Structural changes in root and shoot ofBacopa monniera in response to salt stress

Various concentrations of salt (NaCI) were shown to have an influence on the differentiation of tissues in the root and stem ofBacopa monniera (L) Wettst. Higher concentrations induced drastic changes in roots grown on salt-supplemented media; epidermal and cortical cells experienced changes in shape, size, and orientation and/or were got disintegrated. A low concentration of salt induced a profuse development of root hairs which gradually disappeared at higher concentrations. Air spaces in the stem cortex were enlarged and xylem cell walls in the vascular ring were thickened.     

肠道微生物群加重黑腹果蝇盐胁迫反应

【背景】高盐饮食目前引起普遍关注,肠道微生物与盐胁迫的相互作用正成为研究热点之一。【目的】以黑腹果蝇为宿主模型,探讨肠道微生物对果蝇盐胁迫反应的影响与潜在机理。【方法】利用平板计数法和定量PCR法检测果蝇肠道载菌量;利用存活率和运动能力测定装置测定果蝇适合度;用化学试剂和抗生素处理建立无菌果蝇,测定肠道菌对果蝇盐胁迫反应的影响;利用亮蓝食用色素染料渗透性实验检测果蝇肠道屏障的完整性;应用实时定量PCR检测先天免疫系统的活性。【结果】高盐处理引起果蝇肠道菌群失调,导致其肠道载菌量显著增加。此外,高盐饮食(high salt diet,HSD)降低了黑腹果蝇成虫的存活率和运动能力。经0.75 mol/L NaCl处理,雌性GF (germ-free)果蝇存活率比对照组升高了11%,同时混合抗生素有效地提高了高盐处理后果蝇的存活率。肠道微生物加剧了肠道屏障功能损伤,雌性GF果蝇出现染料渗透性实验现象的百分率比对照组降低了8%。在分子水平上,盐胁迫下雌性GF果蝇体内Attacin-C、Duox基因表达水平分别是CR(conventionally reared)果蝇的2.5倍和1.7倍。【结论】肠道微生物加重果蝇盐胁迫反应,引发高盐诱导的肠屏障功能紊乱,并且抑制高盐诱导的先天免疫活性。     

幼苗期不同水稻材料应答盐胁迫的生理差异分析

为了解耐盐水稻HD96-1幼苗期耐盐生理调控特性，该研究以籼型水稻HD96-1(耐盐性强)和93-11(耐盐性弱)为材料，采用营养液水培法，设置3种NaCl盐浓度(0、60、120 mmol·L^-1),对3叶期幼苗进行了7 d盐处理，测定和分析了两个材料的生长参数和生理生化指标。结果表明：(1)在盐胁迫下，水稻幼苗均表现为株高和假茎宽减小，根冠比增加；与93-11比，HD96-1株高和茎宽减小幅度低，根冠比增加幅度高；地上部和根系干重，HD96-1增加，而93-11减少。(2)盐胁迫后，水稻幼苗的丙二醛(MDA)、超氧阴离子(O₂^-)和过氧化氢(H₂O₂)含量均上升，但HD96-1增幅较93-11低。(3)在盐胁迫下，水稻幼苗体内的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)的活性，以及抗坏血酸(AsA)、谷胱甘肽(GSH)、脯氨酸、可溶性糖和可溶性蛋白的含量均升高，HD96-1增幅高于93-11。综上表明，两个水稻材料幼苗...     

Sam68 relocalization into stress granules in response to oxidative stress through complexing with TIA-1

Sam68 has been implicated in a variety of important cellular processes such as RNA metabolism and intracellular signaling. We have recently shown that Sam68 cytoplasmic mutants induce stress granules (SG) and inhibit HIV-1 nef mRNA translation [J. Henao-Mejia, Y. Liu, I.W. Park, J. Zhang, J. Sanford, J.J. He, Suppression of HIV-1 Nef translation by Sam68 mutant-induced stress granules and nef mRNA sequestration, Mol. Cell 33 (2009) 87-96]. These findings prompted us to investigate the possibility and the underlying mechanisms of the wild-type counterpart Sam68 SG recruitment. Herein, we revealed that Sam68 was significantly recruited into cytoplasmic SG under oxidative stress. We then demonstrated that domain aa269-321 and KH domain were both essential for this recruitment. Nevertheless, Sam68 knockdown had no effects on SG assembly, indicating that Sam68 is not a constitutive component of the SG. Moreover, we showed that Sam68 cytoplasmic mutant-induced SG formation was independent of eIF2α phosphorylation. Lastly, we demonstrated that Sam68 was complexed with T-cell intracellular antigen-1 (TIA-1), a core SG component, and that the complex formation was correlated with Sam68 SG recruitment. Taken together, these results provide direct evidence for the first time that Sam68 is recruited into SG through complexing with TIA-1 in response to oxidative stress and suggest that cytoplasmic SG recruitment of Sam68 and ensuing changes in Sam68 physiological functions are part of the host response to external stressful conditions.     

Genetic analysis of involvement of ETR1 in plant response to salt and osmotic stress

The involvement of ethylene and ethylene receptor Ethylene Response 1 (ETR1) in plant stress responses has been highlighted. However, the physiological processes involved remain unclear. In this study, we have investigated the physiological response of two alleles etr1-1 and etr1-7 mutants during germination and post-germination seedling development in response to salt and osmotic stress. The etr1-1 mutants showed increased sensitivity to osmotic (200 mM or higher mannitol) and salt stress (50 mM NaCl or higher) during germination and seedling development, whereas the etr1-7 mutants displayed enhanced tolerance to the severe stresses (500 mM mannitol or 200 mM NaCl). These results provide physiological and genetic evidence that ethylene receptor ETR1 modulates plant response to abiotic stress. Furthermore, the etr1-1 and etr1-7 mutants showed different responses to exogenous abscisic acid (ABA) inhibition. The etr1-1 mutants were more sensitive to ABA than the wild type during germination, and young seedling development. In sharp contrast, the etr1-7 mutants showed enhanced insensitivity to ABA treatment (>1 μM ABA) in post-germination development including root elongation and greening of cotyledons of the treated seedlings, although the germination was not greatly altered at the tested doses of ABA. The results suggest that ETR1-modulated stress response may mediate ABA. Youning Wang and Tao Wang contributed equally to this report.     

HY5-HDA9 orchestrates the transcription of HsfA2 to modulate salt stress response in Arabidopsis

Integration of light signaling and diverse abiotic stress responses contribute to plant survival in a changing environment. Some reports have indicated that light signals contribute a plant's ability to deal with heat, cold, and stress. However, the molecular link between light signaling and the salt-response pathways remains unclear. We demonstrate here that increasing light intensity elevates the salt stress tolerance of plants. Depletion of HY5, a key component of light signaling, causes Arabidopsis thaliana to become salinity sensitive. Interestingly, the small heat shock protein (sHsp) family genes are upregulated in hy5-215 mutant plants, and HsfA2 is commonly involved in the regulation of these sHsps. We found that HY5 directly binds to the G-box motifs in the HsfA2 promoter, with the cooperation of HISTONE DEACETYLASE 9 (HDA9), to repress its expression. Furthermore, the accumulation of HDA9 and the interaction between HY5 and HDA9 are significantly enhanced by salt stress. On the contrary, high temperature triggers HY5 and HDA9 degradation, which leads to dissociation of HY5-HDA9 from the HsfA2 promoter, thereby reducing salt tolerance. Under salt and heat stress conditions, fine tuning of protein accumulation and an interaction between HY5 and HDA9 regulate HsfA2 expression. This implies that HY5, HDA9, and HsfA2 play important roles in the integration of light signaling with salt stress and heat shock response.     

Accumulation of a 22-kDa protein and its mRNA in the leaves of Raphanus sativus in response to salt stress or water deficit

The response of 10-day-old seedlings of Raphanus sativus L. cv. Fakir to salt stress (100 m M to 200 m M NaCl) was investigated. Three weeks after initiation of salt treatment, the fresh weight of the shoots of salt-treated plants was half that of untreated plants. The salt stress resulted in the accumulation of Na⁺, preferably in the old leaves. The K⁺ level was reduced by as much as 50% in the old leaves of NaCl-treated plants, whereas this reduction was only 20–25% in the young leaves. Free proline accumulated in all aerial organs, and the highest levels were found in the young leaves. Patterns of total proteins extracted from the leaves of control or salt-treated plants were compared. The most obvious change concerned a 22-kDa, pl 7.5 polypeptide, which accumulated after exposure of the plants to NaCl. The appearance of this polypeptide was also mediated by a rapid drought stress, and sequencing indicated that it is related to the Künitz protease inhibitor family. A cDNA clone corresponding to the radish 22-kDa polypeptide was obtained and sequenced. Northern blot analysis showed that salt stress induces a large accumulation of this mRNA in the leaves of radish.     

Hyphal healing mechanism in the arbuscular mycorrhizal fungi Scutellospora reticulata and Glomus clarum differs in response to severe physical stress

The hyphal healing mechanism (HHM) has been shown to differ between Gigasporaceae and Glomeraceae. However, this process has not been considered under (severe) physical stress conditions. Scutellospora reticulata and Glomus clarum strains were cultured monoxenically. The impact of long distance separating cut extremities of hyphae and of multiple injuries within hyphae on the HHM was monitored. For long distances (>5000 microm) separating cut extremities, hyphae healing was observed in half the cases in S. reticulata and was absent in G. clarum. For multiple-injured hyphae, the HHM was always oriented towards the complete recovery of hyphae integrity in S. reticulata, while in G. clarum, the growing hyphal tips (GHTs) could indifferently reconnect cut sections, by-pass cut sections or develop into the environment. Hyphae behaviour under severe physical stress clearly differentiated S. reticulata from G. clarum, suggesting that both fungi have developed different strategies for colony growth to survive under adverse conditions.     

Adaptation of the tonoplast V-type H+-ATPase of Mesembryanthemum crystallinum to salt stress, C3–CAM transition and plant age

Plants of the facultative halophyte and CAM species Mesembryanthemum crystallinum L. (Aizoaceae) were stressed for 8 d with 400 mol m⁻³ NaCl in the root medium. NaCl was then removed from the substratum, and the plants were watered again with NaCl-free solution. A second set of plants was maintained as controls. A small degree of CAM, as indicated by day-night changes in malate levels, was expressed during ageing of the plants. Salinity-stress-dependent CAM induction was reversible by the removal of salt, as indicated by similar Δ malate levels in previously salt-stressed plants and in non-stressed plants on day 19 of the experiment. Tonoplast vesicles were isolated from leaves during the time-course of stress application, stress removal and ageing. Parameters of the tonoplast H⁺-ATPase were correlated to the application of salinity, the expression of CAM and ageing. It was concluded, first, that a pronounced increase in the amount of tonoplast H⁺-ATPase is related to salinity per se and a smaller increase to ageing; secondly, that there is an increase in the specific activity of the enzyme related to ageing; thirdly, that the induction of two new polypeptides with molecular masses of 32 and 28 kDa is correlated in time with the expression of CAM, and, fourthly, that the two new polypeptides are part of the tonoplast H⁺-ATPase holoenzyme.     

Molecular cloning of two novel peroxidases and their response to salt stress and salicylic acid in the living fossil Ginkgo biloba

Background and Aims

Peroxidase isoenzymes play diverse roles in plant physiology, such as lignification and defence against pathogens. The actions and regulation of many peroxidases are not known with much accuracy. A number of studies have reported direct involvement of peroxidase isoenzymes in the oxidation of monolignols, which constitutes the last step in the lignin biosynthesis pathway. However, most of the available data concern only peroxidases and lignins from angiosperms. This study describes the molecular cloning of two novel peroxidases from the ‘living fossil’ Ginkgo biloba and their regulation by salt stress and salicylic acid.

Methods

Suspension cell cultures were used to purify peroxidases and to obtain the cDNAs. Treatments with salicylic acid and sodium chloride were performed and peroxidase activity and gene expression were monitored.

Key Results

A novel peroxidase was purified, which preferentially used p-hydroxycinnamyl alcohols as substrates and was able to form dehydrogenation polymers in vitro from coniferyl and sinapyl alcohols. Two peroxidase full-length cDNAs, GbPrx09 and GbPrx10, were cloned. Both peroxidases showed high similarity to other basic peroxidases with a putative role in cell wall lignification. Both GbPrx09 and GbPrx10 were expressed in leaves and stems of the plant. Sodium chloride enhanced the gene expression of GbPrx09 but repressed GbPrx10, whereas salicylic acid strongly repressed both GbPrx09 and GbPrx10.

Conclusions

Taken together, the data suggest the participation of GbPrx09 and GbPrx10 in the developmental lignification programme of the cell wall. Both peroxidases possess the structural characteristics necessary for sinapyl alcohol oxidation. Moreover, GbPrx09 is also involved in lignification induced by salt stress, while salicylic acid-mediated lignification is not a result of GbPrx09 and GbPrx10 enzymatic activity.