Thylakoid Arrangement Research Articles

Gansulinema gen. nov. and Komarkovaeasiopsis gen. nov.: Novel Oculatellacean genera (Cyanobacteria) isolated from desert soils and hot spring.

To increase the understanding of simple thin filamentous cyanobacteria in harsh environmental areas, we previously isolated and identified four strains (XN101, XN102, GS121, NX122) from desert soils and hot spring in China. As a result, two new Oculatellacean genera of these four strains, Gansulinema gen. nov. and Komarkovaeasiopsis gen. nov., are described based on a polyphasic approach. The ultrastructure of these strains showed a similar arrangement of peripheral thylakoids with three to four parallel layers, indicating that they belonged to the orders Nodosilineales, Oculatellales, or Leptolyngbyales. In the 16S rRNA gene phylogeny, two sequences of the Gansulinema strains and the two sequences of the Komarkovaeasiopsis strains formed two independent and robust clusters, within the order Oculatellales. The 16S rRNA gene sequences of strains of Komarkovaeasiopsis and Gansulinema showed low identity to each other (≤93.2%) and to other sequences of the Oculatellacean genera (≤94.5% and ≤93.3%, respectively). Furthermore, the 16S-23S internal transcribed spacer rRNA region secondary structures of strains of Komarkovaeasiopsis and Gansulinema were not consistent with all existing descriptions of Oculatellacean taxa. These data suggest that cyanobacterial communities are rich sources of new taxa in under-exploited areas, such as desert soils and hot spring in China.

A study of Klisinema koreana sp. nov. (Desertifilaceae, Cyanobacteria) from the Republic of Korea based on morphological, ecological and molecular analyses

SUMMARYGenus Klisinema (Desertifilaceae, Desertifilales) has only one species, Klisinema persicum, reported worldwide, and this species was found in soils around thermal springs (50°C) of high radiation regions. Simple filament cyanobacteria belonging to the genus Klisinema were collected from Korea, and cultured samples were studied through morphological, ecological and molecular analyses. Both Korean K. persicum and Klisinema koreana were found as epilithic species in freshwater gravel, which have different ecological characteristics from previously reported K. persicum. As a result of morphological analysis, keritomized cytoplasm was observed in K. koreana, and this feature was also newly observed in K. persicum that was discovered in Korea. In addition, K. koreana has a larger width/length ratio compared to K. persicum, and both species have an irregular thylakoid arrangement. Furthermore, as a result of phylogenetic analysis of 16S rRNA, the genus Klisinema formed a monophyletic lineage, and K. koreana strains were clearly separated from K. persicum strains to form a phylogenetic tree. Moreover, when comparing the secondary structure of the 16S–23S internal transcribed spacer region, K. koreana has a structural difference from K. persicum, especially in the structure of the Box‐B helix. Therefore, Klisinema koreana sp. nov. was proposed as a new species belonging to the genus Klisinema of family Desertifilaceae.

Polyphasic characterisation of Microcoleusautumnalis (Gomont, 1892) Strunecky, Komárek & J.R.Johansen, 2013 (Oscillatoriales, Cyanobacteria) using a metabolomic approach as a complementary tool.

As a result of the continuous revision of cyanobacterial taxonomy, Phormidiumautumnale (Agardh) Trevisan ex Gomont, 1892 has been transferred to the genus Microcoleus as Microcoleusautumnalis (Gomont, 1892) Strunecky, Komárek & J.R.Johansen, 2013. This transfer was based on a single strain and literature data. In the present study, we revise the taxonomic position of Microcoleusautumnalis by applying the classical approach of polyphasic taxonomy and additionally using metabolomics. Cyanobacterial strains identified as Phormidiumautumnale and Microcoleusvaginatus (type species of the genus Microcoleus) were used for comparative analyses. In addition, the taxonomic relationship between the species Phormidiumautumnale and Phormidiumuncinatum was determined on the basis of polyphasic characteristics. Monitoring of the morphological variability of Phormidiumautumnale and Microcoleusvaginatus strains showed a difference in the morphology concerning the ends of the trichomes, the shape of the apical cells, as well as the presence/absence of the calyptra and its shape. The performed TEM analysis of the thylakoid arrangement of the studied strains showed parietal arrangement of the thylakoids in the representatives of genus Phormidium and fascicular arrangement in genus Microcoleus. Molecular genetic analyses, based on 16S rDNA, revealed grouping of the investigated P.autumnale strains in a separate clade. This clade is far from the subtree, which is very clearly formed by the representatives of the type species of genus Microcoleus, namely M.vaginatus. The metabolomic analysis involving P.autumnale and M.vaginatus strains identified 39 compounds that could be used as potential biochemical markers to distinguish the two cyanobacterial species. Based on the data obtained, we suggest changing of the current status of Microcoleusautumnalis by restoring its previous appurtenance to the genus Phormidium under the name Phormidiumautumnale (Agardh) Trevisan ex Gomont, 1892 and distinguishing this species from genus Microcoleus.

Effects of Drought Stress On Growth, Photosynthesis And Ultrstructure of Mesophyll Cell of Ulmus Szechuanica Fang Seedlings

Effects of drought stress on growth, photosynthesis and ultrastructure of mesophyll cells of Ulmus szechuanica Fang seedlings were studied. Results showed that under drought stress both leaf water content (LWC) and relative water content (RWC) decreased significantly and height growth (GH) and base diameter growth (GD) declined. Pn, Tr, Gs, Ci and Ls were significantly affected by water deficit. With the continuing of drought, Pn decreased significantly, the change of Gs, Ci, Tr was same. There existed significant effects of drought on stomatal density (SD), stomatal length (SL), stomatal width (SW), individual stomatal area (As) and percentage of individual stomatal area (At) too. Under drought condition, change of structure and chloroplast morphology of the leaves was evident, the number of chloroplasts and orophil granules increased, their proportion in cells amplified. The number of starch granules became smaller, the arrangement of thylakoids among chloroplasts swollen and tend to be disordered. Bangladesh J. Bot. 51(3): 461-468, 2022 (September)

Growth, ROS accumulation site, and photosynthesis inhibition mechanism of Chlorella vulgaris by triclosan.

Although the addition of triclosan (TCS) in consumer products has been strictly restricted, its continuous applications in hospitals and other medical facilities and its numerous residues still pose a potential risk to aquatic organisms and aquatic ecosystems. In this study, we investigated the growth, biochemical alterations, and physiological responses of Chlorella vulgaris exposed to different concentrations of TCS. The potential toxicity mechanisms associated with excessive production of reactive oxygen species (ROS) and disruption of photosynthetic system II (PSII) were also analyzed. The results indicated that the growth, cellular ultrastructure, and physiology of C. vulgaris were severely affected by TCS in a dose-effect dependent manner. TCS inhibited the growth of C. vulgaris, leading to mitochondria enlargement, the disordering of the arrangement of thylakoids, cell wall rupture, organelles loss, and the cytoplasm lysis. TCS induced severe oxidative damage characterized by ROS accumulation, elevated malondialdehyde (MDA), and up-regulation of antioxidant enzyme activities. Moreover, in TCS-induced algal cells, the main sites of ROS accumulation were chloroplasts, mitochondria, and cell membranes, with ROS accumulating most in the mitochondria. In addition, TCS caused damage to the reaction center (RC inactivation), donor side (OEC damage), and accepted side (electron transport from QA to QB) of PSII in C. vulgaris, leading to inhibition of photosynthetic activity. These results could provide novel insights into the mechanisms of TCS-induced ROS accumulation and photosynthetic inhibition in C. vulgaris, which would contribute to a deep understanding of TCS toxicity on algae.

Introducing Petrachlorosaceae fam. nov., Petrachloros gen. nov. and Petrachloros mirabilis sp. nov. (Synechococcales, Cyanobacteria) Isolated from a Portuguese UNESCO monument.

The Synechococcales is a large cyanobacterial order comprising both unicellular and filamentous forms, with parietal thylakoid arrangement. Previously, this order has been the subject of taxonomic revisions with new families being erected. During studies of the phototrophic communities on the limestone walls of the Old Cathedral of Coimbra (UNESCO monument), a coccoid Aphanocapsa-like cyanobacterium was isolated. It was characterized using a polyphasic approach, based on morphology, 16S rRNA phylogenetic and phylogenomic analyses, internal transcribed spacer (ITS) secondary structure, and ecology. The 16S rRNA phylogenetic analyses showed that this strain is placed in a separate and highly supported family-level clade, as part of a large group comprising the families Prochlorococcaceae and Prochlorotrichaceae, with Lagosinema as the closest (although quite distant) taxon. Additionally, the phylogenomic analysis also placed this strain in a separate lineage, situated distantly apart from the family Thermosynechococcaceae, but with strains assigned to Acaryochloris marina MBIC 11017 and Aphanocapsa montana BDHKU210001 as the closest taxa. Based on these data, as well as on the results from the secondary ITS structure, morphology, and ecology, we here propose the establishment of Petrachlorosaceae fam. nov., along with the description of Petrachloros gen. nov. and Petrachloros mirabilis sp. nov. We also address additional considerations regarding some cyanobacterial taxa within the order Synechococcales, which we believe deserve further revisions.

Effect of Cadmium Ions on Some Biophysical Parameters and Ultrastructure of Ankistrodesmus sp. В-11 Cells

Effects of low concentrations of cadmium ions on growth, photosynthesis, and cell ultrastructure of microalga Ankistrodesmus sp. B-11 were investigated. The addition of cadmium to growth medium at concentrations of 0.005–0.02 mg/L led to a significant decrease in the number of Ankistrodesmus sp. B-11 cells relatively to that in the untreated culture. The addition of cadmium at concentrations >0.05 mg/L completely stopped cell growth. Cadmium ions induced ultrastructural changes in the arrangement of thylakoids within the stroma, the detachment of thylakoid membranes with the formation of void interthylakoid spaces, and a significant increase in vacuolization of microalgal cells. Simultaneous measurements of fluorescence induction curves and redox transformations of photosystem I components on a microsecond time scale by means of a M‑PEA-2 fluorometer revealed that cadmium ions inhibit electron transport in photosystem II (PSII). The quantum yield of electron transport in PSII (φEo) and the performance index (PIABS) were found to decrease; the photoreduction of P700 pigment was decelerated, while energy dissipation (DI0/RC) and ΔpH-dependent nonphotochemical quenching (qE) increased significantly under the action of cadmium. The performance index (PIABS) was the most sensitive parameter; it can be used for the detection of early toxic effects of cadmium ions on algae.

Involvement of Lhcb6 and Lhcb5 in Photosynthesis Regulation in Physcomitrella patens Response to Abiotic Stress.

There are a number of highly conserved photosystem II light-harvesting antenna proteins in moss whose functions are unclear. Here, we investigated the involvement of chlorophyll-binding proteins, Lhcb6 and Lhcb5, in light-harvesting and photosynthesis regulation in Physcomitrella patens. Lhcb6 or Lhcb5 knock-out resulted in a disordered thylakoid arrangement, a decrease in the number of grana membranes, and an increase in the number of starch granule. The absence of Lhcb6 or Lhcb5 did not noticeably alter the electron transport rates. However, the non-photochemical quenching activity in the lhcb5 mutant was dramatically reduced when compared to wild-type or lhcb6 plants under abiotic stress. Lhcb5 plants were more sensitive to photo-inhibition, while lhcb6 plants showed little difference compared to the wild-type plants under high-light stress. Moreover, both mutants showed a growth malformation phenotype with reduced chlorophyll content in the gametophyte. These results suggested that Lhcb6 or Lhcb5 played a unique role in plant development, thylakoid organization, and photoprotection of PSII in Physcomitrella, especially when exposed to high light or osmotic environments.

Spatial organization of thylakoid network in higher plants

ABSTRACTAn intricate network of internal plastid membrane is formed in chloroplasts during plant ontogenesis. The network develops directly from a simple membrane system in proplastids or through a paracrystalline tubular prolamellar body (PLB) in etioplasts. A complex spatial structure of PLB interconnected with porous prothylakoids (PTs) is formed when the seedling growth proceeds without light. Upon illumination, PLB transforms through a multistage process into a lamellar system of stacked (grana) and loosely arranged (stroma) thylakoids. The chloroplast thylakoid network, the site of photochemical reactions, is one of the most important as well as most complicated membrane systems in nature. Thus, extensive studies on its possible spatial rearrangements are important for a better understanding of the crucial role of the thylakoid structure in the regulation of photosynthesis. Complementary structural methods are necessary to provide a complex image of spatial thylakoid arrangement. Therefore, in this review, we describe the results obtained by methods using both fixed and in vivo samples. The main goal of this review is to present the state of research on the three-dimensional (3D) structure of internal plastid membrane network, its spatial arrangement during plant ontogenesis and its modifications caused by different factors. Influence of different membrane components on the formation of the thylakoid network shape is also described. Additionally, we summarize recent 3D structural results in the field of thylakoid dynamics induced by environmental factors, especially of light-triggered changes related to rearrangements of the photosynthetic complexes.

Different ecophysiological and structural strategies of toxic and non-toxic Microcystis aeruginosa (cyanobacteria) strains assessed under culture conditions

Microcystis aeruginosa causes severe problems in freshwater environments worldwide due to its capacity to form blooms and produce toxins. Natural populations contain a mixture of strains that vary in morphology, genotype and microcystin production. Beyond its toxic effect in animals, the possible role of microcystin in the metabolism of the producing cell is also a topic of interest. Recent studies pointed to a protective role against cellular oxidative stress. Since natural populations include microcystin producing and non-producing strains, the latter must rely on other ecophysiological traits to thrive. Here, we compared a toxic and a non-toxic strain of M. aeruginosa displaying different morphotypes and growth behaviors, aiming to explore the role of microcystin in an integrated way to the primary metabolism. The toxic strain formed large floating colonies (150–1850 μm) with densely aggregated cells, numerous gas vesicles and lipid inclusions and a typical irregular thylakoid arrangement. The non-toxic strain remained submerged, formed small colonies (< 100 μm) with a dense mucilage covering few sparse cells with rare gas vesicles and various types of thylakoids. It showed a higher abundance of carboxysomes, cyanophycin and polyphosphate granules and also greater amounts of pigments than the toxic strain. The antioxidant potential was higher for the toxic strain and it presented a higher expression of proteins related to photosynthesis, protein folding and cellular redox homeostasis. These traits of the toxic strain were compatible with growth under higher irradiance and microcystin can be a key factor to this adaptation. Growing submerged, the non-toxic strain showed preference for a lower light intensity and invested in intracellular reserves. This study illustrates different adaptive strategies of M. aeruginosa morphotypes that can be valuable in nature, enabling this species to widely exploit freshwater ecosystems.

Evolutionary Patterns of Thylakoid Architecture in Cyanobacteria.

While photosynthetic processes have become increasingly understood in cyanobacterial model strains, differences in the spatial distribution of thylakoid membranes among various lineages have been largely unexplored. Cyanobacterial cells exhibit an intriguing diversity in thylakoid arrangements, ranging from simple parietal to radial, coiled, parallel, and special types. Although metabolic background of their variability remains unknown, it has been suggested that thylakoid patterns are stable in certain phylogenetic clades. For decades, thylakoid arrangements have been used in cyanobacterial classification as one of the crucial characters for definition of taxa. The last comprehensive study addressing their evolutionary history in cyanobacteria was published 15 years ago. Since then both DNA sequence and electron microscopy data have grown rapidly. In the current study, we map ultrastructural data of >200 strains onto the SSU rRNA gene tree, and the resulting phylogeny is compared to a phylogenomic tree. Changes in thylakoid architecture in general follow the phylogeny of housekeeping loci. Parietal arrangement is resolved as the original thylakoid organization, evolving into complex arrangement in the most derived group of heterocytous cyanobacteria. Cyanobacteria occupying intermediate phylogenetic positions (greater filamentous, coccoid, and baeocytous types) exhibit fascicular, radial, and parallel arrangements, partly tracing the reconstructed course of phylogenetic branching. Contrary to previous studies, taxonomic value of thylakoid morphology seems very limited. Only special cases such as thylakoid absence or the parallel arrangement could be used as taxonomically informative apomorphies. The phylogenetic trees provide evidence of both paraphyly and reversion from more derived architectures in the simple parietal thylakoid pattern. Repeated convergent evolution is suggested for the radial and fascicular architectures. Moreover, thylakoid arrangement is constrained by cell size, excluding the occurrence of complex architectures in cyanobacteria smaller than 2 μm in width. It may further be dependent on unknown (eco)physiological factors as suggested by recurrence of the radial type in unrelated but morphologically similar cyanobacteria, and occurrence of special features throughout the phylogeny. No straightforward phylogenetic congruences have been found between proteins involved in photosynthesis and thylakoid formation, and the thylakoid patterns. Remarkably, several postulated thylakoid biogenesis factors are partly or completely missing in cyanobacteria, challenging their proposed essential roles.

In pea stipules a functional photosynthetic electron flow occurs despite a reduced dynamicity of LHCII association with photosystems

The flexible association of the light harvesting complex II (LHCII) to photosystem (PS) I and PSII to balance their excitation is a major short-term acclimation process of the thylakoid membrane, together with the thermal dissipation of excess absorbed energy, reflected in non-photochemical quenching of chlorophyll fluorescence (NPQ). In Pisum sativum, the leaf includes two main photosynthetic parts, the basal stipules and the leaflets. Since the stipules are less efficient in carbon fixation than leaflets, the adjustments of the thylakoid system, which safeguard the photosynthetic membrane against photodamage, were analysed. As compared to leaflets, the stipules experienced a decay in PSII photochemical activity. The supramolecular organization of photosystems in stipules showed a more conspicuous accumulation of large PSII-LHCII supercomplexes in the grana, but also a tendency to retain the PSI-LHCI-LHCII state transition complex and the PSI-LHCI-PSII-LHCII megacomplexes probably located at the interface between appressed and stroma-exposed membranes. As a consequence, stipules had a lower capacity to perform state transitions and the overall thylakoid architecture was less structurally flexible and ordered than in leaflets. Yet, stipules proved to be quite efficient in regulating the redox state of the electron transport chain and more capable of inducing NPQ than leaflets. It is proposed that, in spite of a relatively static thylakoid arrangement, LHCII interaction with both photosystems in megacomplexes can contribute to a regulated electron flow.

Characterisation of Pseudanabaena amphigranulata (Synechococcales) isolated from a man-made pond, Malaysia: a polyphasic approach

A filamentous benthic cyanobacteria strain isolated from a tropical man-made pond in Malaysia was characterised using combined phenotypic and genetic approaches. Morphological and ultrastructural observations were performed together with growth measurements. Cell dimensions, thylakoid arrangement and apical cell shape with aerotopes were consistent with the description of Pseudanabaena amphigranulata (Goor) Anagnostidis. Molecular characterisation of the16S rRNA gene gave 94% pairwise sequence identity with Pseudanabaena sp. PCC 6802,which corresponds to the genus identification threshold value while also suggesting that the strain is distinctly different to the species of Pseudanabaena currently represented in available databases. The strain showed identical 16S-23S ITS configuration with other strains of Pseudanabaena apart from having a larger spacer region. Cultures of the strain were exposed to various temperature and photoperiod treatments and harvested at exponential phase in order to examine phenotypic plasticity. Significant relationships between environmental conditions and morphological characteristics (cell dimensions and shape) were identified for the first time within the genus Pseudanabaena. The maximum cell length (5.7 ± 0.07 μm) was observed at 25 °C under 12:12 light to dark, while the greatest cell width (3.2 ± 0.11 μm) was also observed at 25 °C but under 16:8 light to dark. The strain showed high plasticity in cell dimensions and shape under different temperature and photoperiod treatments, with25 °C under 12:12 light to dark providing the optimal conditions for its growth.

Neolyngbya gen. nov. (Cyanobacteria, Oscillatoriaceae): A new filamentous benthic marine taxon widely distributed along the Brazilian coast

Brazil has an extensive and environmentally diverse coastline, which favors the occurrence of numerous cyanobacterial morpho- and ecotypes. Nevertheless, this coastline is still poorly studied and its diversity is underestimated. Considering the family Oscillatoriaceae, Lyngbya deserves special attention. It includes many clades which are phylogenetically non-related but morphologically similar. Such clades occur in marine and freshwater environments and are traditionally treated as a single genus. In the current study, we sampled both mediolittoral and estuarine zones along the Brazilian coast. Based on a polyphasic characterization, we described a new genus of marine filamentous cyanobacteria: Neolyngbya. It includes six new species sampled in Brazil, which are described in this study (N. maris-brasilis, N. granulosa, N. irregularis, N. nodulosa, N. arenicola and N. tenuis). Additionally, the characterization included a Neolyngbya sp. from Japan in the clade, but only based on molecular data. All species presented irregular arrangement of thylakoids as described for Oscillatoriaceae. The new genus shares morphological characteristics with species in different clades of the Lyngbya complex. The ultrastructural analyses of Neolyngbya, however, showed numerous gas vesicles, especially in the interthylakoid space; such feature is not observed in benthic Lyngbya species. Neolyngbya formed a well-supported clade (16S rRNA phylogeny), however distantly related to L. aestuarii and L. confervoides, both marine species clusters. The Limnoraphis clade is in a sister relationship to the Neolyngbya clade, however the former occurs in freshwater plankton. Secondary structures of 16S–23S rRNA ITS sequences were congruent with the phylogeny. The polyphasic characterization was helpful to clarify the diversity and ecological aspects of benthic filamentous cyanobacteria and the evolutionary history of the group. This favors a better understanding of inter and infrageneric taxa. The number of novel taxa described in this study emphasizes the importance of conducting additional floristic surveys, mainly in underexplored marine environments, to reveal the real cyanobacterial biodiversity in these areas.

Identification and phenotypic plasticity of Pseudanabaena catenata from the Svalbard archipelago

Abstract A filamentous benthic cyanobacteria, strain USMAC16, was isolated from the High Arctic Svalbard archipelago, Norway, and a combination of morphological, ultrastructural and molecular characterisation (16S rRNA gene sequence) used to identify to species level. Cell dimensions, thylakoid arrangement and apical cell shape are consistent with the Pseudanabaena genus description. The molecular characterisation of P. catenata gave 100% similarity with Pseudanabaena catenata SAG 1464-1, originally reported from Germany. Strain USMAC16 was cultured under a range of temperature and photoperiod conditions, in solid and liquid media, and harvested at exponential phase to examine its phenotypic plasticity. Under different culture conditions, we observed considerable variations in cell dimensions. The longest cell (5.91±0.13 μm) was observed at 15°C under 12:12 light:dark, and the widest cell (3.24±0.06 μm) at 4°C under 12:12 light: dark in liquid media. The study provides baseline data documenting the morphological variation of P. catenata in response to changing temperature regimes.

Impairment of ntcA gene revealed its role in regulating iron homeostasis, ROS production and cellular phenotype under iron deficiency in cyanobacterium Anabaena sp. PCC 7120

Iron deficiency ends up into several unavoidable consequences including damaging oxidative stress in cyanobacteria. NtcA is a global nitrogen regulator controls wide range of metabolisms in addition to regulation of nitrogen metabolism. In present communication, NtcA based regulation of iron homeostasis, ROS production and cellular phenotype under iron deficiency in Anabaena 7120 has been investigated. NtcA regulates the concentration dependent iron uptake by controlling the expression of furA gene. NtcA also regulated pigment synthesis and phenotypic alterations in Anabaena 7120. A significant increase in ROS production and corresponding reduction in the activities of antioxidative enzymes (SOD, CAT, APX and GR) in CSE2 mutant strain in contrast to wild type Anabaena 7120 also suggested the possible involvement of NtcA in protection against oxidative stress in iron deficiency. NtcA has no impact on the expression of furB and furC in spite of presence of consensus NtcA binding site (NBS) and -10 boxes in their promoter. NtcA also regulates the thylakoid arrangement as well as related photosynthetic and respiration rates under iron deficiency in Anabaena 7120. Overall results suggested that NtcA regulates iron acquisition and in turn protect Anabaena cells from the damaging effects of oxidative stress induced under iron deficiency.

Limnolyngbya circumcreta gen. & comb. nov. (Synechococcales, Cyanobacteria) with three geographical (provincial) genotypes in China

:Five strains that were morphologically identified as Planktolyngbya circumcreta were isolated from three geographical regions in China. The strains were phylogenetically and taxonomically characterised based on a polyphasic approach that merged morphological and genetic characteristics, as well as ultrastructure. The ultrastructure of these strains showed a similar arrangement of thylakoids, with four to eight parallel layers that were parietally distributed, suggesting that they belonged to the order Synechococcales, family Leptolyngbyaceae. As inferred from 16S rRNA gene sequence analysis, these pure cultures share ≥ 98.5% similarity and were grouped into a unique and robust cluster with high bootstrap values. This unique cluster was separated from a clade composed of two strains of Planktolyngbya limnetica, which belonged to the type species of the genus Planktolyngbya. Thus, we transferred these five P. circumcreta strains to the new genus Limnolyngbya. The species Limnolyngbya circumcreta nov. comb. was designated as the type of the genus.

Chloroplast thylakoid structure in evergreen leaves employing strong thermal energy dissipation

In nature, photosynthetic organisms cope with highly variable light environments – intensities varying over orders of magnitudes as well as rapid fluctuations over seconds-to-minutes – by alternating between (a) highly effective absorption and photochemical conversion of light levels limiting to photosynthesis and (b) powerful photoprotective thermal dissipation of potentially damaging light levels exceeding those that can be utilized in photosynthesis. Adjustments of the photosynthetic apparatus to changes in light environment involve biophysical, biochemical, and structural adjustments. We used electron micrographs to assess overall thylakoid grana structure in evergreen species that exhibit much stronger maximal levels of thermal energy dissipation than the more commonly studied annual species. Our findings indicate an association between partial or complete unstacking of thylakoid grana structure and strong reversible thermal energy dissipation that, in contrast to what has been reported for annual species with much lower maximal levels of energy dissipation, is similar to what is seen under photoinhibitory conditions. For a tropical evergreen with tall grana stacks, a loosening, or vertical unstacking, of grana was seen in sun-grown plants exhibiting pronounced pH-dependent, rapidly reversible thermal energy dissipation as well as for sudden low-to-high-light transfer of shade-grown plants that responded with photoinhibition, characterized by strong dark-sustained, pH-independent thermal energy dissipation and photosystem II (PSII) inactivation. On the other hand, full-sun exposed subalpine confers with rather short grana stacks transitioned from autumn to winter via conversion of most thylakoids from granal to stromal lamellae concomitant with photoinhibitory photosynthetic inactivation and sustained thermal energy dissipation. We propose that these two types of changes (partial or complete unstacking of grana) in thylakoid arrangement are both associated with the strong non-photochemical quenching (NPQ) of chlorophyll fluorescence (a measure of photoprotective thermal energy dissipation) unique to evergreen species rather than with PSII inactivation per se.

Effect of exogenous 24-epibrassinolide on chlorophyll fluorescence, leaf surface morphology and cellular ultrastructure of grape seedlings (Vitis vinifera L.) under water stress

The effects of 24-epibrassinolide (EBR) on chlorophyll fluorescence, leaf surface morphology and cellular ultrastructure of grape seedlings (Vitis vinifera L.) under water stress were investigated. The grape seedlings were subjected to 10 % (w/v) polyethylene glycol (PEG-6000) and treated with 0.05, 0.10 or 0.20 mg L−1 EBR, respectively. EBR application increased chlorophyll contents, the effective photochemical quantum yield of PSII, maximum photochemical efficiency of PSII, maximal fluorescence and non-photochemical quenching coefficient under water stress in each concentration. Compared with water stress control, higher stomatal density and stomatal length were observed in young leaves under EBR treatments, but not in mature leaves. In-depth analysis of the ultrastructure of leaves indicated that water stress induced disappearance of nucleus, chloroplast swelling, fractured mitochondrial cristae and disorder of thylakoid arrangement both in young leaves and mature leaves. However, EBR application counteracted the detrimental effects of water stress on the structure of the photosynthetic apparatus better in young leaves than in mature leaves. Compared to the other treatments, treatment of 0.10 mg L−1 EBR had best ameliorative effect against water stress. These results suggested that exogenous EBR could alleviate water stress-induced inhibition of photosynthesis on grape possibly through increasing chlorophyll content, lessening the stomatal and non-stomatal limitation of photosynthesis performance.

Analysis of obtained chloroplast transformants of tobacco (Nicotiana tabacum L.) plants with marker expression cassette of aadA au gene, changing the color of leaves

Transplastomic tobacco Nicotiana tabacum cv. Petit Havana plants were obtained by ballistic transformation. The modified expression cassette aadA au was used as a marker, which confers the resistance to streptomycin and spectinomycin and causes the golden color of the leaf when planted in the soil after selection on selective medium. Plants were transferred into soil and screened for the golden leaf color. Molecular analysis was performed to confirm the transplastomic nature of the plants. The differences in plastid ultrastructure of mesophyll cells between the leaves of tobacco plants of wild-type (with green leaf fragments) and plastids with altered pigmentation (old leaves of wild-type and yellow pieces of the leaf with transformed chloroplasts) were analyzed by electron microscopy. It was shown that the ultrastructural organization of plastids of transplastomic plants with golden color had distinct differences from the chloroplasts of plants in the control group by the number and arrangement of thylakoids, the number and sizes of starch grains and plastoglobules. Decreased number of thylakoids and starch grain inclusions was marked in the mesophyll cells on a background of their increased number in the stroma and grana. There were also significantly more light areas of the stroma in transplastomic plants, which was typical for nucleoid areas.