Shading-Dependent Greening Process of the Leaves in the Light-Sensitive Albino Tea Plant 'Huangjinya': Possible Involvement of the Light-Harvesting Complex II Subunit of Photosystem II in the Phenotypic Characteristic.

The light-sensitive albino tea plant can produce pale-yellow shoots with high levels of amino acids which are suitable to process high-quality tea. In order to understand the mechanism of the albino phenotype formation, the changes in the physio-chemical characteristics, chloroplast ultrastructure, chlorophyll-binding proteins, and the relevant gene expression were comprehensively investigated in the leaves of the light-sensitive albino cultivar 'Huangjinya' ('HJY') during short-term shading treatment. In the content of photosynthetic pigments, the ultrastructure of the chloroplast, and parameters of the photosynthesis in the leaves of 'HJY' could be gradually normalized along with the extension of the shading time, resulting in the leaf color transformed from pale yellow to green. BN-PAGE and SDS-PAGE revealed that function restoration of the photosynthetic apparatus was attributed to the proper formation of the pigment-protein complexes on the thylakoid membrane that benefited from the increased levels of the LHCII subunits in the shaded leaves of 'HJY', indicating the low level of LHCII subunits, especially the lack of the Lhcb1 might be responsible for the albino phenotype of the 'HJY' under natural light condition. The deficiency of the Lhcb1 was mainly subject to the strongly suppressed expression of the Lhcb1.x which might be modulated by the chloroplast retrograde signaling pathway GUN1 (GENOMES UNCOUPLED 1)-PTM (PHD type transcription factor with transmembrane domains)-ABI4 (ABSCISIC ACID INSENSITIVE 4).

Restoration of photosynthetic activity and supercomplexes from severe iron starvation in Chlamydomonas reinhardtii.

The eukaryotic alga Chlamydomonas (C.) reinhardtii is used as a model organism to study photosynthetic efficiency. We studied the organization and protein profile of thylakoid membranes under severe iron (Fe2+) deficiency condition and iron supplement for their restoration. Chlorophyll (Chl) a fluorescence fast OJIP transients were decreased in the severe Fe2+ deficient cells resulting in the reduction of the photochemical efficiency. The circular dichroism (CD) results from Fe2+ deficient thylakoid membranes show a significant change in pigment-pigment and pigment-protein excitonic interactions. The organization of super-complexes was also affected significantly. Furthermore, super-complexes of photosystem (PS) II and PSI, along with its dimers, were severely reduced. The complexes separated using sucrose gradient centrifugation shows that loss of super-complexes and excitonic pigment-pigment interactions were restored in the severely Fe2+ deficient cells upon Fe supplementation for three generations. Additionally, the immunoblots demonstrated that both PSII, PSI core, and their light-harvesting complex antenna proteins were differentially decreased. However, reduced core proteins were aggregated, which in turn proteins were unfold and destabilized the supercomplexes and its function. Interestingly, the aggregated proteins were insoluble after n-Dodecyl ß-D-maltoside solubilization. Further, they were identified in the pellet form. When Fe2+ was added to the severely deficient cells, the photosynthetic activity, pigment-proteins complexes, and proteins were restored to the level of control after 3rd generation.

Chloroplast ultrastructure in plants.

The chloroplast organelle in mesophyll cells of higher plants represents a sunlight-driven metabolic factory that eventually fuels life on our planet. Knowledge of the ultrastructure and the dynamics of this unique organelle is essential to understanding its function in an ever-changing and challenging environment. Recent technological developments promise unprecedented insights into chloroplast architecture and its functionality. The review highlights these new methodical approaches and provides structural models based on recent findings about the plasticity of the thylakoid membrane system in response to different light regimes. Furthermore, the potential role of the lipid droplets plastoglobuli is discussed. It is emphasized that detailed structural insights are necessary on different levels ranging from molecules to entire membrane systems for a holistic understanding of chloroplast function.

Excitation energy transfer in the far-red absorbing violaxanthin/vaucheriaxanthin chlorophyll a complex from the eustigmatophyte alga FP5.

This work highlights spectroscopic investigations on a new representative of photosynthetic antenna complexes in the LHC family, a putative violaxanthin/vaucheriaxanthin chlorophyll a (VCP) antenna complex from a freshwater Eustigmatophyte alga FP5. A representative VCP-like complex, named as VCP-B3 was studied with both static and time-resolved spectroscopies with the aim of obtaining a deeper understanding of excitation energy migration within the pigment array of the complex. Compared to other VCP representatives, the absorption spectrum of the VCP-B3 is strongly altered in the range of the chlorophyll a Qy band, and is substantially red-shifted with the longest wavelength absorption band at 707 nm at 77 K. VCP-B3 shows a moderate xanthophyll-to-chlorophyll a efficiency of excitation energy transfer in the 50-60% range, 20-30% lower from comparable VCP complexes from other organisms. Transient absorption studies accompanied by detailed data fitting and simulations support the idea that the xanthophylls that occupy the central part of the complex, complementary to luteins in the LHCII, are violaxanthins. Target analysis suggests that the primary route of xanthophyll-to-chlorophyll a energy transfer occurs via the xanthophyll S1 state.

Effects of Thylakoid-Rich Spinach Extract on the Pharmacokinetics of Drugs in Rats.

Thylakoid-rich spinach extract is being used as dietary weight-loss supplements in Japan. A recent rat study has suggested that intake of thylakoid-rich spinach extract with dietary oil inhibits dietary fat absorption via binding to bile acids, which promotes excretion of bile acids in feces. While, we confirmed that a serving size of thylakoid-rich spinach extract contains a large amount of calcium (130 mg/5 g). Therefore, using rats, we evaluated whether one-time ingestion of thylakoid-rich spinach extract affects the gastrointestinal absorption of water-insoluble drugs, such as griseofulvin (GF) and indomethacin (IM), or ciprofloxacin (CPFX) that chelate with polyvalent metal cations. Pretreatment of the rats with thylakoid-rich spinach extract (100 or 300 mg/kg) for 15 min prior to oral administration of GF (50 mg/kg) or IM (10 mg/kg) did not significantly alter the pharmacokinetic properties of either drug. Meanwhile, co-administration of thylakoid-rich spinach extract (500 mg/kg) and CPFX (20 mg/kg) significantly reduced the peak plasma concentration and the area under the plasma concentration-time curve of CPFX to 25 and 40%, respectively in rats. In vitro studies demonstrated that when a mixture of thylakoid-rich spinach extract and CPFX was centrifuged, there was a significant reduction in the supernatant concentration of CPFX relative to the control. When the experiment was repeated in the presence of ethylenediaminetetraacetic acid, the concentration of CPFX was unchanged. These results suggest that the intake of thylakoid-rich spinach extract may reduce the absorption of drugs that form a chelate with polyvalent metal cations, such as CPFX.

Thylakoid proteome modulation in pea plants grown at different irradiances: quantitative proteomic profiling in a non-model organism aided by transcriptomic data integration.

Plant thylakoid membranes contain hundreds of proteins that closely interact to cope with ever-changing environmental conditions. We investigated how Pisum sativum L. (pea) grown at different irradiances optimizes light-use efficiency through the differential accumulation of thylakoid proteins. Thylakoid membranes from plants grown under low (LL), moderate (ML) and high (HL) light intensity were characterized by combining chlorophyll fluorescence measurements with quantitative label-free proteomic analysis. Protein sequences retrieved from available transcriptomic data considerably improved thylakoid proteome profiling, increasing the quantifiable proteins from 63 to 194. The experimental approach used also demonstrates that this integrative omics strategy is powerful for unravelling protein isoforms and functions that are still unknown in non-model organisms. We found that the different growth irradiances affect the electron transport kinetics but not the relative abundance of photosystems (PS) I and II. Two acclimation strategies were evident. The behaviour of plants acclimated to LL was compared at higher irradiances: (i) in ML, plants turn on photoprotective responses mostly modulating the PSII light-harvesting capacity, either accumulating Lhcb4.3 or favouring the xanthophyll cycle; (ii) in HL, plants reduce the pool of light-harvesting complex II and enhance the PSII repair cycle. When growing at ML and HL, plants accumulate ATP synthase, boosting both cyclic and linear electron transport by finely tuning the ΔpH across the membrane and optimizing protein trafficking by adjusting the thylakoid architecture. Our results provide a quantitative snapshot of how plants coordinate light harvesting, electron transport and protein synthesis by adjusting the thylakoid membrane proteome in a light-dependent manner.

Normalizing Tumor Microenvironment Based on Photosynthetic Abiotic/Biotic Nanoparticles.

Tumor hypoxia has attained the status of a core hallmark of cancer that globally affects the entire tumor phenotype. Reversing tumor hypoxia might offer alternative therapeutic opportunities for current anticancer therapies. In this research, a photosynthetic leaf-inspired abiotic/biotic nano-thylakoid (PLANT) system was designed by fusing the thylakoid membrane with synthetic nanoparticles for efficient O2 generation in vivo. Under 660 nm laser irradiation, the PLANT system exhibited intracellular O2 generation and the anaerobic respiration of the multicellular tumor spheroid was suppressed by PLANT as well. In vivo, it was found that PLANT could not only normalize the entire metabolic network but also adjust the abnormal structure and function of the tumor vasculature. It was demonstrated that PLANT could significantly enhance the efficacy of phototherapy or antiangiogenesis therapy. This facile approach for normalizing the tumor microenvironment will find great potential in tumor therapy.

Dynamic remobilization of leaf nitrogen components in relation to photosynthetic rate during grain filling in maize.

Remobilization of leaf nitrogen (N) contributes greatly to grain N in maize, but leads to low photosynthetic rate (Pn). Pn is determined by various N components involving in light harvest and CO2 reduction. However, it is less clear which N component is the major contributor for the reduction of photosynthesis in modern stay-green maize hybrids. In this study, we analyzed the relationship between remobilization of different N components and Pn during grain filling stage under low N (no N application) and high N (180 kg N ha-1) in a field experiment. The remobilization efficiency of photosynthetic enzymes (PEPc, PPDK and Rubisco) in the leaf was much higher than that of thylakoid N and other N components. Low N supply increased the remobilization efficiency of all the leaf N components. During grain filling stage, the amount of all the N components decreased together with Pn. The ratio of Pn to the N in the PEPc, PPDK and Rubisco kept increase in the whole grain filling stage, while the ratio of Pn to chlorophyll and thylakoid-N decreased. Correlation analysis indicated that Pn was more related to the content of photosynthetic enzymes than to chlorophyll and thylakoid N. It is concluded that photosynthetic enzymes serve as an N storage reservoir at early grain filling stage and their degradation is critical in the reduction of Pn during later grain filling stage. Future breeding targets may be focused on enhancing the efficiency of photosynthetic enzymes during late grain filling stage.

An optimized protocol for the preparation of oxygen-evolving thylakoid membranes from Cyclotella meneghiniana provides a tool for the investigation of diatom plastidic electron transport.

BACKGROUND: The preparation of functional thylakoid membranes from diatoms with a silica cell wall is still a largely unsolved challenge. Therefore, an optimized protocol for the isolation of oxygen evolving thylakoid membranes of the centric diatom Cyclotella meneghiniana has been developed. The buffer used for the disruption of the cells was supplemented with polyethylene glycol based on its stabilizing effect on plastidic membranes. Disruption of the silica cell walls was performed in a French Pressure cell and subsequent linear sorbitol density gradient centrifugation was used to isolate the thylakoid membrane fraction. RESULTS: Spectroscopic characterization of the thylakoids by absorption and 77 K fluorescence spectroscopy showed that the photosynthetic pigment protein complexes in the isolated thylakoid membranes were intact. This was supported by oxygen evolution measurements which demonstrated high electron transport rates in the presence of the artificial electron acceptor DCQB. High photosynthetic activity of photosystem II was corroborated by the results of fast fluorescence induction measurements. In addition to PSII and linear electron transport, indications for a chlororespiratory electron transport were observed in the isolated thylakoid membranes. Photosynthetic electron transport also resulted in the establishment of a proton gradient as evidenced by the quenching of 9-amino-acridine fluorescence. Because of their ability to build-up a light-driven proton gradient, de-epoxidation of diadinoxanthin to diatoxanthin and diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence could be observed for the first time in isolated thylakoid membranes of diatoms. However, the ∆pH, diadinoxanthin de-epoxidation and diatoxanthin-dependent NPQ were weak compared to intact diatom cells or isolated thylakoids of higher plants. CONCLUSIONS: The present protocol resulted in thylakoids with a high electron transport capacity. These thylakoids can thus be used for experiments addressing various aspects of the photosynthetic electron transport by, e.g., employing artificial electron donors and acceptors which do not penetrate the diatom cell wall. In addition, the present isolation protocol yields diatom thylakoids with the potential for xanthophyll cycle and non-photochemical quenching measurements. However, the preparation has to be further refined before these important topics can be addressed systematically.

Photosystem II-cyclic electron flow powers exceptional photoprotection and record growth in the microalga Chlorella ohadii.

The desert microalga Chlorella ohadii was reported to grow at extreme light intensities with minimal photoinhibition, tolerate frequent de/re-hydrations, yet minimally employs antenna-based non-photochemical quenching for photoprotection. Here we investigate the molecular mechanisms by measuring Photosystem II charge separation yield (chlorophyll variable fluorescence, Fv/Fm) and flash-induced O2 yield to measure the contributions from both linear (PSII-LEF) and cyclic (PSII-CEF) electron flow within PSII. Cells grow increasingly faster at higher light intensities (µE/m2/s) from low (20) to high (200) to extreme (2000) by escalating photoprotection via shifting from PSII-LEF to PSII-CEF. This shifts PSII charge separation from plastoquinone reduction (PSII-LEF) to plastoquinol oxidation (PSII-CEF), here postulated to enable proton gradient and ATP generation that powers photoprotection. Low light-grown cells have unusually small antennae (332 Chl/PSII), use mainly PSII-LEF (95%) and convert 40% of PSII charge separations into O2 (a high O2 quantum yield of 0.06mol/mol PSII/flash). High light-grown cells have smaller antenna and lower PSII-LEF (63%). Extreme light-grown cells have only 42 Chl/PSII (no LHCII antenna), minimal PSII-LEF (10%), and grow faster than any known phototroph (doubling time 1.3h). Adding a synthetic quinone in excess to supplement the PQ pool fully uncouples PSII-CEF from its natural regulation and produces maximum PSII-LEF. Upon dark adaptation PSII-LEF rapidly reverts to PSII-CEF, a transient protection mechanism to conserve water and minimize the cost of antenna biosynthesis. The capacity of the electron acceptor pool (plastoquinone pool), and the characteristic times for exchange of (PQH2)B with PQpool and reoxidation of (PQH2)pool were determined.

Dietary thylakoids reduce visceral fat mass and increase expression of genes involved in intestinal fatty acid oxidation in high-fat fed rats.

Thylakoids reduce body weight gain and body fat accumulation in rodents. This study investigated whether an enhanced oxidation of dietary fat-derived fatty acids in the intestine contributes to the thylakoid effects. Male Sprague-Dawley rats were fed a high-fat diet with (n = 8) or without thylakoids (n = 8) for 2 wk. Body weight, food intake, and body fat were measured, and intestinal mucosa was collected and analyzed. Quantitative real-time PCR was used to measure gene expression levels of key enzymes involved in fatty acid transport, fatty acid oxidation, and ketogenesis. Another set of thylakoid-treated (n = 10) and control rats (n = 10) went through indirect calorimetry. In the first experiment, thylakoid-treated rats (n = 8) accumulated 25% less visceral fat than controls. Furthermore, fatty acid translocase (Fat/Cd36), carnitine palmitoyltransferase 1a (Cpt1a), and mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (Hmgcs2) genes were upregulated in the jejunum of the thylakoid-treated group. In the second experiment, thylakoid-treated rats (n = 10) gained 17.5% less weight compared with controls and their respiratory quotient was lower, 0.86 compared with 0.91. Thylakoid-intake resulted in decreased food intake and did not cause steatorrhea. These results suggest that thylakoids stimulated intestinal fatty acid oxidation and ketogenesis, resulting in an increased ability of the intestine to handle dietary fat. The increased fatty acid oxidation and the resulting reduction in food intake may contribute to the reduced fat accumulation in thylakoid-treated animals.

The Evolutionarily Conserved Protein PHOTOSYNTHESIS AFFECTED MUTANT71 Is Required for Efficient Manganese Uptake at the Thylakoid Membrane in Arabidopsis.

In plants, algae, and cyanobacteria, photosystem II (PSII) catalyzes the light-driven oxidation of water. The oxygen-evolving complex of PSII is a Mn4CaO5 cluster embedded in a well-defined protein environment in the thylakoid membrane. However, transport of manganese and calcium into the thylakoid lumen remains poorly understood. Here, we show that Arabidopsis thaliana PHOTOSYNTHESIS AFFECTED MUTANT71 (PAM71) is an integral thylakoid membrane protein involved in Mn(2+) and Ca(2+) homeostasis in chloroplasts. This protein is required for normal operation of the oxygen-evolving complex (as evidenced by oxygen evolution rates) and for manganese incorporation. Manganese binding to PSII was severely reduced in pam71 thylakoids, particularly in PSII supercomplexes. In cation partitioning assays with intact chloroplasts, Mn(2+) and Ca(2+) ions were differently sequestered in pam71, with Ca(2+) enriched in pam71 thylakoids relative to the wild type. The changes in Ca(2+) homeostasis were accompanied by an increased contribution of the transmembrane electrical potential to the proton motive force across the thylakoid membrane. PSII activity in pam71 plants and the corresponding Chlamydomonas reinhardtii mutant cgld1 was restored by supplementation with Mn(2+), but not Ca(2+) Furthermore, PAM71 suppressed the Mn(2+)-sensitive phenotype of the yeast mutant Δpmr1 Therefore, PAM71 presumably functions in Mn(2+) uptake into thylakoids to ensure optimal PSII performance.

Iron- and manganese-assisted cadmium tolerance in Oryza sativa L.: lowering of rhizotoxicity next to functional photosynthesis.

MAIN CONCLUSION: Cadmium toxicity is alleviated by iron and manganese supplements because of reduction in cadmium accumulation and upholding of redox regulation that prevent cadmium-inducible damage to root growth and photosynthesis. Cadmium toxicity in Oryza sativa L. MTU 7029 was investigated in the presence of different concentrations of the micronutrients Fe and Mn. It had been observed that these micronutrients reduce Cd uptake and minimize Cd-inducible rhizotoxicity. The photosynthetic electron transport chain, which is the hub of Fe containing metalloproteins, was severely affected by Cd and resulted in reduced bioproductivity under Cd stress. However, exogenous Fe restored the photosynthetic electron transport. Thus, due to the maintenance of the photosynthetic electron transport, the Cd tolerance was improved during Fe supplement. Both antioxidant enzymes and non-enzymatic antioxidant metabolites were found to play important roles in the alleviation of Cd stress under Fe or Mn supplement. It is concluded that the presence of excess Fe and Mn protects rice plants from Cd stress.

Membrane glycerolipid remodeling triggered by nitrogen and phosphorus starvation in Phaeodactylum tricornutum.

Diatoms constitute a major phylum of phytoplankton biodiversity in ocean water and freshwater ecosystems. They are known to respond to some chemical variations of the environment by the accumulation of triacylglycerol, but the relative changes occurring in membrane glycerolipids have not yet been studied. Our goal was first to define a reference for the glycerolipidome of the marine model diatom Phaeodactylum tricornutum, a necessary prerequisite to characterize and dissect the lipid metabolic routes that are orchestrated and regulated to build up each subcellular membrane compartment. By combining multiple analytical techniques, we determined the glycerolipid profile of P. tricornutum grown with various levels of nitrogen or phosphorus supplies. In different P. tricornutum accessions collected worldwide, a deprivation of either nutrient triggered an accumulation of triacylglycerol, but with different time scales and magnitudes. We investigated in depth the effect of nutrient starvation on the Pt1 strain (Culture Collection of Algae and Protozoa no. 1055/3). Nitrogen deprivation was the more severe stress, triggering thylakoid senescence and growth arrest. By contrast, phosphorus deprivation induced a stepwise adaptive response. The time scale of the glycerolipidome changes and the comparison with large-scale transcriptome studies were consistent with an exhaustion of unknown primary phosphorus-storage molecules (possibly polyphosphate) and a transcriptional control of some genes coding for specific lipid synthesis enzymes. We propose that phospholipids are secondary phosphorus-storage molecules broken down upon phosphorus deprivation, while nonphosphorus lipids are synthesized consistently with a phosphatidylglycerol-to-sulfolipid and a phosphatidycholine-to-betaine lipid replacement followed by a late accumulation of triacylglycerol.

Physiological and proteomic analysis in chloroplasts of Solanum lycopersicum L. under silicon efficiency and salinity stress.

Tomato plants often grow in saline environments in Mediterranean countries where salt accumulation in the soil is a major abiotic stress that limits its productivity. However, silicon (Si) supplementation has been reported to improve tolerance against several forms of abiotic stress. The primary aim of our study was to investigate, using comparative physiological and proteomic approaches, salinity stress in chloroplasts of tomato under silicon supplementation. Tomato seedlings (Solanum lycopersicum L.) were grown in nutrient media in the presence or absence of NaCl and supplemented with silicon for 5 days. Salinity stress caused oxidative damage, followed by a decrease in silicon concentrations in the leaves of the tomato plants. However, supplementation with silicon had an overall protective effect against this stress. The major physiological parameters measured in our studies including total chlorophyll and carotenoid content were largely decreased under salinity stress, but were recovered in the presence of silicon. Insufficient levels of net-photosynthesis, transpiration and stomatal conductance were also largely improved by silicon supplementation. Proteomics analysis of chloroplasts analyzed by 2D-BN-PAGE (second-dimensional blue native polyacrylamide-gel electrophoresis) revealed a high sensitivity of multiprotein complex proteins (MCPs) such as photosystems I (PSI) and II (PSII) to the presence of saline. A significant reduction in cytochrome b6/f and the ATP-synthase complex was also alleviated by silicon during salinity stress, while the complex forms of light harvesting complex trimers and monomers (LHCs) were rapidly up-regulated. Our results suggest that silicon plays an important role in moderating damage to chloroplasts and their metabolism in saline environments. We therefore hypothesize that tomato plants have a greater capacity for tolerating saline stress through the improvement of photosynthetic metabolism and chloroplast proteome expression after silicon supplementation.

Adaptive changes in photosynthetic performance and secondary metabolites during white dead nettle micropropagation.

The white dead nettle, Lamium album L., is an herb that has been successfully cultivated under in vitro conditions. The L. album micropropagation system offers a combination of factors (light intensity, temperature, carbon dioxide (CO2) level, humidity) that are limiting for plant growth and bioactive capacity. To get a better understanding of the mechanism of plant acclimation towards environmental changes, we performed a comparative investigation on primary and secondary metabolism in fully expanded L. album leaves during the consecutive growth in in situ, in vitro, and ex vitro conditions. Although the genetic identity was not affected, structural and physiological deviations were observed, and the level of bioactive compounds was modified. During in vitro cultivation, the L. album leaves became thinner with unaffected overall leaf organization, but with a reduced number of palisade mesophyll layers. Structural deviation of the thylakoid membrane system was detected. In addition, the photosystem 2 (PS2) electron transport was retarded, and the plants were more vulnerable to light damage as indicated by the decreased photoprotection ability estimated by fluorescence parameters. The related CO2 assimilation and transpiration rates were subsequently reduced, as were the content of essential oils and phenolics. Transfer of the plants ex vitro did not increase the number of palisade numbers, but the chloroplast structure and PS2 functionality were recovered. Strikingly, the rates of CO2 assimilation and transpiration were increased compared to in situ control plants. While the phenolics content reached normal levels during ex vitro growth, the essential oils remained low. Overall, our study broadens the understanding about the nature of plant responses towards environmental conditions.

Dual role for phospholipid:diacylglycerol acyltransferase: enhancing fatty acid synthesis and diverting fatty acids from membrane lipids to triacylglycerol in Arabidopsis leaves.

There is growing interest in engineering green biomass to expand the production of plant oils as feed and biofuels. Here, we show that phospholipid:diacylglycerol acyltransferase1 (PDAT1) is a critical enzyme involved in triacylglycerol (TAG) synthesis in leaves. Overexpression of PDAT1 increases leaf TAG accumulation, leading to oil droplet overexpansion through fusion. Ectopic expression of oleosin promotes the clustering of small oil droplets. Coexpression of PDAT1 with oleosin boosts leaf TAG content by up to 6.4% of the dry weight without affecting membrane lipid composition and plant growth. PDAT1 overexpression stimulates fatty acid synthesis (FAS) and increases fatty acid flux toward the prokaryotic glycerolipid pathway. In the trigalactosyldiacylglycerol1-1 mutant, which is defective in eukaryotic thylakoid lipid synthesis, the combined overexpression of PDAT1 with oleosin increases leaf TAG content to 8.6% of the dry weight and total leaf lipid by fourfold. In the plastidic glycerol-3-phosphate acyltransferase1 mutant, which is defective in the prokaryotic glycerolipid pathway, PDAT1 overexpression enhances TAG content at the expense of thylakoid membrane lipids, leading to defects in chloroplast division and thylakoid biogenesis. Collectively, these results reveal a dual role for PDAT1 in enhancing fatty acid and TAG synthesis in leaves and suggest that increasing FAS is the key to engineering high levels of TAG accumulation in green biomass.

Assessment of the LuminoTox leachate phase assay as a complement to the LuminoTox solid phase assay: effect of fine particles in natural sediments.

The LuminoTox solid phase assay (Lum-SPA), developed to assess the potential ecotoxicity of natural polluted sediments, employs stabilized thylakoids isolated from spinach plant extracts. When thylakoids are exposed to polluted samples, the action of pollutants can interfere with transmission of chlorophyll fluorescence linked to Photosystems I and II, causing a decrease in fluorescence emission. To differentiate between bulk and leachate effects, we developed a complementary assay of the Lum-SPA named the LuminoTox leachate phase assay (Lum-LPA). Twelve natural sediments were selected on the basis of their potential ecotoxicity and different quantities of fines. Results showed that in the Lum-LPA, the IC50s were always lower than those observed in the Lum-SPA. Significant inverse correlations were found between the IC50s obtained with the Lum-SPA and the percentage of fines (silt+clay fraction). In order to identify the cause of the higher ecotoxicity found in the Lum-LPA, we tested the supernatant of the liquid phase recovered after centrifugation (3000 g), and it appeared far less toxic than the Lum-LPA filtrates. To confirm the hypothesis that sensitivity in the Lum-LPA could be due to the presence of very fine particles, Photosynthetic Enzyme Complexes (PECs) were exposed to two kinds of clay materials with and without copper (0.6 mg L(-1)). Similar results were obtained in the Lum-LPA for both cases, revealing the sensitivity of this test to very fine particles.

Responses of photosynthetic properties and chloroplast ultrastructure of Bryum argenteum from a desert biological soil crust to elevated ultraviolet-B radiation.

Our understanding of plant responses to enhanced ultraviolet-B (UV-B) radiation has improved over recent decades. However, research on cryptogams is scarce and it remains controversial whether UV-B radiation causes changes in physiology related to photosynthesis. To investigate the effects of supplementary UV-B radiation on photosynthesis and chloroplast ultrastructure in Bryum argenteum Hedw., specimens were cultured for 10 days under four UV-B treatments (2.75, 3.08, 3.25 and 3.41 W m(-2) ), simulating depletion of 0% (control), 6%, 9% and 12% of stratospheric ozone at the latitude of Shapotou, a temperate desert area of northwest China. Analyses showed malondialdehyde content significantly increased, whereas chlorophyll (Chl) fluorescence parameters and Chl contents decreased with increased UV-B intensity. These results corresponded with changes in thylakoid protein complexes and chloroplast ultrastructure. Overall, enhanced UV-B radiation leads to significant decreases in photosynthetic function and serious destruction of the chloroplast ultrastructure of B. argenteum. The degree of negative influences increased with the intensity of UV-B radiation. These results may not only provide a potential mechanism for supplemental UV-B effects on photosynthesis of moss crust, but also establish a theoretical basis for further studies of adaptation and response mechanisms of desert ecosystems under future ozone depletion.

[Study on hemiparasitic mechanism of Thesium chinense].

OBJECTIVE: To study the hemiparasitic mechanism of Thesium chinense. METHOD: The anatomical structure of T. chinense was studied by using paraffin slice and electron microscope slice. Chlorophyll content was measured by UV spectrometry. Foliar photosynthesis (P(n)) and gas exchange were measured by using a LI-6400 photosynthesis system. RESULT: Chloroplast possesses intact granal thylakoid system, lamella was strong. Vascular tissue of T. chinense was strong. Vessel aperture and its transport power were strong both in root and stem. There were many global haustoriums on lateral roots. Vascular tissues were strong inside haustorium, haustorial stylet penetrated epidermis and cortex of host root, and reached pith place, haustorial vessel was integrated with host root vessel. The maximum of P(n) of T. chinense reached 7.06 micromol x m(-2) x s(-1), its water use efficiency was lower, about 0.735 mmol x mol(-1), its transpiration varied notable in daytime and was relatively invariant at nighttime, and the value of daytime was greatly exceed that of nighttime. CONCLUSION: T. chinense despoils water and nutrition from its host by haustorium. T. chinense can mostly be independent as for C supply by photosynthesis.