Variations in the content of tonoplast lipids under abiotic stress

Melatonin Mitigates Lead-Induced Oxidative Stress and Modifies Phospholipid Profile in Tobacco BY-2 Suspension Cells

Many studies have shown that melatonin (an indoleamine) is an important molecule in plant physiology. It is known that this indoleamine is crucial during plant stress responses, especially by counteracting secondary oxidative stress (efficient direct and indirect antioxidant) and switching on different defense plant strategies. In this report, we present exogenous melatonin's potential to protect lipid profile modification and membrane integrity in Nicotiana tabacum L. line Bright Yellow 2 (BY-2) cell culture exposed to lead. There are some reports of the positive effect of melatonin on animal cell membranes; ours is the first to report changes in the lipid profile in plant cells. The experiments were performed in the following variants: LS: cells cultured on unmodified LS medium-control; (ii) MEL: BY-2 cells cultured on LS medium with melatonin added from the beginning of culture; (iii) Pb: BY-2 cells cultured on LS medium with Pb2+ added on the 4th day of culture; (iv) MEL+Pb: BY-2 cells cultured on LS medium with melatonin added from the start of culture and stressed with Pb2+ added on the 4th day of culture. Lipidomic analysis of BY-2 cells revealed the presence of 40 different phospholipids. Exposing cells to lead led to the overproduction of ROS, altered fatty acid composition and increased PLD activity and subsequently elevated the level of phosphatidic acid at the cost of dropping the phosphatidylcholine. In the presence of lead, double-bond index elevation, mainly by higher quantities of linoleic (C18:2) and linolenic (C18:3) acids in the log phase of growth, was observed. In contrast, cells exposed to heavy metal but primed with melatonin showed more similarities with the control. Surprisingly, the overproduction of ROS caused of lipid peroxidation only in the stationary phase of growth, although considerable changes in lipid profiles were observed in the log phase of growth-just 4 h after lead administration. Our results indicate that the pretreatment of BY-2 with exogenous melatonin protected tobacco cells against membrane dysfunctions caused by oxidative stress (lipid oxidation), but also findings on a molecular level suggest the possible role of this indoleamine in the safeguarding of the membrane lipid composition that limited lead-provoked cell death. The presented research indicates a new mechanism of the defense strategy of plant cells generated by melatonin.

Comparative analysis of metabolic mechanisms in the remediation of Cd-polluted alkaline soil in cotton field by biochar and biofertilizer

To screen environmentally friendly and efficient Cd pollution remediation material, the effects of BC and BF on soil Cd bio-availability and cotton Cd absorption were analyzed under Cd exposure. Besides, the differences in metabolic mechanisms by which biochar (BC) and biofertilizer (BF) affect Cd-contaminated soil and cotton were also analyzed. The results showed that the application of BC and BF increased cotton dry matter accumulation, boll number, and single boll weight, and reduced the Cd content in cotton roots, stems, leaves, and bolls. At harvest, the Cd content in cotton roots in the BC and BF groups reduced by 15.23% and 16.33%, respectively, compared with that in the control. This was attributed to the conversion of carbonate-bound Cd (carbon-Cd) and exchangeable Cd (EX-Cd) by BC and BF into residual Cd (Res-Cd). It should be noted that the soil available Cd (Ava-Cd) content in the BF group was lower than that in the BC group. The metabolomic analysis results showed that for BC vs BF, the relative abundance of differential metabolites Caffeic acid, Xanthurenic acid, and Shikimic acid in soil and cotton roots were up-regulated. Mantel test found that cotton root exudate l-Histinine was correlated with the enrichment of Cd in various organs of cotton. Therefore, the application of BC and BF can alleviate Cd stress by reducing soil Ava-Cd content and cotton's Cd uptake, and BF is superior to BC in reducing Cd content in soil and cotton organs. This study will provide a reference for the development of efficient techniques for the remediation of Cd-polluted alkaline soil, and provide a basis for subsequent metagenomics analysis.

Comparison of the functions of plasma membrane and vacuolar membrane lipids in plant cell protection against hyperosmotic stress

MAIN CONCLUSION

The comparison of the changes of the lipid content in plant cell boundary membranes demonstrates a substantial role of the vacuolar membrane in response to hyperosmotic stress. Comparison of variations in the lipid content of plant cell boundary membranes (vacuolar and plasma membranes) isolated from beet root tissues (Beta vulgaris L.) was conducted after the effect of hyperosmotic stress. Both types of membranes participate in the formation of protective mechanisms, but the role of the vacuolar membrane was considered as more essential. This conclusion was connected with more significant adaptive variations in the content and composition of sterols and fatty acids in the vacuolar membrane (although some of the adaptive variations, especially, in the composition of phospholipids and glycoglycerolipids were similar for both types of membranes). In the plasma membrane under hyperosmotic stress, the increase in the content of sphingolipids was noted that was not observed in the tonoplast.

Detergent-Resistant Membranes in Chloroplasts and Mitochondria of the Halophyte Salicornia perennans under Salt Stress

Halophytes represent important models for studying the key mechanisms of salt tolerance. One approach to the development of new knowledge of salt tolerance is to study the properties of detergent-resistant membranes (DRMs). In this work, the lipid profiles of DRMs of chloroplasts and mitochondria of euhalophyte Salicornia perennans Willd, before and after their exposure to shock concentrations of NaCl, have been investigated. We found that DRMs of chloroplasts are enriched in cerebrosides (CERs) and that sterols (STs) dominate the mass of mitochondrial DRMs. Also, it has been proven that (i) the impact of salinity provokes obvious growth in the content of CERs in DRMs of chloroplasts; (ii) the content of STs in DRMs of chloroplasts does not change under the influence of NaCl; (iii) salinity also causes some elevation in the content of monounsaturated and saturated fatty acids (FAs). Considering the fact that DRMs represent integral parts of both chloroplast and mitochondrial membranes, the authors have come to the conclusion that the cells of euhalophyte S. perennans, under the impact of salinity, presumes the choice (by the cell) of some specific composition of lipids and FAs in the membrane. This may be considered as a specific protection reaction of the plant cell against salinity.

LC-ESI-MS/MS Analysis of Sulfolipids and Galactolipids in Green and Red Lettuce (Lactuca sativa L.) as Influenced by Sulfur Nutrition

Sulfur (S) deprivation leads to abiotic stress in plants. This can have a significant impact on membrane lipids, illustrated by a change in either the lipid class and/or the fatty acid distribution. Three different levels of S (deprivation, adequate, and excess) in the form of potassium sulfate were used to identify individual thylakoid membrane lipids, which might act as markers in S nutrition (especially under stress conditions). The thylakoid membrane consists of the three glycolipid classes: monogalactosyl- (MGDG), digalactosyl- (DGDG), and sulfoquinovosyl diacylglycerols (SQDG). All of them have two fatty acids linked, differing in chain length and degree of saturation. LC-ESI-MS/MS served as a powerful method to identify trends in the change in individual lipids and to understand strategies of the plant responding to stress. Being a good model plant, but also one of the most important fresh-cut vegetables in the world, lettuce (Lactuca sativa L.) has already been shown to respond significantly to different states of sulfur supply. The results showed a transformation of the glycolipids in lettuce plants and trends towards a higher degree of saturation of the lipids and an increased level of oxidized SQDG under S-limiting conditions. Changes in individual MGDG, DGDG, and oxidized SQDG were associated to S-related stress for the first time. Promisingly, oxidized SQDG might even serve as markers for further abiotic stress factors.

Plant transbilayer lipid asymmetry and the role of lipid flippases

Many biological membranes present an asymmetric lipid distribution between the two leaflets that is known as the transbilayer lipid asymmetry. This asymmetry is essential for cell survival and its loss is related to apoptosis. In mammalian and yeast cells, ATP-dependent transport of lipids to the cytosolic side of the biological membranes, carried out by so-called lipid flippases, contributes to the transbilayer lipid asymmetry. Most of these lipid flippases belong to the P4-ATPase protein family, which is also present in plants. In this review, we summarize the relatively scarce literature concerning the presence of transbilayer lipid asymmetry in different plant cell membranes and revise the potential role of lipid flippases of the P4-ATPase family in generation and/or maintenance of this asymmetry.

Long-Chain Acyl-CoA Synthetases Promote Poplar Resistance to Abiotic Stress by Regulating Long-Chain Fatty Acid Biosynthesis

Long-chain acyl-CoA synthetases (LACSs) catalyze fatty acids (FAs) to form fatty acyl-CoA thioesters, which play essential roles in FA and lipid metabolisms and cuticle wax biosynthesis. Although LACSs from Arabidopsis have been intensively studied, the characterization and function of LACSs from poplar are unexplored. Here, 10 poplar PtLACS genes were identified from the poplar genome and distributed to eight chromosomes. A phylogenetic tree indicated that PtLACSs are sorted into six clades. Collinearity analysis and duplication events demonstrated that PtLACSs expand through segmental replication events and experience purifying selective pressure during the evolutionary process. Expression patterns revealed that PtLACSs have divergent expression changes in response to abiotic stress. Interaction proteins and GO analysis could enhance the understanding of putative interactions among protein and gene regulatory networks related to FA and lipid metabolisms. Cluster networks and long-chain FA (LCFA) and very long-chain FA (VLCFA) content analysis revealed the possible regulatory mechanism in response to drought and salt stresses in poplar. The present study provides valuable information for the functional identification of PtLACSs in response to abiotic stress metabolism in poplar.

Modulation of Steroid and Triterpenoid Metabolism in Calendula officinalis Plants and Hairy Root Cultures Exposed to Cadmium Stress

The present study investigated the changes in the content of steroids and triterpenoids in C. officinalis hairy root cultures and plants exposed to cadmium stress. The observed effects included the content and composition of analyzed groups of compounds, particularly the proportions among individual sterols (e.g., stigmasterol-to-sitosterol ratio), their ester and glycoside conjugates. The total sterol content increased in roots (by 30%) and hairy root culture (by 44%), whereas it decreased in shoots (by 15%); moreover, these effects were inversely correlated with Cd-induced growth suppression. Metabolic alterations of sterols and their forms seemed to play a greater role in the response to Cd stress in roots than in shoots. The symptoms of the competition between general metabolites (sterols) and specialized metabolites (triterpenoids) were also observed, i.e., the increase of the sterol biosynthesis parallel to the decrease of the triterpenoid content in C. officinalis plant roots and hairy root culture, and the inverse phenomenon in shoots. The similarity of the metabolic modifications observed in the present study on C. officinalis plant roots and hairy roots confirmed the possibility of application of plant in vitro cultures in initial studies for physiological research on plant response to environmental stresses.

Biosynthesis and the Roles of Plant Sterols in Development and Stress Responses

Plant sterols are important components of the cell membrane and lipid rafts, which play a crucial role in various physiological and biochemical processes during development and stress resistance in plants. In recent years, many studies in higher plants have been reported in the biosynthesis pathway of plant sterols, whereas the knowledge about the regulation and accumulation of sterols is not well understood. In this review, we summarize and discuss the recent findings in the field of plant sterols, including their biosynthesis, regulation, functions, as well as the mechanism involved in abiotic stress responses. These studies provide better knowledge on the synthesis and regulation of sterols, and the review also aimed to provide new insights for the global role of sterols, which is liable to benefit future research on the development and abiotic stress tolerance in plant.

Role of tonoplast microdomains in plant cell protection against osmotic stress

Variations in the content of tonoplast microdomains, isolated with the aid of a non-detergent technique, are induced by osmotic stress and may take part in plant cell adaptive mechanisms. Investigation of tonoplast microdomain lipids isolated with the aid of the non-detergent technique from beetroots (Beta vulgaris L.) subjected to either hyperosmotic or hypoosmotic stress was conducted. Earlier, an important role of tonoplast lipids in the protection of plant cells from stress was demonstrated (Ozolina et al. 2020a). In the present paper, we have put forward a hypothesis that lipids of microdomains of raft nature present in the tonoplast are responsible for this protective function. The variations in the content of lipids of the studied nondetergent-isolated microdomains (NIMs) under hyperosmotic and hypoosmotic stresses were different. Under hyperosmotic stress, in the scrutinized microdomains, some variations in the content of lipids were registered, which were characteristic of the already known protective anti-stress mechanisms. These variations were represented by an increase in sterols and polar lipids capable of stabilizing the bilayer structure of the membranes. The found variations in the content of sterols may be bound up with some intensification of the autophagy process under stress because sterols foster the formation of new membrane contacts necessary for this process. Under hypoosmotic stress, the pattern of redistribution of the lipids in the scrutinized membrane structures was different: the largest part of the lipids appeared to be represented by hydrocarbons, which fulfilled mainly a protective function in plants and could prevent the excess water influx into the vacuole. The results obtained not only demonstrate the possible functions of the vacuolar membrane microdomains but also put forward an assumption on the role of any membrane microdomain in the protection mechanisms of the plant cell.

Lipidomic metabolism associated with acetic acid priming-induced salt tolerance in Carex rigescens

Acetic acid priming may mitigate salt stress to plants by modulating lipid metabolism. Carex rigescens is a stress-tolerant turfgrass species with a widespread distribution in north China. The objective of this study was to figure out whether modification of lipid profiles, including the contents, compositions and saturation levels of leaf lipids, may contribute to acetic acid modulated salt tolerance in C. rigescens. Plants of C. rigescens were primed with or without acetic acid (30 mM) and subsequently exposed to salt stress (300 mM NaCl) for 15 days. Salt stress affected the physiological performance of C. rigescens, while acetic acid-primed plants showed significantly lower malondialdehyde content, proline content, and electrolyte leakage than non-primed plants under salt stress. Acetic acid priming enhanced the contents of phospholipids and glycolipids involved in membrane stabilization and stress signaling (phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulfoquinovosyldiacylglycerol), reduced the content of toxic lipid intermediates (free fatty acids) during subsequent exposure to salt stress. Furthermore, expression levels of genes involved in lipid metabolism such as CK and PLDα changed due to acetic acid priming. These results demonstrated that acetic acid priming could enhance salt tolerance of C. rigescens by regulating lipid metabolism. The lipids could be used as biomarkers to select for salt-tolerant grass germplasm.

Role of Plasmalemma Microdomains (Rafts) in Protection of the Plant Cell Under Osmotic Stress

Lipid-protein microdomains (presumably rafts) of the plasmalemma isolated from the beetroots subjected to hyperosmotic stress and hypoosmotic stress were studied. In these microdomains, the variations in the composition of total lipids, sterols, and fatty acids were observed. These variations differed under hypo- and hyperosmotic types of stress. We presumed that such variations were bound up with different strategies, which are probably related to protecting the cell from osmotic stress. One of the protection tendencies might be related, in our opinion, to credible growth of the content of such lipids as sterols and sterol esters, which are considered as raft-forming. Under osmotic stress, these lipids can contribute to the formation of both new raft structures and new membrane contacts of plasmalemma with intracellular organelles. Another protection tendency may be bound up with the redistribution of membrane phospholipids and phosphoglycerolipids possibly to stabilize the membrane's lamellar structure, which is ensured by credible growth of the content of such lipids as phosphatidylcholines, phosphatidylinositols, and digalactosyldiacylglycerol. The participation of lipid-protein microdomains in the adaptive mechanisms of plant cells may, in our opinion, also be bound up with the redistribution of membrane sterols, which (redistribution) in a number of variants may provoke credible growth in the content of cholesterol or "anti-stress" sterols (campesterol and stigmasterol). So, according to our results, the variations in the content of the plasmalemma lipid-protein microdomains take place under osmotic stress. These variations may influence the functioning of plasmalemma and take part in the adaptive mechanisms of plant cells.

Membrane dynamics during individual and combined abiotic stresses in plants and tools to study the same

The plasma membrane (PM) is possibly the most diverse biological membrane of plant cells; it separates and guards the cell against its external environment. It has an extremely complex structure comprising a mosaic of lipids and proteins. The PM lipids are responsible for maintaining fluidity, permeability and integrity of the membrane and also influence the functioning of membrane proteins. However, the PM is the primary target of environmental stress, which affects its composition, conformation and properties, thereby disturbing the cellular homeostasis. Maintenance of integrity and fluidity of the PM is a prerequisite for ensuring the survival of plants during adverse environmental conditions. The ability of plants to remodel membrane lipid and protein composition plays a crucial role in adaptation towards varying abiotic environmental cues, including high or low temperature, drought, salinity and heavy metals stress. The dynamic changes in lipid composition affect the functioning of membrane transporters and ultimately regulate the physical properties of the membrane. Plant membrane-transport systems play a significant role in stress adaptation by cooperating with the membrane lipidome to maintain the membrane integrity under stressful conditions. The present review provides a holistic view of stress responses and adaptations in plants, especially the changes in the lipidome and proteome of PM under individual or combined abiotic stresses, which cause alterations in the activity of membrane transporters and modifies the fluidity of the PM. The tools to study the varying lipidome and proteome of the PM are also discussed.

Non-detergent Isolation of Membrane Structures from Beet Plasmalemma and Tonoplast Having Lipid Composition Characteristic of Rafts

Vacuolar and plasma membranes were isolated by a detergent-free method from beet roots (Beta vulgaris L.), and were fractionated in a sucrose density gradient of 15-60% by high-speed centrifugation at 200,000×g during 18 h. The membrane material distributed over the sucrose density gradient was analyzed for the presence of lipids characteristic of raft structures in different zones of the gradient. The quantitative and qualitative content of lipids and sterols, and the composition of fatty acids were analyzed. Some membrane structures differing in their biochemical characteristics were revealed to be located in different zones of the sucrose gradient. The results of the analysis allowed us to identify three zones in the sucrose gradient after the vacuolar membrane fractionation and two zones in the plasma membrane where membrane structures, which may be defined as rafts for their lipid composition, were presented.