Hydraulic mechanism of limiting growth and maintaining survival of desert shrubs in arid habitats.

The growth and survival of woody plant species is mainly driven by evolutionary and environmental factors. However, little is known about the hydraulic mechanisms that respond to growth limitation and enable desert shrub survival in arid habitats. To shed light on these hydraulic mechanisms, 9-, 31-, and 56-year-old Caragana korshinskii plants that had been grown under different soil water conditions at the southeast edge of the Tengger Desert, Ningxia, China were used in this study. The growth of C. korshinskii was mainly limited by soil water rather than shrub age in non-watered habitats, which indicated the importance of maintaining shrub survival prior to growth under drought. Meanwhile, higher vessel density, narrower vessels and lower xylem hydraulic conductivity indicated that shrubs enhanced hydraulic safety and reduced their hydraulic efficiency in arid conditions. Importantly, xylem hydraulic conductivity mediated by variation in xylem hydraulic architecture regulated photosynthetic carbon assimilation and growth of C. korshinskii. Our study highlights that the synergistic variation in xylem hydraulic safety and hydraulic efficiency is the hydraulic mechanism limiting growth and maintaining survival of C. korshinskii under drought, providing insights into the strategies for growth and survival of desert shrubs in arid habitats.

Hydraulic trade-off and coordination strategies mediated by leaf functional traits of desert shrubs.

Desert shrubs play important roles in desertification control and vegetation restoration, which are particularly affected by droughts caused by climate change. However, the hydraulic strategies associated with hydraulic functional traits of desert shrubs remain unclear. Here, eight desert shrub species with different life forms and morphologies were selected for a common garden experiment at the southeast edge of the Tengger Desert in northern China to study the hydraulic strategies mediated by leaf hydraulic functional traits. Diurnal leaf water potential change, leaf hydraulic efficiency and safety, hydraulic safety margin, hydraulic capacitance, and water potential and relative water content at the turgor loss point were observed to significantly differ among species, suggesting that leaf hydraulic functional traits were strongly associated with species even when living in the same environment. Additionally, shrubs with greater leaf hydraulic efficiency had lower midday leaf water potential and leaf hydraulic safety, suggesting that leaf hydraulic efficiency had a strong trade-off with hydraulic safety and minimum leaf water potential, whereas there was also a coordination between leaf hydraulic safety and the leaf minimal water potential. Moreover, shrubs with higher leaf hydraulic capacitance had greater hydraulic safety margins, indicating coordination between leaf hydraulic capacitance and hydraulic safety margin. Overall, this study indicated that minimal daily leaf water potential, as an easily measured parameter, may be used preliminarily to predict leaf hydraulic conductivity and the resistance to embolism of desert shrubs, providing critical insights into hydraulic trade-off and coordination strategies for native shrubs as priority species in desert vegetation restoration and reconstruction.

Multistep Fractionation of Coal and Application for Graphene Synthesis.

Despite its complex structure, coal has shown to be a promising precursor for graphene synthesis by chemical vapor deposition (CVD). However, the presence of heteroatoms and aliphatic chains in coal can lead to defects in the graphene lattice, preventing the formation of pristine graphene layers. Therefore, the goal of this study was to formulate a multistep coal fractionation scheme to extract and characterize the most aromatic fractions and explore their potential as graphene precursors. The scheme consisted of direct coal liquefaction under different conditions, Soxhlet extraction with heptane then toluene, and preparative liquid chromatography on silica gel using heptol solutions with different heptane/toluene ratios. The fractions obtained by this process were analyzed by proton nuclear magnetic resonance, thermogravimetric and elemental analyses, and automated SAR-AD (saturates, aromatics, resins-asphaltene determinator) separations. This characterization allowed the identification of two aromatic fractions with and without heteroatoms, which were subsequently used for graphene synthesis by CVD on nickel and copper foils. Raman spectrometry revealed that both fractions primarily formed defect-free multilayered graphene with approximately 11 layers on nickel due to the high solubility of carbon and the defect-healing effect of nickel. On the other hand, these fractions generated amorphous carbon on copper due to the high solubility of hydrogen in copper, which competed with carbon. Molecules in the more aromatic heteroatom-free fraction still contained alkyl pendant substituents and did not share the same planarity and symmetry to form defect-free graphene on copper. Thus, the quality of graphene was governed by the substrate on nickel and by the precursor quality on copper. When deposited directly on lacey carbon-coated copper grids of a transmission electron microscope, the heteroatom-free fraction gave rise to much larger graphene domains. The presence of heteroatoms promoted the formation of small self-assembled agglomerates of amorphous carbon.

More sensitive to drought of young tissues with weak water potential adjustment capacity in two desert shrubs.

Water is the main limiting factor for survival and growth for desert plants, and plants can alleviate water deficits under drought by adjusting water potential (Ψ). However, the water potential adjustment capacity and water-sensitivity at the tissue level among shrub species remains unclear. The objective of this study was to evaluate water potential adjustment capacity and water-sensitivity of different tissues in Artemisia ordosica and Caragana korshinskii through calculating the water relation parameters from pressure-volume (P-V) curves. The present study found that the sensitivity coefficients, -1/ß and -1/b, were gradually decreased with increasing degree of lignification in A. ordosica and C. korshinskii, suggesting that younger tissues with low lignification are more sensitive to water deficit. Additionally, the younger tissues with more negative osmotic potential at full turgor (Ψπ, sat), water potential at turgor loss point (Ψtlp), and lower the bulk modulus of elasticity (ε), the relative water deficit at turgor loss point (RWDtlp), apoplastic water fraction (AWF) and total hydraulic capacitance (Ctotal), which indicated that younger tissues have stronger turgor adjustment capacity compared to osmotic adjustment capacity and them were more easily lose water during times of decreased water potential because of higher cell wall elasticity and weaker water storage capacity. Collectively, the present study highlighted that younger tissues are more sensitive to drought due to their weaker water potential adjustment capacity and provided critical insight into water physiological mechanism or sensitivity of species to drought.

Hydrogen sulfide: Roles in plant abiotic stress response and crosstalk with other signals.

Hydrogen sulfide (H2S) has been recently recognized as an endogenous gas transmitter alongside nitric oxide and carbon monoxide. Exposure of plants to H2S, for example through applicating H2S donors, reveals that H2S play important roles in plant response to abiotic stresses such as heavy metals, salinity, drought and extreme temperatures. Sodium hydrosulfide is the most widely used donor in plants due to its direct and instantaneous release of H2S, followed by GYY4137. H2S can enhance plant tolerance to salt and heavy metal stresses through regulating Na+/K+ homeostasis and the uptake and transport of metal ions. H2S also promotes the H2S-Cys cycle balance under abiotic stress and enhances its roles in regulation of the antioxidant system, alternative respiratory pathway, and heavy metal chelators synthesis. H2S coordinates with gaseous signal molecules, reactive oxygen species and nitric oxide to respond to stress directly through influencing their generation or competing for the regulation of the downstream signaling. Moreover, H2S interacts with phytohormones including abscisic acid, ethylene, salicylic acid and melatonin as well as polyamines to regulate plant response to abiotic stresses. In this review, the application of H2S donors and their functional mechanism are summarized. We propose promising new research directions, which can lead to new insights on the role of this gastrasmitter during plant growth and development.

Three New Metal Complexes with Imidazole-Containing Tripodal Ligands as Fluorophores for Nitroaromatics- and Ion-Selective Sensing.

Three new metal-organic complexes [Cd(TIPA)(suc)0.5(NO3)·1/2H2O]n (1), [Ni(TIPA)(tda)0.5(H2O)·1/4H2O]n (2) and [Cd(TIPA)(tda)0.5·11/2H2O] (3) were synthesized via rigid tripodal ligand tris(4-(1H-imidazol-1-yl)phenyl)amine (TIPA) and three dicarboxylic acids; either succinic acid (H2suc) or 2,5-thiophenedicarboxylic acid (H2tda). Crystallographic data for 1 - 3 reveal three-dimensional (3D) networks and channels in the structures. The structure of 2 is unique featuring an interpenetrating 2D network, 2D + 2D → 3D, with the two associated 2D networks existing in two opposite spiral channels. TGA plots exhibit a loss of mass corresponding to the loss of the solvated water molecules in the 100 - 200 °C temperature region and begin to lose additional fragments only at T > 300 °C revealing the robust nature of the 3D framework in the complexes. The metal-organic frameworks (MOFs) are screened for their potential application in the detection and removal of environmentally hazardous industrial pollutants. Fluorescence emission spectra for 1 and 2 show that the two MOFs are capable of sensing nitrobenzene (NB), with the nickel complex 2 exhibiting significantly higher sensing ability. Powder XRD data measured for 1 and 2 and those of NB-treated 1 and 2 show significant differences in their patterns, providing further support for the strong interaction between the MOF complexes and NB. The fluorescence emission observed for 1 is more effectively quenched by the presence of Fe3+ than the series of 17 other metal ions investigated. Complex 3 possesses some ability to adsorb inorganic pollutants.

Hydrogen gas alleviates postharvest senescence of cut rose 'Movie star' by antagonizing ethylene.

KEY MESSAGE: H2 prolonged the vase life and improved the vase quality of cut roses through repressing endogenous ethylene production and alleviating ethylene signal transduction during the entire senescing period. Recently, the application of hydrogen gas (H2) was shown to improve postharvest quality and longevity in perishable horticultural products, but the specific regulation mechanism remains obscure. Here, endogenous ethylene production and the expression of genes in ethylene biosynthesis and signalling pathway were investigated to explore the crosstalk between H2 and ethylene during the senescence of cut roses. Our results revealed that addition of exogenous ethylene by ethephon accelerated the senescence of cut roses, in which 100 mg L-1 ethephon displayed the most obvious senescent phenotype. While the applied different concentrations (1%, 10%, 50% and 100%) of hydrogen-rich water (HRW) conducted different affects in alleviating the senescence of cut roses, and 1% HRW displayed the best ornamental quality and the longest vase life by reducing ethylene production, supported by the decrease of 1-aminocyclopropene-1-carboxylate (ACC) accumulation, ACC synthase (ACS) and ACC oxidase (ACO) activities, and Rh-ACS3 and Rh-ACO1 expressions in ethylene biosynthesis. In addition, HRW increased the transcripts of ethylene receptor genes Rh-ETR1 at blooming period from day 4 to day 6 and suppressed Rh-ETR3 at senescence phase at day 8 after harvest. Furthermore, the relevant affection of HRW on Rh-ETR1 and Rh-ETR3 expressions still existed when the ethylene production was compromised by adequate addition of exogenous ethylene in HRW-treated cut rose petals, and HRW directly repressed the protein level of Rh-ETR3 in a transient expression assay. Overall, the results suggested that H2 is involved in neutralizing ethylene-mediated postharvest in cut flowers.

Hydrogen gas formation from the photolysis of rhenium hydrides - mechanistic and computational studies.

The photolysis of 4,4'-disubstituted, 2,2'-bipyridine fac-Re(bpy)(CO)3H derivatives produces stoichiometric H2 gas. The rate of production varies greatly depending on the electronic nature of the disubstituted bipyridine (bpy) with halogenated substituents increasing the rate. Isotope labeling studies along with B3LYP geometry optimization DFT modeling studies indicate a mechanism involving a Re-H-Re bridging complex that leads to a dimeric Re-Re(η2-H2) state prior to dissociating H2 gas.

Protein S-nitrosylation in programmed cell death in plants.

Programmed cell death (PCD) is associated with different phases of plant life and provides resistance to different kinds of biotic or abiotic stress. The redox molecule nitric oxide (NO) is usually produced during the stress response and exerts dual effects on PCD regulation. S-nitrosylation, which NO attaches to the cysteine thiol of proteins, is a vital posttranslational modification and is considered as an essential way for NO to regulate cellular redox signaling. In recent years, a great number of proteins have been identified as targets of S-nitrosylation in plants, especially during PCD. S-nitrosylation can directly affect plant PCD positively or negatively, mainly by regulating the activity of cell death-related enzymes or reconstructing the conformation of several functional proteins. Here, we summarized S-nitrosylated proteins that are involved in PCD and provide insight into how S-nitrosylation can regulate plant PCD. In addition, both the importance and challenges of future works on S-nitrosylation in plant PCD are highlighted.

Hydrogen gas promotes the adventitious rooting in cucumber under cadmium stress.

Hydrogen gas (H2) plays an important role in plant development and stress responses. Here, cucumber (Cucumis sativus L.) explants were used to investigate the roles of H2 in adventitious root development under cadmium (Cd) stress and its physiological mechanism. The results showed that hydrogen-rich water (HRW) promoted adventitious rooting under Cd stress and 50% HRW obtained the maximal biological response. Compared with Cd treatment, HRW + Cd treatment significantly reduced the content of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide radical (O2-), thiobarbituric acid reactive substances (TBARS), ascorbic acid (AsA) and reduced glutathione (GSH), as well as relative electrical conductivity (REC), lipoxygenase (LOX) activity, AsA/docosahexaenoic acid (DHA) ratio, and GSH/oxidized glutathione (GSSG) ratio, while increasing DHA and GSSG content. HRW + Cd treatment also significantly increased in the activity and related gene expression of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). Additionally, HRW + Cd treatment increased the contents of osmotic adjustment substances, as well as the activities of peroxidase (POD) and polyphenol oxidase (PPO), while significantly decreasing indoleacetic acid oxidase (IAAO) activity. In summary, H2 could induce adventitious rooting under Cd stress by decreasing the oxidative damage, increasing osmotic adjustment substance content and regulating rooting-related enzyme activity.

Recent Progress in Protein S-Nitrosylation in Phytohormone Signaling.

The free radical nitric oxide (NO) is a critical regulator in modulation of wide range of growth and developmental processes as well as environmental responses in plants. In most cases, NO interacts with plant hormones to regulate these processes. It is clear that NO might work through either transcriptional or post-translational level. The redox-based post-translational modification S-nitrosylation has been recognized as a NO-dependent regulatory mechanism in recent years. In general, S-nitrosylation can be understood as a product of reversible reaction where NO moiety group covalently attaches to thiol of cysteine residue resulting in the formation of S-nitrosothiol in target proteins. Recently, the crosstalk between S-nitrosylation and phytohormones has been emerging. Furthermore, several proteins involved in plant hormone signaling have been reported to undergo S-nitrosylation, which might subsequently mediate plant growth and defense response. In this review, we focus on the recent processes in protein S-nitrosylation in phytohormone signaling. In addition, both importance and challenges of future work on protein S-nitrosylation in plant hormone network are also highlighted.

Mechanistic investigation of photocatalytic degradation of organic dyes by a novel zinc coordination polymer.

A new coordination polymer {[Zn(TIPA)(seb)0.5](NO3)·3.5H2O} n (1) (TIPA = tris(4-(1H-imidazol-1-yl)phenyl)amine, seb = sebacic acid) is prepared and characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD) and single crystal X-ray diffraction. Complex 1 has a three-dimensional (3D) 2-fold interpenetrating diamondoid network, and can be represented by the Schläfli symbol {33·43·54·64·7}. The luminescent, optical, and thermal properties of 1 in the solid state are investigated. Significantly, 1 assists in the photo-degradation of organic dyes in the presence of H2O2 and upon irradiation with UV light (λ = 254 nm). A mechanistic study toward understanding the photocatalytic degradation of organic dye molecules is carried out. The study reveals that the band gap of the fluorophore TIPA is lowered by the charge interaction between the Zn2+ cation and ligand seb2- dianion. The enhanced photocatalysis of 1 is also accompanied by the selective sensing of polar organic solvent nitromethane (NM) and antibiotic ofloxacin (OFX) by a luminescence quenching process. Concurrently, 1 demonstrates excellent ability to adsorb inorganic pollutant permanganate ions likely due to the presence of its unique 3D structural network.

Crystalline Covalent Organic Frameworks from Triazine Nodes as Porous Adsorbents for Dye Pollutants.

The development of covalent organic frameworks (COFs) with nodes and spacers, designed to maximize their functional properties, is a challenge. Triazines exhibit better electron affinity than benzene-based aromatic rings; therefore, structures based on 1,3,5-substituted triazine-centered nodes are more stable than those from 1,3,5-benzene-linked COFs. Compared to COFs prepared from flat, rigid sp2 carbon-linked triazine nodes, the O-linked flexible tripodal triazine-based COF demonstrates several unpredictable properties such as an increase in crystallinity and cavity size. In this study, the COF prepared from O-linked flexible 2,4,6-tris(p-formylphenoxy)-1,3,5-triazine serves as an excellent absorbent for removing methylene blue from water. Our results demonstrate that COF is highly stable in water and functions as a robust adsorbent. Its adsorption isotherm is consistent with the Langmuir model and its adsorption kinetics follows a pseudo-second order model. Moreover, the COF was characterized using elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, solid-state ultraviolet-visible spectroscopy, and X-ray diffraction. It exhibited permanent porosity, a high specific surface area (279.5 m2·g-1), and was chemically and thermally stable. Photophysical studies revealed that the COF exhibits a low bandgap energy value of 3.07 eV, indicating its semiconducting nature.

Comparative Proteomic Analysis during the Involvement of Nitric Oxide in Hydrogen Gas-Improved Postharvest Freshness in Cut Lilies.

Our previous studies suggested that both hydrogen gas (H2) and nitric oxide (NO) could enhance the postharvest freshness of cut flowers. However, the crosstalk of H2 and NO during that process is unknown. Here, cut lilies (Lilium "Manissa") were used to investigate the relationship between H2 and NO and to identify differentially accumulated proteins during postharvest freshness. The results revealed that 1% hydrogen-rich water (HRW) and 150 µM sodium nitroprusside (SNP) significantly extended the vase life and quality, while NO inhibitors suppressed the positive effects of HRW. Proteomics analysis found 50 differentially accumulated proteins in lilies leaves which were classified into seven functional categories. Among them, ATP synthase CF1 alpha subunit (chloroplast) (AtpA) was up-regulated by HRW and down-regulated by NO inhibitor. The expression level of LlatpA gene was consistent with the result of proteomics analysis. The positive effect of HRW and SNP on ATP synthase activity was inhibited by NO inhibitor. Meanwhile, the physiological-level analysis of chlorophyll fluorescence and photosynthetic parameters also agreed with the expression of AtpA regulated by HRW and SNP. Altogether, our results suggested that NO might be involved in H2-improved freshness of cut lilies, and AtpA protein may play important roles during that process.

Hydrogen Sulfide: A Gaseous Molecule in Postharvest Freshness.

Hydrogen sulfide (H2S), as a signaling molecule, is involved in the regulation of growth and development in plants. Recent studies have indicated that H2S also plays important roles in regulating postharvest senescence of horticultural products. The focus of this review is to summarize the synthesis of H2S in plants and its potential roles in alleviating the senescence of cut flowers, fruits, and vegetables during postharvest storage. During postharvest of horticultural products, H2S could scavenge reactive oxygen species via promoting the activity of antioxidant enzymes, thereby, sustaining the integrity of the membrane. In fruits, H2S effectively enhanced the tolerance of chilling by increasing the content of proline and polyphenol compounds. During postharvest storage of perishable fruits and vegetables, H2S significantly alleviated decay, which was caused by fungi by inhibiting the growth of fungi spores. Moreover, H2S interacted with other molecules synergistically (NO) or antagonistically (ethylene) to alleviate senescence of horticultural products. At the transcriptional level, H2S regulated the expression of senescence-related genes, which were related to degradation of proteins and chlorophyll, to delay the senescence of horticultural products. Thus, H2S does not only possess positive antioxidant and antifungal properties, but also significantly regulates the senescence-related gene during postharvest of horticultural products. Future studies of H2S in postharvest storage should focus on its molecular mechanism in the posttranslational modifications of proteins as well as its safety attributes in treated fruits and vegetables.

Involvement of Calcium and Calmodulin in Nitric Oxide-Regulated Senescence of Cut Lily Flowers.

Both nitric oxide (NO) and calcium ion (Ca2+)/calmodulin (CaM) have been shown to regulate the senescence of cut flowers. However, not much is known about the crosstalk between NO and Ca2+/CaM during the senescence of cut flowers. In this study, cut Oriental × Trumpet hybrid lily "Manissa" were used to investigate the roles and relationship between NO and Ca2+/CaM during postharvest freshness. The results show that the effects of CaCl2 or NO donor SNAP on the vase life, maximum flower diameter and hours until full opening were dose-dependent, with an optimum concentration of 20 mM CaCl2 or 100 µM SNAP. However, Ca2+ chelators EGTA or BAPTA/AM, Ca2+ channel inhibitors LaCl3 or nifedipine and CaM antagonists W-7 or TFP inhibited the promotion of SNAP. SNAP applied alone significantly increased the endogenous Ca2+/CaM contents in cut lily flowers, while EGTA, BAPTA/AM, LaCl3, nifedipine, W-7, and TFP decreased the advancement of SNAP. In addition, the SNAP-induced Ca2+-ATPase activity was more than twice as much as the control, but EGTA, BAPTA/AM, LaCl3, nifedipine, W-7, and TFP also reversed the enhancement. Moreover, EGTA, BAPTA/AM, LaCl3, nifedipine, W-7, and TFP prevented the SNAP-induced upregulation of gene expression of CaM, CBL1, and CBL3, which is associated with calcium signaling pathway. Overall, these results suggest that Ca2+/CaM may function as downstream molecules in NO-regulated senescence of cut flowers.

Electrochemical determination of nitrite and iodate based on Pt nanoparticles self-assembled on a chitosan modified glassy carbon electrode.

A promising electrochemical sensor was fabricated by the self-assembling of Pt nanoparticles (nano-Pts) on a chitosan (CS) modified glassy carbon electrode (GCE). A field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and electrochemical techniques were used for characterization of these composites. It has been found that nano-Pts are inserted into the CS layer uniformly, and have a larger surface area compared to the chitosan modified glassy carbon electrode. Electrocatalytic experiments for the oxidation of nitrite and the reduction of iodate have shown that nano-Pts/CS/GCE can decrease the over-potential and increase the faradic current, which can be used for the sensitive determination of nitrite and iodate. Moreover, the prepared modified electrode exhibits good reproducibility and stability, and it is possible that this novel electrochemical sensor can be applied in the sensing and/or biosensing field.

Facile synthesis and platinum complexes of 4',5,5''-trisubstituted-2,2':6',2''-terpyridines.

The synthesis of trisubstituted 4',5,5'' terpyridines is described. The strategy begins with synthesis of 2-acetyl-5-bromopyridine (3) from 2,5-dibromopyridine, substitution of the bromine in 3 using a variety of metal-catalyzed reactions and then formation of the terpyridine using the Krohnke reaction. The complexes have been prepared by reaction of [Pt(PhCN)(2)Cl(2)] with the appropriate silver salt followed by addition of the terpyridyl ligand. The crystal structure of two complexes have been determined via X-ray diffraction and the MLCT (metal-to-ligand charge-transfer) emissions determined by UV/Vis spectroscopy.