Calcium regulates Gladiolus flower senescence by influencing antioxidative enzymes activity

The objective of the present investigation was to study the role of calcium on antioxidative enzymes activity during the post-harvest life of Gladiolus (Gladiolus grandiflorus). Among the various calcium (Ca) treatments, 50 mmol l⁻¹ Ca treatments caused the highest increase in the vase life of the spike, from 5.5 days in control to about 9 days. Relative water content and membrane stability index (MSI) decreased from I to V stage. However, significant increase in relative water content and MSI were observed by 50 mmol l⁻¹ Ca as compared to control. Indices of oxidative stress such as lipid peroxidation and lipoxygenase activity increased from I to V stage, but decreased significantly in 50 mmol l⁻¹ Ca treatment. The activities of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) decreased initially from stage I to II, followed by an increase in stage III and thereafter started to decline at stages IV and V. Ascorbate peroxidase (APX) activity increased initially from stage I to III and thereafter declined in stage IV and V in both control and treatment. However, Ca with concentration of 50 mmol l⁻¹ increased the activities of SOD, CAT and APX at all the stages. The results revealed that spikes treated with Ca (50 mmol l⁻¹) solution maintained higher level of antioxidant enzymes activity and also showed delayed senescence in comparison to control.     

Effects of 28-homobrassinolide on growth, lipid peroxidation and antioxidative enzyme activities in seedlings of Zea mays L. under salinity stress

The effects of 28-homobrassinolide (28-homoBL) on seedling growth, lipid peroxidation and antioxidative enzyme activities in the seedlings of Zea mays L. (var. Partap-1) under salt (NaCl) stress were studied. The surface-sterilized seeds were germinated in petriplates containing different concentrations of NaCl (25, 50, 75 and 100 mM) only, 28-homoBL (10⁻⁷, 10⁻⁹ and 10⁻¹¹ M) only and NaCl supplemented with 28-homoBL for 7 days. The activities of superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APOX, EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) were analysed in 7 day-old seedlings. It was observed that 28-homoBL treatments reduced the toxicity of salt on seedling growth considerably. Lipid peroxidation level was significantly increased under saline stress, but lowered with 28-homoBL applications revealing less oxidative damage. Further 28-homoBL treatments to the seedlings showed an enhancement in activities of SOD, POD, CAT and APOX. The activities of all antioxidative enzymes were further increased in seedlings treated with solution containing 28-homoBL and salt together as compared to seedlings treated with different concentration of salt solution only.     

In vivo evolutionary engineering of a boron-resistant bacterium: <Emphasis Type="Italic">Bacillus boroniphilus</Emphasis>

Boron is an industrially and biologically important element. However, the mechanisms of boron tolerance and its transport in bacteria and many other living systems are still not clearly understood. In this study, the boron resistance level of a boron-tolerant bacterium, Bacillus boroniphilus DSM 17376, was improved up to 300 mmol l⁻¹ boron, by employing an in vivo evolutionary engineering strategy based on batch selection under continuous exposure to gradually increasing boron stress levels. The resistance was heterogeneous within the final mutant population which ranged from about 1- to 16-fold of the wild type resistance at 150 mmol l⁻¹ boron stress level. Boron-resistant mutants had significant cross-resistance to iron and copper stresses, and were also cross-resistant to salt (NaCl) stress, suggesting a common resistance mechanism between these stress types. Additionally, highly boron-resistant mutants had up to 2.8-fold higher boron contents than the wild-type, when exposed to high levels of (150 mmol l⁻¹) continuous boron stress throughout their cultivation. It was shown that evolutionary engineering is a successful approach to significantly increase bacterial boron resistance and investigate the complex mechanism of boron tolerance and transport in microbial systems.     

Effects of cytokinin on callus proliferation associated with physiological and biochemical changes in <Emphasis Type="Italic">Vitis vinifera</Emphasis> L.

The essential role of 6-benzylaminopurine (BA) in plant tissue culture has been widely known; however, physiological and biochemical mechanisms behind BA requirement have not been fully understood yet. BA may have an important role on callus growth by regulating antioxidant enzyme activities and acting as an effective free radical scavenger. To test this hypothesis, the impact of exogenous BA concentrations on antioxidative system in Vitis vinifera L. cv. ‘Bogazkere’ callus was investigated under in vitro conditions. Relative fresh weight growth (RFWG) of calli, total phenolics (TP) content, endogenous hydrogen peroxide (H₂O₂), malondialdehyde (MDA), proline concentrations, percentage of electrolyte leakage (EL), and some of the antioxidant enzyme activities; such as superoxide dismutase (SOD), and guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were measured. Inhibitory effect of high concentrations of BA on antioxidant enzyme activities and RFWG was found. In the presence of BA at 0.1 mg L⁻¹, SOD, POD, and APX activities decreased, while CAT activity increased in comparison with the controls. Exogenous BA treatments higher than 0.1 mg L⁻¹ resulted in an increase in cellular TP, H₂O₂, MDA, proline contents, and percentage of EL, while RFWG of calli decreased. Based on the findings, it may be concluded that only 0.1 mg L⁻¹ BA concentration combined with NAA could play a direct role in reducing the level of free radicals and phenolic production associated with proliferation capacity of grape cells under in vitro conditions. Furthermore, cytokinin was effective in the antioxidative enzyme system, lipid peroxidation, and electrolyte leakage.     

Different antioxidant responses to salt stress in two different provenances of <Emphasis Type="Italic">Carthamus tinctorius</Emphasis> L.

Seedlings of two Tunisian Carthamus tinctorius L. provenances (Kairouan and Tazarka) differing in salt sensitivity were hydroponically grown at 0 and 50 mM NaCl over 21 days. Leaves of Kairouan (salt-sensitive) showed a 48% restriction in their growth at 50 mM NaCl although they accumulated less sodium than those of Tazarka (less salt-sensitive) that maintained an unchanged growth. Salt treatment induced oxidative stress in C. tinctorius and the effect was more pronounced in the leaves of the more salt sensitive provenance, Kairouan. Both provenances exhibited a stimulation of antioxidant enzyme activities with higher catalase (CAT) and superoxide dismutase (SOD) activities in Tazarka and higher peroxidase (POD) activity in Kairouan. But, it seems that antioxidant activities were more correlated with polyphenol content. Actually, leaves of Tazarka experienced higher polyphenol and antioxidant activity than Kairouan at 50 mM NaCl. Hence, moderate salinity (3 g NaCl L⁻¹) enhanced bioactive molecule yield in the less salt sensitive provenance, Tazarka. In addition, C. tinctorius was found rich in ascorbic acid, but the moderate salt stress enhanced its production only in the sensitive provenance.     

Effects of manganese on the growth,photosystem II and SOD activity of the dinoflagellate <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Experimental ecology methods and chlorophyll fluorescence technology were used to study the effects of different concentrations of manganese (10⁻¹²– 10⁻⁴ mol L⁻¹) on the growth, photosystem II and superoxide dismutase (SOD) activity of Amphidinium sp. MACC/D31. The results showed that manganese had a significant effect on the growth rate, fluorescence parameters (maximal photochemical efficiency of PSII (F _v /F _m ), photochemical quenching (qP) and non-photochemical quenching (NPQ)) in the exponential stage (days 1–3) and SOD activity of Amphidinium sp. (P < 0.05). F _v/F _m in the exponential stage in 10⁻¹² mol L⁻¹ manganese concentration was significantly lower whilst qP and NPQ significantly higher than those in the other concentrations. F _v /F _m (days 6–9) in 10⁻⁴ mol L⁻¹ manganese was significantly higher than those in the other concentrations. F _v /F _m (days 3–6) increased with increased concentration of manganese from 10⁻¹² to 10⁻⁴ mol L⁻¹. The values of qP and NPQ decreased with decreased concentrations of manganese, except for those in days 4–6. F _v /F _m under each concentration increased earlier and decreased later with culture stage whilst NPQ decreased earlier and increased later. The SOD activity increased with increased concentration of manganese from 10⁻¹² to 10⁻⁸ mol L⁻¹. The SOD activity in 10⁻⁴ mol L⁻¹ manganese was significantly higher than those in the other concentrations and in 10⁻¹² mol L⁻¹ manganese, it was significantly lower than those in the other concentrations.     

Effect of aeration strategy on the metabolic flux of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> producing 1,3-propanediol in continuous cultures at different glycerol concentrations

The microbial production of 1,3-propaneidol (1,3-PD) by Klebsiella pneumoniae in continuous fermentation was investigated under low, medium and high glycerol concentrations in the absence and presence of oxygen. The production of 1,3-PD increased with increasing glycerol concentrations, reaching a maximum (266 mmol l⁻¹) under high glycerol concentration (760 mmol l⁻¹) with air sparging at 0.04 vvm. The yield of 1,3-PD, however, decreased gradually with increasing glycerol concentrations, with the highest yield (0.52 mol mol⁻¹) obtained for low glycerol concentration (270 mmol l⁻¹) under anaerobic condition. Enzyme activity assays showed that the specific activity of glycerol dehydratase was highest (0.04 U mg⁻¹) for culture sparged with 0.04 vvm air under high glycerol concentration. The specific activities of glycerol dehydrogenase and 1,3-propanediol oxidoreductase were also improved for all glycerol concentrations and in the presence of oxygen, implying that the dha operon was not repressed under microaerobic conditions. Analysis of metabolic fluxes showed that more carbon flux was shifted to the oxidative pathway with increasing glycerol concentrations, resulting in a reduced flux to 1,3-PD formation. However, the increases in carbon fluxes were not evenly distributed among the oxidative branches of the pathway. Furthermore, ethanol and acetic acid levels were slightly increased whereas 2,3-butanediol and lactic levels were greatly enhanced.     

Adaptability to elevated temperature and nitrogen addition is greater in a high-elevation population than in a low-elevation population of Hippophae rhamnoides

Hippophae rhamnoides L. is a broadleaf deciduous woody shrub occurring in southwest China, where it has been widely used in ecological restoration. In this study we investigated growth and physiological responses of 2-year-old healthy seedlings to elevated temperature, nitrogen (N) addition and their combination in two contrasting populations from high and low elevations. In closed-top chamber experiments, two populations were subjected to two temperature conditions (ambient temperature and temperature elevated by 2.2 ± 0.2°C) and two N levels (0 and 25 g N m⁻² a⁻¹). Compared with the control, increases in total leaf area (TLA), total chlorophyll content (TC), light-saturated photosynthetic rate (P _max), guaiacol peroxidase activity (POD), catalase activity (CAT) and carbon isotope composition (δ¹³C) were greater in the high-elevation population than in the low-elevation population under elevated temperature. On the other hand, decreases in root and shoot biomass ratio (RS), TC, P _max, light saturation point (L _SP), light compensation point (L _CP), superoxide dismutase (SOD), POD, CAT and δ¹³C were lower in the high-elevation population than in the low-elevation population under N addition. Moreover, the combination of elevated temperature and N addition decreased RS, P _max, apparent quantum efficiency (Φ), SOD, POD and δ¹³C significantly more in the low-elevation population than in the high-elevation population. These results demonstrated that there are different adaptive strategies among H. rhamnoides populations, the high-elevation population exhibiting higher adaptability to elevated temperature and N addition than the low-elevation population.     

An alginate-derived oligosaccharide enhanced wheat tolerance to cadmium stress

Hydroponic experiments were carried out to study the role of alginate-derived oligosaccharides (ADO) in enhancing wheat (Triticum aestivum L.) tolerance to cadmium stress. Data were collected on plant biomass, chlorophyll content, photosynthetic rate, antioxidant enzyme activity and malondialdehyde (MDA) content. Under 100 μM Cd stress, plant growth was significantly inhibited. Shoot length, root length, fresh and dry weight were sharply reduced by 24.21, 34.59, 22.1 and 14.7%, respectively of the control after 10 day of Cd exposure. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were increased and MDA content increased. Wheat seeds were soaked for 5 h in 1,000 mg L⁻¹ ADO solution before cadmium stress. ADO pretreatment alleviated cadmium toxicity symptoms, which were reflected by increasing root and shoot lengths, fresh and dry weight, chlorophyll content and photosynthetic rate (P _n ). Furthermore, ADO pretreatment significantly increased antioxidant enzyme (SOD, CAT and POD) activities and reduced MDA content in leaves and roots. The results indicated that ADO pretreatment partially protected the seedlings from cadmium toxicity during the following growth period.     

Does exogenous application of 24-epibrassinolide ameliorate salt induced growth inhibition in wheat (Triticum aestivum L.)?

A greenhouse experiment was conducted to assess whether exogenously applied 24-epibrassionlide (24-epiBL) could alleviate the adverse effects of salt on wheat. Two hexaploid wheat (Triticum aestivum L.) cultivars, S-24 (salt tolerant) and MH-97 (moderately salt sensitive), were grown under control (0 mM NaCl in full strength Hoagland’s nutrient solution) or saline conditions (150 mM of NaCl in full strength Hoagland’s nutrient solution). After 41 days growth of wheat plants under saline conditions, 24-epiBL was applied as a foliar spray. Four levels of BR were used as 0 (water spray), 0.0125, 0.025, and 0.0375 mg l⁻¹. Application of 24-epiBL increased plant biomass and leaf area per plant of both cultivars under non-saline conditions. However, under saline conditions, improvement in growth due to exogenous 24-epiBL was observed only in S-24. Photosynthetic rate was reduced due to salt stress in both cultivars, but this inhibitory effect was ameliorated significantly by the exogenous application of 24-epiBL. Exogenously applied 24-epiBL also enhanced the photosystem-II efficiency in both cultivars measured as F _v /F _m ratio. Although the activities of antioxidant enzymes, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) were increased due to salt stress in both wheat cultivars, exogenously applied 24-epiBL had a varying effect on the antioxidant system. The activity of SOD remained unaffected in both cultivars due to 24-epiBL application, but that of POD and CAT was promoted in the salt stressed plants of cv. S-24 only. In conclusion, improvement in growth in both wheat cultivars due to foliar applied 24-epiBL was found to be associated with 24-epiBL-induced enhancement in photosynthetic capacity. The 24-epiBL-induced regulation of antioxidant enzymes or growth under saline conditions was cultivar specific.     

Effects of metalaxyl enantiomers stress on root activity and leaf antioxidant enzyme activities in tobacco seedlings

The objective of this experiment was to study the effects of metalaxyl enantiomers on the activity of roots and antioxidative enzymes in tobacco seedlings. Water culture experiment was conducted to analyze the effects of different concentrations of metalaxyl enantiomers (30 and 10 mg L^?1) on root activity and leaf superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and malondialdehyde (MDA) content of tobacco seedlings. The results showed that metalaxyl significantly inhibited root activity and significantly improved leaf SOD, POD, and CAT activities and MDA content. A better physiological response in tobacco seedlings was observed at 30 mg L^?1 than at 10 mg L^?1 metalaxyl. The stereoselectivity for different enantiomers had no obvious effect on root activity and the leaf POD activity, but it affected significantly the SOD and CAT activities and MDA content. The SOD activity was promoted more by R‐enantiomer than by S‐enantiomer at 30 mg L^?1 metalaxyl, and the same effect was observed on CAT activity from the beginning to the end of the stress period. The MDA content under the stress by R‐enantiomer was higher than that under the stress by S‐enantiomer at 10 mg L^?1 metalaxyl.     

Growth and physiological activity in <Emphasis Type="Italic">Larix kaempferi</Emphasis> seedlings inoculated with ectomycorrhizae as affected by soil acidification

To evaluate the effect of ectomycorrhizal colonization on growth and physiological activity of Larix kaempferi seedlings grown under soil acidification, we grew L. kaempferi seedlings with three types of ectomycorrhizae for 180 days in acidified brown forest soil derived from granite. The soil had been treated with an acid solution (0 (control), 10, 30, 60, and 90 mmol H⁺ kg⁻¹). The water-soluble concentrations of Ca, Mg, K, Al, and Mn increased with increasing amounts of H⁺ added to the soil. Ectomycorrhizal development significantly increased in soil treated with 10 and 30 mmol H⁺ kg⁻¹ but was significantly reduced in soil treated with 60 and 90 mmol H⁺ kg⁻¹. The concentrations of Al and Mn in needles or roots increased with increasing H⁺ added to the soil. The total N in seedlings significantly increased with increasing H⁺ in soil and colonization with ectomycorrhiza. The maximum net photosynthetic rate at light and CO₂ saturation (P _max) was greater in soil treated with 10 mmol H⁺ kg⁻¹ than in controls, and was less is soils treated with greater than with 30 mmol H⁺ kg⁻¹, especially with 60 and 90 mmol H⁺ kg⁻¹. However, colonization with ectomycorrhiza significantly reduced the concentration of Al and Mn in needles or roots and increased the values of P _max and total dry mass (TDM). The relative TDM of L. kaempferi seedlings was approximately 40% at a (BC, base cation)/Al ratio of 1.0. However, ectomycorrhizal seedlings had a 100–120% greater TDM at a BC/Al ratio of 1.0 than non-ectomycorrhizal seedlings, even though the acid treatment reduced their overall growth.     

Sucrose regulated enhanced induction of anthraquinone,phenolics, flavonoids biosynthesis and activities of antioxidant enzymes in adventitious root suspension cultures of <Emphasis Type="Italic">Morinda citrifolia</Emphasis> (L.)

The effect of initial sucrose concentration was investigated in root suspension cultures of Morinda citrifolia to improve root growth and secondary metabolites production, i.e. anthraquinone, phenolics and flavonoids. Besides, oxidative stress level, antioxidant enzymes activity and membranes damage under different sucrose concentration were estimated. A 5% sucrose supply was shown to be optimal for the production of root dry mass, but higher sucrose concentrations of 7–9% inhibited the accumulation of root dry weight (DW). However, the maximum production of anthraquinone (251.89 g L⁻¹ DW), phenolics (165.14 g L⁻¹ DW) and flavonoids (163.56 g L⁻¹ DW) were achieved at 1% sucrose-treated culture, which may be a source carbon skeletons for secondary metabolism. At the same time was observed low oxidative damage, which could be associated with high levels of secondary metabolites and the increased activity of catalase. Although, catalase (CAT) activity were stimulated at 7–9% sucrose-treated cultures, high accumulation of hydrogen peroxide (H₂O₂) and peroxidation of lipid (MDA) was induced. The observed high activity of CAT and guaiacol peroxidase (G-POD) were not sufficient enough to mitigate the toxic effect of H₂O₂.     

Salt stress responses of a halophytic grass <Emphasis Type="Italic">Aeluropus lagopoides</Emphasis> and subsequent recovery

To investigate the salt tolerance mechanisms, Aeluropus lagopoides as a halophytic plant was used. Plants were treated with 0, 150, 450, 600, and 750 mM NaCl and harvested at 0, 4, 8, and 10 days after treatment and 1 day and 1 week after recovery. Optimal growth, measured as fresh and dry weights, occurred at 150 mM NaCl, but it was suppressed by 450, 600, and 750 mM NaCl. Recovery significantly increased fresh and dry weights only in 750 mM NaCl-treated plants. Water content was decreased after NaCl treatment and increased after recovery. Na⁺ and proline contents and activity of superoxide dismutase (SOD) were increased after NaCl treatment and decreased after recovery in all treated plants. In contrast, K⁺ content and ascorbate peroxidase activity decreased after NaCl treatment and increased after recovery in all treated plants. Catalase (CAT) was activated only in 750 mM NaCl-treated plants. Total content of soluble protein was slightly changed after NaCl treatment. It was concluded that proline accumulation for osmotic adjustment, SOD activation for O₂^·− scavenging, and CAT activation at the higher level of salt stress to detoxify produced H₂O₂ were main A. lagopoides strategies under salt stress. A. lagopoides salt tolerance was not based on the restriction of Na⁺ uptake.     

外源一氧化氮对硝酸盐胁迫下黄瓜幼苗生长及抗氧化酶活性的影响

采用营养液培养试验,通过添加不同浓度(0.05、0.1、0.2、0. mmol·L^-1)的硝普钠（SNP）作为NO供体,研究外源NO对NO₃-胁迫下黄瓜幼苗生长及叶片抗氧化酶活性的影响.结果表明： 140 mmol·L^-1 NO₃-胁迫下,外加0.1 mmol·L^-1 SNP处理1 d和7 d后,黄瓜幼苗叶片中SOD、CAT和APX活性显著升高;MDA含量显著降低,可溶性蛋白含量增加,说明外加0.1 mmol·L^-1 SNP增强了黄瓜幼苗对活性氧的清除能力,降低了膜脂过氧化程度,幼苗生长势增加,对高浓度NO₃-胁迫的抗性增强;当SNP浓度达0.3 mmol·L^-1处理7 d后,SOD、POD、CAT和APX活性均开始降低,MDA含量增加,黄瓜幼苗受害加重.外加一定浓度(0.1～0.2 mmol·L^-1)的外源NO可缓解NO₃^-胁迫对黄瓜幼苗的影响.     

The Possible Roles of Priming with ZnO Nanoparticles in Mitigation of Salinity Stress in Lupine (Lupinus termis) Plants

To our knowledge, little attention has been paid to evaluating ZnO nanoparticles (ZNPs) roles in plants grown under salinity stress. In this study, seeds of lupine (Lupinus termis) plants were grown in plastic pots and exposed to 0 (control) and 150 (S) mM NaCl with or without priming with different concentrations of ZnO [20 mg L^?1 (ZNPs1), 40 mg L^?1 (ZNPs2), and 60 mg L^?1 (ZNPs3)] for 20 days. Salinized plants showed a reduction in plant growth parameters (root length, shoot length, fresh weight, and dry weight) and in the contents of photosynthetic pigments (chlorophyll a and b, and carotenoids) and Zn, as well as in the activity of catalase (CAT) against control plants. On the other side, salinity stress boosted the contents of organic solutes (soluble sugar, soluble protein, total free amino acids, and proline), total phenols, malondialdehyde (MDA), ascorbic acid and Na, as well as the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) in stressed plants over control plants. However, seed-priming with ZNPs mostly stimulated growth of stressed plants, which was accompanied by reinforcement in the levels of photosynthetic pigments, organic solutes, total phenols, ascorbic acid and Zn, as well as in the activities of SOD, CAT, POD, and APX enzymes over stressed plants alone. On the contrary, priming with ZNPs caused a decrement in the contents of MDA and Na in stressed plants relative to salinized plants alone. It is worthy to mention that, this improvement in salt tolerance of plants primed with ZNPs was more obvious in plants primed with ZNPs3 and grown both in unstressed and stressed regimes. Thus, our findings suggest that seed-priming with ZNPs, especially 60 mg L^?1 ZnO is an effective strategy that can be used to enhance salt tolerance of lupine plants.

     

Characteristics of cadmium accumulation and tolerance in <Emphasis Type="Italic">Rorippa globosa</Emphasis> (Turcz.) Thell., a species with some characteristics of cadmium hyperaccumulation

Characteristics of cadmium (Cd) accumulation and tolerance in Rorippa globosa (Turcz.) Thell., a species with some characteristics of cadmium hyperaccumulation were further investigated and compared with a closely related species, Rorippa islandica. The results showed that there was no phytotoxicity for R. globosa leaves or reduction in biomass when treated with 25 μg Cd g⁻¹, although the concentration of Cd accumulated in the leaves was up to 218.9 μg Cd g⁻¹ dry weight (DW). On the contrary, Cd toxicity was observed in R. islandica leaves by way of determining changes in fresh weight (FW), malondialdehyde (MDA) level and chlorophyll content while treated with 25 μg Cd g⁻¹ DW. R. globosa had stronger self-protection ability than R. islandica to adapt to oxidative stress caused by Cd. Application of Cd significantly increased the activity of superoxide dismutase (SOD) in leaves, the activity of peroxidase (POD) in roots, and the activity of catalase (CAT) in leaves and roots of R. globosa. By contrast, in R. islandica, the activity of antioxidant enzymes was inhibited or unchanged by various Cd treatments. However, R. globosa leaves had higher activity of antioxidant enzymes such as SOD and POD than that of R. islandica. The antioxidative defense systems in R. globosa might play an important role in Cd tolerance. The Cd treatments significantly induced the synthesis of phytochelatins (PCs) in the two species. Leaf PCs and Cd accumulation by R. globosa were much greater than those by R. islandica, but root PCs and Cd accumulation by R. islandica were much greater than those by R. globosa, suggesting that PCs in leaves may be a biomarker of Cd hyperaccumulation, and the synthesis of PCs may be related to an increase in the uptake of Cd ions into the cytoplasm, not the primary mechanism for Cd tolerance.     

In vitro selection of salt tolerant variants following <Superscript>60</Superscript>Co gamma irradiation of long-term callus cultures of <Emphasis Type="Italic">Zoysia matrella</Emphasis> [L.] Merr.

To study growth in the presence of NaCl, in vitro plantlets regenerated from callus of manilagrass (Zoysia matrella [L.] Merr.) were cultured on regeneration medium supplemented with or without 0.3 M NaCl. The results indicated that growth was significantly inhibited by NaCl, with the leaves becoming relatively shorter and thicker. The differences of in vitro plantlets grown under NaCl stress provided specific criteria for the selection of salt tolerant variants. The 6-year maintained calli were treated with different doses (0, 5, 10, 20, 40, 80, 100, 150, 200, 250, and 300 Gy) of ₆₀Co γ rays. Regeneration rate and regeneration capacity of the calli were highest after treatment with 20 Gy ⁶⁰Co γ rays, 27.08 and 91.67% respectively. When the irradiation dose was increased to 100 Gy, 10.42% of the calli developed shoots, but at 150 Gy, both regeneration capacity and regeneration rate declined significantly, and no shoot was observed after 6 weeks of regeneration. Therefore, 100–150 Gy is the most appropriate irradiation span for inducing somaclonal variation. The irradiated calli were selected in vitro for NaCl tolerance. Five NaCl tolerant variant lines, Ze1, Fv1, Te1, Tw1, Fr1, were selected on subculture medium supplemented with 0.35 M NaCl, then transferred to regeneration medium containing 0.25 M NaCl, and grown in a greenhouse. The dark green colour index (DGCI) was used to identify the amount of injury caused by NaCl treatment. This was significantly higher in four of the lines, Ze1, Fv1, Te1, Fr1 (30.88, 31.17, 30.45 and 37.70%, respectively) compared to the control line (CK), which was regenerated from calli subcultured monthly (27.39%), indicating that watering with NaCl caused less injury in these four lines. These lines had lower proline contents than CK under salt stress. The superoxide dismutase (SOD) activity was higher in Ze1 under control condition and its peroxidase (POD) activity increased significantly under salt stress. With Fr1 catalase (CAT) activity was higher under salt stress. The higher activity of these antioxidant enzymes may contribute to the enhanced salt tolerance of the four plant lines.     

外源5-氨基乙酰丙酸对盐胁迫下菘蓝种子萌发及幼苗抗氧化酶活性的影响

采用砂培方式,研究了外源5-氨基乙酰丙酸(ALA)对盐胁迫下菘蓝种子的萌发、幼苗叶片的可溶性糖含量、丙二醛(MDA)含量及其抗氧化酶活性的影响,探讨ALA缓解菘蓝受盐胁迫伤害的响应机制。结果显示:(1)菘蓝种子萌发及幼苗生长在100 mmol·L^-1 NaCl胁迫下受到明显的抑制,种子发芽率、发芽势、发芽指数、活力指数与自然含水量均显著降低,丙二醛含量、可溶性糖含量以及超氧化物歧化酶(SOD)、过氧化物酶(POD)活性显著升高。(2)盐胁迫下适宜浓度的ALA处理显著提高了种子萌发率、自然含水量及SOD、POD和CAT活性,降低了可溶性糖和丙二醛的含量,并以16.7 mg·L^-1 ALA处理盐胁迫下菘蓝种子的发芽率、发芽势最大,其幼苗的SOD、POD、CAT活性最强。研究表明,盐胁迫显著抑制菘蓝种子的萌发及幼苗生长,适宜浓度的ALA能够有效缓解盐胁迫对菘蓝种子萌发及幼苗生长的伤害,提高植株的抗盐性,并以16.7 mg·L^-1 ALA处理效果最佳。     

Roles of cortisol and carbonic anhydrase in acid–base compensation in rainbow trout, <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

Fish compensate for acid–base disturbances primarily by modulating the branchial excretion of acid–base equivalents, with a supporting role played by adjustment of urinary acid excretion. The present study used metabolic acid–base disturbances in rainbow trout, Oncorhynchus mykiss, to evaluate the role played by cortisol in stimulating compensatory responses. Trout infused with acid (an iso-osmotic solution of 70 mmol L⁻¹ HCl), base (140 mmol L⁻¹ NaHCO₃) or saline (140 mmol L⁻¹ NaCl) for 24 h exhibited significant elevation of circulating cortisol concentrations. Acid infusion significantly increased both branchial (by 328 μmol kg⁻¹ h⁻¹) and urinary (by 5.9 μmol kg⁻¹ h⁻¹) net acid excretion, compensatory responses that were eliminated by pre-treatment of trout with the cortisol synthesis inhibitor metyrapone (2-methyl-1,2-di-3-pyridyl-1-propanone). The significant decrease in net acid excretion (equivalent to enhanced base excretion) of 203 μmol kg⁻¹ h⁻¹ detected in base-infused trout was unaffected by metyrapone treatment. Acid- and base-infusions also were associated with significant changes in the relative mRNA expression of branchial and renal cytosolic carbonic anhydrase (tCAc) and renal membrane-linked CA IV (tCA IV). Cortisol treatment caused changes in CA gene expression that tended to parallel those observed with acid but not base infusion. For example, significant increases in renal relative tCA IV mRNA expression were detected in both acid-infused (~2x) and cortisol-treated (~10x) trout, whereas tCA IV mRNA expression was significantly reduced (~5x) in base-infused fish. Despite changes in CA gene expression in acid- or base-infused fish, neither acid nor base infusion affected CAc protein levels in the gill, but both caused significant increases in branchial CA activity. Cortisol treatment similarly increased branchial CA activity in the absence of an effect on branchial CAc protein expression. Taken together, these findings provide support for the hypothesis that in rainbow trout, cortisol is involved in mediating acid–base compensatory responses to a metabolic acidosis, and that cortisol exerts its effects at least in part through modulation of CA.