Programmed cell death of secretory cavity cells of citrus fruits is associated with Ca2+ accumulation in the nucleus

Key message

An increase in Ca ²⁺ concentration in the nucleus may activate the PCD of secretory cavity cells, and further Ca ²⁺ accumulation contributes to the regulation of nuclear DNA degradation.

Abstract

Calcium plays an important role in plant programmed cell death (PCD). Previously, we confirmed that PCD was involved in the degradation of secretory cavity cells in Citrus sinensis (L.) Osbeck fruits. To further explore the function of calcium in the PCD of secretory cavity cells, we used potassium pyroantimonate precipitation to detect and locate calcium dynamics. At the precursor cell stage of the secretory cavity, Ca²⁺ was only distributed in the cell walls. At the early stage of secretory cavity initial cells, Ca²⁺ in the cell walls was gradually transported into the cytoplasm via pinocytotic vesicles. Although a small amount of Ca²⁺ was present in the nucleus, the TUNEL signal was scarcely observed. At the middle stage of initial cells, a large number of pinocytotic vesicles were transferred to the nucleus, where the vesicle membrane fused with the nuclear membrane to release calcium into the nucleoplasm. In addition, abundant Ca²⁺ aggregated in the condensed chromatin and nucleolus, where the TUNEL signal appeared the strongest. At the late stage of initial cells, the chromatin and nucleolus gradually degraded and disappeared, and the nucleus appeared broken-like, as Ca²⁺ in the cell wall had nearly completely disappeared, and Ca²⁺ in the nucleus was also rapidly reduced. Furthermore, the TUNEL signal also disappeared. These phenomena indicated that an increase in Ca²⁺ concentration in the nucleus might activate the PCD of secretory cavity cells, and further Ca²⁺ accumulation contributed to the regulation of nuclear DNA degradation.     

Apoplastic calmodulin promotes self-incompatibility pollen tube growth by enhancing calcium influx and reactive oxygen species concentration in Pyrus pyrifolia

Key message

This study indicated that Ca ²⁺ , ROS and actin filaments were involved with CaM in regulating pollen tube growth and providing a potential way for overcoming pear self-incompatibility.

Abstract

Calmodulin (CaM) has been associated with various physiological and developmental processes in plants, including pollen tube growth. In this study, we showed that CaM regulated the pear pollen tube growth in a concentration-dependent bi-phasic response. Using a whole-cell patch-clamp configuration, we showed that apoplastic CaM induced a hyperpolarization-activated calcium ion (Ca²⁺) current, and anti-CaM largely inhibited this type of Ca²⁺ current. Moreover, upon anti-CaM treatment, the reactive oxygen species (ROS) concentration decreased and actin filaments depolymerized in the pollen tube. Interestingly, CaM could partially rescue the inhibition of self-incompatible pear pollen tube growth. This phenotype could be mediated by CaM-enhanced pollen plasma membrane Ca²⁺ current, tip-localized ROS concentration and stabilized actin filaments. These data indicated that Ca²⁺, ROS and actin filaments were involved with CaM in regulating pollen tube growth and provide a potential way for overcoming pear self-incompatibility.     

Protocol for the BAG-RECALL clinical trial: a prospective, multi-center, randomized, controlled trial to determine whether a bispectral index-guided protocol is superior to an anesthesia gas-guided protocol in reducing intraoperative awareness with explicit recall in high risk surgical patients

Background

Sevoflurane has been demonstrated to vasodilate the foeto-placental vasculature. We aimed to determine the contribution of modulation of potassium and calcium channel function to the vasodilatory effect of sevoflurane in isolated human chorionic plate arterial rings.

Methods

Quadruplicate ex vivo human chorionic plate arterial rings were used in all studies. Series 1 and 2 examined the role of the K⁺ channel in sevoflurane-mediated vasodilation. Separate experiments examined whether tetraethylammonium, which blocks large conductance calcium activated K⁺ (K_Ca++) channels (Series 1A+B) or glibenclamide, which blocks the ATP sensitive K⁺ (K_ATP) channel (Series 2), modulated sevoflurane-mediated vasodilation. Series 3 – 5 examined the role of the Ca⁺⁺ channel in sevoflurane induced vasodilation. Separate experiments examined whether verapamil, which blocks the sarcolemmal voltage-operated Ca⁺⁺ channel (Series 3), SK&F 96365 an inhibitor of sarcolemmal voltage-independent Ca⁺⁺ channels (Series 4A+B), or ryanodine an inhibitor of the sarcoplasmic reticulum Ca⁺⁺ channel (Series 5A+B), modulated sevoflurane-mediated vasodilation.

Results

Sevoflurane produced dose dependent vasodilatation of chorionic plate arterial rings in all studies. Prior blockade of the K_Ca++ and K_ATP channels augmented the vasodilator effects of sevoflurane. Furthermore, exposure of rings to sevoflurane in advance of TEA occluded the effects of TEA. Taken together, these findings suggest that sevoflurane blocks K⁺ channels. Blockade of the voltage-operated Ca⁺⁺channels inhibited the vasodilator effects of sevoflurane. In contrast, blockade of the voltage-independent and sarcoplasmic reticulum Ca⁺⁺channels did not alter sevoflurane vasodilation.

Conclusion

Sevoflurane appears to block chorionic arterial K_Ca++ and K_ATP channels. Sevoflurane also blocks voltage-operated calcium channels, and exerts a net vasodilatory effect in the in vitro foeto-placental circulation.     

AtHSP17.8 overexpression in transgenic lettuce gives rise to dehydration and salt stress resistance phenotypes through modulation of ABA-mediated signaling

Key message

Transgenic Arabidopsis and lettuce plants overexpressing AtHSP17.8 showed ABA-hypersensitive but abiotic stress-resistant phenotypes. ABA treatment caused a dramatic induction of early ABA-responsive genes in AtHSP17.8 -overexpressing transgenic lettuce.

Abstract

Plant small heat shock proteins function as chaperones in protein folding. In addition, they are involved in responses to various abiotic stresses, such as dehydration, heat and high salinity in Arabidopsis. However, it remains elusive how they play a role in the abiotic stress responses at the molecular level. In this study, we provide evidence that Arabidopsis HSP17.8 (AtHSP17.8) positively regulates the abiotic stress responses by modulating abscisic acid (ABA) signaling in Arabidopsis, and also in lettuce, a heterologous plant when ectopically expressed. Overexpression of AtHSP17.8 in both Arabidopsis and lettuce leads to hypersensitivity to ABA and enhanced resistance to dehydration and high salinity stresses. Moreover, early ABA-responsive genes, ABI1, ABI5, NCED3, SNF4 and AREB2, were rapidly induced in AtHSP17.8-overexpressing transgenic Arabidopsis and lettuce. Based on these data, we propose that AtHSP17.8 plays a crucial role in abiotic stress responses by positively modulating ABA-mediated signaling in both Arabidopsis and lettuce. Moreover, our results suggest that stress-tolerant lettuce can be engineered using the genetic and molecular resources of Arabidopsis.     

A flavonoid, 5-hydroxy-3,7-dimethoxyflavone,from Kaempferia parviflora Wall. Ex. Baker as an inhibitor of Ca2+ signal-mediated cell-cycle regulation in yeast

Calcium (Ca²⁺) signal transduction pathways play important roles in the regulation of diverse biological processes in eukaryotes ranging from unicellular (e.g., yeasts) to complex multicellular (e.g., humans) organisms. Small-molecule inhibitors of Ca²⁺-signaling pathways in humans can be of great medical importance, as represented by the immunosuppressants FK506 and cyclosporine A. A high-throughput drug screening assay for inhibitors of Ca²⁺-signaling has been developed on the basis of the ability of test compounds to restore the severe growth defect of a Ca²⁺-sensitive zds1 null-mutant strain YNS17 of Saccharomyces cerevisiae in a medium containing a high concentration of calcium ions. A previous screening of Thai medicinal plants using this yeast-based assay indicated that the crude extract of Kaempferia parviflora Wall. Ex. Baker contains a potent inhibitory activity. The aim of this study was to isolate and characterize the pure compound(s) responsible for this inhibitory activity against Ca²⁺-mediated cell-cycle regulation in yeast. Dichloromethane and methanol extracts of K. parviflora rhizomes were subjected to bioassay-mediated chromatographic fractionation using this yeast [YNS17 (Δzds1) strain]-based assay to screen for and select positive fractions. From the dichloromethane extract, four known flavonoid compounds with significant inhibitory bioactivity were obtained: compounds 1 (5-hydroxy-3,7-dimethoxyflavone), 2 (5-hydroxy-7-methoxyflavone), 3 (5-hydroxy-3,7,4’-trimethoxyflavone) and 4 (5,7-dimethoxyflavone). The inhibitory activity of all four compounds was dose-dependent. Compound 1 exhibited the highest activity and with no observed cytotoxic activity against the yeast. The Ca²⁺ induced severe growth defect, abnormal budding morphology, and G2 cell-cycle delay of the Δzds1 yeast strain were all alleviated or abrogated by 200 μM compound 1. Therefore, we conclude that 5-hydroxy-3,7-dimethoxyflavone possesses a potent inhibitory activity against the Ca²⁺-mediated cell-cycle regulation.     

Overexpression of a novel salt stress-induced glycine-rich protein gene from alfalfa causes salt and ABA sensitivity in Arabidopsis

Key message

We cloned a novel salt stress-induced glycine-rich protein gene ( MsGRP ) from alfalfa. Its overexpression retards seed germination and seedling growth of transgenic Arabidopsis after salt and ABA treatments.

Abstract

Since soil salinity is one of the most significant abiotic stresses, salt tolerance is required to overcome salinity-induced reductions in crop productivity. Many glycine-rich proteins (GRPs) have been implicated in plant responses to environmental stresses, but the function and importance of some GRPs in stress responses remain largely unknown. Here, we report on a novel salt stress-induced GRP gene (MsGRP) that we isolated from alfalfa. Compared with some glycine-rich RNA-binding proteins, MsGRP contains no RNA recognition motifs and localizes in the cell membrane or cell wall according to the subcellular localization result. MsGRP mRNA is induced by salt, abscisic acid (ABA), and drought stresses in alfalfa seedlings, and its overexpression driven by a constitutive cauliflower mosaic virus-35S promoter in Arabidopsis plants confers salinity and ABA sensitivity compared with WT plants. MsGRP retards seed germination and seedling growth of transgenic Arabidopsis plants after salt and ABA treatments, which implies that MsGRP may affect germination and growth through an ABA-dependent regulation pathway. These results provide indirect evidence that MsGRP plays important roles in seed germination and seedling growth of alfalfa under some abiotic stress conditions.     

Expression profiling and functional characterization of a CBL-interacting protein kinase gene from Populus euphratica

Key message

This is the first report on the function of a member of the CIPK family in Populus euphratica.

Abstract

The Ca²⁺-dependent salt overly sensitive (SOS) pathway has been shown to play an essential role in maintaining ion homeostasis and conferring salt tolerance. One component of the SOS pathway, SOS1, was identified in the salt-resistant tree P. euphratica. In this study, we identified and functionally characterized another component of the SOS pathway in this tree called PeSOS2 or PeCIPK26. On the basis of protein sequence similarity and complementation studies in Arabidopsis, PeCIPK26 was concluded to be the functional homolog of Arabidopsis AtSOS2. Yeast two-hybrid assays revealed that PeCIPK26 can interact with four calcineurin B-like (CBL) genes, i.e., PeCBL1, PeCBL4/PeSOS3, PeCBL9 and PeCBL10. Autophosphorylation assays showed that PeCIPK26 is an active protein kinase. Expression profile analysis demonstrated that PeCIPK26 is expressed in root, stem and leaf, and throughout the cell including cell membrane, cytoplasm and nucleus; in addition, it can be induced under salt-stress treatment. Functions of PeCIPK26 in salt tolerance were evaluated by gene overexpression in Arabidopsis cipk24 mutants. The better salt tolerance of transgenic plants relative to mutants was shown by their higher germination rate, lower Na⁺ accumulation and higher capacity to discharge Na⁺ when grown with NaCl. These results suggest the involvement of PeCIPK26 in the salt-stress response of P. euphratica.     

Optical chemosensors for Cu(II) ion based on BODIPY derivatives: an experimental and theoretical study

Two BODIPY derivatives for Cu²⁺ ion chemosensors containing 4-[2-(diethylamino)-2-oxoethoxy]phenyl (BDP1) and 3,4-bis[2-(diethylamino)-2-oxoethoxy]phenyl (BDP2) were synthesized by coupling appropriate N,N-diethyl-2-(4-formylphenoxy)acetamide and 2,4-dimethylpyrrole moieties in the presence of trifluoroacetic acid and anhydrous dichloromethane at room temperature. The binding abilities between these chemosensors and 50 equivalents of Na⁺, K⁺, Ag⁺, Ca²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ ions were studied using UV-vis and fluorescence spectrophotometry. The results show that, compared to other ions, both the UV-vis absorption and fluorescence emission intensity of BDP2 decreased dramatically when Cu²⁺ ion was added. To explain this behavior, ab initio quantum chemical calculations were performed using correlated second-order Møller-Plesset perturbation theory (MP2/LanL2DZ). The calculated orbital energies indicated that the decrease in UV-vis absorption intensity and the quenching of fluorescene emission were due to the single-electron reduction of Cu²⁺ to Cu⁺ ion.

Pepper mildew resistance locus O interacts with pepper calmodulin and suppresses Xanthomonas AvrBsT-triggered cell death and defense responses

Main conclusion

Pepper CaMLO2 specifically interacts with CaCaM1 and translocates cytoplasmic CaCaM1 to the plasma membrane, leading to the suppression of Xanthomonas AvrBsT-triggered Ca ²⁺ influx, hypersensitive cell death and defense responses.

Abstract

Pathogen-induced cell death is closely linked with disease susceptibility and resistance in plants. Pepper (Capsicum annuum) mildew resistance locus O (CaMLO2) and calmodulin (CaCaM1) genes are required for disease-associated cell death and hypersensitive cell death, respectively. Here, we demonstrate that pathogen-responsive CaMLO2 interacts with CaCaM1 in yeast and in planta. Bimolecular fluorescence complementation and co-immunoprecipitation analyses confirm a specific interaction between CaMLO2 and CaCaM1 at the plasma membrane (PM) in plant cells. Subcellular localization analyses of CaCaM1 fused to green fluorescent protein reveals that treatment with Ca²⁺ and co-expression with CaMLO2 induce translocation of cytosolic CaCaM1 to the PM where CaMLO2 is localized. Transient CaMLO2 expression negatively regulates CaCaM1 accumulation in Nicotiana benthamiana. Xanthomonas avrBsT-triggered Ca²⁺ influx and hypersensitive cell death are disrupted by CaCaM1 and/or CaMLO2 expression. CaMLO2 silencing in pepper significantly enhances reactive oxygen species burst, cell death, and resistance responses to Xanthomonas campestris pv. vesicatoria Ds1 and Ds1 (avrBsT), which is accompanied by enhanced induction of CaCaM1, CaPR1 (PR-1), and CaPO2 (peroxidase). These results suggest that CaMLO2 interacts with CaCaM1 and suppresses AvrBsT-triggered cell death and defense responses.     

Mechanisms of thaxtomin A-induced root toxicity revealed by a thaxtomin A sensitive <Emphasis Type="Italic">Arabidopsis</Emphasis> mutant (<Emphasis Type="Italic">ucu2</Emphasis>-<Emphasis Type="Italic">2/gi</Emphasis>-<Emphasis Type="Italic">2</Emphasis>)

Key message

The Arabidopsis mutant ( ucu2 - 2/gi - 2 ) is thaxtomin A, isoxaben and NPA-sensitive indicated by root growth and ion flux responses providing new insights into these compounds mode of action and interactions.

Abstract

Thaxtomin A (TA) is a cellulose biosynthetic inhibitor (CBI) that promotes plant cell hypertrophy and cell death. Electrophysiological analysis of steady-state K⁺ and Ca²⁺ fluxes in Arabidopsis thaliana roots pretreated with TA for 24 h indicated a disturbance in the regulation of ion movement across the plant cell membrane. The observed inability to control solute movement, recorded in rapidly growing meristematic and elongation root zones, may partly explain typical root toxicity responses to TA treatment. Of note, the TA-sensitive mutant (ucu2-2/gi-2) was more susceptible with K⁺ and Ca²⁺ fluxes altered between 1.3 and eightfold compared to the wild-type control where fluxes altered between 1.2 and threefold. Root growth inhibition assays showed that the ucu2-2/gi-2 mutant had an increased sensitivity to the auxin 2,4-D, but not IAA or NAA; it also had increased sensitivity to the auxin efflux transport inhibitor, 1-naphthylphthalamic acid (NPA), but not 2,3,5- Triiodobenzoic acid (TIBA), when compared to the WT. The NPA sensitivity data were supported by electrophysiological analysis of H⁺ fluxes in the mature (but not elongation) root zone. Increased sensitivity to the CBI, isoxaben (IXB), but not dichlobenil was recorded. Increased sensitivity to both TA and IXB corresponded with higher levels of accumulation of these toxins in the root tissue, compared to the WT. Further root growth inhibition assays showed no altered sensitivity of ucu2-2/gi-2 to two other plant pathogen toxins, alternariol and fusaric acid. Identification of a TA-sensitive Arabidopsis mutant provides further insight into how this CBI toxin interacts with plant cells.

     

Ectopic expression of phloem motor protein pea forisome PsSEO-F1 enhances salinity stress tolerance in tobacco

Key message

PsSEOF-1 binds to calcium and its expression is upregulated by salinity treatment. PsSEOF - 1 -overexpressing transgenic tobacco showed enhanced salinity stress tolerance by maintaining cellular ion homeostasis and modulating ROS-scavenging pathway.

Abstract

Calcium (Ca²⁺) plays important role in growth, development and stress tolerance in plants. Cellular Ca²⁺ homeostasis is achieved by the collective action of channels, pumps, antiporters and by Ca²⁺ chelators present in the cell like calcium-binding proteins. Forisomes are ATP-independent mechanically active motor proteins known to function in wound sealing of injured sieve elements of phloem tissue. The Ca²⁺-binding activity of forisome and its role in abiotic stress signaling were largely unknown. Here we report the Ca²⁺-binding activity of pea forisome (PsSEO-F1) and its novel function in promoting salinity tolerance in transgenic tobacco. Native PsSEO-F1 promoter positively responded in salinity stress as confirmed using GUS reporter. Overexpression of PsSEO-F1 tobacco plants confers salinity tolerance by alleviating ionic toxicity and increased ROS scavenging activity which probably results in reduced membrane damage and improved yield under salinity stress. Evaluation of several physiological indices shows an increase in relative water content, electrolyte leakage, proline accumulation and chlorophyll content in transgenic lines as compared with null-segregant control. Expression of several genes involved in cellular homeostasis is perturbed by PsSEO-F1 overexpression. These findings suggest that PsSEO-F1 provides salinity tolerance through cellular Ca²⁺ homeostasis which in turn modulates ROS machinery providing indirect link between Ca²⁺ and ROS signaling under salinity-induced perturbation. PsSEO-F1 most likely functions in salinity stress tolerance by improving antioxidant machinery and mitigating ion toxicity in transgenic lines. This finding should make an important contribution in our better understanding of the significance of calcium signaling in phloem tissue leading to salinity stress tolerance.

     

Endogenous nitric oxide generation in protoplast chloroplasts

Key message

NO generation is studied in the protoplast chloroplasts. NO, ONOO ^? and ROS (O ₂ ^? and H ₂ O ₂ ) are generated in chloroplasts. Nitric oxide synthase-like protein appears to be involved in NO generation.

Abstract

Nitric oxide stimulates chlorophyll biosynthesis and chloroplast differentiation. The present study was conducted to better understand the process of NO generation in the leaf chloroplasts and protoplasts. NO, peroxynitrite and superoxide anion were investigated in the protoplasts and isolated chloroplasts using specific dyes, confocal laser scanning and light microscopy. The level of NO was highest after protoplast isolation and subsequently decreased during culture. Suppression of NO signal in the presence of PTIO, suggests that diaminofluorescein-2 diacetate (DAF-2DA) detected NO. Detection of peroxynitrite, a reaction product of NO and superoxide anion, further suggests NO generation. Moreover, generation of NO and peroxynitrite in the chloroplasts of wild-type Arabidopsis and their absence or weak signals in the leaf-derived protoplasts of Atnoa1 mutants confirmed the reactivity of DAF-2DA and aminophenyl fluorescein to NO and peroxynitrite, respectively. Isolated chloroplasts also showed signal of NO. Suppression of NO signal in the presence of 100 μM nitric oxide synthase inhibitors [l-NNA, Nω-nitro-l-arginine and PBIT, S,S′-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea] revealed that nitric oxide synthase-like system is involved in NO synthesis. Suppression of NO signal in the protoplasts isolated in the presence of cycloheximide suggests de novo synthesis of NO generating protein during the process of protoplast isolation. Furthermore, the lack of inhibition of NO production by sodium tungstate (250 μM) and inhibition by l-NNA, and PBIT suggest involvement NOS-like protein, but not nitrate reductase, in NO generation in the leaf chloroplasts and protoplasts.     

Polyphenols from Parabarium huaitingii and their positive inotropic and anti-myocardial infarction effects in rats

Eight phenolic compounds, including (−)-epicatechin (1) and seven proanthocyanidins (2-8), were obtained from the butanol extract of Parabarium huaitingii (PHB). Their chemical structures were identified based on analyses of mass spectra (MS), NMR, CD spectra, and partial acid catalyzed thiolytic degradation. The observation made by laser scanning confocal microscope found a significant increase of the concentration of intracellular Ca²⁺ ([Ca²⁺]_i) in single myocytes when the PHB was added, while compounds 1 and 3 had the same physiological effect. Further investigations showed PHB had a dose-dependent positive inotropic effect on isolated right atria and papillary muscle of left ventricle of the rat, while having no significant influence on the spontaneous beating rate of the isolated right atria. The inotropic effect of PHB could be greatly abolished by pretreating the myocardium in Ca²⁺-free solution. These findings indicated that PHB could significantly increase [Ca²⁺]_i in myocytes, which was greatly dependent on the influx of extracellular Ca²⁺. Compounds 1 and 3 might be the effective ingredients of the inotropic effect of PHB. In addition, PHB could also significantly decrease the infarct size of the heart on acute myocardial infarction (AMI) model rats, which suggested its myocardial protective effect on ischemic myocardium. The positive inotropic effect of PHB, together with its myocardial protective effect on AMI, suggested that PHB had a promising potential for the prevention and treatment of heart failure, especially the one that was caused by AMI.     

Cosuppression of RBCS3B in Arabidopsis leads to severe photoinhibition caused by ROS accumulation

Key message

Cosuppression of an Arabidopsis Rubisco small subunit gene RBCS3B at Arabidopsis resulted in albino or pale green phenotypes which were caused by ROS accumulation

Abstract

As the most abundant protein on Earth, Rubisco has received much attention in the past decades. Even so, its function is still not understood thoroughly. In this paper, four Arabidopsis transgenic lines (RBCS3B-7, 18, 33, and 35) with albino or pale green phenotypes were obtained by transformation with a construct driving expression of sense RBCS3B, a Rubisco small subunit gene. The phenotypes produced in these transgenic lines were found to be caused by cosuppression. Among these lines, RBCS3B-7 displayed the most severe phenotypes including reduced height, developmental arrest and plant mortality before flowering when grown under normal light on soil. Chloroplast numbers in mesophyll cells were decreased compared to WT, and stacked thylakoids of chloroplasts were broken down gradually in RBCS3B-7 throughout development. In addition, the RBCS3B-7 line was light sensitive, and PSII activity measurement revealed that RBCS3B-7 suffered severe photoinhibition, even under normal light. We found that photoinhibition was due to accumulation of ROS, which accelerated photodamage of PSII and inhibited the repair of PSII in RBCS3B-7.     

Characterization of bio-related vanadium and zinc complexes containing tetradentate dithiolate-disulfide, -diamine and -amine-amide ligands

The reaction of [VCl₃(PMe₂Ph)₃] _{with HSS′S′SH (where the HS are thiophenolate and the S′ thioether functions, respectively), H2–1, yields [VCl(μ-SS′S′S)]2 (3) with one of the thiolate groups of each of the two ligands in the bridging mode. Reaction of Na2–1 with [VOCl2(thf)2] leads to a polymeric product of composition [VO(SS′S′S)]x (4). The products obtained from the reaction between [VOCl2(thf)2] and NaSNNSNa, Na2–2, (S is thiophenolate, N the amine function) depend on subtle changes in the diamine backbone of this ligand: If the amine functions are linked by -CH2CH2– (2a), the tetranuclear V^IV complex [V(SNNS)μ-O]4 (5) is formed alongside the V^III complex [VCl(SNNS)]. If the backbone is -CH(Me)CH(Me)- (2b), [VO(SNNS)] (7) and the dinuclear, asymmetrically oxo-bridged V^IV complex [{(SNN ^– S)(thf)V}μ-O{V(SNN ^– S)}] (8) are obtained. In 8, one amine of each of the two ligands is deprotonated to the amide group. In either case, the complexation is accompanied by oxidation of the thiolates to disulfides, leading to the generation of teraazatetrathio-cycloeicosanes (6a/b). Compounds 5 and 8·2THF have been structurally characterized by X-ray analyses. The connectivities have further been established for 3·2CH2Cl2 and for 6b, which exhibits the same conformation as formally characterized 6a. The cluster compound 5 is stabilized by an extended intramolecular N-H...O and N-H...S) hydrogen-bonding network. In 7·2THF, one of the THFs of crystallization is hydrogen-bonded to the NH of the penta-coordinated {VO(SNN ^– S)} moiety; further, there is an intramolecular hydrogen bond between one of the thiolates of this tetragonal-pyramidal half of the molecule and the NH of the octahedral {VO(SNN ^– S)thf} half. The generation of the ligand 2b from its precursor compound, the zinc complex [Zn(SNNS)] (9) leads to the structural characterization of 9·CH3OH with a large SZnS bite angle and a strong hydrogen bond between the methanolic OH and one of the thiolate sulfurs. The relevance of these compounds in biological systems is discussed.}     

Root proteomics reveals cucumber 24-epibrassinolide responses under Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> stress

Key message

The application of exogenous 24-epibrassinolide promotes Brassinosteroids intracellular signalling in cucumber, which leads to differentially expressed proteins that participate in different life process to relieve Ca(NO ₃ ) ₂ damage.

Abstract

NO₃ ^? and Ca²⁺ are the main anion and cation of soil secondary salinization during greenhouse cultivation. Brassinosteroids (BRs), steroidal phytohormones, regulate various important physiological and developmental processes and are used against abiotic stress. A two-dimensional electrophoresis gel coupled with MALDI-TOF/TOF MS was performed to investigate the effects of exogenous 24-epibrassinolide (EBL) on proteomic changes in cucumber seedling roots under Ca(NO₃)₂ stress. A total of 80 differentially accumulated protein spots in response to stress and/or exogenous EBL were identified and grouped into different categories of biological processes according to Gene Ontology. Under Ca(NO₃)₂ stress, proteins related to nitrogen metabolism and lignin biosynthesis were induced, while those related to cytoskeleton organization and cell-wall neutral sugar metabolism were inhibited. However, the accumulation of abundant proteins involved in protein modification and degradation, defence mechanisms against antioxidation and detoxification and lignin biosynthesis by exogenous EBL might play important roles in salt tolerance. Real-time quantitative PCR was performed to investigate BR signalling. BR signalling was induced intracellularly under Ca(NO₃)₂ stress. Exogenous EBL can alleviate the root indices, effectively reduce the Ca²⁺ content and increase the K⁺ content in cucumber roots under Ca(NO₃)₂ stress. This study revealed the differentially expressed proteins and BR signalling-associated mRNAs induced by EBL in cucumber seedling roots under Ca(NO₃)₂ stress, providing a better understanding of EBL-induced salt resistance in cucumber seedlings. The mechanism for alleviation provides valuable insight into improving Ca(NO₃)₂ stress tolerance of other horticultural plants.