Changes in Polar Lipid Composition in Balsam Fir during Seasonal Cold Acclimation and Relationship to Needle Abscission.

Needle abscission in balsam fir has been linked to both cold acclimation and changes in lipid composition. The overall objective of this research is to uncover lipid changes in balsam fir during cold acclimation and link those changes with postharvest abscission. Branches were collected monthly from September to December and were assessed for cold tolerance via membrane leakage and chlorophyll fluorescence changes at -5, -15, -25, -35, and -45 °C. Lipids were extracted and analyzed using mass spectrometry while postharvest needle abscission was determined gravimetrically. Cold tolerance and needle retention each significantly (p < 0.001) improved throughout autumn in balsam fir. There were concurrent increases in DGDG, PC, PG, PE, and PA throughout autumn as well as a decrease in MGDG. Those same lipids were strongly related to cold tolerance, though MGDG had the strongest relationship (R2 = 55.0% and 42.7% from membrane injury and chlorophyll fluorescence, respectively). There was a similar, albeit weaker, relationship between MGDG:DGDG and needle retention (R2 = 24.3%). Generally, a decrease in MGDG:DGDG ratio resulted in better cold tolerance and higher needle retention in balsam fir, possibly due to increased membrane stability. This study confirms the degree of cold acclimation in Nova Scotian balsam fir and presents practical significance to industry by identifying the timing of peak needle retention. It is suggested that MGDG:DGDG might be a beneficial tool for screening balsam fir genotypes with higher needle retention characteristics.

Phenothiazines alter plasma membrane properties and sensitize cancer cells to injury by inhibiting annexin-mediated repair.

Repair of damaged plasma membrane in eukaryotic cells is largely dependent on the binding of annexin repair proteins to phospholipids. Changing the biophysical properties of the plasma membrane may provide means to compromise annexin-mediated repair and sensitize cells to injury. Since, cancer cells experience heightened membrane stress and are more dependent on efficient plasma membrane repair, inhibiting repair may provide approaches to sensitize cancer cells to plasma membrane damage and cell death. Here, we show that derivatives of phenothiazines, which have widespread use in the fields of psychiatry and allergy treatment, strongly sensitize cancer cells to mechanical-, chemical-, and heat-induced injury by inhibiting annexin-mediated plasma membrane repair. Using a combination of cell biology, biophysics, and computer simulations, we show that trifluoperazine acts by thinning the membrane bilayer, making it more fragile and prone to ruptures. Secondly, it decreases annexin binding by compromising the lateral diffusion of phosphatidylserine, inhibiting the ability of annexins to curve and shape membranes, which is essential for their function in plasma membrane repair. Our results reveal a novel avenue to target cancer cells by compromising plasma membrane repair in combination with noninvasive approaches that induce membrane injuries.

The combined effect of water deficit stress and TiO2 nanoparticles on cell membrane and antioxidant enzymes in Helianthus annuus L.

Nanotechnology has become one of the several approaches attempting to ameliorate the severe effect of drought on plant's production and to increase the plants tolerance against water deficit for the water economy. In this research, the effect of foliar application of TiO2, nanoparticles or ordinary TiO2, on Helianthus annuus subjected to different levels of water deficit was studied. Cell membrane injury increased by increasing the level of water deficit and TiO2 concentration, and both types of TiO2 affected the leaves in analogous manner. Ord-TiO2 increased H2O2 generation by 67-240% and lipid peroxidation by 4-67% in leaves. These increases were more than that induced by Nano-TiO2 and the effect was concentration dependent. Proline significantly increased in leaves by water deficit stress, reaching at 25% field capacity (FC) to more than fivefold compared to that in plants grown on full FC. Spraying plants with water significantly decreased the activities of enzymes in the water deficit stressed roots. The water deficit stress exerted the highest magnitude of effect on the changes of cell membrane injury, MDA, proline content, and activities of CAT and GPX. Nano-TiO2 was having the highest effect on contents of H2O2 and GPX activity. In roots, the level of water deficit causes highest effect on enzyme activities, but TiO2 influenced more on the changes of MDA and H2O2 contents. GPX activity increased by 283% in leaves of plants treated with 50 and 150 ppm Nano-TiO2, while increased by 170% in those treated with Ord-TiO2, but APX and CAT activities increased by 17-197%, in average, with Ord-TiO2. This study concluded that Nano-TiO2 didn't ameliorate the effects of drought stress on H. annuus but additively increased the stress, so its use in nano-phytotechnology mustn't be expanded without extensive studies. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01153-z.

Actin Cytoskeletal Dynamics in Single-Cell Wound Repair.

The plasma membrane protects the eukaryotic cell from its surroundings and is essential for cell viability; thus, it is crucial that membrane disruptions are repaired quickly to prevent immediate dyshomeostasis and cell death. Accordingly, cells have developed efficient repair mechanisms to rapidly reseal ruptures and reestablish membrane integrity. The cortical actin cytoskeleton plays an instrumental role in both plasma membrane resealing and restructuring in response to damage. Actin directly aids membrane repair or indirectly assists auxiliary repair mechanisms. Studies investigating single-cell wound repair have often focused on the recruitment and activation of specialized repair machinery, despite the undeniable need for rapid and dynamic cortical actin modulation; thus, the role of the cortical actin cytoskeleton during wound repair has received limited attention. This review aims to provide a comprehensive overview of membrane repair mechanisms directly or indirectly involving cortical actin cytoskeletal remodeling.

Loss of calpains-1 and -2 prevents repair of plasma membrane scrape injuries, but not small pores, and induces a severe muscular dystrophy.

The ubiquitous calpains, calpain-1 and -2, play important roles in Ca2+-dependent membrane repair. Mechanically active tissues like skeletal muscle are particularly reliant on mechanisms to repair and remodel membrane injury, such as those caused by eccentric damage. We demonstrate that calpain-1 and -2 are master effectors of Ca2+-dependent repair of mechanical plasma membrane scrape injuries, although they are dispensable for repair/removal of small wounds caused by pore-forming agents. Using CRISPR gene-edited human embryonic kidney 293 (HEK293) cell lines, we established that loss of both calpains-1 and -2 (CAPNS1-/-) virtually ablates Ca2+-dependent repair of mechanical scrape injuries but does not affect injury or recovery from perforation by streptolysin-O or saponin. In contrast, cells with targeted knockout of either calpain-1 (CAPN1-/-) or -2 (CAPN2-/-) show near-normal repair of mechanical injuries, inferring that both calpain-1 and calpain-2 are equally capable of conducting the cascade of proteolytic cleavage events to reseal a membrane injury, including that of the known membrane repair agent dysferlin. A severe muscular dystrophy in a murine model with skeletal muscle knockout of Capns1 highlights vital roles for calpain-1 and/or -2 for health and viability of skeletal muscles not compensated for by calpain-3 (CAPN3). We propose that the dystrophic phenotype relates to loss of maintenance of plasma membrane/cytoskeletal networks by calpains-1 and -2 in response to directed and dysfunctional Ca2+-signaling, pathways hyperstimulated in the context of membrane injury. With CAPN1 variants associated with spastic paraplegia, a severe dystrophy observed with muscle-specific loss of calpain-1 and -2 activity identifies CAPN2 and CAPNS1 as plausible candidate neuromuscular disease genes.

Exogenous application of spermine and putrescine mitigate adversities of drought stress in wheat by protecting membranes and chloroplast ultra-structure.

Polyamines (PAs) are positively charged molecules known to mitigate drought stress; however, little is known about their mechanism of alleviating drought stress. We investigated the effects of PAs exogenously applied as a seed primer and as a foliar spray on the growth, membrane stability (MS), electrolyte leakage (EL), Na+ and K+ cations, reactive oxygen species (ROS), catalase (CAT; EC 1.11.1.6) and guaiacol peroxidase (GPX; EC 1.11.1.7) activity and chloroplast ultra-structure in wheat (Triticum aestivum L.; cv. Sakha-94) under drought stress. Three PA solutions, namely, putrescine, spermine and a mixture of the two (Mix), were each applied at a concentration of 100 µM. Our study demonstrated that the retardation of chlorophyll loss and elevation of Rubisco levels were involved in PA-enhanced growth under drought stress. These relationships were mainly reflected in elevated fresh weight and dry weight in response to foliar spraying with all PA solutions and seed priming with the Mix solution. The elevated growth seemed to be due to increased photosynthetic pigments, protein and Rubisco. In contrast, drought decreased growth, photosynthetic pigments, protein and Rubisco. MS was enhanced by PAs applied as a seed primer or foliar spray, as shown by clear reductions in EL %, malondialdehyde (MDA) content and the Na+/K+ ratio as well as reduced ROS markers and elevated CAT (but not GPX) activity. Further study showed that the Mix solution of PAs, applied either during seed priming or as a foliar spray, improved chloroplast ultra-structure, suggesting that improvements in Rubisco and photosynthetic pigments were involved in PA maintenance of chloroplast stability. Therefore, the present study showed that elevated CAT activity is the main mechanism through which PAs reduce ROS and MDA, thereby improving MS and protecting mesophyll cells structurally and functionally under drought stress in wheat.

Temperature-dependency on the inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles.

Temperature-dependency on cell membrane injury and inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles (MBCO2) was investigated. The number of surviving S. pastorianus cells after MBCO2 treatment detected with yeast and mould agar (YMA, an optimum agar) was higher than that with YMA adding 2.5 g/L sodium chloride and yeast nitrogen base agar (a minimum agar). However, the decrease of the surviving number by thermal treatment was not changed among above agars used. The fluorescence polarization (FP), which indicated the phase transition of the membrane of S. pastorianus cells treated with MBCO2 increased with increasing temperature. The activity of the alkaline phosphatase (AP), a periplasmic enzyme, in S. pastorianus cells after MBCO2 and thermal treatments increased with the FP but was reduced by further increasing temperature. The FP and AP activities after MBCO2 treatment increased at a temperature lower than the temperature of the thermal treatment. In addition, intracellular pH of S. pastorianus decreased by the MBCO2 treatment at lower temperature with increasing pressure. Therefore, it was revealed that phase transition of the cell membrane and inactivation of S. pastorianus was caused by MBCO2 treatment at lower temperature than thermal treatment and that the effect was induced by the dissolved CO2 and increased with increasing pressure.

Alveolar epithelial cell integrity: A venerable target in the lung.

Eukaryotic cells have developed a litany of conserved mechanisms to deal with membrane injuries. The first line of defense consists of homeostatic regulation of membrane tension as a preventative measure against the occurrence of injury. When these measures fail, cells can engage in elaborate signaling mechanisms aimed at quickly restoring integrity. Based on the overall direction of membrane lipid trafficking, these repair mechanisms can be divided into three broad categories: exocytosis, endocytosis, and ectocytosis. For alveolar epithelial cells (AECs), repair of endogenous cell populations is especially important for the prevention of severe lung pathologies. We provide a focus on the pulmonary setting within this chapter while incorporating relevant findings from other cell types. We emphasize the signals and molecular moieties that have demonstrated critical involvement in the repair process within AECs and other cell types that constantly encounter threats to their membrane integrity.

Structural and signaling role of lipids in plasma membrane repair.

The plasma membrane forms the physical barrier between the cytoplasm and extracellular space, allowing for biochemical reactions necessary for life to occur. Plasma membrane damage needs to be rapidly repaired to avoid cell death. This relies upon the coordinated action of the machinery that polarizes the repair response to the site of injury, resulting in resealing of the damaged membrane and subsequent remodeling to return the injured plasma membrane to its pre-injury state. As lipids comprise the bulk of the plasma membrane, the acts of injury, resealing, and remodeling all directly impinge upon the plasma membrane lipids. In addition to their structural role in shaping the physical properties of the plasma membrane, lipids also play an important signaling role in maintaining plasma membrane integrity. While much attention has been paid to the involvement of proteins in the membrane repair pathway, the role of lipids in facilitating plasma membrane repair remains poorly studied. Here we will discuss the current knowledge of how lipids facilitate plasma membrane repair by regulating membrane structure and signaling to coordinate the repair response, and will briefly note how lipid involvement extends beyond plasma membrane repair to the tissue repair response.

Mechanosensitive ATP release in the lungs: New insights from real-time luminescence imaging studies.

Extracellular ATP and other nucleotides are important autocrine/paracrine mediators that stimulate purinergic receptors and regulate diverse processes in the normal lungs. They are also associated with pathogenesis of a number of respiratory diseases and clinical complications including acute respiratory distress syndrome and ventilator induced lung injury. Mechanical forces are major stimuli for cellular ATP release but precise mechanisms responsible for this release are still debated. The present review intends to provide the current state of knowledge of the mechanisms of ATP release in the lung. Putative pathways of the release, including the contribution of cell membrane injury and cell lysis are discussed addressing their strength, weaknesses and missing evidence that requires future study. We also provide an overview of the recent technical advances in studying cellular ATP release in vitro and ex vivo. Special attention is given to new insights into lung ATP release obtained with the real-time luminescence ATP imaging. This includes recent data on stretch-induced mechanosensitive ATP release in a model and primary cells of lung alveoli in vitro as well as inflation-induced ATP release in airspaces and pulmonary blood vessels of lungs, ex vivo.

Antifungal activity of zedoary turmeric oil against Phytophthora capsici through damaging cell membrane.

Phytophthora capsici is a plant oomycete pathogen, which causes many devastating diseases on a broad range of hosts. Zedoary turmeric oil (ZTO) is a kind of natural plant essential oil that has been widely used in pharmaceutical applications. However, the antifungal activity of ZTO against phytopathogens remains unknown. In this study, we found ZTO could inhibit P. capsici growth and development in vitro and in detached cucumber and Nicotiana benthamiana leaves. Besides, ZTO treatment resulted in severe damage to the cell membrane of P. capsici, leading to the leakage of intracellular contents. ZTO also induced a significant increase in relative conductivity, malondialdehyde concentration and glycerol content. Furthermore, we identified 50 volatile organic compounds from ZTO, and uncovered Curcumol, ß-elemene, curdione and curcumenol with strong inhibitory activities against mycelial growth of P. capsici. Overall, our results not only shed new light on the antifungal mechanism of ZTO, but also imply a promising alternative for the control of phytophthora blight caused by P. capsici.

Effects of axial forearm instability on force transmission across the elbow.

BACKGROUND: The interosseous membrane (IOM) and distal radioulnar joint (DRUJ) provide axial stability to the forearm. Our hypothesis was that injury to these structures alters force transmission through the elbow. METHODS: A custom-designed apparatus that applies axial loads from the wrist to the elbow was used to test 10 cadaveric upper limbs under the following simulated conditions (1) intact, (2) DRUJ injury, (3) IOM injury, or (4) IOM + DRUJ injury. IOM injury was simulated by osteotomies of the IOM attachment to the radius, and DRUJ injury was simulated by distal ulnar oblique osteotomy. We applied 160 N of axial force during cyclic and functional range of forearm rotation (40o pronation/40o supination), and force, contact pressure, and contact area through the elbow joint were measured simultaneously. RESULTS: The force across the radiocapitellar joint was significantly higher in the IOM + DRUJ injury and the IOM injury groups than in the intact and DRUJ injury groups. The mean force across the radiocapitellar joint was not significantly different between the intact and DRUJ injury groups or between the IOM + DRUJ injury and the IOM injury groups. Forces across the ulnohumeral joint showed an inverse pattern to those in the radiocapitellar joint. CONCLUSIONS: These findings suggest that injury to the IOM contributes more to the disruption of the normal distribution of axial loads across the elbow than injury to the DRUJ.

Chronic Essex-Lopresti injury: a systematic review of current treatment options.

INTRODUCTION: Essex-Lopresti lesion (ELL) is a severe injury. Most of ELL is recognized in chronic phase representing a therapeutic challenge for orthopaedic surgeons. The aim of this systematic review is to highlight and criticize current concepts in the surgical treatment. MATERIALS AND METHODS: The search was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guideline. A comprehensive research of Pubmed database was made using the following Mesh term: ((Essex-Lopresti injury) OR (Essex Lopresti) OR (distal radio ulnar dissociation) OR (distal radio ulnar dislocation) OR (longitudinal forearm instability)). Quality assessment of each article was performed according to Coleman score by two authors. RESULTS: Eight full articles were included to the systematic review. Surgical treatment was differentiated in five categories according to the most common procedure reported in clinical series. The mean Coleman Score was 51.13 ± 9.76. DISCUSSION: Case series reported in the literature include a limited number of patients with chronic ELL. Currently, salvage procedure devoted to treat a wrong diagnosis and an incorrect treatment is used. Radial head replacement together with ulnar shortening osteotomy and interosseous membrane reconstruction are the most common treatments of choice, but at present, there is not yet a shared scheme of management for patients with chronic ELL. CONCLUSIONS: According to current literature, a case-by-case treatment must always be considered. Further investigations, with higher level of evidence, quality of study design, and number of patients, are needed to better assess clinical results and complication of each technique. LEVEL OF EVIDENCE: IV.

iTRAQ-Based Protein Profiling and Biochemical Analysis of Two Contrasting Rice Genotypes Revealed Their Differential Responses to Salt Stress.

Salt stress is one of the key abiotic stresses causing huge productivity losses in rice. In addition, the differential sensitivity to salinity of different rice genotypes during different growth stages is a major issue in mitigating salt stress in rice. Further, information on quantitative proteomics in rice addressing such an issue is scarce. In the present study, an isobaric tags for relative and absolute quantitation (iTRAQ)-based comparative protein quantification was carried out to investigate the salinity-responsive proteins and related biochemical features of two contrasting rice genotypes-Nipponbare (NPBA, japonica) and Liangyoupeijiu (LYP9, indica), at the maximum tillering stage. The rice genotypes were exposed to four levels of salinity: 0 (control; CK), 1.5 (low salt stress; LS), 4.5 (moderate salt stress; MS), and 7.5 g of NaCl/kg dry soil (high salt stress, HS). The iTRAQ protein profiling under different salinity conditions identified a total of 5340 proteins with 1% FDR in both rice genotypes. In LYP9, comparisons of LS, MS, and HS compared with CK revealed the up-regulation of 28, 368, and 491 proteins, respectively. On the other hand, in NPBA, 239 and 337 proteins were differentially upregulated in LS and MS compared with CK, respectively. Functional characterization by KEGG and COG, along with the GO enrichment results, suggests that the differentially expressed proteins are mainly involved in regulation of salt stress responses, oxidation-reduction responses, photosynthesis, and carbohydrate metabolism. Biochemical analysis of the rice genotypes revealed that the Na⁺ and Cl- uptake from soil to the leaves via the roots was increased with increasing salt stress levels in both rice genotypes. Further, increasing the salinity levels resulted in increased cell membrane injury in both rice cultivars, however more severely in NPBA. Moreover, the rice root activity was found to be higher in LYP9 roots compared with NPBA under salt stress conditions, suggesting the positive role of rice root activity in mitigating salinity. Overall, the results from the study add further insights into the differential proteome dynamics in two contrasting rice genotypes with respect to salt tolerance, and imply the candidature of LYP9 to be a greater salt tolerant genotype over NPBA.

Profiling membrane glycerolipids during γ-ray-induced membrane injury.

BACKGROUND: γ-rays are high-energy radiation that cause a range of random injuries to plant cells. Most studies on this issue have focused on γ-ray-induced nucleotide damage and the production of reactive oxygen species in cells, so little is known about the glycerolipid metabolism during γ-rays induced membrane injury. Using an ESI-MS/MS-based lipidomic method, we analysed the lipidome changes in wild-type and phospholipase D (PLD)δ- and α1-deficient Arabidopsis after γ-ray treatment. The aim of this study was to investigate the role of PLD-mediated glycerolipid metabolism in γ-ray-induced membrane injury. RESULTS: The ion leakage of Arabidopsis leaves after 2885-Gy γ-ray treatment was less than 10%. High does γ-ray treatment could induce the accumulation of intracellular reactive oxygen species (ROS). Inhibition of PLDα1 caused severe lipid degradation under γ-ray treatment. γ-ray-induced glycerolipid degradation mostly happened in chloroplastidic lipids, rather than extraplastidic ones. The levels of lysophosphatidylcholine (lysoPC) and lysophosphatidylethanolamine (lysoPE) were maintained in the WS ecotypes during γ-ray treatments, while increased significantly in the Col ecotype treated with 1100 Gy. After 210- and 1100-Gy γ-ray treatments, the level of lysophosphatidylglycerol (lysoPG) decreased significantly in the four genotypes of Arabidopsis. CONCLUSIONS: γ-ray-induced membrane injury may occur via an indirect mechanism. The degradation of distinct lipids is not synchronous, and that interconversions among lipids can occur. During γ-ray-induced membrane injury, the degradation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) may be mediated by PLDζ1 or phospholipase A1. The degradation of phosphatidylglycerol was not mediated by PLA, PLDδ or PLDα1, but by phospholipase C or other PLDs. γ-rays can decrease the double-bond index and increase the acyl chain length in membrane lipids, which may make membranes more rigid and further cause injury in membranes.

Oleyl group-functionalized insulating gate transistors for measuring extracellular pH of floating cells.

The extracellular ionic microenvironment has a close relationship to biological activities such as by cellular respiration, cancer development, and immune response. A system composed of ion-sensitive field-effect transistors (ISFET), cells, and program-controlled fluidics has enabled the acquisition of real-time information about the integrity of the cell membrane via pH measurement. Here we aimed to extend this system toward floating cells such as T lymphocytes for investigating complement activation and pharmacokinetics through alternations in the plasma membrane integrity. We functionalized the surface of tantalum oxide gate insulator of ISFET with oleyl-tethered phosphonic acid for interacting with the plasma membranes of floating cells without affecting the cell signaling. The surface modification was characterized by X-ray photoelectron spectroscopy and water contact angle measurements. The Nernst response of -37.8 mV/pH was obtained for the surface-modified ISFET at 37 °C. The oleyl group-functionalized gate insulator successfully captured Jurkat T cells in a fluidic condition without acute cytotoxicity. The system was able to record the time course of pH changes at the cells/ISFET interface during the process of instant addition and withdrawal of ammonium chloride. Further, the plasma membrane injury of floating cells after exposure by detergent Triton™ X-100 was successfully determined using the modified ISFET with enhanced sensitivity as compared with conventional hemolysis assays.

Fish Oil Supplement Mitigates Muscle Injury In Vivo and In Vitro: A Preliminary Report.

Background: Following injury, older adults exhibit slow recovery of muscle function. Age-related impairment of sarcolemmal membrane repair may contribute to myocyte death, increasing the need for myogenesis and prolonging recovery. Dietary fish oil (FO) is a common nutritional supplement that may alter plasma membrane composition to enhance the response to membrane injury. Methods: We assessed effects of an 8-week dietary intervention on muscle contractile recovery in aged (22 mo.) rats on control (n = 5) or FO (control + 33 g/kg FO (45% eicosapentaenoic acid; 10% docosahexaenoic acid); n = 5) diets 1-week after contusion injury, as well as adult (8 mo., n = 8) rats on the control diet. Results: Recovery was reduced in aged rats on the control diet vs. adults (63 vs. 80%; p = 0.042), while those on the FO diet recovered similarly to (78%) adults. To directly assess sarcolemma injury, C2C12 cells were cultured in media with and without FO (1, 10, and 100 µg/mL; 24 or 48 h) and injured with an infrared laser in medium containing FM4-64 dye as a marker of sarcolemmal injury. FO reduced the area under the FM4-64 fluorescence-time curve at all concentrations after both 24 and 48 h supplementation. Conclusions: These preliminary data suggest FO might aid recovery of muscle function following injury in older adults by enhancing membrane resealing and repair.

Engineered nanomaterials exert sublethal bacterial stress at very low doses: Effects of concentration, light, and media on cell membrane permeability.

Engineered nanomaterials (ENMs) can alter surface properties of cells and disturb cellular functions and gene expression through direct and indirect contact, exerting unintended impacts on human and ecological health. However, the effects of interactions among environmental factors, such as light, surrounding media, and ENM mixtures, on the mechanisms of ENM toxicity, especially at sublethal concentrations, are much less explored and understood. Therefore, we evaluated cell viability and outer membrane permeability of E. coli as a function of exposure to environmentally relevant concentrations of ENMs, including metal (n-Ag) and metal oxide (n-TiO2, n-Al2O3, n-ZnO, n-CuO, and n-SiO2) nanoparticles under dark and simulated sunlight illumination in MOPS, a synthetic buffer, and Lake Michigan Water (LMW), a freshwater medium. We found that light activates the phototoxicity of n-TiO2 and n-Ag by inducing significant increases in bacterial outer membrane permeability at sublethal doses (< 1 mg/L). Other ENMs, including n-ZnO, n-CuO, n-Al2O3, and n-SiO2, have small to minimal impacts. Toxicities of ENMs were greater in LMW than MOPS due to their different ionic strength and chemical composition. Physical and chemical interactions between n-TiO2 and n-Ag lead to amplified toxic effects of the ENM mixtures that are greater than the additive effects of individual ENMs acting alone. Our results revealed the significant sublethal bacterial stress exerted by ENMs and ENM mixtures at the cell surface in natural environments at low doses, which can potentially lead to further cellular damage and eventually impact overall ecological health.

Does Potassium Modify the Response of Zinnia (Zinnia elegans Jacq.) to Long-Term Salinity?

Salinity is one of the major abiotic stress factors hindering crop production, including ornamental flowering plants. The present study examined the response to salt stress of Zinnia elegans 'Lilliput' supplemented with basic (150 mg·dm-3) and enhanced (300 mg·dm-3) potassium doses. Stress was imposed by adding 0.96 and 1.98 g of NaCl per dm-3 of the substrate. The substrate's electrical conductivity was 1.1 and 2.3 dS·m-1 for lower potassium levels and 1.2 and 2.4 dS·m-1 for higher potassium levels. Salt stress caused a significant and dose-dependent reduction in leaf RWC, increased foliar Na and Cl concentrations, and reduced K. About 15% and 25% of cell membrane injury at lower and higher NaCl doses, respectively, were accompanied by only slight chlorophyll reduction. Salt stress-induced proline increase was accompanied by increased P5CS activity and decreased PDH activity. More than a 25% reduction in most growth parameters at EC 1.1-1.2 dS·m-1 but only a slight decrease in chlorophyll and a 25% reduction in the decorative value (number of flowers produced, flower diameter) only at EC 2.3-2.4 dS·m-1 were found. Salt stress-induced leaf area reduction was accompanied by increased cell wall lignification. An enhanced potassium dose caused a reduction in leaf Na and Cl concentrations and a slight increase in K. It was also effective in membrane injury reduction and proline accumulation. Increasing the dose of potassium did not improve growth and flowering parameters but affected the lignification of the leaf cell walls, which may have resulted in growth retardation. Zinnia elegans 'Lilliput' may be considered sensitive to long-term salt stress.

Sensitivity of the Photosynthetic Apparatus in Maize and Sorghum under Different Drought Levels.

Drought is one of the main environmental stress factors affecting plant growth and yield. The impact of different PEG concentrations on the photosynthetic performance of maize (Zea mays L. Mayflower) and sorghum (Sorghum bicolor L. Foehn) was investigated. The activity of the photosynthetic apparatus was assessed using chlorophyll fluorescence (PAM and JIP test) and photooxidation of P700. The data revealed that water deficiency decreased the photochemical quenching (qP), the ratio of photochemical to nonphotochemical processes (Fv/Fo), the effective quantum yield of the photochemical energy conversion in PSII (ΦPSII), the rate of the electron transport (ETR), and the performance indexes PItotal and PIABS, as the impact was stronger in sorghum than in maize and depended on drought level. The PSI photochemistry (P700 photooxidation) in sorghum was inhibited after the application of all studied drought levels, while in maize, it was registered only after treatment with higher PEG concentrations (30% and 40%). Enhanced regulated energy losses (ΦNPQ) and activation of the state transition under drought were also observed in maize, while in sorghum, an increase mainly in nonregulated energy losses (ΦNO). A decrease in pigment content and relative water content and an increase in membrane damage were also registered after PEG treatment. The experimental results showed better drought tolerance of maize than sorghum. This study provides new information about the role of regulated energy losses and state transition for the protection of the photosynthetic apparatus under drought and might be a practical approach to the determination of the drought tolerance of plants.