Dynamic changes in membrane lipid composition of leaves of winter wheat seedlings in response to PEG-induced water stress

Chlorophyll fluorescence characteristics and lipid metabolism in endangered Cycas panzhihuaensis exposed to drought, high temperature and their combination1

Cycas panzhihuaensis, an endangered species distributed in the dry-hot valleys of southwestern China, faces drought (D), heat (H), and their combination (DH) under current and future climatic conditions. To explore the responses of C. panzhihuaensis to D, H, and DH, chlorophyll fluorescence and the lipid and fatty acid profiles were determined. Leaf water loss and leaf damage only occurred following DH treatment. The photochemical activity was least impacted by D stress and most severely impacted by DH stress. D treatment reduced the levels of most lipid categories and total fatty acids. Both the H and DH treatments led to a significant decrease in the levels of saccharolipids, lysophospholipids, sphingolipids, and fatty acyls, while significantly increasing the levels of neutral glycerolipids and fatty acids. Moreover, odd-numbered fatty acids and trans-fatty acids-C18:2ttn-6 accumulated significantly following both H and DH treatments. However, the levels of both total fatty acids and total lipids were significantly lower after DH stress compared to H stress. The proportion of saturated fatty acids increased after D treatment and that of polyunsaturated fatty acids increased after both H and DH treatments. Following various treatments, the degree of unsaturation in total phospholipids decreased, while that in total saccharolipids remained unchanged. Additionally, the unsaturation levels of diacylglycerol and triacylglycerol showed no change after D stress, but increased after H and DH treatments. In conclusion, C. panzhihuaensis exhibited varying levels of tolerance to D, H, and DH treatments, which may be related to the differential adjustments in lipid composition and unsaturation levels.

Lipid metabolism in Cycas panzhihuaensis exposed to combined stress of drought and high temperatures and subsequent recovery

Cycas panzhihuaensis inhabits regions where summer temperatures can exceed 40 °C, and these extreme conditions may intensify with ongoing global warming. However, how this species adapts to such thermal extremes is not well understood. To investigate the responses of C. panzhihuaensis to heat stress, some physiological characteristics along with lipid and fatty acid profiles were analyzed. The results show that heat stress induced soil water loss but did not cause leaf water loss and visible symptoms of leaf damage. However, photoinhibition was induced and heat dissipation was inhibited under the stress. In the recovered plants, both heat dissipation and maximum photochemical efficiency exhibited significant increases compared to the stressed plants but did not return to the control level. Most lipid categories including phospholipids and saccharolipids accumulated significantly following both the stress and subsequent recovery. However, the content of total neutral glycerolipids maintained unchanged after various treatments. The ratio of phosphatidylcholine/phosphatidylethanolamine decreased significantly and the ratios of both digalactosyldiacylglycerol/monogalactosyldiacylglycerol and triacylglycerol/diacylglycerol increased significantly in the stressed plants. Compared to the control plants, the relative content of polyunsaturated fatty acids significantly increased, while that of both saturated and monounsaturated fatty acids significantly declined in both stressed and recovered plants. Under stress conditions, the unsaturation levels of total neutral glycerolipids and their constituent components significantly increased, whereas those of phosphatidylglycerol and total saccharolipids exhibited a marked decrease. In conclusion, C. panzhihuaensis can tolerate extremely high temperatures to some extent which might be associated with the adjustments in lipid composition and unsaturation levels.

Dynamics of nonstructural carbohydrates and glycerolipids following unexpected freezing stress and subsequent recovery in Cycas multipinnata

The frequency of unexpected freezing events that occur in late spring and early autumn is predicted to increase in certain areas. Based on our observations, endangered Cycas multipinnata is sensitive to unexpected freezing stress, and leaf damage symptoms gradually emerge during the recovery period. To explore the mechanisms of freezing-induced damage, chlorophyll fluorescence parameters and nonstructural carbohydrate and glycerolipid contents were measured following unexpected freezing stress and subsequent recovery. Photochemical activity declined continuously in C. multipinnata, but the starch amount remained unchanged after freezing and recovery treatments. Freezing reduced the soluble sugar content, which increased significantly in plants recovered for 1 d but then returned to their initial levels after 7 d of recovery. Compared to the control, the hexose to sucrose ratio increased by approximately 86 times after 7 d of recovery. Neutral glycerolipids continuously accumulated following freezing and recovery treatments. However, phospholipids and saccharolipids were significantly degraded after freezing treatment and further substantially degraded after 7 d of recovery. Compared to the control, the phospholipid unsaturation level did not change significantly after freezing treatment, decreased significantly after 1 d of recovery, but improved significantly after 7 d of recovery. However, the saccharolipid unsaturation level was not affected by the freezing or recovery treatments. In conclusion, freezing-induced leaf damage in C. multipinnata might be associated with the severe degradation of membrane glycerolipids and an increase in membrane fluidity. However, the roles of metabolic adjustment of soluble sugars in freezing-induced leaf senescence need to be further confirmed.

Biochemical, photosynthetic and metabolomics insights of single and combined effects of salinity, heat, cold and drought in Arabidopsis

Ensuring food security is one of the main challenges related to a growing global population under climate change conditions. The increasing soil salinity levels, drought, heatwaves, and late chilling severely threaten crops and often co-occur in field conditions. This work aims to provide deeper insight into the impact of single vs. combined abiotic stresses at the growth, biochemical and photosynthetic levels in Arabidopsis thaliana (L.). Reduced QY max was recorded in salinity-stressed plants, NPQ increased in heat and salinity single and combined stresses, and qP decreased in combined stresses. MDA and H2O2 content were consistently altered under all stress conditions, but higher values were recorded under salinity alone and in combination. Salinity alone and in stress combinations (especially with cold) provided a stronger hierarchical effect. Despite glycine and GABA osmolytes not significantly changing, proline highlighted the hierarchically stronger impact of salinity, while glycine-betaine was decreased under drought combinations. Untargeted metabolomics pointed out distinct metabolic reprogramming triggered by the different stress conditions, alone or in combination. Pathway analysis revealed that abiotic stresses significantly affected hormones, amino acids and derivates, and secondary metabolites. Flavonoids accumulated under drought (alone and combined with heat and cold stresses), while N-containing compounds decreased under all combined stresses. Looking at the interactions across the parameters investigated, antagonistic, additive, or synergistic effects could be observed depending on the biochemical process considered. Notwithstanding, these results contribute to delving into the impact of various stress combinations, hierarchically highlighting the stress-specific effects and pointing out different combinations.

Drought Tolerance in Plants: Physiological and Molecular Responses

Drought, a significant environmental challenge, presents a substantial risk to worldwide agriculture and the security of food supplies. In response, plants can perceive stimuli from their environment and activate defense pathways via various modulating networks to cope with stress. Drought tolerance, a multifaceted attribute, can be dissected into distinct contributing mechanisms and factors. Osmotic stress, dehydration stress, dysfunction of plasma and endosome membranes, loss of cellular turgidity, inhibition of metabolite synthesis, cellular energy depletion, impaired chloroplast function, and oxidative stress are among the most critical consequences of drought on plant cells. Understanding the intricate interplay of these physiological and molecular responses provides insights into the adaptive strategies plants employ to navigate through drought stress. Plant cells express various mechanisms to withstand and reverse the cellular effects of drought stress. These mechanisms include osmotic adjustment to preserve cellular turgor, synthesis of protective proteins like dehydrins, and triggering antioxidant systems to counterbalance oxidative stress. A better understanding of drought tolerance is crucial for devising specific methods to improve crop resilience and promote sustainable agricultural practices in environments with limited water resources. This review explores the physiological and molecular responses employed by plants to address the challenges of drought stress.

Mitigating gadolinium toxicity in guar (Cyamopsis tetragonoloba L.) through the symbiotic associations with arbuscular mycorrhizal fungi: physiological and biochemical insights

BACKGROUND

Gadolinium (Gd) is an increasingly found lanthanide element in soil; thus, understanding its impact on plant physiology, biochemistry, and molecular responses is crucial. Here, we aimed to provide a comprehensive understanding of Gd (150 mg kg- 1) impacts on guar (Cyamopsis tetragonoloba L.) plant yield and metabolism and whether the symbiotic relationship with arbuscular mycorrhizal fungi (AMF) can mitigate Gd toxicity of soil contamination.

RESULTS

AMF treatment improved mineral nutrient uptake and seed yield by 38-41% under Gd stress compared to non-inoculated stressed plants. Metabolic analysis unveiled the defense mechanisms adopted by AMF-treated plants, revealing carbon and nitrogen metabolism adaptations to withstand Gd contamination. This included an increase in the synthesis of primary metabolites, such as total sugar (+ 39% compared to control), soluble sugars (+ 29%), starch (+ 30%), and some main amino acids like proline (+ 57%) and phenylalanine (+ 87%) in the seeds of AMF-treated plants grown under Gd contamination. Furthermore, fatty acid and organic acid profile changes were accompanied by the production of secondary metabolites, including tocopherols, polyamines, phenolic acids, flavones, and anthocyanins.

CONCLUSIONS

Overall, the coordinated synthesis of these compounds underscores the intricate regulatory mechanisms underlying plant-AMF interactions and highlights the potential of AMF to modulate plant secondary metabolism for enhanced Gd stress tolerance.

Dynamic Membrane Lipid Changes in Physcomitrium patens Reveal Developmental and Environmental Adaptations

Membrane lipid composition is critical for an organism's growth, adaptation, and functionality. Mosses, as early non-vascular land colonizers, show significant adaptations and changes, but their dynamic membrane lipid alterations remain unexplored. Here, we investigated the temporal changes in membrane lipid composition of the moss Physcomitrium patens during five developmental stages and analyzed the acyl content and composition of the lipids. We observed a gradual decrease in total lipid content from the filamentous protonema stage to the reproductive sporophytes. Notably, we found significant levels of very long-chain polyunsaturated fatty acids, particularly arachidonic acid (C20:4), which are not reported in vascular plants and may aid mosses in cold and abiotic stress adaptation. During vegetative stages, we noted high levels of galactolipids, especially monogalactosyldiacylglycerol, associated with chloroplast biogenesis. In contrast, sporophytes displayed reduced galactolipids and elevated phosphatidylcholine and phosphatidic acid, which are linked to membrane integrity and environmental stress protection. Additionally, we observed a gradual decline in the average double bond index across all lipid classes from the protonema stage to the gametophyte stage. Overall, our findings highlight the dynamic nature of membrane lipid composition during moss development, which might contribute to its adaptation to diverse growth conditions, reproductive processes, and environmental challenges.

The physiochemical characteristics and glycerolipid profile of Cycas panzhihuaensis in response to individual and combined drought and freezing temperature stress

The frequency and intensity of the occurrence of drought (D) events during winter are increasing in most areas of China. To explore the interactive effects of D and freezing temperature (F) on plants of endangered Cycas panzhihuaensis, some physiochemical characteristics and the lipid profile were determined. Drought and F stress had no or little impact on the traits of leaves, which, however, bleached following a combination of D and F treatment (DF). Drought treatment did not affect the chlorophyll fluorescence parameters and the flavonoid content of C. panzhihuaensis. Besides the increase in flavonoid content, a decrease of photochemical efficiency and an increase of heat dissipation were induced by both F and DF treatment, with the effects being greater in the latter treatment. The malondialdehyde content decreased significantly and the total antioxidant capacity increased significantly in the plants exposed to both D and DF treatments. The D treatment did not impact the amount of phospholipids but led to an accumulation of saccharolipids. Additionally, the amount of both phospholipids and saccharolipids remained unchanged following F treatment but decreased significantly following DF treatment compared with those of the control. The unsaturation level did not change significantly in most lipid classes of membrane glycerolipids following various stresses but increased significantly in phosphatidylserine, monogalactosylmonoacylglycerol, digalactosyldiacylglycerol and sulphoquinovosyldiacylglycerol following D or both D and F treatments. Generally, plants of C. panzhihuaensis showed relatively strong tolerance to individual D stress, while D aggravated the F-induced damage, which was likely caused by the degradation of the membrane glycerolipids.

Exploring lipid signaling in plant physiology: From cellular membranes to environmental adaptation

Lipids have evolved as versatile signaling molecules that regulate a variety of physiological processes in plants. Convincing evidence highlights their critical role as mediators in a wide range of plant processes required for survival, growth, development, and responses to environmental conditions such as water availability, temperature changes, salt, pests, and diseases. Understanding lipid signaling as a critical process has helped us expand our understanding of plant biology by explaining how plants sense and respond to environmental cues. Lipid signaling pathways constitute a complex network of lipids, enzymes, and receptors that coordinate important cellular responses and stressing plant biology's changing and adaptable traits. Plant lipid signaling involves a wide range of lipid classes, including phospholipids, sphingolipids, oxylipins, and sterols, each of which contributes differently to cellular communication and control. These lipids function not only as structural components, but also as bioactive molecules that transfer signals. The mechanisms entail the production of lipid mediators and their detection by particular receptors, which frequently trigger downstream cascades that affect gene expression, cellular functions, and overall plant growth. This review looks into lipid signaling in plant physiology, giving an in-depth look and emphasizing its critical function as a master regulator of vital activities.

The metabolism of nonstructural carbohydrates, lipids, and energy in two Cycas species with differential tolerance to unexpected freezing stress

Introduction

With the climate warming, the occurrence of freezing events is projected to increase in late spring and early autumn in the Northern Hemisphere. Observation of morphological traits showed that Cycas panzhihuaensis was more tolerant to unexpected freezing stress than C. bifida. Energy balance is crucial for plant tolerance to stress. Here, we aimed to determine whether the different responses of the two species to the unpredicted freezing stress were associated with the metabolism of energy and related substances.

Methods

The effects of unexpected freezing temperatures on C. panzhihuaensis and C. bifida were studied by measuring chlorophyll fluorescence parameters, energy charge and the profile of nonstructural carbohydrates (NSC) and lipids.

Results

C. panzhihuaensis exhibited higher stability of photosynthetic machinery than C. bifida under unpredicted freezing events. Significant interaction between species and treatments were observed in the energy charge, the level of NSC and its most components and the amount of most lipid categories and lipid classes. The decrease of soluble sugar and the increase of neutral glycerolipids at the early freezing stage, the accumulation of membrane glycerolipids at the late freezing stage and the continuous decrease of energy charge during the freezing period were the characteristics of C. panzhihuaensis responding to unexpected freezing stress. The degradation of membrane glycerolipids and the continuous decrease of soluble sugar during the freezing period and the accumulation of neutral glycerolipids and energy charge at the late freezing stage represented the characteristics of C. bifida responses.

Discussion

The different freezing sensitivity between C. panzhihuaensis and C. bifida might be associated with the differential patterns of the metabolism of energy, NSC and lipids. C. panzhihuaensis possesses the potential to be introduced to the areas of higher latitudes and altitudes.

Biochemical Alterations in Triticale Seedlings Pretreated with Selective Herbicide and Subjected to Drought or Waterlogging Stress

Waterlogging and drought disrupt crop development and productivity. Triticale is known to be relatively tolerant to different stress factors. In natural conditions, plants are rather subjected to multiple environmental factors. Serrate® (Syngenta) is a systemic selective herbicide suitable for cereal crops such as triticale and wheat to restrain annual grass and broadleaf weeds. Triticale (×Triticosecale Wittm., cv. Rozhen) was grown as soil culture under controlled conditions. Seventeen-day-old plantlets were leaf sprayed with Serrate®. The water stress (drought or waterlogging) was applied after 72 h for 7 days, and then the seedlings were left for recovery. The herbicide does not provoke sharp alterations in the antioxidant state (stress markers level, and antioxidant and xenobiotic-detoxifying enzymes activity). The water stresses and combined treatments enhanced significantly the content of stress markers (malondialdehyde, proline, hydrogen peroxide), non-enzymatic (total phenolics and thiol groups-containing compounds), and enzymatic (activities of superoxide dismutase, catalase, guaiacol peroxidase, glutathione reductase) antioxidants, and xenobiotic-detoxifying enzymes (activities of glutathione S-transferase, NADPH:cytochrome P450 reductase, NADH:cytochrome b5 reductase). These effects were more severely expressed after the drought stress, suggesting that this cultivar is more tolerant to waterlogging than to drought stress.

A group III patatin-like phospholipase gene pPLAIIIδ regulates lignin biosynthesis and influences the rate of seed germination in Arabidopsis thaliana

The lignification of plant secondary walls is an important process that provides plants with mechanical support. However, the presence of lignin in the secondary walls affects the readily availability of cellulose required in various industries, including the biofuel, paper, and textile industries. Thus, plants with less lignin are ideal for usage in such industries. Molecular studies have identified genes that regulate plant lignification, including group III plant-specific patatin-related phospholipase genes. Recent studies have reported decreased lignin content when pPLAIIIα, pPLAIIIγ (from Arabidopsis thaliana), and pPLAIIIβ (from Panax ginseng) were overexpressed in Arabidopsis. However, the role played by a closely related gene pPLAIIIδ in lignin biosynthesis has not yet been reported. In this study, we found that overexpression of the pPLAIIIδ significantly reduced the lignin content in secondary cell walls, whereas the silencing of the gene increased secondary walls lignification. Transcript level analysis showed that the key structural and regulatory genes involved in the lignin biosynthesis pathway decreased in overexpression, and increased in plants with silenced pPLAIIIδ. Further analysis revealed that pPLAIIIδ played an influential role in several physiological processes including seed germination, and chlorophyll accumulation. Moreover, the gene also influenced the size of plants and plant organs, including leaves, seeds, and root hairs. Generally, our study provides important insights toward the use of genetic engineering for lignin reduction in plants and provides information about the agronomical and physiological suitability of pPLAIIIδ transgenic plants for utilization in biomass processing industries.

Deuterium- and Alkyne-Based Bioorthogonal Raman Probes for In Situ Quantitative Metabolic Imaging of Lipids within Plants

Plants can rapidly respond to different stresses by activating multiple signaling and defense pathways. The ability to directly visualize and quantify these pathways in real time using bioorthogonal probes would have practical applications, including characterizing plant responses to both abiotic and biotic stress. Fluorescence-based labels are widely used for tagging of small biomolecules but are relatively bulky and with potential effects on their endogenous localization and metabolism. This work describes the use of deuterium- and alkyne-derived fatty acid Raman probes to visualize and track the real-time response of plants to abiotic stress within the roots. Relative quantification of the respective signals could be used to track their localization and overall real-time responses in their fatty acid pools due to drought and heat stress without labor-intensive isolation procedures. Their overall usability and low toxicity suggest that Raman probes have great untapped potential in the field of plant bioengineering.

Endoplasmic reticulum membrane contact sites: cross-talk between membrane-bound organelles in plant cells

Eukaryotic cells contain organelles surrounded by monolayer or bilayer membranes. Organelles take part in highly dynamic and organized interactions at membrane contact sites, which play vital roles during development and response to stress. The endoplasmic reticulum extends throughout the cell and acts as an architectural scaffold to maintain the spatial distribution of other membrane-bound organelles. In this review, we highlight the structural organization, dynamics, and physiological functions of membrane contact sites between the endoplasmic reticulum and various membrane-bound organelles, especially recent advances in plants. We briefly introduce how the combined use of dynamic and static imaging techniques can enable monitoring of the cross-talk between organelles via membrane contact sites. Finally, we discuss future directions for research fields related to membrane contact.

Functions and interaction of plant lipid signalling under abiotic stresses

Lipids are the primary form of energy storage and a major component of plasma membranes, which form the interface between the cell and the extracellular environment. Several lipids - including phosphoinositide, phosphatidic acid, sphingolipids, lysophospholipids, oxylipins, and free fatty acids - also serve as substrates for the generation of signalling molecules. Abiotic stresses, such as drought and temperature stress, are known to affect plant growth. In addition, abiotic stresses can activate certain lipid-dependent signalling pathways that control the expression of stress-responsive genes and contribute to plant stress adaptation. Many studies have focused either on the enzymatic production and metabolism of lipids, or on the mechanisms of abiotic stress response. However, there is little information regarding the roles of plant lipids in plant responses to abiotic stress. In this review, we describe the metabolism of plant lipids and discuss their involvement in plant responses to abiotic stress. As such, this review provides crucial background for further research on the interactions between plant lipids and abiotic stress.

The impact of boron nutrient supply in mulberry (Morus alba) response to metabolomics, enzyme activities, and physiological parameters

Boron (B) is essential for normal and healthy plant growth. Therefore, Boron stress is a common abiotic stress that limits plant growth and productivity. However, how mulberry copes with boron stress remains unclear. In this study, seedlings of the Morus alba cultivar, Yu-711, were treated with five different concentrations of boric acid (H₃BO₃), including deficient (0 and 0.02 mM), sufficient (0.1 mM) and toxic (0.5 and 1 mM) levels. Physiological parameters, enzymatic activities and non-targeted liquid chromatography-mass spectrometry (LC-MS) technique were employed to evaluate the effects of boron stress on the net photosynthetic rate (Pn), chlorophyll content, stomatal conductance (Gs), transpiration rate (Tr), intercellular CO₂ concentration (Ci) and metabolome signatures. Physiological analysis revealed that Boron deficiency and toxicity induced a decline in P_n, C_i, G_s, T_r, and chlorophyll content. Also, enzymatic activities, including catalase (CAT) and superoxide dismutase (SOD), decreased, while POD activity increased in response to Boron stress. Osmotic substances such as soluble sugars, soluble proteins, and proline (PRO) presented elevated levels under all Boron concentrations. Metabolome analysis indicated that differential metabolites, including amino acids, secondary metabolites, carbohydrates, and lipids, played a key role in Yu-711's response to Boron stress. These metabolites were mainly involved in amino acid metabolism, biosynthesis of other secondary metabolites, lipid metabolism, metabolism of cofactors and vitamins, and metabolism of other amino acids pathways. Our findings reveal the various metabolites pathways in mulberry response to boron nutrient supply and may serve as fundamental knowledge in breeding resistance mulberry plants, so that it can cope with climate changes.

Localization of Lipid Droplets in Embryonic Axis Radicle Cells of Soybean Seeds under Various Imbibition Regimes Indicates Their Role in Desiccation Tolerance

Desiccation tolerance allows plant seeds to remain viable during desiccation and subsequent re-hydration. In this study, we tried to develop an experimental system to understand the difference between desiccation tolerant and desiccation sensitive radicle cells by examining excised embryonic axes after re-desiccation and subsequent imbibition under various regimes. Embryonic axes excised from soybean (Glycine max (L.) Merr.) seeds imbibed for 3 h to 15 h which remained attached to the cotyledons during imbibition would grow normally after 24 h of desiccation and re-imbibition on wet filter paper. By contrast, when the embryonic axes excised after 3 h imbibition of seeds were kept on wet filter paper for 12 h to 16 h, their growth was significantly retarded after 24 h of desiccation and subsequent re-imbibition. Numerous lipid droplets were observed lining the plasma membrane and tonoplasts in radicle cells of desiccation tolerant embryonic axes before and after desiccation treatment. By contrast, the lipid droplets lining the plasma membrane and tonoplasts became very sparse in radicle cells that were placed for longer times on wet filter paper before desiccation. We observed a clear correlation between the amount of lipid droplets lining plasma membranes and the ability to grow after desiccation and re-imbibition of the excised embryonic axes. In addition to the reduction of lipid droplets in the cells, a gradual increase in starch grains was observed. Large starch grains accumulated in the radicle cells of those axes that failed to grow further.

Metabolism of crown tissue is crucial for drought tolerance and recovery after stress cessation in Lolium/Festuca forage grasses

A process of plant recovery after drought cessation is a complex trait which has not been fully recognized. The most important organ associated with this phenomenon in monocots, including forage grasses, is the crown tissue located between shoots and roots. The crown tissue is a meristematic crossroads for metabolites and other compounds between these two plant organs. Here, for the first time, we present a metabolomic and lipidomic study focused on the crown tissue under drought and recovery in forage grasses, important for agriculture in European temperate regions. The plant materials involve high (HDT) and low drought-tolerant (LDT) genotypes of Festuca arundinacea, and Lolium multiflorum/F. arundinacea introgression forms. The obtained results clearly demonstrated that remodeling patterns of the primary metabolome and lipidome in the crown under drought and recovery were different between HDT and LDT plants. Furthermore, HDT plants accumulated higher contents of primary metabolites under drought in the crown tissue, especially carbohydrates which could function as osmoprotectants and storage materials. On the other hand, LDT plants characterized by higher membranes damage under drought, simultaneously accumulated membrane phospholipids in the crown and possessed the capacity to recover their metabolic functions after stress cessation to the levels observed in HDT plants.

Biofertilisation with a consortium of growth-promoting bacterial strains improves the nutritional status of wheat grain under control, drought, and salinity stress conditions

We investigated the effect of plant growth-promoting bacterial strains (PGPB) as biofertilisers on the grain metabolic composition of durum wheat (Triticum durum Desf.). To this aim, we conducted a greenhouse experiment where we grew durum wheat plants supplied with a biofertiliser consortium of four PGPB and/or chemical fertiliser (containing nitrogen, phosphorus, potassium, and zinc), under non-stress, drought (at 40% field capacity), or salinity (150 mM NaCl) conditions. Nutrient accumulations in the grain were increased in plants treated with the biofertiliser consortium, alone or with a half dose of chemical fertilisers, compared to those in no fertilisation treatment. A clear benefit of biofertiliser application in the improvement of protein, soluble sugar, starch, and lipid contents in the grains was observed in comparison with untreated controls, especially under stress conditions. The most striking observation was the absence of significant differences between biofertiliser and chemical fertiliser treatments for most parameters. Moreover, the overall response to the biofertiliser consortium was accompanied by greater changes in amino acids, organic acids, and fatty acid profiles. In conclusion, PGPB improved the metabolic and nutrient status of durum wheat grains to a similar extent as chemical fertilisers, particularly under stress conditions, demonstrating the value of PGPB as a sustainable fertilisation treatment.

The pivotal role of cultivar affinity to arbuscular mycorrhizal fungi in determining mycorrhizal responsiveness to water deficit

Arbuscular mycorrhizal fungi (AMF) have gained remarkable importance, having been proved to alleviate drought stress-induced damage in wheat due to their ability to ameliorate plant water use efficiency and antioxidant enzyme activity. However, despite the current relevance of the topic, the molecular and physiological processes at the base of this symbiosis never consider the single cultivar affinity to mycorrhization as an influencing factor for the metabolic response in the AMF-colonized plant. In the present study, the mycorrhizal affinity of two durum wheat species (T. turgidum subsp. durum (Desf.)) varieties, Iride and Ramirez, were investigated. Successively, an untargeted metabolomics approach has been used to study the fungal contribution to mitigating water deficit in both varieties. Iride and Ramirez exhibited a high and low level of mycorrhizal symbiosis, respectively; resulting in a more remarkable alteration of metabolic pathways in the most colonised variety under water deficit conditions. However, the analysis highlighted the contribution of AMF to mitigating water deficiency in both varieties, resulting in the up- and down-regulation of many amino acids, alkaloids, phenylpropanoids, lipids, and hormones.

Effects of heat shock on photosynthesis-related characteristics and lipid profile of Cycas multipinnata and C. panzhihuaensis

BACKGROUND

Cycas multipinnata and C. panzhihuaensis are two attractive ornamental tree species. With the global climate change, the temperature in the natural habitats of both the species shows a marked rising trend. However, how the two species respond to extreme high temperatures are not clear. Chlorophyll fluorescence parameters, chlorophyll content, chloroplast ultrastructure and lipid metabolism in the two species were determined following plant exposure to heat stress.

RESULTS

The results demonstrated that the photosynthetic efficiency decreased significantly in both the species following heat shock and recovery, but to a greater extent in C. panzhihuaensis. Compared to the control, chlorophyll content of C. multipinnata did not change significantly following heat stress and recovery. However, chlorophyll content of C. panzhihuaensis increased significantly after 1 d of recovery in comparison with the control. Chloroplast ultrastructures of C. panzhihuaensis were more severely affected by heat shock than C. multipinnata. C. multipinnata and C. panzhihuaensis followed a similar change trend in the amounts of most of the lipid categories after heat stress. However, only the amounts of lysophospholipids and fatty acyls differed significantly between the two species following heat treatment. Additionally, the unsaturation levels of the major lipid classes in C. multipinnata were significantly lower than or equal to those in C. panzhihuaensis.

CONCLUSIONS

C. multipinnata was less affected by extremely high temperatures than C. panzhihuaensis. The differential stability of chlorophyll and chloroplast ultrastructure and the differential adjustment of lipid metabolism might contribute to the different responses to heat shock between the two species.

Effect of Drought Stress on Degradation and Remodeling of Membrane Lipids in Nostoc flagelliforme

Nostoc flagelliforme is a kind of terrestrial edible cyanobacteria with important ecological and economic value which has developed special mechanisms to adapt to drought conditions. However, the specific mechanism of lipidome changes in drought tolerance of N. flagelliforme has not been well understood. In this study, the ultra-high-performance liquid chromatography and mass spectrometry were employed to analyze the lipidome changes of N. flagelliforme under dehydration. A total of 853 lipid molecules were identified, of which 171 were significantly different from that of the control group. The digalactosyldiacylglycerol/monogalactosyldiacylglycerol (DGDG/MGDG) ratio was increased. The amount of wax ester (WE) was sharply decreased during drought stress, while Co (Q10) was accumulated. The levels of odd chain fatty acids (OCFAs) were increased under dehydration, positively responding to drought stress according to the energy metabolism state. In conclusion, the lipidomic data corroborated that oxidation, degradation, and biosynthesis of membrane lipids took place during lipid metabolism, which can respond to drought stress through the transformation of energy and substances. Besides, we constructed a lipid metabolic model demonstrating the regulatory mechanism of drought stress in N. flagelliforme. The present study provides insight into the defense strategies of cyanobacteria in lipid metabolic pathways.

32Pi Labeled Transgenic Wheat Shows the Accumulation of Phosphatidylinositol 4,5-bisphosphate and Phosphatidic Acid Under Heat and Osmotic Stress

The ensuing heat stress drastically affects wheat plant growth and development, consequently compromising its grain yield. There are many thermoregulatory processes/mechanisms mediated by ion channels, lipids, and lipid-modifying enzymes that occur in the plasma membrane and the chloroplast. With the onset of abiotic or biotic stresses, phosphoinositide-specific phospholipase C (PI-PLC), as a signaling enzyme, hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP₂) to generate inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol (DAG) which is further phosphorylated into phosphatidic acid (PA) as a secondary messenger and is involved in multiple processes. In the current study, a phospholipase C (PLC) signaling pathway was investigated in spring wheat (Triticum aestivum L.) and evaluated its four AtPLC5 overexpressed (OE)/transgenic lines under heat and osmotic stresses through ³²P_i radioactive labeling. Naturally, the wheat harbors only a small amount of PIP₂. However, with the sudden increase in temperature (40°C), PIP₂ levels start to rise within 7.5 min in a time-dependent manner in wild-type (Wt) wheat. While the Phosphatidic acid (PA) level also elevated up to 1.6-fold upon exposing wild-type wheat to heat stress (40°C). However, at the anthesis stage, a significant increase of ∼4.5-folds in PIP₂ level was observed within 30 min at 40°C in AtPLC5 over-expressed wheat lines. Significant differences in PIP₂ level were observed in Wt and AtPLC5-OE lines when treated with 1200 mM sorbitol solution. It is assumed that the phenomenon might be a result of the activation of PLC/DGK pathways. Together, these results indicate that heat stress and osmotic stress activate several lipid responses in wild-type and transgenic wheat and can explain heat and osmotic stress tolerance in the wheat plant.

Integrated Lipidomic and Transcriptomic Analysis Reveals Phospholipid Changes in Somatic Embryos of Picea asperata in Response to Partial Desiccation

Partial desiccation treatment (PDT) is an effective technology for promoting the germination and conversion of conifer somatic embryos (SEs). PDT, as a drought stress, induces intensive physiological responses in phospholipid metabolism, which are not well understood in the conifer SEs. Here, we integrated lipidomics, transcriptomics and proteomics analyses to reveal the molecular basis of lipid remodeling under PDT in Picea asperata SEs. Among the 82 lipid molecular species determined by mass spectrometry, phosphatidic acid (PA) had a significant effect after PDT and was the most critical lipid in the response to PDT. The transcriptomics results showed that multiple transcripts in the glycerolipid and glycerophospholipid metabolism pathways were differentially expressed, and these included five PLDα1 transcripts that catalyze the conversion of phosphatidylcholine (PC) to PA. Furthermore, the enzyme activity of this phospholipase D (PLD) was significantly enhanced in response to PDT, and PDT also significantly increased the protein level of PLDα1 (MA_10436582g0020). In addition, PA is a key factor in gibberellin, abscisic acid and ethylene signal transduction. One GDI1, one DELLA, three ABI1s, two SnRK2s, one CTR and 12 ERFs showed significantly differential expression between SEs before and after PDT in this study. Our data suggest that the observed increases in the PA contents might result from the activation of PLDα by PDT. PA not only affects the physical and chemical properties of the cell membrane but also participates in plant hormone signal transduction. Our work provides novel insight into the molecular mechanism through which PDT promotes the germination of SEs of coniferous tree species and fills the gap in the understanding of the mechanism of somatic embryo lipid remodeling in response to PDT.

Enhanced Adaptability to Limited Water Supply Regulated by Diethyl Aminoethyl Hexanoate (DA-6) Associated With Lipidomic Reprogramming in Two White Clover Genotypes

Membrane lipid reprogramming is one of the most important adaptive strategies in plant species under unfavorable environmental circumstances. Therefore, the present experiment was conducted to elucidate the effect of diethyl aminoethyl hexanoate (DA-6), a novel synthetic plant growth regulator, on oxidative damage, photosynthetic performance, changes in lipidomic profile, and unsaturation index of lipids in two white clover (Trifolium repens) cultivars (drought-sensitive "Ladino" and drought-resistant "Riverdel") under PEG-6000-induced water-deficit stress. Results revealed that water-deficit stress significantly enhanced oxidative damage and decreased photosynthetic functions in both cultivars. However, the damage was less in Riverdel. In addition, water-deficit stress significantly decreased the relative content of monogalactocyl-diacylglycerols (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acisd (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), sphingomyelins (SM), and sphingosines (Sph) in both cultivars, but a more pronounced decline was observed in Ladino. Exogenous application of DA-6 significantly increased the relative content of digalactocyl-diacylglycerols (DGDG), monogalactocyl-diacylglycerolsabstra (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acids (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-inositols (PI), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), neutral glycosphingolipids (CerG2GNAc1), and sphingosines (Sph) in the two cultivars under water-deficit stress. DA-6-treated Riverdel exhibited a significantly higher DGDG:MGDG ratio and relative content of sphingomyelins (SM) than untreated plants in response to water deficiency. Furthermore, the DA-6-pretreated plants increased the unsaturation index of phosphatidic acids (PA) and phosphatidylinositols (PI) in Ladino, ceramides (Cer) and hexosylmonoceramides (Hex1Cer) in Riverdel, and sulfoquinovosyl-diacylglycerols (SQDG) in both cultivars under water stress. These results suggested that DA-6 regulated drought resistance in white clover could be associated with increased lipid content and reprogramming, higher DGDG:MGDG ratio, and improved unsaturation index of lipids, contributing to enhanced membrane stability, integrity, fluidity, and downstream signaling transduction.

Multiomic analyses of two sorghum cultivars reveals the change of membrane lipids in their responses to water deficit

Drought is one of the main abiotic stresses influencing crop production all over the world. Membranes are sensitive to drought stress and easy to be degraded and modified. Lipidome and transcriptome analyses were applied to analyze the responses of membrane lipids to drought stress in two sorghum (Sorghum bicolor (L.) Moench) cultivars, drought-sensitive cv. Hongyingzi and drought-tolerant cv. Kangsi. In total, 156 lipid compounds were identified and the contents of the predominant ones changed significantly under drought stress. Drought significantly decreased the unsaturation indices (UI) of digalactosyl-diacylglycerol (DGDG), monogalactosyl-diacylglycerol (MGDG), phosphatidylglycerol (PG) and phosphatidylcholine (PC) in both cultivars, except for insignificant changes of UI for DGDG in cv. Kangsi. Transcriptome sequencing analysis identified genes related to membrane lipid remodeling such as phospholipase D α1 (PLDα1), phospholipase D δ (PLDδ), and phospholipase A 2 (PLA2). By integrating transcriptome data and lipidome data, weighted gene co-expression network analysis (WGCNA) identified hub genes, transcription factors and the genes involved in lipid metabolism. Then, the protein and protein interaction (PPI) was analyzed using STRING and the possible candidate genes regulating membrane lipids under drought stress were obtained, including CCT2, CER1, DGK1, DGK5, EMB3174, KCS4, LCB2, PAH1, PLDP1, PKP-β1, and KCS11. The results from this study have the potential to accelerate the process to breed drought-tolerant sorghum lines.

The specific glycerolipid composition is responsible for maintaining the membrane stability of Physcomitrella patens under dehydration stress

Land colonization is a major event in plant evolution. Little is known about the evolutionary characteristics of lipids during this process. Here, we proved that Physcomitrella patens, a bryophyte that appeared in the early evolution of terrestrial plants, has short-term desiccation resistance. The maintenance of membrane integrity is related to its specific glycerolipid composition and key genes for lipid metabolism. We analyzed 414 types of lipid molecules, and found that phospholipids accounted for 61.7%, mainly PC and PI; glycolipids accounted for only 26.5%, with a special MGDG molecular map. The most abundant MDGD, that is, MGDG34:6, contained rare 15- and 19-carbon acyl chains; the level of neutral lipids was higher. This was consistent with the results observed by TEM, with fewer lamellae and obvious lipid droplets. Slight dehydration accumulated a large number of TAG molecules, and severe dehydration degraded phospholipids and caused membrane leakage, but PA and MGDG fluctuated less. The key genes of lipid metabolism, DGAT and PAP, were actively transcribed, suggesting that PA was one of the main DAG sources for TAG synthesis. This work proves that Physcomitrella patens adopts high-constitutive PC and PI similar to plant seeds, abundant TAG, and its own specific MGDG to resist extreme dehydration. This result provides a new insight into the lipid evolution of early terrestrial plants against unfavorable terrestrial environments.

Comparative Molecular and Metabolic Profiling of Two Contrasting Wheat Cultivars under Drought Stress

Drought is one of the most important threats to plants and agriculture; therefore, understanding of the mechanisms of drought tolerance is crucial for breeding of new tolerant varieties. Here, we assessed the effects of a long-term water deficit stress simulated on a precision phenotyping system on some morphological criteria and metabolite traits, as well as the expression of drought associated transcriptional factors of two contrasting drought-responsive African wheat cultivars, Condor and Wadielniel. The current study showed that under drought stress Wadielniel exhibits significant higher tillering and height compared to Condor. Further, we used gas chromatography and ultra-high performance liquid chromatography mass-spectrometry to identify compounds that change between the two cultivars upon drought. Partial least square discriminant analysis (PLS-DA) revealed that 50 metabolites with a possible role in drought stress regulation were significantly changed in both cultivars under water deficit stress. These metabolites included several amino acids, most notably proline, some organic acids, and lipid classes PC 36:3 and TAG 56:9, which were significantly altered under drought stress. Here, the results discussed in the context of understanding the mechanisms involved in the drought response of wheat cultivars, as the phenotype parameters, metabolite content and expression of drought associated transcriptional factors could also be used for potential crop improvement under drought stress.

Effects of repeated drought stress on the physiological characteristics and lipid metabolism of Bombax ceiba L. during subsequent drought and heat stresses

BACKGROUND

Trees of Bombax ceiba L. could produce a large number of viable seeds in the dry-hot valleys. However, the seedling regeneration of the species is difficult in these areas as mild drought often occur repeatedly which might be followed by heat stress. However, how the repeated drought affects the subsequent drought and heat tolerance of B. ceiba is not clear. In this study, chlorophyll fluorescence, soluble sugar content and lipid metabolism were measured for the drought-treated seedlings and heat-treated seedlings with or without drought hardening.

RESULTS

Neither the first nor third dehydration treatments affected the photosynthetic activity and soluble sugar content of B. ceiba seedlings. However, they differentially affected the fluidity of the local membranes and the levels of diacylglycerol and phosphatidic acid. Heat shock severely decreased the photosynthetic efficiency but drought priming reduced the effects of heat shock. Moreover, heat shock with or without drought priming had differential effects on the metabolism of soluble sugars and some lipids. In addition, the unsaturation level of membrane glycerolipids increased following heat shock for non-drought-hardened seedlings which, however, maintained for drought-hardened seedlings.

CONCLUSIONS

The results suggest that two cycles of dehydration/recovery can affect the metabolism of some lipids during the third drought stress and may enhance the heat tolerance of B. ceiba by adjusting lipid composition and membrane fluidity.

Differences in lipid homeostasis and membrane lipid unsaturation confer differential tolerance to low temperatures in two Cycas species

BACKGROUND

C. panzhihuaensis is more tolerant to freezing than C. bifida but the mechanisms underlying the different freezing tolerance are unclear. Photosynthesis is one of the most temperature-sensitive processes. Lipids play important roles in membrane structure, signal transduction and energy storage, which are closely related to the stress responses of plants. In this study, the chlorophyll fluorescence parameters and lipid profiles of the two species were characterized to explore the changes in photosynthetic activity and lipid metabolism following low-temperature exposure and subsequent recovery.

RESULTS

Photosynthetic activity significantly decreased in C. bifida with the decrease of temperatures and reached zero after recovery. Photosynthetic activity, however, was little affected in C. panzhihuaensis. The lipid composition of C. bifida was more affected by cold and freezing treatments than C. panzhihuaensis. Compared with the control, the proportions of all the lipid categories recovered to the original level in C. panzhihuaensis, but the proportions of most lipid categories changed significantly in C. bifida after 3 d of recovery. In particular, the glycerophospholipids and prenol lipids degraded severely during the recovery period of C. bifida. Changes in acyl chain length and double bond index (DBI) occurred in more lipid classes immediately after low-temperature exposure in C. panzhihuaensis compare with those in C. bifida. DBI of the total main membrane lipids of C. panzhihuaensis was significantly higher than that of C. bifida following all temperature treatments.

CONCLUSIONS

The results of chlorophyll fluorescence parameters confirmed that the freezing tolerance of C. panzhihuaensis was greater than that of C. bifida. The lipid metabolism of the two species had differential responses to low temperatures. The homeostasis and plastic adjustment of lipid metabolism and the higher level of DBI of the main membrane lipids may contribute to the greater tolerance of C. panzhihuaensis to low temperatures.

Mechanisms and functions of membrane lipid remodeling in plants

Lipid remodeling, defined herein as post-synthetic structural modifications of membrane lipids, play crucial roles in regulating the physicochemical properties of cellular membranes and hence their many functions. Processes affected by lipid remodeling include lipid metabolism, membrane repair, cellular homeostasis, fatty acid trafficking, cellular signaling and stress tolerance. Glycerolipids are the major structural components of cellular membranes and their composition can be adjusted by modifying their head groups, their acyl chain lengths and the number and position of double bonds. This review summarizes recent advances in our understanding of mechanisms of membrane lipid remodeling with emphasis on the lipases and acyltransferases involved in the modification of phosphatidylcholine and monogalactosyldiacylglycerol, the major membrane lipids of extraplastidic and photosynthetic membranes, respectively. We also discuss the role of triacylglycerol metabolism in membrane acyl chain remodeling. Finally, we discuss emerging data concerning the functional roles of glycerolipid remodeling in plant stress responses. Illustrating the molecular basis of lipid remodeling may lead to novel strategies for crop improvement and other biotechnological applications such as bioenergy production.

Identification and Expression Profiling of Nonphosphorus Glycerolipid Synthase Genes in Response to Abiotic Stresses in Dendrobium catenatum

Dendrobium catenatum, a valuable Chinese herb, frequently experiences abiotic stresses, such as cold and drought, under natural conditions. Nonphosphorus glycerolipid synthase (NGLS) genes are closely linked to the homeostasis of membrane lipids under abiotic stress in plants. However, there is limited information on NGLS genes in D. catenatum. In this study, a total of eight DcaNGLS genes were identified from the D. catenatum genome; these included three monogalactosyldiacylglycerol synthase (DcaMGD1, 2, 3) genes, two digalactosyldiacylglycerol synthase (DcaDGD1, 2) genes, and three sulfoquinovosyldiacylglycerol synthase (DcaSQD1, 2.1, 2.2) genes. The gene structures and conserved motifs in the DcaNGLSs showed a high conservation during their evolution. Gene expression profiling showed that the DcaNGLSs were highly expressed in specific tissues and during rapid growth stages. Furthermore, most DcaNGLSs were strongly induced by freezing and post-freezing recovery. DcaMGD1 and DcaSQDs were greatly induced by salt stress in leaves, while DcaDGDs were primarily induced by salt stress in roots. Under drought stress, most DcaNGLSs were regulated by circadian rhythms, and DcaSQD2 was closely associated with drought recovery. Transcriptome analysis also revealed that MYB might be regulated by circadian rhythm and co-expressed with DcaNGLSs under drought stress. These results provide insight for the further functional investigation of NGLS and the regulation of nonphosphorus glycerolipid biosynthesis in Dendrobium.

Galactolipid and Phospholipid Profile and Proteome Alterations in Soybean Leaves at the Onset of Salt Stress

Salinity is a major environmental factor that constrains soybean yield and grain quality. Given our past observations using the salt-sensitive soybean (Glycine max [L.] Merr.) accession C08 on its early responses to salinity and salt-induced transcriptomic modifications, the aim of this study was to assess the lipid profile changes in this cultivar before and after short-term salt stress, and to explore the adaptive mechanisms underpinning lipid homeostasis. To this end, lipid profiling and proteomic analyses were performed on the leaves of soybean seedlings subjected to salt treatment for 0, 0.5, 1, and 2 h. Our results revealed that short-term salt stress caused dynamic lipid alterations resulting in recycling for both galactolipids and phospholipids. A comprehensive understanding of membrane lipid adaption following salt treatment was achieved by combining time-dependent lipidomic and proteomic data. Proteins involved in phosphoinositide synthesis and turnover were upregulated at the onset of salt treatment. Salinity-induced lipid recycling was shown to enhance jasmonic acid and phosphatidylinositol biosyntheses. Our study demonstrated that salt stress resulted in a remodeling of membrane lipid composition and an alteration in membrane lipids associated with lipid signaling and metabolism in C08 leaves.

Lipid Compositions and Geographical Discrimination of 94 Geographically Authentic Wheat Samples Based on UPLC-MS with Non-Targeted Lipidomic Approach

Wheat is the staple food for the world’s major populations. However, chemical characters of geographically authentic wheat samples, especially for the lipids, have not been deeply studied. The present research aimed to investigate lipid compositions of Chinese wheat samples and clarify the major markers that contribute to the geographical differences. A total of 94 wheat samples from eight main wheat-producing provinces in China were evaluated to differentiate their lipid compositions. Based on the data collected from ultra-high-performance-liquid-chromatography tandem time-of-flight mass spectrometry (UPLC-Q/TOF MS), an optimized non-targeted lipidomic method was utilized for analyses. As the results, 62 lipid compounds, including fatty acids, phospholipids, galactolipids, triglycerides, diglycerides, alkylresorcinol, and ceramide were tentatively identified. Partial least squares discriminant analysis (PLS-DA) demonstrated a more satisfying performance in distinguishing wheat samples from different origins compared with principal component analysis (PCA). Further, the abundances of triglycerides and glycerophospholipids with more unsaturated fatty acids were found greater in wheat samples from northern origins of China, while more glycolipids and unsaturated fatty acids arose in southern original wheat samples. These findings describe the lipid profiles of wheat samples in China and could contribute to the quality and safety control for the wheat flour products.