On the path from xylem hydraulic failure to downstream cell death.

Xylem hydraulic failure (HF) has been identified as a ubiquitous factor in triggering drought-induced tree mortality through the damage induced by the progressive dehydration of plant living cells. However, fundamental evidence of the mechanistic link connecting xylem HF to cell death has not been identified yet. The main aim of this study was to evaluate, at the leaf level, the relationship between loss of hydraulic function due to cavitation and cell death under drought conditions and discern how this relationship varied across species with contrasting resistances to cavitation. Drought was induced by withholding water from potted seedlings, and their leaves were sampled to measure their relative water content (RWC) and cell mortality. Vulnerability curves to cavitation at the leaf level were constructed for each species. An increment in cavitation events occurrence precedes the onset of cell mortality. A variation in cells tolerance to dehydration was observed along with the resistance to cavitation. Overall, our results indicate that the onset of cellular mortality occurs at lower RWC than the one for cavitation indicating the role of cavitation in triggering cellular death. They also evidenced a critical RWC for cellular death varying across species with different cavitation resistance.

A model for extracellular freezing based on observations on Equisetum hyemale.

In frost hardy plants, the lethal intracellular formation of ice crystals has to be prevented during frost periods. Besides the ability for supercooling and pre-frost dehydration of tissues, extracellular ice formation is another strategy to control ice development in tissues. During extracellular ice formation, partially large ice bodies accumulate in intercellular spaces, often at preferred sites which can also be expandable. In this contribution, the physico-chemical processes underlying the water movements towards the sites of extracellular ice formation are studied theoretically, based on observations on the frost hardy horsetail species Equisetum hyemale, with the overall aim to obtain a better understanding of the physical processes involved in extracellular ice formation. In E. hyemale, ice accumulates in the extensive internal canal system. The study focuses on the processes which are triggered in the cellular osmotic-mechanic system by falling, and especially subzero temperatures. It can be shown that when the temperature falls, (1) water flow out of cells is actuated and (2) "stiff-walled" cells lose less water than "soft-walled" cells. Furthermore, (3) cell water loss increases with increasing (= less negative) turgor loss point. These processes are not related to any specific activities of the cell but are solely a consequence of the structure of the cellular osmotic system. On this basis, a directed water flow can be initiated triggered by subzero temperatures. The suggested mechanism may be quite common in frost hardy species with extracellular ice formation.

Total Serum Magnesium Levels and Calcium-To-Magnesium Ratio in Sickle Cell Disease.

Background and objectives: Imbalance of calcium/magnesium ratio could lead to clinical complications in sickle cell disease (SCD). Low levels of magnesium have been associated with sickling, increased polymerization and vaso-occlusion (VOC) in sickle cell due to cell dehydration. The K-Cl cotransport plays a very important role in sickle cell dehydration and is inhibited by significantly increasing levels of magnesium. The study evaluated total serum magnesium levels and computed calcium/magnesium ratio in SCD patients and "healthy" controls. Materials and methods: The study was a case-control cross-sectional one, involving 120 SCD patients (79 Haemoglobin SS (HbSS)and 41 Haemoglobin SC (HbSC)) at the steady state and 48 "healthy" controls. Sera were prepared from whole blood samples (n = 168) and total magnesium and calcium measured using a Flame Atomic Absorption Spectrometer (Variant 240FS manufactured by VARIAN Australia Pty Ltd., Melbourne, VIC, Australia). Calcium/magnesium ratios were calculated in patients and the controls. Results: The prevalence of hypomagnesemia and hypocalcaemia among the SCD patients was observed to be 39.17% and 52.50% respectively, higher than the controls (4.17% and 22.92%, for hypomagnesemia and hypocalcaemia, respectively). Level of magnesium was significantly lower in the SCD patients compared to their healthy counterparts (p = 0.002). The magnesium level was further reduced in the HbSS patients but not significantly different from the HbSC patients (p = 0.584). calcium/magnesium ratio was significantly higher in the SCD patients (p = 0.031). Although calcium/magnesium ratio was higher in the HbSC patients compared to those with the HbSS genotype, the difference was not significant (p = 0.101). Conclusion: The study shows that magnesium homeostasis are altered in SCD patients, and their levels are lower in HbSS patients. Although calcium/magnesium ratio is significantly higher in SCD patients compared with controls, there is no significant difference between patients with HbSS and HbSC genotypes. Magnesium supplementation may be required in sickle cell patients.

Potassium dynamics in sickle cell anemia: clinical implications and pathophysiological insights.

Potassium dynamics are critical in the pathophysiology of sickle cell anemia (SCA), a genetic disorder characterized by the presence of abnormally shaped red blood cells that lead to various complications such as vaso-occlusive crises and hemolytic anemia. This review focuses on the clinical implications and pathophysiological insights of potassium regulation in SCA, highlighting its impact on disease progression and potential therapeutic strategies. The dysregulation of potassium transport in SCA leads to significant K+ efflux and cellular dehydration, exacerbating the sickling process. Dehydrated sickle cells, due to potassium loss, become more rigid and prone to causing blockages in small blood vessels, leading to painful vaso-occlusive crises and ischemia. Furthermore, chronic hemolysis in SCA, aggravated by potassium imbalance, contributes to severe anemia and systemic complications. These insights underscore the importance of maintaining potassium homeostasis to mitigate disease severity and improve patient outcomes. Therapeutic strategies targeting potassium regulation show promise in managing SCA. Inhibitors of the Gardos channel, such as senicapoc, have demonstrated potential in reducing sickling and hemolysis. Additionally, hydration therapy plays a crucial role in maintaining electrolyte balance and preventing RBC dehydration. A comprehensive approach that includes monitoring and correcting electrolyte imbalances, along with standard treatments like hydroxyurea and blood transfusions, is essential for effective disease management.

Cell dehydration enables massive production of engineered membrane vesicles with therapeutic functions.

Extracellular vesicles (EVs) have emerged as promising biomaterials for the treatment of different disease. However, only handful types of EVs with clinical transformation potential have been reported to date, and their preparation on a large scale under biosafety-controlled conditions is limited. In this study, we characterize a novel type of EV with promising clinical application potential: dehydration-induced extracellular vesicles (DIMVs). DIMV is a type of micron-diameter cell vesicle that contains more bioactive molecules, such as proteins and RNA, but not DNA, than previously reported cell vesicles. The preparation of DIMV is extraordinarily straightforward, which possesses a high level of biosafety, and the protein utilization ratio is roughly 600 times greater than that of naturally secreted EVs. Additional experiments demonstrate the viability of pre- or post-isolation DIMV modification, including gene editing, nucleic acid encapsulation or surface anchoring, size adjustment. Finally, on animal models, we directly show the biosafety and immunogenicity of DIMV, and investigate its potential application as tumour vaccine or drug carrier in cancer treatment.

Coping with the cold: unveiling cryoprotectants, molecular signaling pathways, and strategies for cold stress resilience.

Low temperature stress significantly threatens crop productivity and economic sustainability. Plants counter this by deploying advanced molecular mechanisms to perceive and respond to cold stress. Transmembrane proteins initiate these responses, triggering a series of events involving secondary messengers such as calcium ions (Ca2+), reactive oxygen species (ROS), and inositol phosphates. Of these, calcium signaling is paramount, activating downstream phosphorylation cascades and the transcription of cold-responsive genes, including cold-regulated (COR) genes. This review focuses on how plants manage freeze-induced damage through dual strategies: cold tolerance and cold avoidance. Tolerance mechanisms involve acclimatization to decreasing temperatures, fostering gradual accumulation of cold resistance. In contrast, avoidance mechanisms rely on cryoprotectant molecules like potassium ions (K+), proline, glycerol, and antifreeze proteins (AFPs). Cryoprotectants modulate intracellular solute concentration, lower the freezing point, inhibit ice formation, and preserve plasma membrane fluidity. Additionally, these molecules demonstrate antioxidant activity, scavenging ROS, preventing protein denaturation, and subsequently mitigating cellular damage. By forming extensive hydrogen bonds with water molecules, cryoprotectants also limit intercellular water movement, minimizing extracellular ice crystal formation, and cell dehydration. The deployment of cryoprotectants is a key adaptive strategy that bolsters plant resilience to cold stress and promotes survival in freezing environments. However, the specific physiological and molecular mechanisms underlying these protective effects remain insufficiently understood. Therefore, this review underscores the need for further research to elucidate these mechanisms and assess their potential impact on crop productivity and sustainability, contributing to the progressive discourse in plant biology and environmental science.

Structural aspects of cypsela and seed development of Trichocline catharinensis (Cabrera): a Brazilian endemic species.

This is the first study to describe in a timescale morphohistological and ultrastructural characteristics of fruit (cypsela) and seed development in Trichocline catharinensis, which was completed 21 days after anthesis (DAA). At anthesis, we identified an ovary with three differentiated regions, including the inner epidermis, inner part, and outer epidermis. The mature ovule showed an integument with the outer epidermis, integumentary parenchyma, and endothelium. Cells around the endothelium form the periendothelial zone with thick cell walls that showed Periodic acid-Schiff (PAS)-positive reaction. The periendothelial zone and endothelium showed degradation of the cells during embryogenesis. The main stages of embryo development from fecundation through mature seed were identified. The ripe cypsela showed the pericarp (exocarp), seed coat (exotesta), and remaining endosperm surrounding the embryo. Mature embryos were straight with shoot apical meristem (SAM), and root apical meristem (RAM) was separated by the hypocotyl. Light microscopy (LM) and transmission electron microscopy (TEM) analyses indicate cells with characteristics of meristem cells, as well as proteins and lipid bodies and mitochondria with few cristae in cotyledon cells. Our findings provide insight into taxonomic and physiological studies by detailing cypsela and seed ontogenesis from an endemic and vulnerable Asteraceae from southern Brazil. This study is also a starting point for establishing the biological criteria for seed harvesting and future studies of seed physiology and conservation of plant genetic resource.

Enhanced cell dehydration tolerance and photosystem stability facilitate the occupation of cold alpine habitats by a homoploid hybrid species, Picea purpurea.

Homoploid hybrid speciation (HHS), characterized by hybrid speciation without a change in chromosome number and facilitated by ecological divergence, is well known in angiosperms but rare in gymnosperms. Picea purpurea as one of two demonstrably conifer diploid hybrid species in gymnosperms has been found to occupy colder alpine habitats than its parents. However, studies on whether leaf frost tolerance and hydraulic safety exhibit transgressive segregation and thus play a role in conifer HHS are still lacking. In this study, we compared the frost tolerance of photosystem stability (the maximum efficiency of PSII, F v/F m), pressure-volume parameters, and xylem resistance to dysfunction of leaves (current-year twigs) and stems (annual shoots) between P. purpurea and its progenitors. The results indicated that P. purpurea had significantly lower osmotic potential at full turgor, water potential at turgor loss point, water potential at 12 % loss of conductance of stem, the maximum hydraulic conductance of stem and the temperature causing a 50 % reduction in initial F v/F m than its parental species. In contrast, the leaf and stem xylem pressure inducing 50 % loss of hydraulic conductivity (leaf Ψ50 and stem Ψ50, respectively) and hydraulic safety margin in leaf Ψ50, stem Ψ50 in P. purpurea showed no significant difference with those of P. wilsonii, but significantly larger than those of P. likiangensis. This suggests that the frost tolerance of photosystem stability and the cell dehydration tolerance in P. purpurea are superior to its parental species, facilitating its successful colonization and establishment in colder habitats.

Enhanced killing of HepG2 during cryosurgery with Fe3O4-nanoparticle improved intracellular ice formation and cell dehydration.

Cryosurgery is a minimally invasive treatment that utilize extreme low temperatures to destroy abnormal tissues. The clinical monitoring methods for cryosurgery are almost based on the visualization of the iceball. However, for a normal cryosurgery process, the effective killing region is always smaller than the iceball. As a result, the end of the cryosurgery process can only be judged by the surgeons according to their experience. The subjective judgement is one of the main reasons for poor estimation of tumor ablation, and it sparks high probability of recurrence and metastasis associate with cryosurgery. Being different from the previous optimization studies, we develop a novel approach with the aid of nanoparticles to enlarge the effective killing region of entire iceball, and thus it greatly decrease the difficulty of precise judgement of the cryosurgery only by applying the common clinical imaging methods. To verify this approach, both the experiments on a tissue-scale phantom with embedded living HepG2 cells in agarose and on a cell-scale cryo-microscopic freeze-thaw stage are performed. The results indicate that the introduction of the self-synthesized Fe3O4 nanoparticles significantly improved cell killing in the cryosurgery and the range of killing is extended to the entire iceball. The potential mechanism is further revealed by the cryo-microscopic experiments, which verifies the presence of Fe3O4 nanoparticles can significantly enhance the probability of intracellular ice formation and the cell dehydration during freezing hence it promote precise killing of the cells. These findings may further promote the widespread clinical application of modern cryosurgery.