Lipids of bryophytes

Decoupling Distribution of n-Alkanes in Aeolian Sand and Vegetation of the Northern Ulan Buh Desert, China: Insight into Organic Matter Preservation in Arid Regions

Fallen leaves and their decomposition directly deposit leaf wax n-alkanes into sediments, which can be used to identify local flora. These n-alkanes are important for studying past vegetation and climate, but their distribution in sediments must be known. Aeolian sand n-alkanes are particularly important for understanding paleoclimates in arid regions, despite the challenges of extraction due to their extremely low abundance. To investigate the preservation of plant leaf wax n-alkanes in deserts, we analyzed n-alkanes in aeolian sands from the Northern Ulan Buh Desert (UBD), China, and compared them to the surrounding vegetation. We calculated the total n-alkane concentration (ΣALK), average chain length (ACL21-35), and carbon preference index (CPI21-35). In the Northern UBD, aeolian sand n-alkanes have lower ΣALK, indicating microbial degradation. The eastern aeolian sand has lower CPI21-35 and ACL21-35 than the adjacent vegetation, whereas the western sand values are consistent with the plants, likely due to the transport of plant-derived materials by wind and water from the nearby mountains. Our study shows that sedimentary n-alkane signatures are not only determined by local vegetation but also influenced by environmental factors like temperature and precipitation. Additionally, local deposition processes play a significant role in determining the properties of these n-alkanes.

Natural Peroxides from Plants: Historical Discovery, Biosynthesis, and Biological Activities

Naturally occurring peroxides received great interest and attention from scientific research groups worldwide due to their structural diversity, versatile biological activities, and pharmaceutical properties. In the present review, we describe the historical discovery of natural peroxides from plants systematically and update the researchers with recently explored ones justifying their structural caterogrization and biological/pharmaceutical properties intensively. Till the end of 2023, 192 peroxy natural products from plants were documented herein for the first time implying most categories of natural scaffolds (e. g. terpenes, polyketides, phenolics and alkaloids). Numerically, the reported plants' peroxides have been classified into seventy-four hydro-peroxides, hundred seven endo-peroxides and eleven acyl-peroxides. Endo-peroxides (cyclic alkyl peroxides) are an important group due to their high variety of structural frameworks, and we have further divided them into "four-, five-, six and seven"-membered rings. Biosynthetically, a shedding light on the intricate mechanisms behind the formation of plant-derived peroxides are addressed as well.

Chemotaxonomic and evolutionary perspectives of Bryophyta based on multivariate analysis of fatty acid fingerprints of Eastern Himalayan mosses

Bryophyta comprises one of the earliest lineages of land plants that had implemented remarkable innovations to their lipid metabolic systems for successful adaptation to terrestrial habitat. This study presents a comprehensive investigation of fatty acid profiles of mosses from Eastern Himalayas with an aim to trace their chemotaxonomic and evolutionary implications. Fatty acid compositions of 40 random mosses belonging to major families of Bryophyta were explored by gas chromatographic analysis. A diverse array of saturated, monounsaturated and polyunsaturated fatty acids including rare acetylenic fatty acids were detected. Hexadecanoic acid (C16:0), 9,12 (Z,Z)-octadecadienoic acid (C18:2n6) and 9,12,15 (Z,Z,Z)-octadecatrienoic acid (C18:3n3) were the predominant fatty acids in all the mosses. However, quantitative variation of C20 polyunsaturated fatty acids (PUFAs), specifically 5,8,11,14 (Z,Z,Z,Z)-eicosatetraenoic acid (C20:4n6), among the investigated mosses was the most prominent outcome. The diplolepidous members of Bryidae, especially the mosses of Hypnales, Bryales and Bartramiales contained higher amount of C20 PUFAs compared with the haplolepidous orders. Principal component analyses based on individual fatty acids and other related parameters validated C20:4n6 content and the ratio of C20:4n6/C18:2n6 as the apparent chemotaxonomic discriminants. The prevalent notion of considering 9,12,15-octadecatrien-6-ynoic acid (C18:4a) as the chemomarker of Dicranaceae has also been challenged, since the compound was detected not only in different families of Dicranales, but also in a Pottiales member, Leptodontium viticulosoides. Therefore, an ensemble of fatty acids instead of a single one can be considered as the chemical signature for taxonomic interpretation which may also be vital from an evolutionary standpoint.

Valuable Fatty Acids in Bryophytes-Production, Biosynthesis, Analysis and Applications

Bryophytes (mosses, liverworts and hornworts) often produce high amounts of very long-chain polyunsaturated fatty acids (vl-PUFAs) including arachidonic acid (AA, 20:4 Δ5,8,11,14) and eicosapentaenoic acid (EPA, 20:5 Δ5,8,11,14,17). The presence of vl-PUFAs is common for marine organisms such as algae, but rarely found in higher plants. This could indicate that bryophytes did not lose their marine origin completely when they landed into the non-aqueous environment. Vl-PUFA, especially the omega-3 fatty acid EPA, is essential in human diet for its benefits on healthy brain development and inflammation modulation. Recent studies are committed to finding new sources of vl-PUFAs instead of fish and algae oil. In this review, we summarize the fatty acid compositions and contents in the previous studies, as well as the approaches for qualification and quantification. We also conclude different approaches to enhance AA and EPA productions including biotic and abiotic stresses.

Membrane Lipids, Waxes and Oxylipins in the Moss Model Organism Physcomitrella patens

The moss Physcomitrella patens receives increased scientific interest since its genome was sequenced a decade ago. As a bryophyte, it represents the first group of plants that evolved in a terrestrial habitat still without a vascular system that developed later in tracheophytes. It is easily transformable via homologous recombination, which enables the formation of targeted loss-of-function mutants. Even though genetics, development and life cycle in Physcomitrella are well studied nowadays, research on lipids in Physcomitrella is still underdeveloped. This review aims on presenting an overview on the state of the art of lipid research with a focus on membrane lipids, surface lipids and oxylipins. We discuss in this review that Physcomitrella possesses very interesting features regarding its membrane lipids. Here, the presence of very-long-chain polyunsaturated fatty acids (VLC-PUFA) still shows a closer similarity to marine microalgae than to vascular plants. Unlike algae, Physcomitrella has a cuticle comparable to vascular plants composed of cutin and waxes. The presence of VLC-PUFA in Physcomitrella also leads to a greater variability of signaling lipids even though the phytohormone jasmonic acid is not present in this organism, which is different to vascular plants. In summary, the research on lipids in Physcomitrella is still in its infancy, especially considering membrane lipids. We hope that this review will help to promote the further advancement of lipid research in this important model organism in the future, so we can better understand how lipids are involved in the evolution of land plants.

Antiproliferative and Antimicrobial Activities of Selected Bryophytes

One-hundred and sixty-eight aqueous and organic extracts of 42 selected bryophyte species were screened in vitro for antiproliferative activity on a panel of human gynecological cancer cell lines containing HeLa (cervix epithelial adenocarcinoma), A2780 (ovarian carcinoma), and T47D (invasive ductal breast carcinoma) cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and for antibacterial activity on 11 strains using the disc-diffusion method. A total of 99 extracts derived from 41 species exerted ≥25% inhibition of proliferation of at least one of the cancer cell lines at 10 μg/mL. In the cases of Brachythecium rutabulum, Encalypta streptocarpa, Climacium dendroides, Neckera besseri, Pleurozium schreberi, and Pseudoleskeella nervosa, more than one extract was active in the antiproliferative assay, whereas the highest activity was observed in the case of Paraleucobryum longifolium. From the tested families, Brachytheciaceae and Amblystegiaceae provided the highest number of antiproliferative extracts. Only 19 samples of 15 taxa showed moderate antibacterial activity, including the most active Plagiomnium cuspidatum, being active on 8 tested strains. Methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus were the most susceptible to the assayed species. This is the first report on the bioactivities of these 14 species.

A review on algae and plants as potential source of arachidonic acid

Some of the essential polyunsaturated fatty acids (PUFAs) as ARA (arachidonic acid, n-6), EPA (eicosapentaenoic acid, n-3) and DHA (Docosahexaenoic acid, n-3) cannot be synthesized by mammals and it must be provided as food supplement. ARA and DHA are the major PUFAs that constitute the brain membrane phospholipid. n-3 PUFAs are contained in fish oil and animal sources, while the n-6 PUFAs are mostly provided by vegetable oils. Inappropriate fatty acids consumption from the n-6 and n-3 families is the major cause of chronic diseases as cancer, cardiovascular diseases and diabetes. The n-6: n-3 ratio (lower than 10) recommended by the WHO can be achieved by consuming certain edible sources rich in n-3 and n-6 in daily food meal. Many researches have been screened for alternative sources of n-3 and n-6 PUFAs of plant origin, microbes, algae, lower and higher plants, which biosynthesize these valuable PUFAs needed for our body health. Biosynthesis of C18 PUFAs, in entire plant kingdom, takes place through certain pathways using elongases and desaturases to synthesize their needs of ARA (C20-PUFAs). This review is an attempt to highlight the importance and function of PUFAs mainly ARA, its occurrence throughout the plant kingdom (and others), its biosynthetic pathways and the enzymes involved. The methods used to enhance ARA productions through environmental factors and metabolic engineering are also presented. It also deals with advising people that healthy life is affected by their dietary intake of both n-3 and n-6 FAs. The review also addresses the scientist to carry on their work to enrich organisms with ARA.

Profiling Abscisic Acid-Induced Changes in Fatty Acid Composition in Mosses

In plants, change in lipid composition is a common response to various abiotic stresses. Lipid constituents of bryophytes are of particular interest as they differ from that of flowering plants. Unlike higher plants, mosses have high content of very long-chain polyunsaturated fatty acids. Such lipids are considered to be important for survival of nonvascular plants. Here, using abscisic acid (ABA )-induced changes in lipid composition in Physcomitrella patens as an example, a protocol for total lipid extraction and quantification by gas chromatography (GC) coupled with flame ionization detector (FID) is described.

Comparison of headspace-oxylipin-volatilomes of some Eastern Himalayan mosses extracted by sample enrichment probe and analysed by gas chromatography-mass spectrometry

Mosses have an inherent adaptability against different biotic and abiotic stresses. Oxylipins, the volatile metabolites derived from polyunsaturated fatty acids (PUFAs), play a key role in the chemical defence strategy of mosses. In the present study, a comparative survey of these compounds, including an investigation into their precursor fatty acids (FAs), was carried out for the first time on the mosses Brachymenium capitulatum (Mitt.) Paris, Hydrogonium consanguineum (Thwaites & Mitt.) Hilp., Barbula hastata Mitt., and Octoblepharum albidum Hedw. collected from the Eastern Himalayan Biodiversity hotspot. Their headspace volatiles were sampled using a high-efficiency sample enrichment probe (SEP) and were characterized by gas chromatography-mass spectrometric analysis. FAs from neutral lipid (NL) and phospholipid (PL) fractions were also evaluated. Analysis of the oxylipin volatilome revealed the generation of diverse metabolites from C₅ to C₁₈, dominated by alkanes, alkenes, saturated and unsaturated alcohols, aldehydes, ketones and cyclic compounds, with pronounced structural variations. The C₆ and C₈ compounds dominated the total volatilome of all the samples. Analyses of FAs from membrane PL and storage NL highlighted the involvement of C₁₈ and C₂₀ PUFAs in oxylipin generation. The volatilome of each moss is characterized by a 'signature oxylipin mixture'. Quantitative differences in the C₆ and C₈ metabolites indicate their phylogenetic significance.

Long-chain polyunsaturated fatty acids and the preterm infant: a case study in developmentally sensitive nutrient needs in the United States

The vast majority of infant formulas in the United States contain the long-chain polyunsaturated fatty acids (PUFAs) docosahexaenoic acid (22:6n-3) and arachidonic acid (20:4n-6), which were first permitted by the US Food and Drug Administration in 2001. As a scientific case study, preclinical animal studies of these nutrients definitively influenced the design and interpretation of human clinical studies. Early studies were tied to the availability of test substances, and in hindsight suggest re-evaluation of the essential fatty acid concept in light of the totality of available evidence. Research in the 1950s established the essentiality of n-6 PUFAs for skin integrity; however, widespread recognition of the essentiality of n-3 PUFAs came decades later despite compelling evidence of their significance. Barriers to an understanding of the essentiality of n-3 PUFAs were as follows: 1) their role is in neural function, which is measured only with difficulty compared with skin lesions and growth faltering that are apparent for n-6 PUFAs; 2) the experimental use of vegetable oils as PUFA sources that contain the inefficiently used C18 PUFAs rather than the operative C20 and C22 PUFAs; 3) the shift from reliance on high-quality animal studies to define mechanisms that established the required nutrients in the first part of the 20th century to inherently challenging human studies. Advances in nutrition of premature infants require the best practices and opinions available, taking into account the totality of preclinical and clinical evidence.

Chemical Composition Analysis, Antimicrobial Activity and Cytotoxicity Screening of Moss Extracts (Moss Phytochemistry)

Mosses have been neglected as a study subject for a long time. Recent research shows that mosses contain remarkable and unique substances with high biological activity. The aim of this study, accordingly, was to analyze the composition of mosses and to screen their antimicrobial and anticancer activity. The total concentration of polyphenols and carbohydrates, the amount of dry residue and the radical scavenging activity were determined for a preliminary evaluation of the chemical composition of moss extracts. In order to analyze and identify the substances present in mosses, two types of extrahents (chloroform, ethanol) and the GC/MS and LC-TOF-MS methods were used. The antimicrobial activity was tested on four bacteria strains, and the anticancer activity on six cancer cell lines. The obtained results show the presence of a high number of primary (fatty acids and amino acids), but mainly secondary metabolites in moss extracts—including, sterols, terpenoids, polyphenols and others—and a high activity with respect to the studied test organisms.

Structural characterization and chemical classification of some bryophytes found in Latvia

Bryophytes are the second largest taxonomic group in the plant kingdom; yet, studies conducted to better understand their chemical composition are rare. The aim of this study was to characterize the chemical composition of bryophytes common in Northern Europe by using elemental, spectral, and non-destructive analytical methods, such as Fourier transform IR spectrometry (FT-IR), solid-phase (13) C-NMR spectrometry, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), for the purpose of investigating their chemotaxonomic relationships on the basis of chemical-composition data. The results of all these analyses showed that bryophytes consist mainly of carbohydrates. Judging by FT-IR spectra, the OH groups in combination of CO groups were the most abundant groups. The (13) C-NMR spectra provided information on the presence of such compounds as phenolics and lipids. It was found that the amount of phenolic compounds in bryophytes is relatively small. This finding definitely confirmed the absence of lignin in the studied bryophytes. Cluster analysis was used to better understand differences in the chemical composition of bryophyte samples and to evaluate possible usage of these methods in the chemotaxonomy of bryophytes.

Survey of volatile oxylipins and their biosynthetic precursors in bryophytes

Oxylipins are metabolites which are derived from the oxidative fragmentation of polyunsaturated fatty acids. These metabolites play central roles in plant hormonal regulation and defense. Here we survey the production of volatile oxylipins in bryophytes and report the production of a high structural variety of C5, C6, C8 and C9 volatiles of mosses. In liverworts and hornworts oxylipin production was not as pronounced as in the 23 screened mosses. A biosynthetic investigation revealed that both, C18 and C20 fatty acids serve as precursors for the volatile oxylipins that are mainly produced after mechanical wounding of the green tissue of mosses.

Oil bodies and oleosins in Physcomitrella possess characteristics representative of early trends in evolution

Searches of sequenced genomes of diverse organisms revealed that the moss Physcomitrella patens is the most primitive organism possessing oleosin genes. Microscopy examination of Physcomitrella revealed that oil bodies (OBs) were abundant in the photosynthetic vegetative gametophyte and the reproductive spore. Chromatography illustrated the neutral lipids in OBs isolated from the gametophyte to be largely steryl esters and triacylglycerols, and SDS-PAGE showed the major proteins to be oleosins. Reverse transcription-PCR revealed the expression of all three oleosin genes to be tissue specific. This tissue specificity was greatly altered via alternative splicing, a control mechanism of oleosin gene expression unknown in higher plants. During the production of sex organs at the tips of gametophyte branches, the number of OBs in the top gametophyte tissue decreased concomitant with increases in the number of peroxisomes and level of transcripts encoding the glyoxylate cycle enzymes; thus, the OBs are food reserves for gluconeogenesis. In spores during germination, peroxisomes adjacent to OBs, along with transcripts encoding the glyoxylate cycle enzymes, appeared; thus, the spore OBs are food reserves for gluconeogenesis and equivalent to seed OBs. The one-cell-layer gametophyte could be observed easily with confocal microscopy for the subcellular OBs and other structures. Transient expression of various gene constructs transformed into gametophyte cells revealed that all OBs were linked to the endoplasmic reticulum (ER), that oleosins were synthesized in extended regions of the ER, and that two different oleosins were colocated in all OBs.

Biodiversity of the chemical constituents in the epiphytic lichenized ascomycete Ramalina lacera grown on difference substrates Crataegus sinaicus, Pinus halepensis, and Quercus calliprinos

AIM

The identification and evaluation of lichen metabolite production by the epiphytic lichenized ascomycete Ramalina lacera collected from different substrates: Crataegus sinaicus, Pinus halepensis, and Quercus calliprinos.

METHODS

Chemical constituents were characterized by GC MS, HPLC, HR TLC, and other chemical methods.

RESULTS

The most abundant fatty acids were alpha-linolenic acid, oleic acid, and palmitic acid but a considerable variability of the ester composition from one to another was found. A comparison of neutral lipids, glycolipids, polar lipids and fatty acid composition of the tree growing lichen Ramalina lacera was done. Diacylglyceryl N,N,N trimethylhomoserine, diaclyglycerylhydroxymethyl N,N,N trimethyl beta alanine, phosphatidylcholine, and phosphatidylinositol were found as major components among polar lipids. Diffractaic, lecanoric, norstictic, protocetric, and usnic acids were isolated as major aromatic compounds in all samples of R. lacera.

CONCLUSIONS

We evaluated a diversity of fatty acids, lipids, and aromatic compounds produced by the samples of Ramalina lacera growing on different tree substrates, Crataegus sinaicus, Pinus halepensis and Quercus calliprinos.

Physcomitrella patens has lipoxygenases for both eicosanoid and octadecanoid pathways

Mosses have substantial amounts of long chain C20 polyunsaturated fatty acids, such as arachidonic and eicosapentaenoic acid, in addition to the shorter chain C18 alpha-linolenic and linoleic acids, which are typical substrates of lipoxygenases in flowering plants. To identify the fatty acid substrates used by moss lipoxygenases, eight lipoxygenase genes from Physcomitrella patens were heterologously expressed in Escherichia coli, and then analyzed for lipoxygenase activity using linoleic, alpha-linolenic and arachidonic acids as substrates. Among the eight moss lipoxygenases, only seven were found to be enzymatically active in vitro, two of which selectively used arachidonic acid as the substrate, while the other five preferred alpha-linolenic acid. Based on enzyme assays using a Clark-type oxygen electrode, all of the active lipoxygenases had an optimum pH at 7.0, except for one with highest activity at pH 5.0. HPLC analyses indicated that the two arachidonic acid lipoxygenases form (12S)-hydroperoxy eicosatetraenoic acid as the main product, while the other five lipoxygenases produce mainly (13S)-hydroperoxy octadecatrienoic acid from alpha-linolenic acid. These results suggest that mosses may have both C20 and C18 based oxylipin pathways.

Identification and functional characterization of the moss Physcomitrella patens delta5-desaturase gene involved in arachidonic and eicosapentaenoic acid biosynthesis

The moss Physcomitrella patens contains high levels of arachidonic acid and lesser amounts of eicosapentaenoic acid. Here we report the identification and characterization of a delta5-desaturase from P. patens that is associated with the synthesis of these fatty acids. A full-length cDNA for this desaturase was identified by data base searches based on homology to sequences of known delta5-desaturase cDNAs from fungal and algal species. The resulting P. patens cDNA encodes a 480-amino acid polypeptide that contains a predicted N-terminal cytochrome b5-like domain as well as three histidine-rich domains. Expression of the enzyme in Saccharomyces cerevisiae resulted in the production of the delta5-containing fatty acid arachidonic acid in cells that were provided di-homo-gamma-linolenic acid. In addition, the expressed enzyme generated delta5-desaturation products with the C20 substrates omega-6 eicosadienoic and omega-3 eicosatrienoic acids, but no products were detected with the C18 fatty acid linoleic and alpha-linolenic acids or with the C22 fatty acid adrenic and docosapentaenoic acids. When the corresponding P. patens genomic sequence was disrupted by replacement through homologous recombination, a dramatic alteration in the fatty acid composition was observed, i.e. an increase in di-homo-gamma-linolenic and eicosatetraenoic acids accompanied by a concomitant disappearance of the delta5-fatty acid arachidonic and eicosapentaenoic acids. In addition, overexpression of the P. patens cDNA in protoplasts isolated from a disrupted line resulted in the restoration of arachidonic acid synthesis.

Isolation and functional characterization of fatty acid delta5-elongase gene from the liverwort Marchantia polymorpha L

Bryophyte Marchantia polymorpha L. produces C22 very-long-chain polyunsaturated fatty acid (VLCPUFA). Thus far, no enzyme that mediates elongation of C20 VLCPUFAs has been identified in land plants. Here, we report the isolation and characterization of the gene MpELO2, which encodes an ELO-like fatty acid elongase in M. polymorpha. Heterologous expression in yeast demonstrated that MpELO2 encodes delta5-elongase, which mediates elongation of arachidonic (20:4) and eicosapentaenoic acids (20:5). Phylogenetic and gene structural analysis indicated that the MpELO2 gene is closely related to bryophyte Delta6-elongase genes for C18 fatty acid elongation and diverged from them by local gene duplication.

A multifunctional lipoxygenase with fatty acid hydroperoxide cleaving activity from the moss Physcomitrella patens

A complex mixture of fatty acid-derived aldehydes, ketones, and alcohols is released upon wounding of the moss Physcomitrella patens. To investigate the formation of these oxylipins at the molecular level we isolated a lipoxygenase from P. patens, which was identified in an EST library by sequence homology to lipoxygenases from plants. Sequence analysis of the cDNA showed that it exhibits a domain structure similar to that of type2 lipoxygenases from plants, harboring an N-terminal import signal for chloroplasts. The recombinant protein was identified as arachidonate 12-lipoxygenase and linoleate 13-lipoxygenase with a preference for arachidonic acid and eicosapentaenoic acid. In contrast to any other lipoxygenase cloned so far, this enzyme exhibited in addition an unusual high hydroperoxidase and also a fatty acid chain-cleaving lyase activity. Because of these unique features the pronounced formation of (2Z)-octen-1-ol, 1-octen-3-ol, the dienal (5Z,8Z,10E)-12-oxo-dodecatrienoic acid and 12-keto eicosatetraenoic acid was observed when arachidonic acid was administered as substrate. 12-Hydroperoxy eicosatetraenoic acid was found to be only a minor product. Moreover, the P. patens LOX has a relaxed substrate tolerance accepting C(18)-C(22) fatty acids giving rise to even more LOX-derived products. In contrast to other lipoxygenases a highly diverse product spectrum is formed by a single enzyme accounting for most of the observed oxylipins produced by the moss. This single enzyme might, in a fast and effective way, be involved in the formation of signal and/or defense molecules thus contributing to the broad resistance of mosses against pathogens.

Arsenolipids

Natural arsenolipids are analogues of neutral lipids, like monoglycerides, glycolipids, phospho- and also phosphonolipids. They have been found in microorganisms, fungi, plants, lichens, in marine mollusks, sponges, other invertebrates, and in fish tissues. This review presented structures of natural arsenolipids (and derivatives), their distribution, biogenesis in algae and invertebrates, synthesis, and also biological activity. Arsenolipids are thought to be end products of arsenate detoxification processes, involving reduction and oxidative methylation and adenosylation. The proposed biogenesis of arsenolipids is based on the natural occurrence of arsenic metabolites, and all the intermediates in the proposed pathway have been identified as natural products of algal origin. Different arseno species are shown to be inhibitors of glycerol kinase, bovine carbonic anhydrase, and also is an effective therapy for acute promyelocytic leukemia, and there has been promising activity noted in other hematologic and solid tumors. Arsonoliposomes demonstrated high anti-trypanosomal activity against Trypanosoma brucei and inhibit growth of some types of cancer cells (HL-60,C6 and GH3).

Abscisic acid modifies the changes in lipids brought about by water stress in the moss Atrichum androgynum

•  Mosses are particularly able to withstand drought stress. Moreover, abscisic acid (ABA), which is intimately involved during stress in higher plants, has also been implicated in bryophytes. Because membrane damage is a common feature of drought stress, we have studied changes in lipid composition during desiccation and rehydration of the moss Atrichum androgynum and the effect of exogenous ABA on these processes. •  In order to correlate any membrane changes with drought stress, we analysed different lipid classes by thin-layer chromatography, fatty acid composition by gas-liquid chromatography and lipid peroxidation. •  Water stress caused changes in phosphoglyceride composition consistent with an activation of phospholipase D and of phosphatidylinositol metabolism. Recovery of phosphoglyceride composition towards original levels occurred during rehydration and ABA treatment reduced the overall extent of changes. Reduction in thylakoid lipids and chlorophyll coincided with loss of photosynthesis. •  The data show that mosses respond to drought stress similarly to higher plants and that ABA may reduce membrane damage by diminishing the lipid changes.

Cloning and functional characterisation of an enzyme involved in the elongation of Delta6-polyunsaturated fatty acids from the moss Physcomitrella patens

The moss Physcomitrella patens contains high proportions of polyunsaturated very-long-chain fatty acids with up to 20 carbon atoms. Starting from preformed C18 polyunsaturated fatty acids, their biosynthesis involves a sequence of Delta6-desaturation, Delta6-elongation and Delta5-desaturation. In this report we describe for the first time the characterisation of a cDNA (PSE1) of plant origin with homology to the ELO-genes from Saccharomyces cerevisiae, encoding a component of the Delta6-elongase. Functional expression of PSE1 in S. cerevisiae led to the elongation of exogenously supplied Delta6-polyunsaturated fatty acids. By feeding experiments with different trienoic fatty acids of natural and synthetic origin, both substrate specificity and substrate selectivity of the enzyme were investigated. The activity of Pse1, when expressed in yeast, was not sensitive to the antibiotic cerulenin, which is an effective inhibitor of fatty acid synthesis and elongation. Furthermore, the PSE1 gene was disrupted in the moss by homologous recombination. This led to a complete loss of all C20 polyunsaturated fatty acids providing additional evidence for the function of the cDNA as coding for a component of the Delta6-elongase. The elimination of the elongase was not accompanied by a visible alteration in the phenotype, indicating that C20-PUFAs are not essential for viability of the moss under phytotron conditions.

Lipid metabolism in the moss Rhytidiadelphus squarrosus (Hedw.) Warnst. from lead-contaminated and non-contaminated populations

Lipid metabolism and the effect of Pb(2+) and Cu(2+) on this process was studied in the moss Rhytidiadelphus squarrosus collected from both a lead-contaminated and a non-contaminated site. Total radiolabelling of lipids from [1-(14)C]acetate was similar in both populations and Cu or Pb (1 microM, 10 microM) did not cause much alteration in acute exposure experiments. However, there were significant qualitative changes. Of the major labelled neutral lipid classes, samples from the lead-polluted site showed a decrease in labelling of triacylglycerols and an increase in wax esters. Acute lead exposure caused similar effects. Cu caused a decrease in the labelling of wax esters and an increase in diacylglycerols. These data suggest that heavy metals cause a change in carbon flux through the acylation reactions associated with the Kennedy pathway. R. squarrosus obtained from the Pb-contaminated site also showed changes in polar lipid labelling compared to the uncontaminated site. The labelling of phosphatidylcholine was more than halved and replaced by increased labelling of other zwitterionic lipids. The chloroplast glycerolipids were also increasingly labelled. Acute exposure to Pb, however, caused little alteration of labelling patterns within 24 h. R. squarrosus contains high levels of polyunsaturated fatty acids (PUFAs), but moss obtained from the Pb-polluted site had significantly less PUFAs containing three or more double bonds. Such samples, when incubated with [1-(14)C]acetate also showed decreased PUFA labelling. By contrast, acute exposure to Pb produced different results. These data provide a foundation for examining lipid metabolism in bryophytes and the effects of pollution in this important class of organism. The results also emphasize that acute and chronic exposure to heavy metals may produce different effects and that caution must be exercised in extrapolating data from one system to another.

Identification of a novel delta 6-acyl-group desaturase by targeted gene disruption in Physcomitrella patens

The moss Physcomitrella patens contains high levels of arachidonic acid. For its synthesis from linoleic acid by desaturation and elongation, novel delta 5- and delta 6-desaturases are required. To isolate one of these, PCR-based cloning was used, and resulted in the isolation of a full-length cDNA coding for a putatively new desaturase. The deduced amino acid sequence has three domains: a N-terminal segment of about 100 amino acids, with no similarity to any sequence in the data banks, followed by a cytochrome b5-related region and a C-terminal sequence with low similarity (27% identify) to acyl-lipid desaturases. To elucidate the function of this protein, we disrupted its gene by transforming P. patens with the corresponding linear genomic sequence, into which a positive selection marker had been inserted. The molecular analysis of five transformed lines showed that the selection cartridge had been inserted into the corresponding genomic locus of all five lines. The gene disruption resulted in a dramatic alteration of the fatty acid pattern in the knockout plants. The large increase in linoleic acid and the concomitant disappearance of gamma-linolenic and arachidonic acid in all knockout lines suggested that the new cDNA coded for a delta 6-desaturase. This was confirmed by expression of the cDNA in yeast and analysis of the resultant fatty acids by GC-MS. Only the transformed yeast cells were able to introduce a further double bond into the delta 6-position of unsaturated fatty acids. To our knowledge, this is the first report of a successful gene disruption in a multicellular plant resulting in a specific biochemical phenotype.