Pea plant responsiveness under elevated [CO2] is conditioned by the N source (N2 fixation versus NO3− fertilization)

The main goal of this study was to test the effect of [CO₂] on C and N management in different plant organs (shoots, roots and nodules) and its implication in the responsiveness of exclusively N₂-fixing and NO₃⁻-fed plants. For this purpose, exclusively N₂-fixing and NO₃⁻-fed (10 mM) pea (Pisum sativum L.) plants were exposed to elevated [CO₂] (1000 μmol mol⁻¹ versus 360 μmol mol⁻¹ CO₂). Gas exchange analyses, together with carbohydrate, nitrogen, total soluble proteins and amino acids were determined in leaves, roots and nodules. The data obtained revealed that although exposure to elevated [CO₂] increased total dry mass (DM) in both N treatments, photosynthetic activity was down-regulated in NO₃⁻-fed plants, whereas N₂-fixing plants were capable of maintaining enhanced photosynthetic rates under elevated [CO₂]. In the case of N₂-fixing plants, the enhanced C sink strength of nodules enabled the avoidance of harmful leaf carbohydrate build up. On the other hand, in NO₃⁻-fed plants, elevated [CO₂] caused a large increase in sucrose and starch. The increase in root DM did not contribute to stimulation of C sinks in these plants. Although N₂ fixation matched plant N requirements with the consequent increase in photosynthetic rates, in NO₃⁻-fed plants, exposure to elevated [CO₂] negatively affected N assimilation with the consequent photosynthetic down-regulation.     

Effects of salt stress on ion content,antioxidant enzymes and protein profile in different tissues of Broussonetia papyrifera

Although some plant responses to salinity have been characterized, the precise mechanisms by which salt stress damages plants are still poorly understood especially in woody plants. In the present study, the physiological and biochemical responses of Broussonetia papyrifera, a tree species of the family, Moraceae, to salinity were studied. In vitro-produced plantlets of B. papyrifera were treated with varying levels of NaCl (0, 50, 100 and 150 mM) in hydroponic culture. Changes in ion contents, accumulation of H₂O₂, as well as the activities and isoform profiles of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the leaves, stems and roots were investigated. Under salt stress, there was higher Na⁺ accumulation in roots than in stems and leaves, and Ca^2 +, Mg^2 + and P^3 + content, as well as K⁺/Na⁺ ratio were affected. NaCl treatment induced an increase in H₂O₂ contents in the tissues of B. papyrifera. The work demonstrated that activities of antioxidant defense enzymes changed in parallel with the increased H₂O₂ and salinity appeared to be associated with differential regulation of distinct SOD and POD isoenzymes. Moreover, SDS-PAGE analysis of total proteins extracted from leaves and roots of control and NaCl-treated plantlets revealed that in the leaves salt stress was associated with decrease or disappearance of some protein bands, and induction of a new protein band after exposure to 100 and 150 mM NaCl. In contrast, NaCl stress had little effect on the protein pattern in the roots. In summary, these findings may provide insight into the mechanisms of the response of woody plants to salt stress.     

In vitro seed maturation in Brassica rapa L.: Relationship of silique atmosphere to storage reserve deposition

The Brassica rapa L. silique is a self-contained environment that maintains hypoxia around the developing seeds, and in which carbon dioxide accumulates to very high concentrations (>30,000 ppm). How the silique microenvironment modulates the composition and amount of storage reserves in the seeds is of interest because of the important agricultural role played by canola (B. rapa and Brassica napus) as an oilseed. Because of the small volume and dynamic nature of this microenvironment in Brassica, a standardized system was needed to study the environmental role played in storage reserve deposition. For this purpose we have developed a silique culture system that permits maturation of seed in vitro. Siliques excised from plants just 11 days after pollination complete the ripening of their seeds after 20 days of culture in light (200 μmol/m²/s) on MS medium containing 30 g/l sucrose, 0.25 mg/l BAP, and 0.025 mg/l NAA. Cytochemical localization and biochemical analyses revealed that storage reserves were affected by the in vitro maturation system. Although following a comparable ripening timeline to that occurring on the plant, and producing fully germinable seeds, in vitro maturation resulted in a 40% reduction in seed weight and the mature seeds contained decreased lipid, but increased protein, starch and soluble carbohydrates. To study the internal atmosphere surrounding the seeds, we developed a method to capture silique gases in helium with subsequent quantification of O₂ and CO₂ in the sample by gas chromatography. Analysis of the internal silique atmosphere showed that in vitro siliques provided seeds with a less oxygenated environment than they experience attached to the plant. Carbon dioxide concentrations remained high later into the maturation sequence in vitro than on the plant. When sampling gases from siliques attached to plants, we found multiple samples from the same plant resulted in higher variance than when only a single silique was sampled, suggesting that connection to the plant directly influences internal silique gases. Lower O₂ in the in vitro siliques was correlated with depressed lipid content in their mature seeds, supporting the conclusion that oxygen availability limits lipid accumulation. Previous studies showed how environmental factors influence Brassica embryos grown in tissue culture. These systems fail to preserve the component of metabolic regulation that is enforced by the silique wall tissues. Our in vitro maturation system provides a useful tool for specialized investigations since both the gaseous and hormonal environments can be readily manipulated.     

Modulation of antioxidant enzyme activities and metabolites ratios by nitric oxide in short-term salt stressed soybean root nodules

Several abiotic factors cause molecular damage to plants either directly or through the accumulation of reactive oxygen species such as hydrogen peroxide (H₂O₂). We investigated if application of nitric oxide (NO) donor 2,2′-(hydroxynitrosohydrazono) bis-ethanimine (DETA/NO) could reduce the toxic effect resulting from short-term salt stress. Salt treatment (150 mM NaCl) alone and in combination with 10 μM DETA/NO or 10 μM DETA were given to matured soybean root nodules for 24 h. Salt stress resulted in high H₂O₂ level and lipid peroxidation while application of DETA/NO effectively reduced H₂O₂ level and prevented lipid peroxidation in the soybean root nodules. NO treatment increased the activities of ascorbate peroxidase and dehydroascorbate reductase under salt stress. Whereas short-term salt stress reduced AsA/DHAsA and GSH/GSSG ratios, application of the NO donor resulted in an increase of the reduced form of the antioxidant metabolites thus increasing the AsA/DHAsA and GSH/GSSG ratios. Our data suggests a protective role of NO against salt stress.     

Sap flow measurements as a basis for assessing trace-gas exchange of trees

The assessment of trace-gas uptake by plants is of basic interest in plant ecophysiology and atmospheric chemistry. For tall vegetation and extensive canopies micrometeorological methods and modelling of deposition or combinations of both are usually the methods of choice. However, distinguishing between the aerodynamically driven components of deposition and stomatal uptake is difficult and estimates of plant uptake remain uncertain. Canopy conductance derived from sapflow measurements of trees represents an important and highly variable component to determine the uptake of trace gases by trees under free atmospheric conditions. The theory of the assessment of trace-gas uptake by the sapflow-based approach is reviewed and exemplified for the uptake of ozone, nitrogen oxides, and ammonia into coniferous and deciduous tree species. First results on the stomatal ammonia compensation point (χ_s=0.11–0.27 nmol mol⁻¹) of the coniferous tree species Picea abies determined by a bio-assay are reported and compared with published values on herbaceous plants and gas-exchange approaches for P. abies. For a summer period in 2003, the ground-area scaled uptake rate of gaseous NH₃ by P. abies was more than twice as high (1.38 nmol m⁻² s⁻¹) than the uptake of NO_x (0.53 nmol m⁻² s⁻¹). Estimates of ground-area scaled O₃ uptake and phytomedically relevant O₃ doses of Fagus sylvatica were found to be significantly less under dry conditions in August 2003 (cumulative uptake 2.3 mmol m⁻²) than in years with sufficient soil water supply despite higher atmospheric O₃ concentrations in 2003. Cumulative ground-area scaled O₃ uptake of Pinus cembra reached 150 mmol m⁻² during the growing season at an alpine site. Preliminary results and future perspectives are discussed for the transfer of the approach to the uptake of carbon dioxide and hence to determine total net primary production of trees. This novel approach has the potential to reduce uncertainties of C fluxes measured by the eddy-covariance technique and biogeochemical plot studies. It also allows to determine flux components like heterotrophic and autotrophic respiration separately as residuals from budget equations. Overall, it is concluded that the sapflow-based methodology contributes a new quality of flux data significantly improving our current understanding of biospheric aspects of trace-gas fluxes into tall vegetation.     

Induction in the antioxidative systems and lipid peroxidation in suspension culture roots of Panax ginseng induced by oxygen in bioreactors

Roots of mountain ginseng (Panax ginseng) were exposed to various levels of oxygen (O₂) (30, 40 and 50%) for 15, 30 and 45 days in 5 L (working volume 4 L) airlift bioreactors. Ginsenoside accumulation and dry weight was enhanced up to 40% O₂; but thereafter declined ginsenoside and dry weight of the roots by increasing level of O₂. Gradual increase in H₂O₂ content and lipoxygenase activity (LOX), resulting in cellular damage and oxidative stress as indicated by increased malondialdehyde (MDA) content after 30 and 45 days at all O₂ levels was shown. Increased levels of O₂ (above ambient) resulted in increases in non-protein thiol (NP-SH) and cysteine content. Higher activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), catalase (CAT), guaiacol peroxidase (G-POD), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S transferase (GST) activities indicated that antioxidant enzymes played an important role in protecting the roots from O₂ up to 45 days, except at 50% O₂ where GR, GST and GPx decreased compared to the control. However, after 45 days, SOD activity decreased significantly compared to the control in the O₂-treated roots. This reflects the sensitivity of enzymes to O₂ toxicity. In stress related experiment, roots showed increased synthesis of ginsenosides when 25 and 50 μM H₂O₂ was applied. However, higher dose and increasing treatment inhibited ginsenoside synthesis. The results indicate that plant roots could grow and protect themselves from O₂ stress by coordinated induction of various antioxidant enzymes and metabolite contents. These results suggest that O₂ supplementation is useful for ginsenoside accumulation using 5-L bioreactors.     

Silicon improves salinity tolerance in wheat plants

Durum wheat (Triticum durum cv. Gediz-75) and bread wheat (Triticum aestivum cv. Izmir-85) were grown in a complete nutrient solution in a growth room to investigate effect of silicone supplied to the nutrient solution on plants grown at salt stress. The experiment was a 2 × 2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 100 mM, and two levels of silicone (Si) in nutrient solution, 0.25 and 0.50 mM, as Na₂SiO₃. The plants grown at 100 mM NaCl produced less dry matter and chlorophyll content than those without NaCl. Supplementary Si at both 0.25 and 0.5 mM ameliorated the negative effects of salinity on plant dry matter and chlorophyll content. Membrane permeability and proline content in leaves increased with addition of 100 mM NaCl and these increases were decreased with Si treatments. Sodium (Na) concentration in plant tissues increased in both leaves and roots of plants in the high NaCl treatment and Si treatments lowered significantly the concentrations of Na in both leaves and roots. Bread wheat was more tolerant to salinity than durum wheat. The accumulation of Na in roots indicates a possible mechanism whereby bread wheat copes with salinity in the rooting medium and/or may indicate the existence of an inhibition mechanism of Na transport to leaves. Concentrations of both Ca and K were lower in the plants grown at high NaCl than in those in the control treatment and these two element concentrations were increased by Si treatments in both shoots and roots but remained lower than control values in most cases.     

Nitric oxide interacts with mitochondrial complex III producing antimycin-like effects

The effect of NO between cytochromes b and c of the mitochondrial respiratory chain were studied using submitochondrial particles (SMP) from bovine heart and GSNO and SPER-NO as NO sources. Succinate-cytochrome c reductase (complex II-III) activity (222±4 nmol/min. mg protein) was inhibited by 51% in the presence of 500 μM GSNO and by 48% in the presence of 30 μM SPER-NO, in both cases at ~1.25 μM NO. Neither GSNO nor SPER-NO were able to inhibit succinate-Q reductase activity (complex II; 220±9 nmol/min. mg protein), showing that NO affects complex III. Complex II-III activity was decreased (36%) when SMP were incubated with l-arginine and mtNOS cofactors, indicating that this effect is also produced by endogenous NO. GSNO (500 μM) reduced cytochrome b₅₆₂ by 71%, in an [O₂] independent manner. Hyperbolic increases in O₂^•- (up to 1.3±0.1 nmol/min. mg protein) and H₂O₂ (up to 0.64±0.05 nmol/min. mg protein) productions were observed with a maximal effect at 500 μM GSNO. The O₂^•-/H₂O₂ ratio was 1.98 in accordance with the stoichiometry of the O₂^•- disproportionation. Moreover, H₂O₂ production was increased by 72–74% when heart coupled mitochondria were exposed to 500 μM GSNO or 30 μM SPER-NO. SMP incubated in the presence of succinate showed an EPR signal (g=1.99) compatible with a stable semiquinone. This EPR signal was increased not only by antimycin but also by GSNO and SPER-NO. These signals were not modified under N₂ atmosphere, indicating that they are not a consequence to the effect of NOx species on complex III area. These results show that NO interacts with ubiquinone-cytochrome b area producing antimycin-like effects. This behaviour comprises the inhibition of electron transfer, the interruption of the oxidation of cytochromes b, and the enhancement of [UQH^•]_ss which, in turn, leads to an increase in O₂^•- and H₂O₂ mitochondrial production rates.     

Discrimination against 15N among recombinant inbred lines of Phaseolus vulgaris L. contrasting in phosphorus use efficiency for nitrogen fixation

Although isotopic discrimination processes during nitrogen (N) transformations influence the outcome of ¹⁵N based quantification of N₂ fixation in legumes, little attention has been given to the effects of genotypic variability and environmental constraints such as phosphorus (P) deficiency, on discrimination against ¹⁵N during N₂ fixation. In this study, six Phaseolus vulgaris recombinant inbred lines (RILs), i.e. RILs 115, 104, 34 (P deficiency tolerant) and 147, 83, 70 (P deficiency sensitive), were inoculated with Rhizobium tropici CIAT899, and hydroaeroponically grown with P-sufficient (250 μmol P plant⁻¹ week⁻¹) versus P-deficient (75 μmol P plant⁻¹ week⁻¹) supply. Two harvests were done at 15 (before nodule functioning) and 42 (flowering stage) days after transplanting. Nodulation, plant biomass, P and N contents, and the ratios of ¹⁵N over total N content (¹⁵N/Nt) for shoots, roots and nodules were determined. The results showed lower ¹⁵N/Nt in shoots than in roots, both being much lower than in nodules. P deficiency caused a larger decrease in ¹⁵N/Nt in shoots (−0.18%) than in nodules (−0.11%) for all of the genotypes, and the decrease in shoots was greatest for RILs 34 (−0.33%) and 104 (−0.25%). Nodule ¹⁵N/Nt was significantly related to both the quantity of N₂ fixed (R² = 0.96***) and the P content of nodules (R² = 0.66*). We conclude that the discrimination against ¹⁵N in the legume N₂-fixing symbiosis of common bean with R. tropici CIAT899 is affected by P nutrition and plant genotype, and that the ¹⁵N/Nt in nodules may be used to screen for genotypic variation in P use efficiency for N₂ fixation.     

Bafouoside C,a new triterpenoid saponin from the roots of Cussonia bancoensis Aubrev. & Pellegr.

A new triterpenoid saponin named bafouoside C 3-O-β-d-glucopyranosyl-(1 → 4)-[β-d-galactopyranosyl-(1 → 2)]-β-d-glucuronopyranosyloleanolic acid 28-O-β-d-glucopyranosyl ester; (1), together with five known compounds 3-O-β-d-galactopyranosyl-(1 → 2)-β-d-glucuronopyranosyloleanolic acid (2), 23-hydroxyursolic acid (3), 28-O-α-l-rhamnopyranosyl-(1 → 4)-O-β-d-glucopyranosyl-(1 → 6)-O-β-d-glucopyranosyl-23-hydroxyursolic acid (4), 3-O-β-d-glucopyranosyl-23-hydroxyursolic acid (5), and 3-O-α-l-arabinopyranosyl-23-hydroxyursolic acid (6), were isolated from the roots of Cussonia bancoensis Aubrev. & Pellegr. Their structures were established on the basis of 1D- and 2D NMR data, mass spectrometry and chemical methods. The NMR data of the known compounds, as far as we know, are herein reported for the first time in CD₃OD. Compound 3 exhibited a weak cytotoxic activity against MDA-MB 231 human breast adenocarcinoma, A375 human malignant melanoma, and HCT116 human colon carcinoma cell lines.     

Dihydrochalcone glucosides and antioxidant activity from the roots of Anneslea fragrans var. lanceolata

Bioassay-guided fractionation of the roots of Anneslea fragrans var. lanceolata led to the isolation of four dihydrochalcone glucosides, davidigenin-2′-O-(6″-O-4″′-hydroxybenzoyl)-β-glucoside (1), davidigenin-2′-O-(2″-O-4″′-hydroxybenzoyl)-β-glucoside (2), davidigenin-2′-O-(3″-O-4″′-hydroxybenzoyl)-β-glucoside (3), and davidigenin-2′-O-(6″-O-syringoyl)-β-glucoside (4), and 13 known compounds. The structures were identified by means of spectroscopic analysis. Davidigenin-2′-O-(6″-O-syringoyl)-β-glucoside (4), 1-O-3,4-dimethoxy-5-hydroxyphenyl-6-O-(3,5-di-O-methylgalloyl)-β-glucopyranoside (5), lyoniresinol (10), and syringic acid (13) showed ABTS [2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)] cation radical scavenging activity, with SC₅₀ values of 52.6 ± 5.5, 26.0 ± 0.7, 6.0 ± 0.2, and 27.5 ± 0.6 μg/mL in 20 min, respectively. Lyoniresinol (10), isofraxidin (12), and syringic acid (13) also showed DPPH [1,1-diphenyl-2-picrylhydrazyl] radical scavenging activity, with SC₅₀ values of 8.4 ± 1.8, 51.6 ± 2.2, and 4.3 ± 0.7 μg/mL in 30 min, respectively.     

Gibberellic acid mediated induction of salt tolerance in wheat plants: Growth,ionic partitioning,photosynthesis, yield and hormonal homeostasis

In order to elucidate the GA₃-priming-induced physiochemical changes responsible for induction of salt tolerance in wheat, the primed and non-primed seeds of two spring wheat (Triticum aestivum L.) cultivars, namely, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant) were sown in a field treated with 15 dS m⁻¹ NaCl salinity. Although all the three concentrations (100, 150 and 200 mg L⁻¹) of GA₃ were effective in improving grain yield in both cultivars, the effect of 150 mg L⁻¹ GA₃ was much pronounced particularly in the salt intolerant cultivar when under salt stress. Seed priming with GA₃ altered the pattern of accumulation of different ions between shoots and roots in the adult plants of wheat under saline conditions. Treatment with GA₃ (150 mg L⁻¹) decreased Na⁺ concentrations both in the shoots and roots and increased Ca²⁺ and K⁺ concentrations in the roots of both wheat cultivars. GA₃-priming did not show consistent effect on gaseous exchange characteristics and the concentrations of auxins in the salt stressed plants of both wheat cultivars. However, all concentrations of GA₃ reduced leaf free ABA levels in the salt intolerant, while reverse was true in the salt tolerant cultivar under saline conditions. Priming with GA₃ (150 mg L⁻¹) was very effective in enhancing salicylic acid (SA) concentration in both wheat cultivars when under salt stress. Treatment with GA₃ (100–150 mg L⁻¹) lowered leaf free putrescine (Put) and spermidine (Spd) concentrations in the plants of both wheat cultivars. The decrease in polyamines (Put and Spd) and ABA concentrations in the salt stressed plants of the salt intolerant cultivar treated with GA₃ suggested that these plants might have faced less stress compared with control. Thus, physiologically, GA₃-priming-induced increase in grain yield was attributed to the GA₃-priming-induced modulation of ions uptake and partitioning (within shoots and roots) and hormones homeostasis under saline conditions.     

Flow velocity affects internal oxygen conditions in the seagrass Cymodocea nodosa

The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures (pO₂) in the Mediterranean seagrass, Cymodocea nodosa. We measured the internal pO₂ in the horizontal rhizomes of C. nodosa in darkness at different mainstream flow velocities, combined with different levels of water column oxygen pO₂ using an experimental flume in the laboratory. Flow velocity clearly had an effect on the internal oxygen status. In stagnant, but fully aerated water the mean internal pO₂ was 6.9 kPa, corresponding to about 30% of air saturation. The internal pO₂ increased with increasing flow velocity reaching saturation of around 12.2 kPa (60% of air saturation) at flow velocities ≥7 cm s⁻¹. Flow had a relatively larger influence on internal pO₂ at lower water column oxygen concentrations. By extrapolating linear relationships between internal and water column pO₂ in this experimental setup, rhizomes would become anoxic at a water column oxygen pO₂ of 4–4.5 kPa (∼20% of air saturation) in flowing water, but already at 6.4 kPa (∼30% of air saturation) in stagnant water. Water flow may play an important role for seagrass performance and survival in areas with poor water column oxygen conditions and may, in general, be of importance for the distribution of submerged rooted plants.     

Low stomatal density and reduced transpiration facilitate strawberry adaptation to salinity

Water and soil salinization are major constraints to agricultural productions because plant adaptation to hyperosmotic environments is generally associated to reduced growth and ultimately yield loss. Understanding the physiological/molecular mechanisms that link adaptation and growth is one of the greatest challenges in plant stress research since it would allow us to better define strategies to improve crop salt tolerance. In this study we attempted to establish a functional link between morphological and physiological traits in strawberry in order to identify margins to “uncouple” plant growth and stress adaptation. Two strawberry cultivars, Elsanta and Elsinore, were grown under 0, 10, 20 and 40 mM NaCl. Upon salinization Elsanta plants maintained a larger and more functional leaf area compared to Elsinore plants, which were irreversibly damaged at 40 mM NaCl. The tolerance of Elsanta was correlated with a constitutive reduced transpirational flux due to low stomatal density (173 vs. 234 stomata mm⁻² in Elsanta and Elsinore, respectively), which turned out to be critical to pre-adapt plants to the oncoming stress. The reduced transpiration rate of Elsanta (14.7 g H₂O plant⁻¹ h⁻¹) respect to Elsinore (17.7 g H₂O plant⁻¹ h⁻¹) most likely delayed the accumulation of toxic ions into the leaves, preserved tissues dehydration and consented to adjust more effectively to the hyperosmotic environment. Although we cannot rule out the contribution of other physiological and molecular mechanisms to the relatively higher tolerance of Elsanta, here we demonstrate that low stomatal density may be beneficial for cultivars prescribed to be used in marginal environments in terms of salinity and/or drought.     

Chemical constituents from Saussurea cordifolia

Thirty-six naturally occurring compounds, including four C₁₀-acetylenic glycosides and a lignan, were isolated from the whole plants of Saussurea cordifolia. Their structures were elucidated by means of spectroscopic and chemical methods to be 4,6-decadiyne-1-O-β-d-apiofuranosyl-(1 → 6)-β-d-glucopyranoside (1), 4,6-decadiyne-1-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside (2), (8E)-decaene-4, 6-diyn-1-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside (3), (8Z)-decaene-4,6-diyn-1-O-β-d-apiofuranosyl-(1 → 6)-β-d-glucopyranoside (4), and (2R, 3S, 4S)-4-(4-hydroxy-3-methoxybenzyl)-2-(5-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-tetrahydrofuran-3-ol (5).     

Termination of a toxic Alexandrium bloom with hydrogen peroxide

The dinoflagellate Alexandrium ostenfeldii is a well-known harmful algal species that can potentially cause paralytic shellfish poisoning (PSP). Usually A. ostenfeldii occurs in low background concentrations only, but in August of 2012 an exceptionally dense bloom of more than 1 million cells L⁻¹ occurred in the brackish Ouwerkerkse Kreek in The Netherlands. The A. ostenfeldii bloom produced both saxitoxins and spirolides, and is held responsible for the death of a dog with a high saxitoxin stomach content. The Ouwerkerkse Kreek routinely discharges its water into the adjacent Oosterschelde estuary, and an immediate reduction of the bloom was required to avoid contamination of extensive shellfish grounds. Previously, treatment of infected waters with hydrogen peroxide (H₂O₂) successfully suppressed cyanobacterial blooms in lakes. Therefore, we adapted this treatment to eradicate the Alexandrium bloom using a three-step approach. First, we investigated the required H₂O₂ dosage in laboratory experiments with A. ostenfeldii. Second, we tested the method in a small, isolated canal adjacent to the Ouwerkerkse Kreek. Finally, we brought 50 mg L⁻¹ of H₂O₂ into the entire creek system with a special device, called a water harrow, for optimal dispersal of the added H₂O₂. Concentrations of both vegetative cells and pellicle cysts declined by 99.8% within 48 h, and PSP toxin concentrations in the water were reduced below local regulatory levels of 15 μg L⁻¹. Zooplankton were strongly affected by the H₂O₂ treatment, but impacts on macroinvertebrates and fish were minimal. A key advantage of this method is that the added H₂O₂ decays to water and oxygen within a few days, which enables rapid recovery of the system after the treatment. This is the first successful field application of H₂O₂ to suppress a marine harmful algal bloom, although Alexandrium spp. reoccurred at lower concentrations in the following year. The results show that H₂O₂ treatment provides an effective emergency management option to mitigate toxic Alexandrium blooms, especially when immediate action is required.     

Ornamental characters,ion accumulation and water status in Arbutus unedo seedlings irrigated with saline water and subsequent relief and transplanting

Arbutus unedo seedlings were grown in a greenhouse and submitted to three irrigation treatments (salinity period) using solutions with an EC of 0.85 dS m^?1 (control treatment), 5.45 dS m^?1 (S1) and 9.45 dS m^?1 (S2). After 16 weeks, growth and ornamental characters, leaf water potentials, gas exchange and ion concentrations were determined. After the salinity period, plants were exposed to a relief period for 1 month, whereby half of the plants were transplanted to field conditions and the other half into 24 cm diameter plastic pots. Salinity induced a significant decrease in shoot biomass and leaf area but root/shoot ratio was increased. Plant height was significantly inhibited by salinity. The ornamental characters were affected in the treated plants, with symptoms of salt injury, such as burning of leaf margin. Leaf water potentials decreased with increasing salinity, more significantly at predawn than at midday. The relationship between net photosynthesis (P_n) and leaf conductance (g_l) was linear for all treatments and the same values of P_n are associated with lower values of g_l for the saline treatments than for control treatment. The concentration of Cl^? in leaves increased with increasing salinity and was higher than the corresponding concentration of Na⁺. Na⁺ and Cl^? contents were higher in the leaves than in the roots in both saline treatments. The K⁺ and Ca²⁺ levels were lower in the treated plants than in control plants and applied salinity reduced the K⁺/Na⁺ ratio in leaves, stems and roots, the decrease being much greater for leaves than for roots. The Ca²⁺/Na⁺ ratio fell with salinity in all parts of the plants. At the end of the relief period leaf water potentials were recovered mainly in field conditions. S2 treatment showed lower values of P_n and g_l than control and S1 treatments in pot conditions and in field conditions S1 showed the lowest values for P_n and g_l.     

Oxygen concentration affects nodule anatomy and nitrogenase activity of Alnus maritima

Alnus maritima is a shrub that associates with N₂-fixing Frankia in the wetlands in which it is native. Despite low concentrations in waterlogged soils, O₂ is critical to the maintenance of this symbiosis, and Frankia-infected nodules exist on roots of plants in native stands. The objective of the present study was to determine how root-zone O₂ concentration influences N₂ fixation and the anatomy of nodules on A. maritima. Root zones of plants inoculated with soil from native stands were exposed to eight O₂ concentrations. Nitrogenase activity increased with increasing O₂ concentration. Photosynthetic rate, plant dry mass, leaf N content, and nodule fresh mass were maximal in plants maintained with 15–25% O₂ in the root zone. Nodule counts were maximal on roots maintained at 10% and above 25% O₂, and nodules that developed at ≤ 2% O₂ were < 2 mm in diameter and single-lobed. Mean total area of air spaces within nodules decreased, and mean area per space increased, with increasing O₂ concentration. Seasonal and O₂-dependent nodule pigmentation was observed. Our data illustrate that O₂ is critical to the development of functional symbioses, and that nodules of this species, which are submersed in nature, possess mechanisms for responding to their low-O₂ environment.     

Nitric oxide protects sour pummelo (Citrus grandis) seedlings against aluminum-induced inhibition of growth and photosynthesis

Limited data are available on the amelioration of nitric oxide (NO) on aluminum (Al)-toxicity. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 0 and 1.2 mM AlCl₃·6H₂O × 0 and 10 μM sodium nitroprusside (SNP, an NO donor). Under Al stress, SNP increased root phosphorus (P) and Al, but decreased shoot Al. Al decreased photosynthesis, maximum quantum yield of primary photochemistry (F_v/F_m) and total performance index (PI_tot,sbs), but increased inactivation of oxygen-evolving complex (OEC), K-band and relative variable fluorescence at I-steps (V_I). SNP alleviated Al-induced changes for all these parameters. SNP stimulated Al-induced secretion of malate and citrate by excised roots from Al-treated seedlings, while Al did not increase their contents in roots. Antioxidant system in leaves and roots was up- and down-regulated by Al, respectively. SNP prevented Al-induced accumulation of malondialdehyde (MDA) in roots and leaves. In conclusion, SNP alleviates Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain. This occurs through increasing Al-immobilization and P level in roots and Al-induced secretion of malate and citrate from roots, and decreasing Al accumulation in shoots. Thus, the decrease of photosynthesis is prevented. Increased P level and Al-immobilization in roots through SNP may be effected through enhanced secretion of malate and citrate.