A high-temperature water vapor equilibration method to determine non-exchangeable hydrogen isotope ratios of sugar,starch and cellulose

The analysis of the non-exchangeable hydrogen isotope ratio (δ²H_ne) in carbohydrates is mostly limited to the structural component cellulose, while simple high-throughput methods for δ²H_ne values of non-structural carbohydrates (NSC) such as sugar and starch do not yet exist. Here, we tested if the hot vapor equilibration method originally developed for cellulose is applicable for NSC, verified by comparison with the traditional nitration method. We set up a detailed analytical protocol and applied the method to plant extracts of leaves from species with different photosynthetic pathways (i.e., C₃, C₄ and CAM). δ²H_ne of commercial sugars and starch from different classes and sources, ranging from ?157.8 to +6.4‰, were reproducibly analysed with precision between 0.2‰ and 7.7‰. Mean δ²H_ne values of sugar are lowest in C₃ (?92.0‰), intermediate in C₄ (?32.5‰) and highest in CAM plants (6.0‰), with NSC being ²H-depleted compared to cellulose and sugar being generally more ²H-enriched than starch. Our results suggest that our method can be used in future studies to disentangle ²H-fractionation processes, for improving mechanistic δ²H_ne models for leaf and tree-ring cellulose and for further development of δ²H_ne in plant carbohydrates as a potential proxy for climate, hydrology, plant metabolism and physiology.     

Patterns in nonstructural carbohydrate contents at the tree organ level in response to drought duration

Nonstructural carbohydrates (NSCs) facilitate the adaptation of trees to drought stress. There have been a large number of studies exploring NSC changes in individual plant species and individual organ under drought and showed different trends; however, an understanding of the universal pattern of the plant NSCs responses to drought, particularly to drought duration, is still lacking. Here, we compiled data from 47 experimental studies on 52 tree species and conducted a meta‐analysis to evaluate the responses of soluble sugars, starch, and TNSC (total nonstructural carbohydrates including both soluble sugars and starch) concentrations in different tree organs (leaf, stem, and root) to drought intensity and duration. We found that starch in all organs decreased and soluble sugars in leaf increased with prolonged experiment time, and the changes in soluble sugars in all organs were stronger under severe drought than under slight‐to‐moderate drought. Under slight‐to‐moderate drought, the NSC content of each organ varied with time, while with the extension of the drought duration, the NSCs gradually approached the control value (no drought stress); this trend remained in the late drought, which means that trees activated physiological regulation processes to increase carbon storage and reduce the risks of carbon starvation. In contrast, long‐term severe drought could lead to a net loss of carbohydrates, especially in the root, implying that prolonged severe drought could lead to NSC depletion in the whole plant. As prolonged drought duration has occurred in and is projected for many regions, this paper could shed light into studies on how trees respond and adapt extending drought duration through nonstructural carbon production, transportation, and reallocation.     

Balancing the risks of hydraulic failure and carbon starvation: a twig scale analysis in declining Scots pine

Understanding physiological processes involved in drought‐induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought‐exposed trees. However, little is known about the specific responses of leaves and supporting twigs, despite their critical role in balancing carbon acquisition and water loss. Comparing healthy (non‐defoliated) and unhealthy (defoliated) Scots pine at the same site, we measured the physiological variables involved in regulating carbon and water resources. Defoliated trees showed different responses to summer drought compared with non‐defoliated trees. Defoliated trees maintained gas exchange while non‐defoliated trees reduced photosynthesis and transpiration during the drought period. At the branch scale, very few differences were observed in non‐structural carbohydrate concentrations between health classes. However, defoliated trees tended to have lower water potentials and smaller hydraulic safety margins. While non‐defoliated trees showed a typical response to drought for an isohydric species, the physiology appears to be driven in defoliated trees by the need to maintain carbon resources in twigs. These responses put defoliated trees at higher risk of branch hydraulic failure and help explain the interaction between carbon starvation and hydraulic failure in dying trees.     

Computer aided identification of sodium channel blockers in the clinical treatment of epilepsy using molecular docking tools

AbbreviationsAEDs - Antiepileptic drugs, BLAST - Basic Local Alignment Search Tool, CBZ - Carbamazepine, GEFS+ - Generalized Epilepsy with Febrile Seizures Plus, GPCR - G Protein Coupled Receptor, Nav - Sodium channel with specific voltage conduction, PDB - Protein Data Bank, PHT - Phenytoin, PIR - Protein Information resources, SAVES - Structural Analysis and Verification Server, VGSC - Voltage-gated Sodium channels.     

Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L

Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.     

High temperature limits in vivo pollen tube growth rates by altering diurnal carbohydrate balance in field-grown Gossypium hirsutum pistils

It has recently been reported that high temperature slows in vivo pollen tube growth rates in Gossypium hirsutum pistils under field conditions. Although numerous physical and biochemical pollen-pistil interactions are necessary for in vivo pollen tube growth to occur, studies investigating the influence of heat-induced changes in pistil biochemistry on in vivo pollen tube growth rates are lacking. We hypothesized that high temperature would alter diurnal pistil biochemistry and that pollen tube growth rates would be dependent upon the soluble carbohydrate content of the pistil during pollen tube growth. G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures but at the same developmental stage. Diurnal pistil measurements included carbohydrate balance, glutathione reductase (GR; EC 1.8.1.7), soluble protein, superoxide dismutase (SOD; EC 1.15.1.1), NADPH oxidase (NOX; EC 1.6.3.1), adenosine triphosphate (ATP), and water-soluble calcium. Soluble carbohydrate levels in cotton pistils were as much as 67.5% lower under high temperature conditions (34.6 °C maximum air temperature; August 4, 2009) than under cooler conditions (29.9 °C maximum air temperature; August 14, 2009). Regression analysis revealed that pollen tube growth rates were highly correlated with the soluble carbohydrate content of the pistil during pollen tube growth (r² = 0.932). Higher ambient temperature conditions on August 4 increased GR activity in the pistil only during periods not associated with in vivo pollen tube growth; pistil protein content declined earlier in the day under high temperatures; SOD and NOX were unaffected by either sample date or time of day; pistil ATP and water soluble calcium were unaffected by the warmer temperatures. We conclude that moderate heat stress significantly alters diurnal carbohydrate balance in the pistil and suggest that pollen tube growth rate through the style may be limited by soluble carbohydrate supply in the pistil.     

Stem cell factor and granulocyte colony-stimulating factor promote neuronal lineage commitment of neural stem cells

Stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) were originally discovered as growth factors for hematopoietic stem cells (HSCs). It has been well defined that SCF and G-CSF contribute to regulation of lineage commitment for HSCs. However, little is known about whether SCF and G-CSF play roles in the determination and differentiation of neural stem cells (NSCs). Here we demonstrate the novel function of SCF and G-CSF in controlling cell cycle and cell fate determination of NSCs. We also observe that SCF and G-CSF promote neuronal differentiation and inhibit astroglial differentiation at the early stage of differentiation. In addition, our research data reveal that SCF in combination with G-CSF has a dual function in promoting cell cycle exit and directing neuronal fate commitment at the stage of NSC dividing. This coordination effect of SCF+G-CSF on cell cycle arrest and neuronal differentiation is through enhancing neurogenin 1 (Ngn1) activity. These findings extend current knowledge regarding the role of SCF and G-CSF in the regulation of neurogenesis and provide insights into the contribution of hematopoietic growth factors to brain development and remodeling.     

Positive effects of night warming on physiology of coniferous trees in late growing season: Leaf and root

Previous studies about the effects of experimental warming on tree species have focused primarily on response of morphology and physiology in leaf and biomass allocation in the growing season, and a few studies considered the importance of roots. Based on the available evidence, it is unclear whether photosynthesis rate is enhanced by night warming in late autumn an issue that deserves further investigation. Thus, we exposed two coniferous species, Picea asperata and Abies faxoniana, to night warming continued throughout the year to investigate morphological and physiological responses of roots and leaves in the autumn. The results showed that night warming caused significant increases in net influxes of NH₄⁺ and NO₃⁻ in P. asperata seedlings corresponding well with net H⁺ efflux and net influx of O₂. Meanwhile, night warming had a positive effect on foliar gas exchange such as net photosynthesis rate, apparent quantum efficiency, dark respiration rate and maximum quantum efficiency of PS II, and nitrate reductase activity of roots. Additionally, root morphology such as total roots length, surface area, specific root area and specific root length was also stimulated by night warming. In contrast, night warming decreased concentrations of non-structural carbohydrate in leaves and roots of both species in autumn. The present study demonstrates that night warming would enhance late autumn leaf photosynthetic rate, and increase N uptake capacity of roots.     

Depletion of tyrosyl DNA phosphodiesterase 2 activity enhances etoposide-mediated double-strand break formation and cell killing

DNA topoisomerase 2 (Top2) poisons, including common anticancer drugs etoposide and doxorubicin kill cancer cells by stabilizing covalent Top2-tyrosyl-DNA 5′-phosphodiester adducts and DNA double-strand breaks (DSBs). Proteolytic degradation of the covalently attached Top2 leaves a 5′-tyrosylated blocked termini which is removed by tyrosyl DNA phosphodiesterase 2 (TDP2), prior to DSB repair through non-homologous end joining (NHEJ). Thus, TDP2 confers resistance of tumor cells to Top2-poisons by repairing such covalent DNA-protein adducts, and its pharmacological inhibition could enhance the efficacy of Top2-poisons. We discovered NSC111041, a selective inhibitor of TDP2, by optimizing a high throughput screening (HTS) assay for TDP2’s 5′-tyrosyl phosphodiesterase activity and subsequent validation studies. We found that NSC111041 inhibits TDP2’s binding to DNA without getting intercalated into DNA and enhanced etoposide’s cytotoxicity synergistically in TDP2-expressing cells but not in TDP2 depleted cells. Furthermore, NSC111041 enhanced formation of etoposide-induced γ-H2AX foci presumably by affecting DSB repair. Immuno-histochemical analysis showed higher TDP2 expression in a sub-set of different type of tumor tissues. These findings underscore the feasibility of clinical use of suitable TDP2 inhibitors in adjuvant therapy with Top2-poisons for a sub-set of cancer patients with high TDP2 expression.     

亚高山草甸植物群落对气候变化的响应

为了研究气温升高、氮素增加和人为干扰对亚高山草甸植物生长和非结构性碳水化合物(NSC)的影响,该研究采用开顶式生长箱(OTC)模拟增温,同时进行施加氮肥和除草处理,对青藏高原东南缘邛崃山脉东坡巴郎山(四川盆地向青藏高原的过渡地带)的亚高山草甸植物的生长和NSC含量进行测定分析。结果显示:(1)各处理土壤全磷(P)和全钾(K)含量与对照均无显著差异,增温加施肥处理的土壤全氮(N)含量与对照无显著差异,但增温处理、施肥处理、除草处理、增温加除草处理、施肥加除草处理和增温加施肥加除草处理的土壤全氮含量较对照均显著降低。(2)增温促进禾本科和杂类草功能群生长,抑制莎草科功能群生长,提高禾本科功能群重要值,降低杂类草功能群重要值,且对莎草科功能群重要值的作用受施氮和除草的影响;施肥促进禾本科和杂类草功能群的高生长,并且促进莎草科功能群生长;除草促进莎草科功能群生长,抑制禾草科和杂类草功能群的生长;而施肥和除草的交互作用有利于禾草科功能群生长,施肥和除草都提高了莎草科功能群的重要值,降低了禾草科功能群的重要值。(3)不同物种NSC含量及分配对于各处理的响应有所不同,紫地榆的NSC含量与物种分盖度相关性显著,珠芽蓼的NSC含量与物种高度相关性显著。研究表明,气候变暖和土壤氮素增加有利于禾本科和莎草科植物的生长,并使植物改变体内非结构性碳水化合物的分配来抵御环境压力。