Physiological and proteomic analysis of salinity tolerance in Puccinellia tenuiflora

Soil salinity poses a serious threat to agriculture productivity throughout the world. Studying mechanisms of salinity tolerance in halophytic plants will provide valuable information for engineering plants for enhanced salt tolerance. Monocotyledonous Puccinellia tenuiflora is a halophytic species that widely distributed in the saline-alkali soil of the Songnen plain in northeastern China. Here we investigate the molecular mechanisms underlying moderate salt tolerance of P. tenuiflora using a combined physiological and proteomic approach. The changes in biomass, inorganic ion content, osmolytes, photosynthesis, defense-related enzyme activities, and metabolites in the course of salt treatment were analyzed in the leaves. Comparative proteomic analysis revealed 107 identities (representing 93 unique proteins) differentially expressed in P. tenuiflora leaves under saline conditions. These proteins were mainly involved in photosynthesis, stress and defense, carbohydrate and energy metabolism, protein metabolism, signaling, membrane, and transport. Our results showed that reduction of photosynthesis under salt treatment was attributed to the down-regulation of the light-harvesting complex (LHC) and Calvin cycle enzymes. Selective uptake of inorganic ions, high K(+)/Na(+) ratio, Ca(2+) concentration changes, and an accumulation of osmolytes contributed to ion balance and osmotic adjustment in leaf cells. Importantly, P. tenuiflora plants developed diverse reactive oxygen species (ROS) scavenging mechanisms in their leaves to cope with moderate salinity, including enhancement of the photorespiration pathway and thermal dissipation, synthesis of the low-molecular-weight antioxidant α-tocopherol, and an accumulation of compatible solutes. This study provides important information toward improving salt tolerance of cereals.     

Effects of exogenous polyamines on nitrate tolerance in cucumber

Putrescine (Put), spermidine (Spd), and spermine (Spm) are the major polyamines (PAs) in plant, which are not only involved in the regulation of plant developmental and physiological processes, but also play key roles in modulating the defense response of plants to diverse environmental stresses. In this study, Cucumis sativus L. seedlings were cultivated in nutrient solution and sprayed with three kinds of PAs (Put, Spd, and Spm). The effects of PAs were investigated on excess nitrate stress tolerance of C. sativus by measuring growth and nitrogen (N) metabolism parameters. The contents of NO_3-^?N, NH_4-⁺N, proline and soluble protein in leaves were increased; while plant height, leaf area, shoot fresh and dry weight, root fresh weight were decreased under 140 mM NO₃^? treatment for 7 d. In addition, the activities of nitrate reductase (NR), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) were significantly inhibited under 140 mM NO₃^? treatment for 7 d. With foliar treatment by 1 mM Spd or Spm under stress treatment, the contents of Spm, Put, and Spd in leaves increased significantly, except that Spm content decreased under Spd treatment. The activities of NR, glutamine synthetase (GS), GOGAT and GDH and plant height, leaf area, shoot fresh and dry weights were significantly increased. The contents of proline and soluble protein in leaves were significantly enhanced. In contrast, the accumulation of NO_3-^?N and NH_4-⁺N were significantly decreased. However, there were minor differences in activities of N metabolism enzymes and the content of osmotic adjustment substances under 1 mM Put treatment. These findings suggest that 1 mM exogenous Spm or Spd could enhance the capacity of N metabolism, promote growth and increase resistance to high concentrations of NO₃^?. The ameliorating effect of Spd was the best, and that of Put the worst.     

Comparative proteomic analysis of Listeria monocytogenes tolerance to bile stress

The ability of the food-borne pathogen Listeria monocytogenes to tolerate bile is critical to its successful infection and colonization in the human gastrointestinal tract. Using comparative proteomics, a total of 48 proteins were identified in this study in the presence of moderate (0.3 %) or high (3 %) level of bile salts in the wild-type strain EGD. Identified proteins fell into 14 functional categories covering most of the biochemical functions of bacterial cells, indicating that there were complex physiological mechanisms involved in L. monocytogenes tolerance of bile stress. Among them, 16, 14, and 18 proteins were expressed differently in the isogenic deletion mutants of L. monocytogenes EGDΔsigB, EGDΔprfA, and EGDΔprfAΔsigB, respectively, compared with their parent strain EGD at corresponding concentrations of bile salts. All proteins identified in EGDΔsigB and EGDΔprfAΔsigB were all down-expressed in the presence of bile salts, whereas several proteins were up-expressed in EGDΔprfA, in particular at the high level of bile (3 %), indicating that SigB plays an essential positive role in L. monocytogenes tolerance of bile stress and that the negative effect of PrfA may facilitate its survival in bile in the gastrointestinal tract before its successful colonization and invasion.     

Enhancement of stress tolerance in cucumber seedlings by proanthocyanidins

Proanthocyanidins (PAs) are the main products of the flavonoid biosynthetic pathway in many plants. However, their biological function during environmental stresses in plants is rarely reported. In the present study, the effects of pretreatment with PAs on the response of cucumber (Cucumis sativus L.) seedlings to high irradiance (HI), polyethylene glycol (PEG), and cold stress were investigated. The PAs pretreament alleviated stress-induced oxidative damage in plant cells and increased the activity of alternative oxidase (AOX) and content of abscisic acid (ABA). Furthermore, PAs-pretreated seedlings suffered less damage by the stress conditions, maintained higher content of chlorophyll a+b and AOX proteins in comparison with the control. Therefore, our findings suggest that PAs might contribute to plant tolerance to environmental stresses.     

A transcriptomic analysis reveals the nature of salinity tolerance of a wheat introgression line

The bread wheat cultivar Shanrong No.3 (SR3) is a salinity tolerant derivative of an asymmetric somatic hybrid between cultivar Jinan 177 (JN177) and tall wheatgrass (Thinopyrum ponticum). To reveal some of the mechanisms underlying its elevated abiotic stress tolerance, both SR3 and JN177 were exposed to iso-osmotic NaCl and PEG stress, and the resulting gene expression was analysed using a customized microarray. Some genes associated with stress response proved to be more highly expressed in SR3 than in JN177 in non-stressed conditions. Its unsaturated fatty acid and flavonoid synthesis ability was also enhanced, and its pentose phosphate metabolism was more active than in JN177. These alterations in part accounted for the observed shift in the homeostasis related to reactive oxygen species (ROS). The specific down-regulation of certain ion transporters after a 0.5 h exposure to 340 mM NaCl demonstrated that Na(+) uptake occurred rapidly, so that the early phase of salinity stress imposes more than simply an osmotic stress. We discussed the possible effect of the introgression of new genetic materials in wheat genome on stress tolerance.     

Effects of exogenous spermidine on antioxidant system of tomato seedlings exposed to high temperature stress

The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content and superoxide anion (O₂) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.     

Effects of exogenous putrescine on gas-exchange characteristics and chlorophyll fluorescence of NaCl-stressed cucumber seedlings

The effects of 10 mM putrescine (Put) treated by spraying on leaves on growth, chlorophyll content, photosynthetic gas-exchange characteristics, and chlorophyll fluorescence were investigated by growing cucumber plants (Cucumis sativus L. cv. ChangChun mici) using hydroponics with or without 65 mM NaCl as a salt stress. Salt stress caused the reduction of growth such as leaf area, root volume, plant height, and fresh and dry weights. Furthermore, net photosynthesis rate (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), and transpiration rate (T _r) were also reduced by NaCl, but water use efficiency (WUE; P _n/T _r) showed a tendency to be enhanced rather than reduced by NaCl. However, Put alleviated the reduction of P _n by NaCl, and showed a further reduction of C _i by NaCl. The reduction of g _s and T _r by NaCl was not alleviated at all. The enhancement of WUE by NaCl was shown to have no alleviation at day 1 after starting the treatment, but after that, the enhancement was gradually reduced till the control level. Maximum quantum efficiency of PSII (F _v/F _m) showed no effects by any conditions based on the combination of NaCl and Put, and in addition, kept constant values in plants grown in each nutrient solution during this experimental period. The efficiency of excitation energy capture by open photosystem II (PSII) (F _v′/F _m′), actual efficiency of PSII (Φ_PSII), and the coefficient on photochemical quenching (qP) of plants with NaCl were reduced with time, and the reduction was alleviated till the control level by treatment with Put. The F _v′/F _m′, Φ_PSII, and qP of plants without NaCl and/or with Put showed no variation during the experiment. Non-photochemical quenching of the singlet excited state of chlorophyll a (NPQ) showed quite different manner from the others as mentioned above, namely, continued to enhance during the experiment.     

Role of calcium and calmodulin antagonist in photosynthesis and salinity tolerance inChlorella vulgaris

To cast light upon the role of Ca¹⁺ and calmodulin on photosynthetic rate (P_n), dark respiration (R_D) and amino acid and protein contents in salinity stressed and non-stressedChlorella cultures, the Ca²⁺ chelator EGTA [ethylene glycol-bis-(2-aminoethyl ether)-N,N- tetraacetate] and the calmodulin antagonist TFP (trifluperazine) were used. TFP markedly inhibited P_N while EGTA exerted a slight, if any, effect on P_N. NaCl tolerance, on the other side, was markedly abolished by TFP that inhibited P_N and lowered rate of proline accumulation. Calmodulin might be involved in osmoregulation and salt tolerance ofChlorella. R_D, however, was markedly enhanced by EGTA and Ca²⁺-free medium and hence the Ca²⁺ deprivation increased stress severity exerted by NaCl. Combinations of Na⁺ and Ca²⁺ enhanced P_N, decreased R_D and proline content in comparison with an osmotically equivalent reference culture containing only NaCl. Addition of Ca²⁺ to TFP treated cultures failed to reactivate calmodulin for proline synthesis. However, when Ca²⁺ was added to EGTA-treated cultures, only relatively reduced proline contents were recorded.     

Ammonium enhances the uptake, bioaccumulation, and tolerance of phenanthrene in cucumber seedlings

Aims

Phenanthrene is one of the ubiquitous, persistent organic pollutants commonly found in soil and sediments. The study will provide insight regarding the feasibility of nitrogen-assisted phytoremediation.

Methods

To study the effects of various nitrogen forms on cucumber seedling phenanthrene tolerance, hydroponic experiments were conducted in a greenhouse.

Results

Under phenanthrene stress, decreases in plant growth and biomass were more pronounced with a nitrate supply than with ammonium. In addition, phenanthrene concentrations in plants fed with ammonium were higher than those fed with nitrate. The reduction in plant protein and sugar, increases in nitrogen and phosphate concentrations, and increased activity of antioxidative enzymes may contribute to the phenanthrene stress response and adaptation. Higher peroxidase, superoxide dismutase, and catalase activities were found in ammonium-fed plants as compared to nitrate-fed plants under phenanthrene stress. Moreover, the reduction in soluble protein content and increases in phenanthrene transport and accumulation in non-photosynthetic organs may enable ammonium-fed plants to adapt more effectively to adverse conditions.

Conclusions

Overall, these results suggest that ammonium nutrition could provide a useful tool to improve the growth and adaption of plants under phenanthrene stress.     

Exogenous spermidine affects polyamine metabolism in salinity-stressed Cucumis sativus roots and enhances short-term salinity tolerance

We investigated the effects of short-term salinity stress and spermidine application to salinized nutrient solution on polyamine metabolism and various stress defense reactions in the roots of two cucumber (Cucumis sativus L.) cultivars, Changchun mici and Jinchun No. 2. Seedlings grown in nutrient solution salinized with 50 mM NaCl for 8 d displayed reduced relative water content, net photosynthetic rates and plant growth, together with increased lipid peroxidation and electrolyte leakage in the roots. These changes were more marked in cv. Jinchun No. 2 than in cv. Changchun mici, confirming that the latter cultivar is more salinity-tolerant than the former. Salinity stress caused an increase in superoxide and hydrogen peroxide production, particularly in cv. Jinchun No. 2 roots, while the salinity-induced increase in antioxidant enzyme activities and proline contents in the roots was much larger in cv. Changchun mici than in cv. Jinchun No. 2. In comparison to cv. Jinchun No. 2, cv. Changchun mici showed a marked increase in arginine decarboxylase, ornithine decarboxylase, S-adenosylmethionine decarboxylase and diamine oxidase activities, as well as free spermidine and spermine, soluble conjugated and insoluble bound putrescine, spermidine and spermine contents in the roots during exposure to salinity. On the other hand, spermidine application to salinized nutrient solution resulted in alleviation of the salinity-induced membrane damage in the roots and plant growth and photosynthesis inhibition, together with an increase in polyamine and proline contents and antioxidant enzyme activities in the roots of cv. Jinchun No. 2 but not of cv. Changchun mici. These results suggest that spermidine confers short-term salinity tolerance on cucumber probably through inducing antioxidant enzymes and osmoticants.     

褪黑素对高温胁迫下黄瓜幼苗抗坏血酸代谢系统的影响

以‘津春4号’黄瓜幼苗为试材,采用叶面喷施的方法,研究了外源褪黑素对高温胁迫下黄瓜幼苗叶片抗坏血酸代谢系统的影响.结果表明:高温胁迫后,黄瓜幼苗叶片过氧化氢(H2O2)和丙二醛(MDA)含量明显增加;还原型抗坏血酸(AsA)和还原型谷胱甘肽(GSH)含量持续下降,脱氢抗坏血酸(DHA)和氧化型谷胱甘肽(GSSG)含量逐渐升高,AsA/DHA和GSH/GSSG大幅下降;抗坏血酸过氧化物酶(APx)、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)活性明显升高,并在12 h达到最大.外施褪黑素能有效抑制高温胁迫下黄瓜幼苗叶片H2O2和MDA的积累,提高抗氧化物质AsA和GSH含量及抗坏血酸代谢相关酶APx、MDHAR、DHAR和GR活性,从而增强对H2O2的清除能力,抑制活性氧的产生,维持细胞膜的稳定性,减轻高温对植株造成的伤害,提高黄瓜幼苗抵御高温胁迫的能力.     

外源Spd对盐碱胁迫下番茄幼苗氮代谢及主要矿质元素含量的影响

采用水培方法,研究了盐碱与Spd处理对两品种番茄(中杂9号和金棚朝冠)幼苗氮代谢及主要矿质元素含量的影响.结果表明:盐碱胁迫下,番茄幼苗干生物量显著减少,植株生长受到抑制;叶片和根系硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、谷氨酸合成酶(GOGAT)活性及硝态氮(NO3--N)、全N、全K、Ca2+、Mg2+含量显著降低,铵态氮(NH4+-N)、Na+含量显著增加;两品种叶片及中杂9号根系谷氨酸脱氢酶(GDH)活性显著升高,金棚朝冠根系GDH活性变化不显著;叶片全P含量显著降低,根系全P含量显著升高(金棚朝冠)或无显著变化(中杂9号).Spd处理通过增强NR、GS、GOGAT活性提高了植株对NH4+的同化利用率,有效缓解了盐碱胁迫导致的氮代谢紊乱,进而促进不同器官对P、K、Ca、Mg、Na的吸收、释放或转运,在一定程度上维持了各元素之间的相对平衡,从而增强植株对逆境的适应能力.此外,盐碱对中杂9号的抑制作用及外源Spd对其氮代谢紊乱和营养失衡的缓解作用高于金棚朝冠.     

油菜素内酯对低氧胁迫下黄瓜幼苗叶片线粒体、叶绿体超微结构及光合的影响

在水培条件下,研究24-表油菜素内酯(EBR)对低氧胁迫下黄瓜幼苗叶片叶绿体和线粒体超微结构及光合的影响.结果表明:与正常通气条件相比,低氧胁迫下表观量子效率(AQY)和羧化效率(CE)显著降低,而光补偿点(LCP)、暗呼吸速率(Rd)和CO2补偿点(CCP)显著升高;低氧胁迫并添加油菜素内酯处理下,CE与低氧胁迫处理相比显著提高29.4％,而LCP和Rd分别显著下降15.0％和14.4％.光响应Pn-PPFD曲线和CO2响应Pn-Ci曲线表明,低氧胁迫下净光合速率(Pn)增幅降低,而添加油菜素内酯有利于Pn增幅的提高.低氧胁迫下叶绿体和线粒体结构受到伤害,而油菜素内酯可以缓解低氧胁迫对黄瓜幼苗叶绿体和线粒体超微结构的不良影响,使叶片维持较好的光合性能.     

Comparative analysis of effect of exogenous ammonium on soybean tissue and Chlamydomonas cells

This paper presents a comparative analysis of obtained experimental data on the effect of exogenous ammonium on the protein and chlorophyll content, on the number of ribosomal structures, and on expression of the ribosomal genes encoding protein of small subunit rpS6 and 18S rRNA in cells of the soybean callus culture Glycine max and of unicellular green alga Chlamydomonas reinhardtii. It has been shown that, under the effect of exogenous ammonium. an increase of the number ribosomal structures in cells of the soybean callus, as well as in the alga cells, is not caused by an increase in the activity of the corresponding ribosomal genes. Possible mechanisms of action of ammonium on the content both of ribosomes in cells and of their protein and chlorophyll are discussed.