbon Dots

Abstract: Enhancing solar energy conversion is imperative and maximizing solar energy capture remains significant. Here, nanotechnology toward engineering hybrid photosystem involving biological photosynthetic chloroplasts and dualemissive carbon dots (CDs) is employed for improved photosynthesis by harnessing more effective light. Specifically, the as-prepared CDs show strong absorption in ultraviolet (UV) light region and exhibit intense blue and red light in water, which exactly match the absorption spectrum of chloroplasts. After coating the CDs on the surface of extracted chloroplasts, the hybrid photosystem produces 2.8 times more adenosine triphosphate (ATP) than chloroplasts themselves in vitro. Moreover, CD-induced enhancement of photosynthesis in living plant is proved as well, showing a maximum increase of 25% in electron transport rates over the leaves without CDs, demonstrating the effective nanobionics engineering of plant performance in vivo. This is the first report on employing the unique dual-emission trait of nanoparticles, especially the red emission, to augment photoabsorption of both extracted chloroplasts and intact leaves for enhanced photosynthetic properties. This work provides a promising strategy for engineering biological photosynthetic system with dual-emissive CDs to enhance solar energy conversion both in vivo and in vitro, and promotes the development in the field of nanobionic.

Impacts of climate change on rice production in Africa and causes of simulated yield changes

Abstract: This study is the first of its kind to quantify possible effects of climate change on rice production in Africa. We simulated impacts on rice in irrigated systems (dry season and wet season) and rainfed systems (upland and lowland). We simulated the use of rice varieties with a higher temperature sum as adaptation option. We simulated rice yields for 4 RCP climate change scenarios and identified causes of yield declines. Without adaptation, shortening of the growing period due to higher temperatures had a negative impact on yields (−24% in RCP 8.5 in 2070 compared with the baseline year 2000). With varieties that have a high temperature sum, the length of the growing period would remain the same as under the baseline conditions. With this adaptation option rainfed rice yields would increase slightly (+8%) but they remain subject to water availability constraints. Irrigated rice yields in East Africa would increase (+25%) due to more favourable temperatures and due to CO2 fertilization. Wet season irrigated rice yields in West Africa were projected to change by −21% or +7% (without/with adaptation). Without adaptation irrigated rice yields in West Africa in the dry season would decrease by −45% with adaptation they would decrease significantly less (−15%). The main cause of this decline was reduced photosynthesis at extremely high temperatures. Simulated heat sterility hardly increased and was not found a major cause for yield decline. The implications for these findings are as follows. For East Africa to benefit from climate change, improved water and nutrient management will be needed to benefit fully from the more favourable temperatures and increased CO2 concentrations. For West Africa, more research is needed on photosynthesis processes at extreme temperatures and on adaptation options such as shifting sowing dates.

Prompt chlorophyll fluorescence as a tool for crop phenotyping: an example of barley landraces exposed to various abiotic stress factors

Abstract: The study examined photosynthetic efficiency of two barley landraces (cvs. Arabi Abiad and Arabi Aswad) through a prompt fluorescence technique under influence of 14 different abiotic stress factors. The difference in the behavior of photosynthetic parameters under the same stress factor in–between cv. Arabi Abiad and cv. Arabi Aswad indicated different mechanisms of tolerance and strategies for the conversion of light energy into chemical energy for both the landraces. This study confirmed the suitability of some chlorophyll fluorescence parameters as reliable biomarkers for screening the plants at the level of photosynthetic apparatus.

Arbuscular mycorrhizae improves photosynthesis and water status of Zea mays L. under drought stress

Abstract: The influences of arbuscular mycorrhizal (AM) fungus on growth, gas exchange, chlorophyll concentration, chlo rophyll fluorescence and water status of maize ( Zea mays L.) plants were studied in pot culture under well-watered and drought stress conditions. The maize plants were grown in a sand and black soil mixture for 4 weeks, and then exposed to drought stress for 4 weeks. Drought stress significantly decreased AM colonization and total dry weight. AM symbioses notably enhanced net photosynthetic rate and transpiration rate, but decreased intercellular CO 2 concentration of maize plants regardless of water treatments. Mycorrhizal plants had higher stomatal conductance than non-mycorrhizal plants under drought stress. The concentrations of chlorophyll were higher in mycorrhizal than non-mycorrhizal plants under drought stress. AM colonization significantly increased maximal fluorescence, maximum quantum efficiency of PSII photochemistry and potential photochemical efficiency, but decreased prima ry fluorescence under well-watered and droughted conditions. Mycorrhizal maize plants had higher relative water content and water use efficiency under drought stress compared with non-mycorrhizal plants. The results indicated that AM symbiosis alleviates the toxic effect of drought stress via improving photosynthesis and water status of maize plants.

Plants increase CO2 uptake by assimilating nitrogen via the photorespiratory pathway.

Abstract: Photorespiration is a major bioengineering target for increasing crop yields as it is often considered a wasteful process. Photorespiratory metabolism is integrated into leaf metabolism and thus may have certain benefits. Here, we show that plants can increase their rate of photosynthetic CO2 uptake when assimilating nitrogen de novo via the photorespiratory pathway by fixing carbon as amino acids in addition to carbohydrates. Plants fed NO3- had higher rates of CO2 assimilation under photorespiratory than low-photorespiratory conditions, while plants lacking NO3- nutrition exhibited lower stimulation of CO2 uptake. We modified the widely used Farquhar, von Caemmerer and Berry photosynthesis model to include the carbon and electron requirements for nitrogen assimilation via the photorespiratory pathway. Our modified model improves predictions of photosynthetic CO2 uptake and of rates of photosynthetic electron transport. The results highlight how photorespiration can improve photosynthetic performance despite reducing the efficiency of Rubisco carboxylation.

Nitrogen supply influences photosynthesis establishment along the sugarcane leaf.

Abstract: Nitrogen (N) is a major component of the photosynthetic apparatus and is widely used as a fertilizer in crops. However, to the best of our knowledge, the dynamic of photosynthesis establishment due to differential N supply in the bioenergy crop sugarcane has not been reported to date. To address this question, we evaluated physiological and metabolic alterations along the sugarcane leaf in two contrasting genotypes, responsive (R) and nonresponsive (NR), grown under high- and low-N conditions. We found that the N supply and the responsiveness of the genotype determined the degree of senescence, the carboxylation process mediated by phosphoenolpyruvate carboxylase (PEPcase) and differential accumulation of soluble sugars. The metabolite profiles indicated that the NR genotype had a higher respiration rate in the youngest tissues after exposure to high N. We observed elevated levels of metabolites related to photosynthesis in almost all leaf segments from the R genotype under high-N conditions, suggesting that N supply and the ability to respond to N influenced photosynthesis. Therefore, we observed that N influence on photosynthesis and other pathways is dependent on the genotype and the leaf region.

Chlorophyll fluorescence as a tool for nutrient status identification in rapeseed plants

Abstract: In natural conditions, plants growth and development depends on environmental conditions, including the availability of micro- and macroelements in the soil. Nutrient status should thus be examined not by establishing the effects of single nutrient deficiencies on the physiological state of the plant but by combinations of them. Differences in the nutrient content significantly affect the photochemical process of photosynthesis therefore playing a crucial role in plants growth and development. In this work, an attempt was made to find a connection between element content in (i) different soils, (ii) plant leaves, grown on these soils and (iii) changes in selected chlorophyll a fluorescence parameters, in order to find a method for early detection of plant stress resulting from the combination of nutrient status in natural conditions. To achieve this goal, a mathematical procedure was used which combines principal component analysis (a tool for the reduction of data complexity), hierarchical k-means (a classification method) and a machine-learning method—super-organising maps. Differences in the mineral content of soil and plant leaves resulted in functional changes in the photosynthetic machinery that can be measured by chlorophyll a fluorescent signals. Five groups of patterns in the chlorophyll fluorescent parameters were established: the ‘no deficiency’, Fe-specific deficiency, slight, moderate and strong deficiency. Unfavourable development in groups with nutrient deficiency of any kind was reflected by a strong increase in F o and ΔV/Δt 0 and decline in φ Po, φ Eo δ Ro and φ Ro. The strong deficiency group showed the suboptimal development of the photosynthetic machinery, which affects both PSII and PSI. The nutrient-deficient groups also differed in antenna complex organisation. Thus, our work suggests that the chlorophyll fluorescent method combined with machine-learning methods can be highly informative and in some cases, it can replace much more expensive and time-consuming procedures such as chemometric analyses.

Molecular mechanisms involved in plant photoprotection.

Abstract: Photosynthesis uses sunlight to convert water and carbon dioxide into biomass and oxygen. When in excess, light can be dangerous for the photosynthetic apparatus because it can cause photo-oxidative damage and decreases the efficiency of photosynthesis because of photoinhibition. Plants have evolved many photoprotective mechanisms in order to face reactive oxygen species production and thus avoid photoinhibition. These mechanisms include quenching of singlet and triplet excited states of chlorophyll, synthesis of antioxidant molecules and enzymes and repair processes for damaged photosystem II and photosystem I reaction centers. This review focuses on the mechanisms involved in photoprotection of chloroplasts through dissipation of energy absorbed in excess.

Overexpression of Rubisco subunits with RAF1 increases Rubisco content in maize

Abstract: Rubisco catalyses a rate-limiting step in photosynthesis and has long been a target for improvement due to its slow turnover rate. An alternative to modifying catalytic properties of Rubisco is to increase its abundance within C4 plant chloroplasts, which might increase activity and confer a higher carbon assimilation rate. Here, we overexpress the Rubisco large (LS) and small (SS) subunits with the Rubisco assembly chaperone RUBISCO ASSEMBLY FACTOR 1 (RAF1). While overexpression of LS and/or SS had no discernable impact on Rubisco content, addition of RAF1 overexpression resulted in a >30% increase in Rubisco content. Gas exchange showed a 15% increase in CO2 assimilation (ASAT) in UBI-LSSS-RAF1 transgenic plants, which correlated with increased fresh weight and in vitro Vcmax calculations. The divergence of Rubisco content and assimilation could be accounted for by the Rubisco activation state, which decreased up to 23%, suggesting that Rubisco activase may be limiting Vcmax, and impinging on the realization of photosynthetic potential from increased Rubisco content. Rubisco, which catalyses a major rate-limiting reaction in photosynthesis, is an important target for ‘improvement’. This study shows that rather than specifically engineering Rubisco’s properties, overexpression alone can increase the photosynthetic performance of transgenic maize plants.

Decreased photosynthetic rate under high temperature in wheat is due to lipid desaturation, oxidation, acylation, and damage of organelles

Abstract: High temperature is a major abiotic stress that limits wheat (Triticum aestivum L.) productivity. Variation in levels of a wide range of lipids, including stress-related molecular species, oxidative damage, cellular organization and ultrastructural changes were analyzed to provide an integrated view of the factors that underlie decreased photosynthetic rate under high temperature stress. Wheat plants of cultivar Chinese Spring were grown at optimum temperatures (25/15 °C, maximum/minimum) until the onset of the booting stage. Thereafter, plants were exposed to high temperature (35/25 °C) for 16 d. Compared with optimum temperature, a lower photosynthetic rate was observed at high temperature which is an interplay between thylakoid membrane damage, thylakoid membrane lipid composition, oxidative damage of cell organelle, and stomatal and non-stomatal limitations. Triacylglycerol levels were higher under high temperature stress. Polar lipid fatty acyl unsaturation was lower at high temperature, while triacylglycerol unsaturation was the same at high temperature and optimum temperature. The changes in lipid species indicates increases in activities of desaturating, oxidizing, glycosylating and acylating enzymes under high temperature stress. Cumulative effect of high temperature stress led to generation of reactive oxygen species, cell organelle and membrane damage, and reduced antioxidant enzyme activity, and imbalance between reactive oxygen species and antioxidant defense system. Taken together with recent findings demonstrating that reactive oxygen species are formed from and are removed by thylakoid lipids, the data suggest that reactive oxygen species production, reactive oxygen species removal, and changes in lipid metabolism contribute to decreased photosynthetic rate under high temperature stress.

Impacts of Carbon Dots on Rice Plants: Boosting the Growth and Improving the Disease Resistance

Abstract: A series of ∼5 nm sized carbon dots (CDs) with different oxygen contents were fabricated and employed as a model material with which to explore the impacts of carbon nanoparticles on rice-plant growth. We show that CDs can penetrate into all parts of rice plants, including the cell nuclei. Systematic investigations provide insight into the different processes by which seed germination, root elongation, seedling length, enzyme (RuBisCO) activity, and carbohydrate generation are increased. CDs are capable of entering the cell, reaching the nucleus, loosening the DNA structure, and increasing the thionin (Os06g32600) gene expression, which finally enhanced the rice-plant disease-resistance ability. CDs can be degraded by plant to form plant-hormone analogues and CO2, and then the hormone analogues promote the rice-plant growth, while the CO2 is converted into carbohydrates through the Calvin cycle of photosynthesis. The outcome of these processes is a 14.8% enhancement of the total rice yield and an increase...

5-Aminolevulinic Acid (ALA) Alleviated Salinity Stress in Cucumber Seedlings by Enhancing Chlorophyll Synthesis Pathway.

Abstract: 5-Aminolevulinic acid (ALA) is a common precursor of tetrapyrroles as well as a crucial growth regulator in higher plants. ALA has been proven to be effective in improving photosynthesis and alleviating the adverse effects of various abiotic stresses in higher plants. However, little is known about the mechanism of ALA in ameliorating the photosynthesis of plant under abiotic stress. In this paper, we studied the effects of exogenous ALA on salinity-induced damages of photosynthesis in cucumber (Cucumis sativus L.) seedlings. We found that the morphology (plant height, leave area), light utilization capacity of PS II [qL, Y(II)] and gas exchange capacity (Pn, gs, Ci, and Tr) were significantly retarded under NaCl stress, but these parameters were all recovered by the foliar application of 25 mg L-1 ALA. Besides, salinity caused heme accumulation and up-regulation of gene expression of ferrochelatase (HEMH) with suppression of other genes involved in chlorophyll synthesis pathway. Exogenously application of ALA under salinity down-regulated the heme content and HEMH expression, but increased the gene expression levels of glutamyl-tRNA reductase (HEMA1), Mg-chelatase (CHLH), and protochlorophyllide oxidoreductase (POR). Moreover, the contents of intermediates involved in chlorophyll branch were increased by ALA, including protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX, protochlorophyllide (Pchlide), and chlorophyll (Chl a and Chl b) under salt stress. Ultrastructural observation of mesophyll cell showed that the damages of photosynthetic apparatus under salinity were fixed by ALA. Collectively, the chlorophyll biosynthesis pathway was enhanced by exogenous ALA to improve the tolerance of cucumber under salinity.

Improved photosynthetic efficacy of maize (Zea mays) plants with arbuscular mycorrhizal fungi (AMF) under high temperature stress.

Abstract: In this study, pot experiments were performed to investigate the effects of high temperature stress (44 °C) in maize plants colonized with and without arbuscular mycorrhizal fungi (AMF). Various parameters characterizing photosynthetic activity were measured in order to estimate the photosynthetic efficiency in maize plants. It was observed that density of active reaction centers of PSII, quantum efficiency of photosystem II (PSII), linear electron transport, excitation energy trapping, performance index, net photosynthesis rate increased in AMF (+) plants at 44 °C ± 0.2 °C. Efficiency of primary photochemical reaction (represented as Fv/Fo) increased in AMF (+) plants as compared to AMF (−) plants. AMF seems to have protected water splitting complex followed by enhanced primary photochemistry of PSII under high temperature. Basic morphological parameters like leaf width, plant height and cob number increased in AMF (+) plants as compared to AMF (−) plants. AMF (+) plants grew faster than AMF (−) plants due to larger root systems. Chl content increased in AMF (+) plants as compared to AMF (−) maize plants. AMF hyphae likely increased Mg uptake which in turn increased the total chlorophyll content in AMF (+) maize plants. This subsequently led to a higher production in photosynthate and biomass. Thus AMF (+) plants have shown better photosynthesis performance as compared to AMF (−) maize plants under high temperature stress.

Chloroplasts at the Crossroad of Photosynthesis, Pathogen Infection and Plant Defense

Abstract: Photosynthesis, pathogen infection, and plant defense are three important biological processes that have been investigated separately for decades. Photosynthesis generates ATP, NADPH, and carbohydrates. These resources are utilized for the synthesis of many important compounds, such as primary metabolites, defense-related hormones abscisic acid, ethylene, jasmonic acid, and salicylic acid, and antimicrobial compounds. In plants and algae, photosynthesis and key steps in the synthesis of defense-related hormones occur in chloroplasts. In addition, chloroplasts are major generators of reactive oxygen species and nitric oxide, and a site for calcium signaling. These signaling molecules are essential to plant defense as well. All plants grown naturally are attacked by pathogens. Bacterial pathogens enter host tissues through natural openings or wounds. Upon invasion, bacterial pathogens utilize a combination of different virulence factors to suppress host defense and promote pathogenicity. On the other hand, plants have developed elaborate defense mechanisms to protect themselves from pathogen infections. This review summarizes recent discoveries on defensive roles of signaling molecules made by plants (primarily in their chloroplasts), counteracting roles of chloroplast-targeted effectors and phytotoxins elicited by bacterial pathogens, and how all these molecules crosstalk and regulate photosynthesis, pathogen infection, and plant defense, using chloroplasts as a major battlefield.

Application of chlorophyll fluorescence performance indices to assess the wheat photosynthetic functions influenced by nitrogen deficiency.

Abstract: Nitrogen deficiency influences importantly the plant photosynthetic capacity and crop productivity. Here, we employed the rapid, non-invasive measurements of chlorophyll a fluorescence kinetics for calculation of the integrative fluorescence parameters related to the leaf photosynthetic performance. In pot experiments with winter wheat (Triticum aestivum L.) we cultivated plants during the whole growing period in the soil substrate supplied with four different doses of nitrogen. The leaf nitrogen and chlorophyll content as well as the plant dry mass were analyzed after chlorophyll fluorescence records in three growth stages. Our results indicate that the commonly used parameter F-v/F-m (the maximum quantum yield of photochemistry) was almost insensitive to nitrogen treatment. In contrary, the performance index (PIabs) and total performance index (PItot) were much more responsive and significant differences among plants of different nitrogen treatments as well as between the youngest and third leaf from the top were observed. Parameter PItot shown to express only small diurnal changes, thus being more reliable and more useful for comparison of different samples in field conditions than more frequently used parameter PIabs.

Effects of zinc oxide nanoparticles on the growth, photosynthetic traits, and antioxidative enzymes in tomato plants

Abstract: With the dramatic increase in nanotechnologies, it has become probable that biological systems will be exposed to excess of nanoparticles (NPs). However, the impact of NPs on plants remains to be explored. The aim of this research was to determine the effects of ZnO NPs on tomato (Solanum lycopersicum L.) plants. Plant growth, photosynthetic characteristics, chlorophyll fluorescence parameters, and activities of antioxidative enzymes were measured in 35-d-old plants. The ZnO NP treatments significantly inhibited tomato root and shoot growth, decreased the content of chlorophylls a and b, and reduced photosynthetic efficiency and some other chlorophyll fluorescence parameters in a concentration-dependent manner. However, the supernatant of ZnO NP suspensions did not affect growth of tomato, despite the presence of small amounts of Zn2+. Taken together, these results suggest that toxic effects on tomato plants were from ZnO NPs, not from Zn2+ released into the solution; toxicity was likely caused by reduced chlorophyll content and damaged photochemical system, which in turn limited photosynthesis and led to the reduction in biomass accumulation. Also, ZnO NPs enhanced the transcription of genes related to antioxidant capacity, suggesting that ZnO NPs could enhance the defence response by increasing activities of antioxidant enzymes.

A physiological perspective on the origin and evolution of photosynthesis

Abstract: The origin and early evolution of photosynthesis are reviewed from an ecophysiological perspective. Earth's first ecosystems were chemotrophic, fueled by geological H2 at hydrothermal vents and, required flavin-based electron bifurcation to reduce ferredoxin for CO2 fixation. Chlorophyll-based phototrophy (chlorophototrophy) allowed autotrophs to generate reduced ferredoxin without electron bifurcation, providing them access to reductants other than H2. Because high-intensity, short-wavelength electromagnetic radiation at Earth's surface would have been damaging for the first chlorophyll (Chl)-containing cells, photosynthesis probably arose at hydrothermal vents under low-intensity, long-wavelength geothermal light. The first photochemically active pigments were possibly Zn-tetrapyrroles. We suggest that (i) after the evolution of red-absorbing Chl-like pigments, the first light-driven electron transport chains reduced ferredoxin via a type-1 reaction center (RC) progenitor with electrons from H2S; (ii) photothioautotrophy, first with one RC and then with two, was the bridge between H2-dependent chemolithoautotrophy and water-splitting photosynthesis; (iii) photothiotrophy sustained primary production in the photic zone of Archean oceans; (iv) photosynthesis arose in an anoxygenic cyanobacterial progenitor; (v) Chl a is the ancestral Chl; and (vi), anoxygenic chlorophototrophic lineages characterized so far acquired, by horizontal gene transfer, RCs and Chl biosynthesis with or without autotrophy, from the architects of chlorophototrophy-the cyanobacterial lineage.

Photosynthetic efficiency in sun and shade plants

Abstract: Photosynthesis is amongst the plant cell functions that are highly sensitive to any type of changes. Sun and shade conditions are prevalent in fields as well as dense forests. Dense forests face extreme sun and shade conditions, and plants adapt themselves accordingly. Sun flecks cause changes in plant metabolic processes. In the field, plants have to face high light intensity and survive under such conditions. Sun and shade type of plants develops a respective type of chloroplasts which help plants to survive and perform photosynthesis under adverse conditions. PSII and Rubisco behave differently under different sun and shade conditions. In this review, morphological, physiological, and biochemical changes under conditions of sun (high light) and shade (low light) on the process of photosynthesis, as well as the tolerance and adaptive mechanisms involved for the same, were summarized.

Unique organization of photosystem I-light harvesting supercomplex revealed by cryo-EM from a red alga

Abstract: Photosystem I (PSI) is one of the two photosystems present in oxygenic photosynthetic organisms and functions to harvest and convert light energy into chemical energy in photosynthesis. In eukaryotic algae and higher plants, PSI consists of a core surrounded by variable species and numbers of light-harvesting complex (LHC)I proteins, forming a PSI-LHCI supercomplex. Here, we report cryo-EM structures of PSI-LHCR from the red alga Cyanidioschyzon merolae in two forms, one with three Lhcr subunits attached to the side, similar to that of higher plants, and the other with two additional Lhcr subunits attached to the opposite side, indicating an ancient form of PSI-LHCI. Furthermore, the red algal PSI core showed features of both cyanobacterial and higher plant PSI, suggesting an intermediate type during evolution from prokaryotes to eukaryotes. The structure of PsaO, existing in eukaryotic organisms, was identified in the PSI core and binds three chlorophylls a and may be important in harvesting energy and in mediating energy transfer from LHCII to the PSI core under state-2 conditions. Individual attaching sites of LHCRs with the core subunits were identified, and each Lhcr was found to contain 11 to 13 chlorophylls a and 5 zeaxanthins, which are apparently different from those of LHCs in plant PSI-LHCI. Together, our results reveal unique energy transfer pathways different from those of higher plant PSI-LHCI, its adaptation to the changing environment, and the possible changes of PSI-LHCI during evolution from prokaryotes to eukaryotes.