Rubisco Research Articles

Sustained Photosynthesis in Tobacco Leaves by Fast CO<sub>2</sub>-Fixing Enzymes Encapsulated in Micro-Compartments

Improvement of yield potential in global food crops has hit a breeding road-block which could be solved through genetic engineering. One promising strategy is the introduction of cyanobacterial CO2-concentrating-mechanisms (CCMs) into plant chloroplasts to enhance photosynthesis and yield. CCMs actively accumulate CO2 within specialized microcompartments called carboxysomes, where the enzyme Rubisco rapidly fixes CO2. Here we replaced the endogenous Rubisco large subunit gene with cyanobacterial Form-1A Rubisco and key structural proteins of α- carboxysomes in tobacco chloroplasts. Transformed plants produced purifiable carboxysomes, isometric with those of the source organism Cyanobium marinum. Carboxysomes encapsulated the introduced Rubisco and enabled autotrophic growth at elevated CO2. Our results demonstrate the formation of α-carboxysomes from a minimal gene set, and that cyanobacterial Form-1A Rubisco supports C3 photosynthesis at high CO2. This major advance informs the step-wise construction of fully-functional α-carboxysomes in chloroplasts which, along with other CCM components, are expected to improve crop plant performance.

Tolerance strategies in cyanobacterium Fischerella sp. under pesticide stress and possible role of a carbohydrate-binding protein in the metabolism of methyl parathion (MP)

The tolerance strategy of cyanobacterium Fischerella sp. under methyl parathion (MP) stress was investigated through proteomics analysis using 2-DE technique coupled with MALDI- TOF MS/MS. Proteomic study of the cyanobacterium treated with or without MP for two and eight days exhibited differential expressions of proteins related to photosynthesis, energy and protein metabolism, redox homeostasis, signal transduction and cellular defence. Inhibitory effect of MP on the growth of the test organism was more pronounced after the 2nd day of treatment and the majority of the proteins, except those involved in the protein metabolism (DnaK, Ef-Tu and proteases), were downregulated. However, the growth of the cyanobacterium was significantly less affected after the 8th day of MP treatment and a number of proteins, viz., antioxidative enzymes, signalling protein, chaperones, were induced. Transcript analyses of the genes of few upregulated and downregulated proteins, i.e., phycocyanin α subunit (cpcA), ribulose bisphosphate carboxylase (rbcl), F0F1 ATP synthase subunit α, F0F1 ATP synthase subunit β, SOD (sod), NifH (nif H), DnaK (dnaK) and Peptidase S8 showed similar results after the 8th day of MP treatment. Furthermore, some hypothetical proteins were also found to be upregulated in the cyanobacterium under MP stress. Functional prediction of four of these hypothetical proteins using bioinformatic tools revealed their roles in signalling and carbohydrate metabolism. Interestingly, one hypothetical protein was homologous to lectin and found to possess a binding pocket for MP. Therefore, this lectin-type protein of the cyanobacterium might have a crucial role in the removal and degradation of MP.

Correction: Positively selected amino acid replacements within the RuBisCO enzyme of oak trees are associated with ecological adaptations.

[This corrects the article DOI: 10.1371/journal.pone.0183970.].

Distinguishing Orchid Species by DNA Barcoding: Increasing the Resolution of Population Studies in Plant Biology.

Increasing the resolution of population studies in plant biology is one of the leading frontiers for omics sciences. One of the most pervasive challenges in molecular phylogenetics is the incongruence between phylogenies obtained using different data sets such as individual genes [like ribulose bisphosphate carboxylase large chain (rbcL) and maturase K (matK)] and intergenic spacers (IGS) [like nuclear ribosomal internal transcribed spacer 1 (nrITS 1) and 2 (nrITS 2), and chloroplast IGS between transfer RNA for leucine and phenylalanine (cp trnL-trnF IGS)]. To solve this challenge, we have screened the four well-established candidate gene sequences (i.e., rbcL, matK, trnL-trnF IGS, and 18S-ITS1-5.8S-ITS2-28S nrDNA) of 65 Indian orchid species. We also have included 31 different species of Dendrobium to identify the suitable locus for resolving the phylogeny-related problem below the taxonomic rank of genus. The Consortium for the Barcode of Life has recommended the locus rbcL and matK for barcoding of all land plants, including orchids. However, in this study, matK and rbcL (species resolving capacity 52% and 48%, respectively) were found to work above the taxonomic limit of genus, and thus cannot be considered a suitable tool to resolve closely related species of Dendrobium, whereas, we found that the locus 18S-ITS1-5.8S-ITS2-28S nrDNA is the best choice with the highest species resolving ability (95.23%) and the highest mean Kimura 2-parameter distance (254 for intergeneric and 144 for intrageneric) for phylogeny construction, and thus have been taken as the most promising single-locus barcode for orchids.

Unraveling the molecular mechanism of photosynthetic toxicity of highly fluorescent silver nanoclusters to Scenedesmus obliquus

While the discovery of numerous attractive properties of silver at the nanoscale has increased their demand in many sectors including medicine, optics, sensing, painting and cosmetics, it has also raised wide public concerns about their effect on living organisms in aquatic environment. Despite the continuous effort to understand the various aspects of the toxicity of silver nanomaterials, the molecular level understanding on their cytotoxicity mechanism to biological organisms has remained unclear. Herein, we demonstrated the underlying mechanism of the photosynthetic toxicity against green algae namely, Scenedesmus obliquus by using an emerging silver nanomaterial, called silver nanoclusters (defined as r-Ag NCs). By exploiting the unique fluorescence properties of r-Ag NCs along with various other analytical/biological tools, we proposed that the photosynthetic toxicity of r-Ag NCs was largely attributed to the “joint-toxicity” effect of particulate form of r-Ag NCs and its released Ag+, which resulted in the disruption of the electron transport chain of light reaction and affected the content of key enzymes (RuBP carboxylase/ oxygenase) of Calvin cycle of algae cells. We believe that the present study can also be applied to the assessment of the ecological risk derived from other metal nanoparticles.

Arabidopsis phosphatidylinositol 4-phosphate 5-kinase 2 contains a functional nuclear localization sequence and interacts with alpha-importins.

The Arabidopsis phosphoinositide kinase PIP5K2 has been implicated in the control of membrane trafficking and is important for development and growth. In addition to cytosolic functions of phosphoinositides, a nuclear phosphoinositide system has been proposed, but evidence for nuclear phosphoinositides in plants is limited. Fluorescence-tagged variants of PIP5K2 reside in the nucleus of Arabidopsis root meristem cells, in addition to reported plasma membrane localization. Here we report on the interaction of PIP5K2 with alpha-importins and characterize its nuclear localization sequences (NLSs). The PIP5K2 sequence contains four putative NLSs (NLSa-NLSd) and only a PIP5K2 fragment containing NLSs is imported into nuclei of onion epidermis cells upon transient expression. PIP5K2 interacts physically with alpha-importin isoforms in cytosolic split-ubiquitin-based yeast two-hybrid tests, in dot-blot experiments and in immuno-pull-downs. A 27-amino-acid fragment of PIP5K2 containing NLSc is necessary and sufficient to mediate the nuclear import of a large cargo fusion consisting of two mCherry markers fused to RubisCO large subunit. Substitution of basic residues in NLSc results in reduced import of PIP5K2 or other cargoes into plant nuclei. The data suggest that PIP5K2 is subject to active, alpha-importin-mediated nuclear import, consistent with a nuclear role for PIP5K2 in addition to its reported cytosolic functions. The detection of both substrate and product of PIP5K2 in plant nuclei according to reporter fluorescence and immunofluorescence further supports the notion of a nuclear phosphoinositide system in plants. Variants of PIP5K2 with reduced nuclear residence might serve as tools for the future functional study of plant nuclear phosphoinositides.

Differential ُExpression of RuBisCO large Subunit and its Assembly in Intact Chloroplasts of Pisum sativum L. Treated with NaCl and Jasmonic Acid

THIS STUDY aimed to detect the effect of stress conditions imposed by different treatments of NaCl and jasmonic acid (JA) on the expression pattern and assembly of RuBisCO large subunit (RbcL) and RuBisCO enzyme complex using SDS-PAGE and HDN-PAGE techniques, respectively. Both Total Soluble Proteins (TSPs) and Chloroplast Proteins (ChPs) were variably affected by each treatment. Notably, a unique protein band was detected in the seedlings treated with 150 mM NaCl for 5 days. Surprisingly, this band was not detected under any other salt treatment. Using nano HPLC-ESI-MS/MS MALDI-TOF protein sequencing, this band was identified as downshifted RbcL at approximately 50 kDa in addition to the original one was separated at approximately 55 kDa on SDS-PAGE. The expression of RbcL protein decreased in a dose dependent manner in the plants treated with JA for one and five days. All treatments did not affect the RuBisCO complex assembly at approximately 660 kDa, but triggered stress-induced ChPs at approximately 440 kDa and 1 MDa concomitant with NaCl treatments. RbcL band isolated from intact chloroplast was associated with Coupling Factor (CF1) beta subunit of ATP synthase as revealed by MALDI-TOF protein sequencing analysis. Possible interpretations of these findings have been further discussed in this study.

From chaperonins to Rubisco assembly and metabolic repair.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) mediates the fixation of atmospheric CO2 in photosynthesis by catalyzing the carboxylation of the 5-carbon sugar ribulose-1,5-bisphosphate (RuBP). Despite its pivotal role, Rubisco is an inefficient enzyme and thus has been a key target for bioengineering. However, efforts to increase crop yields by Rubisco engineering remain unsuccessful, due in part to the complex machinery of molecular chaperones required for Rubisco biogenesis and metabolic repair. While the large subunit of Rubisco generally requires the chaperonin system for folding, the evolution of the hexadecameric Rubisco from its dimeric precursor resulted in the dependence on an array of additional factors required for assembly. Moreover, Rubisco function can be inhibited by a range of sugar-phosphate ligands. Metabolic repair of Rubisco depends on remodeling by the ATP-dependent Rubisco activase and hydrolysis of inhibitors by specific phosphatases. This review highlights our work toward understanding the structure and mechanism of these auxiliary machineries.

Morphology, phylogeny and lipid components of an oil-rich microalgal strain

Microalgae have attracted much more attentions for their roles in biofuel exploration recently. In this report, one oil-rich microalgal strain (TY02) was isolated from the lawn soil in a park, Taiyuan, Shanxi, China, and the morphology and phylogeny characters of the strain was systematically analyzed. Observed by light microscopy, scanning electron microscopy, transmission electron microscopy and fluorescent microscopy, the lipid bodies were observed clearly. After extracting the total lipid by chloroform-methanol method, the fatty acid content and composition of the lipid bodies in the strain were detected and analyzed through gas chromatography-mass spectrometry. The results demonstrated that the total lipid content of TY02 was 33.27 ± 1.13%, among the total 7 kinds of fatty acids identified in TY02, the major constituents are C16 and C18 fatty acids, which taking up to 88.15%. Moreover, the predominant fatty acids were Hexadecanoic acid (C16: 0), 9, 12-Octadecadienoic acid (C18: 2) and 9, 12, 15-Octade mcatrienoic acid (C18: 3). Based on the molecular markers of 18S rDNA, rbcL and ITS genes, phylogenetic trees and ITS2 secondary structure analysis all showed that the strain closed to Parachlorella kessleri. All results might bring a new look that some microalgae with potential values can be a raw biodiesel material.

One-third of the plastid genes evolved under positive selection in PACMAD grasses.

We demonstrate that rbcL underwent strong positive selection during the C 3 -C 4 photosynthetic transitions in PACMAD grasses, in particular the 3' end of the gene. In contrast, selective pressures on other plastid genes vary widely and environmental drivers remain to be identified. Plastid genomes have been widely used to infer phylogenetic relationships among plants, but the selective pressures driving their evolution have not been systematically investigated. In our study, we analyse all protein-coding plastid genes from 113 species of PACMAD grasses (Poaceae) to evaluate the selective pressures driving their evolution. Our analyses confirm that the gene encoding the large subunit of RubisCO (rbcL) evolved under strong positive selection after C3-C4 photosynthetic transitions. We highlight new codons in rbcL that underwent parallel changes, in particular those encoding the C-terminal part of the protein. C3-C4 photosynthetic shifts did not significantly affect the evolutionary dynamics of other plastid genes. Instead, while two-third of the plastid genes evolved under purifying selection or neutrality, 25 evolved under positive selection across the PACMAD clade. This set of genes encode for proteins involved in diverse functions, including self-replication of plastids and photosynthesis. Our results suggest that plastid genes widely adapt to changing ecological conditions, but factors driving this evolution largely remain to be identified.

Understanding the Solid Solution–Aqueous Solution Equilibria in the KCl + RbCl + H2O System from Experiments, Atomistic Simulation and Thermodynamic Modeling

The solid solution–aqueous solution (SSAS) equilibria in the KCl + RbCl + H2O system were redetermined at 298.15 K. The experimental data for (K,Rb)Cl were consistent with the formation of a continuous solid solution without miscibility gaps. The Schreinemakers’ wet residues method and an XRD quantitative analysis technique based on the Vegard approach were applied to determine the chemical composition of the solid solution phase of (K,Rb)Cl. The compositions of (K,Rb)Cl derived from the Vegard approach are in accordance with those from the wet residues method. The thermodynamic properties of mixing of the (K,Rb)Cl solid solution were theoretically predicted using atomistic simulations. From these simulations, a regular solution behavior is recognized that is consistent with the knowledge of the thermodynamic properties of mixing of (K,Rb)Cl obtained from SSAS equilibrium studies, but the predicted regular solution model parameter A 0 is significantly larger than that regressed from the SSAS equilibrium data. Finally, a thermodynamic model was developed for representing the SSAS equilibria and element partitioning in the KCl + RbCl + H2O system as a function of temperature that can be used for predicting the SSAS equilibria in the studied system over the temperature range 273.15–373.15 K.

Production of organic matter and diversity of the ribulose bisphosphate carboxylase genes in sediments of the Solnechny Spring, Uzon Caldera, Kamchatka

Production of organic matter and diversity of the ribulose bisphosphate carboxylase genes in sediments of the Solnechny Spring, Uzon Caldera, Kamchatka

Positively selected amino acid replacements within the RuBisCO enzyme of oak trees are associated with ecological adaptations.

Phylogenetic analysis by maximum likelihood (PAML) has become the standard approach to study positive selection at the molecular level, but other methods may provide complementary ways to identify amino acid replacements associated with particular conditions. Here, we compare results of the decision tree (DT) model method with ones of PAML using the key photosynthetic enzyme RuBisCO as a model system to study molecular adaptation to particular ecological conditions in oaks (Quercus). We sequenced the chloroplast rbcL gene encoding RuBisCO large subunit in 158 Quercus species, covering about a third of the global genus diversity. It has been hypothesized that RuBisCO has evolved differentially depending on the environmental conditions and leaf traits governing internal gas diffusion patterns. Here, we show, using PAML, that amino acid replacements at the residue positions 95, 145, 251, 262 and 328 of the RuBisCO large subunit have been the subject of positive selection along particular Quercus lineages associated with the leaf traits and climate characteristics. In parallel, the DT model identified amino acid replacements at sites 95, 219, 262 and 328 being associated with the leaf traits and climate characteristics, exhibiting partial overlap with the results obtained using PAML.

Changes in protein abundance and activity involved in freezing tolerance acquisition in winter barley (Hordeum vulgare L.)

The changes in protein abundance induced by cold hardening were analysed by 2 DE in ten doubled haploid (DH) lines of winter barley, highly differentiated with respect to freezing tolerance level. Among 45 differential proteins identified by MALDI-TOF/TOF, the majority was classified as related to photosynthesis, carbohydrate metabolism, oxidation-reduction reactions and stress response. Among the detected proteins, higher abundance of RuBisCO large and small subunits, RuBisCO activase, two Oxygen-evolving enhancer proteins, Ferredoxin-NADP reductase, Cytochrome P450-dependent fatty acid hydroxylase and 14-3-3 protein was associated with higher freezing tolerance level. Lower relative level of hypothetical ATP synthase beta subunit, uncharacterized mitochondrial protein AtMg00810 and ribosomal RNA small subunit methyltransferase G also seems to be important.The results of proteomic studies were complemented by the evaluation of photosynthetic apparatus acclimation, showing distinctive differences between the studied genotypes in the number of active PSII reaction centres (RC/CSm). Additionally, the analysis of antioxidative enzyme activities suggests the importance of H2O2 as a signalling molecule possibly involved in the initiation of cold-induced plant acclimation. However, in DH lines with high freezing tolerance, H2O2 generation during cold hardening treatment was accompanied by more stable activity of catalase, H2O2-decomposing enzyme. SignificanceIn the study, the changes in protein abundance induced by cold hardening treatment were analysed by two-dimensional gel electrophoresis in ten doubled haploid (DH) lines of winter barley. Harnessing DH technology resulted in distinctive widening of genetic variation with respect to freezing tolerance level. Both the cold-hardening effect on the protein pattern in an individual winter barley DH line as well as the variation among the selected DH lines were investigated, which resulted in the identification of 45 differentiated proteins classified as involved in 14 metabolic pathways and cellular processes. Among them, eight proteins: (1) the precursor of RuBisCO large subunit, (2) RuBisCO small subunit (partial), (3) RuBisCO activase small isoform, (4) the precursor of Oxygen-evolving enhancer protein 1-like (predicted protein), (5) Oxygen-evolving enhancer protein 2, (6) the leaf isozyme of Ferredoxin-NADP reductase, (7) hypothetical protein M569_12509 Cytochrome P450-dependent fatty acid hydroxylase-like and (8) hypothetical protein BRADI_1g11290 (14-3-3 protein A-like) were accumulated to a higher level in leaves of cold-hardened seedlings of freezing tolerant winter barley DH lines in comparison with susceptible ones. Three others: (9) hypothetical protein BRADI_5g05668 F1 ATP synthase beta subunit-like, (10) predicted protein uncharacterized mitochondrial protein AtMg00810-like and (11) BnaA02g08010D Ribosomal RNA small subunit methyltransferase G-like were detected at lower level in freezing tolerant seedlings in comparison with susceptible genotypes. The last two were for the first time linked to cold acclimation. The results of complementary analyses indicate that PSII activity and stability of antioxidative enzymes under low temperature are also very important for freezing tolerance acquisition.

Enhancing photosynthetic biomass productivity of industrial oleaginous microalgae by overexpression of RuBisCO activase

Eukaryotic microalgae are promising cell factories for photosynthesis-driven CO2 sequestration and oil production, however one key challenge has been to genetically enhance their biomass productivity. Here we showed that the biomass productivity of a model industrial oleaginous microalga Nannochloropsis oceanica can be elevated by overexpression of a nuclear-encoded, cbbX-homologous, candidate RuBisCO activase (g1915 or ‘nNoRca-like’) that is transcriptionally induced under air-level CO2 (i.e., 0.04% v/v) as compared to 5% CO2 in wild-type cells. In the mutants, under air-level CO2, growth rate was enhanced by ~32%, biomass accumulation by ~46% and lipid productivity by ~41%, which were also accompanied by ~28% elevation in photosynthesis; furthermore, abundance of RuBisCO large subunit protein increased by ~45%, suggesting nNoRca-like overexpression enhanced microalgal photosynthesis by upregulating the level and activity of RuBisCO. Interestingly, under 5% CO2, no significant enhancement of RuBisCO protein expression was observed. Thus a genetic strategy that activates RuBisCO by augmenting its functional partners was proposed to increase biomass production of industrial microalgae. Our work expands the reservoir of potential photosynthetic gene targets for plant biotechnology and provides a basis for constructing advanced microalgal cell factories for carbon sequestration and biofuel production.

Identification of Reference and Biomarker Proteins in Chlamydomonas reinhardtii Cultured under Different Stress Conditions.

Reference proteins and biomarkers are important for the quantitative evaluation of protein abundance. Chlamydomonas reinhardtii was grown under five stress conditions (dark, cold, heat, salt, and glucose supplementation), and the OD750 and total protein contents were evaluated on days 0, 1, 2, 4, and 6 of culture. Antibodies for 20 candidate proteins were generated, and the protein expression patterns were examined by western blotting. Reference protein(s) for each treatment were identified by calculating the Pearson’s correlation coefficient (PCC) between target protein abundance and total protein content. Histone H3, beta tubulin 1 (TUB-1), ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RBCL), and mitochondrial F1F0 ATP synthase subunit 6 (ATPs-6) were the top reference proteins, because they were expressed stably under multiple stress conditions. The average relative-fold change (ARF) value of each protein was calculated to identify biomarkers. Heat shock protein 90B (HSP90B), flagellar associated protein (FAP127) and ATP synthase CF0 A subunit (ATPs-A) were suitable biomarkers for multiple treatments, while receptor of activated protein kinase C1 (RCK1), biotin carboxylase (BCR1), mitochondrial phosphate carrier protein (MPC1), and rubisco large subunit N-methyltransferase (RMT1) were suitable biomarkers for the dark, cold, heat, and glucose treatments, respectively.

Identification of Endogenous Reference Genes for RT-qPCR Expression Analysis in Urochloa brizantha Under Abiotic Stresses

Urochloa brizantha is one of the most important warm season forage grasses in tropical countries. Despite its importance, there are few studies on gene expression in this species under stressful conditions. Real-time (RT-qPCR) is an accurate technique for gene quantification analysis, but reference genes must be validated under the same conditions used to assess the expression of the target genes. Here, we evaluated the stability of nine reference genes: Actin 12, Eukaryotic initiation factor 4 A, Elongation factor-1 alpha, FTSH protease 4, U2 auxiliary fator, Succinol Co-enzyme A, Tubulin alfa-5, Tubulin beta-6, Ubiquitin conjugating enzyme. Total RNA was extract from leaf tissues of U. brizantha subjected to 6, 12 and 24 h of cold and heat stresses (10 and 45 °C, respectively), and drought, including moderate (−0.5 to −0.7 MPa), severe (−1.1 to −1.8 MPa) and recovery after re-watering. The RefFinder web-based tool was used to rank the most stable reference genes for each stress. Elongation factor-1 alpha, Elongation factor-1 alpha or Ubiquitin conjugating enzyme, and Eukaryotic initiation factor 4 A were the most stable genes for heat, cold and drought stress, respectively. The expression of Rubisco large subunit gene was normalized against the most stable gene selected by ReFfinder for each stress.

Phylogeny and biogeography of the carnivorous plant family Droseraceae with representative Drosera species from Northeast India

Background: Botanical carnivory is spread across four major angiosperm lineages and five orders: Poales, Caryophyllales, Oxalidales, Ericales and Lamiales. The carnivorous plant family Droseraceae is well known for its wide range of representatives in the temperate zone. Taxonomically, it is regarded as one of the most problematic and unresolved carnivorous plant families. In the present study, the phylogenetic position and biogeographic analysis of the genus Drosera is revisited by taking two species from the genus Drosera (D. burmanii and D. Peltata) found in Meghalaya (Northeast India). Methods: The purposes of this study were to investigate the monophyly, reconstruct phylogenetic relationships and ancestral area of the genus Drosera, and to infer its origin and dispersal using molecular markers from the whole ITS (18S, 28S, ITS1, ITS2) region and ribulose bisphosphate carboxylase (rbcL) sequences. Results: The present study recovered most of the findings by previous studies. The basal position of Droseraceae within the non-carnivorous Caryophyllales indicated in the tree topologies and fossil findings strongly support a date of origin for Droseraceae during the Paleocene (55-65 mya). Within the family Droseraceae, the sister relationship between Aldrovanda and Dionaea is supported by our ITS and rbcL dataset. This information can be used for further comparative and experimental studies. Conclusions: Drosera species are best suited as model systems for addressing a wide array of questions concerning evolutionary dynamics and ecological processes governing botanical carnivory.

Dysregulation of photosynthetic genes in oceanic Prochlorococcus populations exposed to organic pollutants

The impact of organic pollutants on oceanic ecosystem functioning is largely unknown. Prochlorococcus, the most abundant known photosynthetic organism on Earth, has been suggested to be especially sensible to exposure to organic pollutants, but the sub-lethal effects of organic pollutants on its photosynthetic function at environmentally relevant concentrations and mixtures remain unexplored. Here we show the modulation of the expression of two photosynthetic genes, rbcL (RuBisCO large subunit) and psbA (PSII D1 protein), of oceanic populations of Prochlorococcus from the Atlantic, Indian and Pacific Oceans when exposed to mixtures of organic pollutants consisting of the non-polar fraction of a seawater extract. This mixture included most persistent organic pollutants, semivolatile aromatic-like compounds, and the unresolved complex mixture of hydrocarbons. Prochlorococcus populations in the controls showed the expected diel cycle variations in expression of photosynthetic genes. However, exposure to a complex mixture at concentrations only 2-fold above the environmental levels resulted in a decrease of expression of both genes, suggesting an effect on the photosynthetic function. While organic pollutant effects on marine phytoplankton have been already demonstrated at the cellular level, this is the first field study showing alterations at the molecular level of the photosynthetic function due to organic pollutants.

Study of the physiological mechanisms of two species of Spiraea during adaptation to drought treatment

The photosynthetic rate, light saturation point, light compensation point, changes in the MDA and SOD activities, and protein expression of two different drought-resistance species, Spiraea fritschiana and Spiraea trichocarpa, were assessed in this study. Furthermore, the drought-resistant physiological mechanisms of both species were analyzed at the protein level. The photosynthetic capacities of two Spiraea species decreased under drought stress, and the light saturation point and light compensation point decreased. However, their capacities to use weak light increased. Spiraea fritschiana, which demonstrated a stronger drought resistance, showed a better ability to adapt to weak light than S. trichocarpa. The content of MDA in S. fritschiana was notably lower than that in S. trichocarpa, indicating that the concentration of the membrane peroxidation products of S. fritschiana was less than those of S. trichocarpa. Compared with S. trichocarpa, S. fritschiana’s SOD activity was higher, and its ability to remove ROS was also better. Sixty-six proteins were identified with significantly different expression behavior and included regulatory, redox homeostasis, metabolism and energy, and cytoskeleton proteins. The results showed that the photosynthesis of S. trichocarpa was significantly affected by the drought stress. Enzymes in photosynthesis changed significantly; the expression of the RuBisCo large subunit decreased; and RuBisCo carboxylase, the chlorophyll a–b binding protein, ATP synthase, OEC 33 kD photosystem II protein and 23 kD OEC protein greatly increased. In addition, four antioxidant enzymes greatly increased, GroES chaperonin decreased, and eIF5A significantly increased under light stress. When S. fritschiana Schneid encountered serious drought stress, in addition to those enzymes that changed significantly under light drought stress in S. trichocarpa Nakai, NAD(P)H-quinone oxidoreductase and eIF5A were up-regulated. Specifically, three heat-shock proteins were induced. The expression of the enzymes of the two Spiraea that were related to photosynthesis, oxidation–reduction and regulation were all affected, but their species and expression patterns were different. In S. trichocarpa Nakai and S. fritschiana Schneid, there were significant changes in the proteins related to energy metabolism and the proteins related to energy transport, respectively. Thus, we considered that, in the case of protein involvement, the differences in the metabolic pathways and adjustment levels might contribute to S. trichocarpa having a weaker drought tolerance than S. fritschiana.