Gold(III) Reduction by the Rhizobacterium Azospirillum brasilense with the Formation of Gold Nanoparticles

For the soil nitrogen-fixing bacterium Azospirillum brasilense, the ability to reduce [AuCl₄]^? and to form gold nanoparticles (GNPs) has been demonstrated, with the appearance of a mauve tint of the culture. To validate the shapes and chemical nature of nanoparticles, transmission electron microscopy (TEM) and X-ray fluorescence analysis were used. For the widely studied agriculturally important wild-type strains A. brasilense Sp7 and Sp245, GNPs formed after 10 days of incubation of cell biomass with 0.25 mM [AuCl₄]^? were shown (using TEM) to be mainly of spherical form (5 to 20 nm in diameter), with rare occasional triangles. In the course of cultivation with [AuCl₄]^?, after 5 days, a mauve tint was already visible for cells of strain Sp245.5, after 6 days for Sp245 and after 10 days for Sp7. Thus, for the mutant strain Sp245.5 (which has significant differences in the structure and composition of cell-surface polysaccharides as compared with Sp245), a more rapid formation of GNPs was observed. Moreover, their TEM images (also obtained after 10 days) showed different shapes: nano-sized spheres, triangles, hexagons and rods, as well as larger round-shaped flower-like nanoparticles about 100 nm in size. Since by the time of GNP formation in our experiments the cells were found to be already not viable, this confirms the dominating role of cell surface structure and chemical composition in shaping the GNPs formed in the course of [AuCl₄]^? reduction to Au⁰. This finding may be useful for understanding the natural biogeochemical mechanisms of gold reduction and formation of GNPs involving microorganisms. The data obtained may also help in developing protocols for environmentally friendly synthesis of nanoparticles and possible use of bacterial cells with modified surface structure and composition for their fabrication.     

Toxicity of biosynthetic silver nanoparticles on the growth,cell ultrastructure and physiological activities of barley plant

Silver nanoparticles (AgNPs) were biosynthesized using the cell-free filtrate of bacterium Proteus mirabilis, reacted with 1 mM of AgNO₃ solutions at 37 °C. The synthesis of AgNPs was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM) equipped with selected area electron diffraction (SAED). The results point to formation of spherical to cubical particles of AgNPs ranging in size from 5 to 35 nm with an average of 25 nm in diameter. The toxicity of Ag on barley (Hordeum vulgare L. cv. Gustoe) that was subjected to Ag⁺ as AgNO₃ and AgNPs was explored. The grain germination and seedling growth of barley decreased in the presence of 0.1 mM Ag⁺ and was inhibited at 1 mM Ag⁺. In contrast, our results indicated that the AgNPs at low concentration (0.1 mM) could be useful for barley grain germination and seedling growth. However, the higher concentrations of AgNPs (0.5 and 1 mM) reduced grain germination and exhibited a stronger reduction in the root length. A decline in the photosynthetic pigments and disorganization of chloroplast grana thylakoids in Ag⁺ and AgNPs-treated plants confirmed the leaf chlorosis. An increase of plastoglobuli within chloroplasts was observed in Ag⁺ and AgNPs-treated leaves. Ag⁺ caused dense aggregation of nuclear chromatin materials and degeneration of mitochondria. Ag⁺ and AgNPs increased contents of malondialdehyde, soluble proteins, total phenolic compounds and activity of guaiacol peroxidase in barley leaves; these results point to activation of plant defence mechanisms against oxidative stress in barley.     

Variation in cell size of the diatom <Emphasis Type="Italic">Coscinodiscus granii</Emphasis> influences photosynthetic performance and growth

Cell size has implications for the package effect in photon absorption as well as for metabolic scaling of metabolism. In this study, we have avoided species-related differences by using isolates of the marine planktonic diatom Coscinodiscus granii with cells of different sizes and grown at different light intensities to investigate their energy allocation strategies. To make full use of incident light, several fold variations in cellular chlorophyll a content were employed across cell size. This modulation of pigment-related light absorbance was deemed effective as similar light absorbing capacities were found in all treatments. Unexpected low values of O₂ evolution rate at the highest irradiance level of 450 μmol photons m^?2 s^?1 were found in medium and large cells, regardless of more photons being absorbed under these conditions, suggesting the operation of alternative electron flows acting as electron sinks. The growth rate was generally larger at higher irradiance levels except for the large cells, in which growth slowed at 450 μmol photons m^?2 s^?1, suggesting that larger cells achieved a balance between growth and photoprotection by sacrificing growth rate when exposed to high light. Although the ratio of carbon demand to rates of uncatalysed CO₂ diffusion to the cell surface reached around 20 in large cells grown under higher irradiance, the carbon fixation rate was not lowered, due to the presence of a highly effective carbon dioxide concentrating mechanism.     

Subcellular distribution of chromium in accumulating plant Leersia hexandra Swartz

The subcellular distribution of chromium in Leersia hexandra Swartz, a Cr-accumulating plant found in China, was studied by differential centrifugation, transmission electron microscope and energy dispersive analysis of X-ray. Subcellular fractionation of Cr-containing tissues showed that most of the accumulated Cr was isolated to the cell walls in roots and the vacuoles in leaves. When the plant was grown in a nutrient solution containing 60 mg L^?1 Cr, 83.2% of the root Cr was localized in the cell wall fraction, while 57.5% of leaf Cr was localized in the vacuole and cytoplasm fraction. Transmission electron microscopic analysis revealed that those cell compartments contained especially electron dense areas. Energy dispersive X-ray spectra showed the electron dense areas contained high Cr. However, the dark electron precipitates were never observed in the plant cells without Cr treatment. In all treatment groups (5, 30 and 60 mg L^?1), the fraction containing the lowest level of Cr was the organelle fraction in roots as well as leaves. These results indicated that Cr accumulated in the L. hexandra was preferentially stored in the cell walls of roots and the vacuoles of leaves. This phenomenon diverted Cr ions from metabolically active compartment (chloroplast, mitochondria), resulting in a reduction of Cr toxicity in the plant cell.     

Chlorophyll fluorescence kinetics, photosynthetic activity, and pigment composition of blue-shade and half-shade leaves as compared to sun and shade leaves of different trees

The chlorophyll (Chl) fluorescence induction kinetics, net photosynthetic CO₂ fixation rates P _N, and composition of photosynthetic pigments of differently light exposed leaves of several trees were comparatively measured to determine the differences in photosynthetic activity and pigment adaptation of leaves. The functional measurements were carried out with sun, half-shade and shade leaves of seven different trees species. These were: Acer platanoides L., Ginkgo biloba L., Fagus sylvatica L., Platanus x acerifolia Willd., Populus nigra L., Quercus robur L., Tilia cordata Mill. In three cases (beech, ginkgo, and oak), we compared the Chl fluorescence kinetics and photosynthetic rates of blue-shade leaves of the north tree crown receiving only blue sky light but no direct sunlight with that of sun leaves. In these cases, we also determined in detail the pigment composition of all four leaf types. In addition, we determined the quantum irradiance and spectral irradiance of direct sunlight, blue skylight as well as the irradiance in half shade and full shade. The results indicate that sun leaves possess significantly higher mean values for the net CO₂ fixation rates P _N (7.8–10.7 μmol CO₂ m^?2 s^?1 leaf area) and the Chl fluorescence ratio R _Fd (3.85–4.46) as compared to shade leaves (mean P _N of 2.6–3.8 μmol CO₂ m^?2 s^?1 leaf area.; mean R _Fd of 1.94–2.56). Sun leaves also exhibit higher mean values for the pigment ratio Chl a/b (3.14–3.31) and considerably lower values for the weight ratio total chlorophylls to total carotenoids, (a + b)/(x + c), (4.07–4.25) as compared to shade leaves (Chl a/b 2.62–2.72) and (a + b)/(x + c) of 5.18–5.54. Blue-shade and half-shade leaves have an intermediate position between sun and shade leaves in all investigated parameters including the ratio F _v/F _o (maximum quantum yield of PS2 photochemistry) and are significantly different from sun and shade leaves but could not be differentiated from each other. The mean values of the Chl fluorescence decrease ratio R _Fd of blue-shade and half-shade leaves fit well into the strong linear correlation with the net photosynthetic rates P _N of sun and shade leaves, thus unequivocally indicating that the determination of the Chl fluorescence decrease ratio R _Fd is a fast and indirect measurement of the photosynthetic activity of leaves. The investigations clearly demonstrate that the photosynthetic capacity and pigment composition of leaves and chloroplasts strongly depend on the amounts and quality of light received by the leaves.     

Photosynthetic capacity of the capsule wall and its contribution to carbon fixation and seed yield in castor (<Emphasis Type="Italic">Ricinus communis</Emphasis> L.)

Defoliation occurs in castor due to several reasons, but the crop has propensity to compensate for the seed yield. Photosynthetic efficiency in terms of functional (gas exchange and chlorophyll fluorescence) and structural characteristics (photosynthetic pigment profiles and anatomical properties) of castor capsule walls under light- and dark-adapted conditions was compared with that of leaves. Capsule wall showed high intrinsic efficiency of photosystem II (F _v/F _m, 0.82) which was comparable to leaves (F _v/F _m, 0.80). With increasing photon flux densities (PFD), actual quantum yields and photochemical quenching coefficients of the capsule walls were similar to that in leaves, while electron transport rates reached a maximum corresponding to about 118 % of the leaves. However, maximum net photosynthetic rate of the capsule walls (2.60 µmol CO₂ m^?2 s^?1) was less than one-fourth of the leaves (15.67 µmol CO₂ m^?2 s^?1) at the CO₂ concentration of 400 µmol mol^?1, and the difference was attributed to about 80 % lower stomatal density and the 75 % lower total chlorophyll content of capsule walls than the leaves. Furthermore, seed weight in dark-adapted capsules was 2.70–12.42 % less as compared to the capsules developed under light. The results indicate that castor capsule walls are photosynthetically active (about 15–30 % of the leaves) and contribute significantly to carbon fixation and seed yield accounting for 10 % photoassimilates towards seed weight.     

Methane oxidation and methane driven redox process during sequential reduction of a flooded soil ecosystem

A laboratory incubation study conducted to assess the temporal variation of CH₄ oxidation during soil reduction processes in a flooded soil ecosystem. A classical sequence of microbial terminal electron accepting process observed following NO₃ ^? reduction, Fe³⁺ reduction, SO₄ ^2? reduction and CH₄ production in flooded soil incubated under initial aerobic and helium-flushed anaerobic conditions. CH₄ oxidation in the slurries was influenced by microbial redox process during slurry reduction. Under aerobic headspace condition, CH₄ oxidation rate (k) was stimulated by 29 % during 5 days (NO₃ ^? reduction) and 32 % during both 10 days (Fe³⁺) and 20 days (early SO₄ ^2? reduction) over unreduced slurry. CH₄ oxidation was inhibited at the later methanogenic period. Contrastingly, CH₄ oxidation activity in anaerobic incubated slurries was characterized with prolonged lag phase and lower CH₄ oxidation. Higher CH₄ oxidation rate in aerobically incubated flooded soil was related to high abundance of methanotrophs (r?=?0.994, p?<?0.01) and ammonium oxidizers population (r?=?0.184, p?<?0.05). Effect of electron donors NH₄ ⁺, Fe^2+, S^2? on CH₄ oxidation assayed to define the interaction between reduced inorganic species and methane oxidation. The electron donors stimulated CH₄ oxidation as well as increased the abundance of methanotrophic microbial population except S^2? which inhibited the methanotrophic activity by affecting methane oxidizing bacterial population. Our result confirmed the complex interaction between methane-oxidizing microbial groups and redox species during sequential reduction processes of a flooded soil ecosystem.     

Novel polyhedral gold nanoparticles: green synthesis,optimization and characterization by environmental isolate of Acinetobacter sp. SW30

Gold nanoparticles have enormous applications in cancer treatment, drug delivery and nanobiosensor due to their biocompatibility. Biological route of synthesis of metal nanoparticles are cost effective and eco-friendly. Acinetobacter sp. SW 30 isolated from activated sewage sludge produced cell bound as well as intracellular gold nanoparticles when challenged with HAuCl₄ salt solution. We first time report the optimization of various physiological parameters such as age of culture, cell density and physicochemical parameters viz HAuCl₄ concentration, temperature and pH which influence the synthesis of gold nanoparticles. Gold nanoparticles thus produced were characterized by various analytical techniques viz. UV–Visible spectroscopy, X-ray diffraction, cyclic voltammetry, transmission electron microscopy, selected area electron diffraction, high resolution transmission electron microscopy, environmental scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and dynamic light scattering. Polyhedral gold nanoparticles of size 20 ± 10 nm were synthesized by 24 h grown culture of cell density 2.4 × 10⁹ cfu/ml at 50 °C and pH 9 in 0.5 mM HAuCl₄. It was found that most of the gold nanoparticles were released into solution from bacterial cell surface of Acinetobacter sp. at pH 9 and 50 °C.     

Proteome analysis of roots of wheat seedlings under aluminum stress

The root apex is considered the first sites of aluminum (Al) toxicity and the reduction in root biomass leads to poor uptake of water and nutrients. Aluminum is considered the most limiting factor for plant productivity in acidic soils. Aluminum is a light metal that makes up 7 % of the earth’s scab dissolving ionic forms. The inhibition of root growth is recognized as the primary effect of Al toxicity. Seeds of wheat cv. Keumkang were germinated on petridish for 5 days and then transferred hydroponic apparatus which was treated without or with 100 and 150 μM AlCl₃ for 5 days. The length of roots, shoots and fresh weight of wheat seedlings were decreased under aluminum stress. The concentration of K⁺, Mg²⁺ and Ca²⁺ were decreased, whereas Al³⁺ and P₂O₅ ^? concentration was increased under aluminum stress. Using confocal microscopy, the fluorescence intensity of aluminum increased with morin staining. A proteome analysis was performed to identify proteins, which are responsible to aluminum stress in wheat roots. Proteins were extracted from roots and separated by 2-DE. A total of 47 protein spots were changed under Al stress. Nineteen proteins were significantly increased such as sadenosylmethionine, oxalate oxidase, malate dehydrogenase, cysteine synthase, ascorbate peroxidase and/or, 28 protein spots were significantly decreased such as heat shock protein 70, O-methytransferase 4, enolase, and amylogenin. Our results highlight the importance and identification of stress and defense responsive proteins with morphological and physiological state under Al stress.     

Fluorescence F 0 of photosystems II and I in developing C3 and C4 leaves,and implications on regulation of excitation balance

This work addresses the question of occurrence and function of photosystem II (PSII) in bundle sheath (BS) cells of leaves possessing NADP-malic enzyme-type C₄ photosynthesis (Zea mays). Although no requirement for PSII activity in the BS has been established, several component proteins of PSII have been detected in BS cells of developing maize leaves exhibiting O₂-insensitive photosynthesis. We used the basal fluorescence emissions of PSI (F _0I) and PSII (F _0II) as quantitative indicators of the respective relative photosystem densities. Chl fluorescence induction was measured simultaneously at 680 and 750 nm. In mature leaves, the F _m(680)/F ₀(680) ratio was 10.5 but less in immature leaves. We propose that the lower ratio was caused by the presence of a distinct non-variable component, F _c, emitting at 680 and 750 nm. After F _c was subtracted, the fluorescence of PSI (F _0I) was detected as a non-variable component at 750 nm and was undetectably low at 680 nm. Contents of Chls a and b were measured in addition to Chl fluorescence. The Chl b/(a + b) was relatively stable in developing sunflower leaves (0.25–0.26), but in maize it increased from 0.09 to 0.21 with leaf tissue age. In sunflower, the F _0I/(F _0I + F _0II) was 0.39 ± 0.01 independent of leaf age, but in maize, this parameter was 0.65 in young tissue of very low Chl content (20–50 mg m^?2) falling to a stable level of 0.53 ± 0.01 at Chl contents >100 mg m^?2. The values of F _0I/(F _0I + F _0II) showed that in sunflower, excitation was partitioned between PSII and PSI in a ratio of 2:1, but the same ratio was 1:1 in the C₄ plant. The latter is consistent with a PSII:PSI ratio of 2:1 in maize mesophyll cells and PSI only in BS cells (2:1:1 distribution). We suggest, moreover, that redox mediation of Chl synthesis, rather than protein accumulation, regulates photosystem assembly to ensure optimum excitation balance between functional PSII and PSI. Indeed, the apparent necessity for two Chls (a and b) may reside in their targeted functions in influencing accumulation of PSI and PSII, respectively, as opposed to their spectral differences.     

The effect of pre-incubation of Allium cepa L. roots in the ATH-rich extract on Pb uptake and localization

The positive influence of anthocyanin (ATH) on toxic metal-treated plant material is well documented; however, it is still not explained if it is caused by changes in element absorption and distribution. Therefore, detailed analysis of the effect of the ATH-rich extract from red cabbage leaves on Pb uptake and localization at morphological, anatomical and ultrastructural level was the goal of this study. Two-day-old adventitious roots of Allium cepa L. (cv. Polanowska) were treated for 2 h with the aqueous solution of Pb(NO₃)₂ at the concentration of 100 μM with or without preliminary incubation in the anthocyanin-rich extract from Brassica oleracea L. var. capitata rubra leaves (250 μM, 3 h). The red cabbage extract did not change the total Pb uptake but it enhanced the translocation of accumulated metal from roots to shoots. Within the pretreated roots, more Pb was deposited in their basal part and definitely smaller amount of the metal was bound in the apoplast of the outer layers of cortex cells. The ultrastructural analysis (transmission electron microscopy and X-ray microanalysis) revealed that the ATH-rich extract lowered the number of Pb deposits in intracellular spaces, cell wall and cytoplasm of root meristematic cells as well as in such organelles important to cell metabolism as mitochondria, plastids and nucleus. The Pb deposits were preferably localised in those vacuoles where ATH also occurred. This sequestration of Pb in vacuoles is probably responsible for reduction of metal cytotoxicity and consequently could lead to better plant growth.     

Carbon and Nitrogen Metabolism in Leaves and Roots of Dwarf Bamboo (Fargesia denudata Yi) Subjected to Drought for Two Consecutive Years During Sprouting Period

Dwarf bamboo is an ecologically and economically important forest resource that is widespread in mountainous regions of eastern Asia and southern America. Fargesia denudata, one of the most important dwarf bamboos, is a staple food of the giant panda, but our knowledge about how F. denudata copes with drought stress is very limited. The objective of this study was to determine the responses of carbon (C) and nitrogen (N) metabolism to drought in leaves and roots of F. denudata plants. Plants were subjected to three water treatments, well-watered [WW, 85 % relative soil water content (RSWC)], moderate drought (MD, 50 % RSWC), and severe drought (SD, 30 % RSWC), for two consecutive years during the sprouting period. Plant growth parameters, levels of carbohydrates and N compounds, and activities of key enzymes involved in C and N metabolism were analyzed. In young leaves, C metabolism was in balance after drought stress, but nitrate (NO₃ ^?) reduction and ammonium (NH₄ ⁺) assimilation were accelerated. In old leaves, drought stress decreased carbohydrate contents by spurring the activities of the main enzymes that participate in C metabolism, whereas N metabolism was enhanced only under SD. Roots showed unchanged C metabolism parameters under MD, together with stable NO₃ ^? reduction and the key enzymes related to NH₄ ⁺ assimilation, whereas they were stimulated by SD. Hydrolysates of carbohydrates in old leaves could be transferred into roots, but only to meet MD. Meanwhile, roots could allocate more N nutrition to young leaves and less to old leaves. These changes regulated the overall metabolic balance of F. denudata. Consequently, the results indicate that different organs with various response strategies will be well adapted to different drought intensities for ensuring regular growth of F. denudata plants at the whole-plant level.     

Growth,physiological, biochemical and ionic responses of pistachio seedlings to mild and high salinity

Key message

Depending on salt concentrations, different mechanisms are involved in the tolerance of pistachio and an acclimation to salinity conditions occurs in the leaves that develop in the presence of salt.

Abstract

Pistachio (Pistacia vera L.) is a salt tolerant species that is considered an alternative crop for cultivation in salinzied orchard soils. In this work, 12-week-old pistachio seedlings cultivated in soil under greenhouse conditions were treated with five levels of salinity including control (0.63 dSm^?1), low (2 and 4 dSm^?1) and high (8 and 10 dSm^?1) salt concentrations for further 12 weeks. Plant growth parameters were not affected by mild salinity; a significant reduction was only observed from 8 dSm^?1. Considerable differences were observed between the young and mature leaves regarding osmotic and ionic stress effects of salt. Main compatible solutes were proline in mature leaves, proline and soluble sugars in young leaves, and soluble sugars and amino acids, other than proline, in roots. Concentration and content of Na in the leaves were not significantly increased at low levels of salinity and the K:Na and Ca:Na ratio of leaves were affected only by higher salt concentrations. Using the sequential extraction procedure for cell wall isolation, we observed that both absolute and relative amounts of Na in the cell wall fraction increased under low salinity, while decreased under higher levels of salt supply. Stable water relations, photochemistry and CO₂ assimilation rates particularly of young leaves, as well as ion homeostasis were mechanisms for maintenance of plants growth under mild salinity. Under severe saline conditions, the impaired ability of mature leaves for synthesis of assimilates, preferent allocation of carbohydrates to roots for maintenance of osmotic homeostasis and finally, reduction of protein synthesis caused growth inhibition in pistachio.     

Physiological responses of Plantago algarbiensis and P. almogravensis shoots and plantlets to low pH and aluminum stress

We investigated the impact of low pH and aluminum (Al) stress on the growth, nutrients concentration, chlorophyll a fluorescence, photosynthetic pigment contents, proline and carbohydrate accumulation in shoots and plantlets (leaves and roots) of Plantago almogravensis and P. algarbiensis. Both species accumulated considerable and similar amounts of Al in their tissues, mainly in the roots. The presence of Al caused a significant reduction on root elongation in P. algarbiensis. Low pH and Al induced significant changes on nutrient accumulation, but no significant alterations on the maximum efficiency of PSII (F _v/F _m), quantum yield of PSII photochemistry (?_PSII), quantum yield of regulated energy dissipation (?_NPQ) and quantum yield of non-regulated energy dissipation (?_NO) were detected in both species in response to these stresses. However, Al increased significantly the non-photochemical quenching and the chlorophyll b content and decreased the PSII excitation pressure (1 ? q _p) in P. almogravensis leaves. Both stress treatments induced carbohydrate accumulation in the shoots and roots of this species, but not in leaves. In P. algarbiensis, low pH and Al decreased the photosynthetic pigment contents in the shoots, whereas Al stimulated the carbohydrate accumulation in the leaves. Although our data showed that both species are tolerant to Al³⁺ and H⁺, P. almogravensis appeared to be more adapted to maintain cellular physiology and growth under those conditions.     

Phyto-synthesis of silver nanoparticles using <Emphasis Type="Italic">Alternanthera tenella</Emphasis> leaf extract: an effective inhibitor for the migration of human breast adenocarcinoma (MCF-7) cells

In this study, phyto-synthesis of silver nanoparticles (AgNPs) was achieved using an aqueous leaf extract of Alternanthera tenella. The phytochemical screening results revealed that flavonoids are responsible for the AgNPs formation. The AgNPs were characterised using UV–visible spectrophotometer, field emission scanning microscopy/energy dispersive X-ray, transmission electron microscopy, fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction. The average size of the nanoparticles was found to be ≈48 nm. The EDX results show that strong signals were observed for the silver atoms. The strong band appearing at 1601–1595 cm^?1 correspond to C–C stretching vibration from dienes in FT-IR spectrum indicating the formation of AgNPs. Human breast adenocarcinoma (MCF-7) cells treated with various concentrations of AgNPs showed a dose-dependent increase in cell inhibition. The IC₅₀ value of the AgNPs was calculated to be 42.5 μg mL^?1. The AgNPs showed a significant reduction in the migration of MCF-7 cells.     

Oxidation and reduction of sulfite contribute to susceptibility and detoxification of SO2 in Populus × canescens leaves

Key Message

The critical level for SO ₂ susceptibility of Populus × canescens is approximately 1.2 μL L ^?1 SO ₂ . Both sulfite oxidation and sulfite reduction and assimilation contribute to SO ₂ detoxification.

Abstract

In the present study, uptake, susceptibility and metabolism of SO₂ were analyzed in the deciduous tree species poplar (Populus × canescens). A particular focus was on the significance of sulfite oxidase (SO) for sulfite detoxification, as SO has been characterized as a safety valve for SO₂ detoxification in herbaceous plants. For this purpose, poplar plants were exposed to different levels of SO₂ (0.65, 0.8, 1.0, 1.2 μL L^?1) and were characterized by visible injuries and at the physiological level. Gas exchange parameters (stomatal conductance for water vapor, CO₂ assimilation, SO₂ uptake) of the shoots were compared with metabolite levels (sulfate, thiols) and enzyme activities [SO, adenosine 5′-phosphosulfate reductase (APR)] in expanding leaves (80–90 % expanded). The critical dosage of SO₂ that confers injury to the leaves was 1.2 μL L^?1 SO₂. The observed increase in sulfur containing compounds (sulfate and thiols) in the expanding leaves strongly correlated with total SO₂ uptake of the plant shoot, whereas SO₂ uptake rate was strongly correlated with stomatal conductance for water vapor. Furthermore, exposure to high concentration of SO₂ revealed channeling of sulfite through assimilatory sulfate reduction that contributes in addition to SO-mediated sulfite oxidation to sulfite detoxification in expanding leaves of this woody plant species.     

Physio-morphological and structural changes in common bermudagrass and Kentucky bluegrass during salt stress

Environmental pollution has increased human attention toward developing green spaces every day. One of the most important goals in developing green spaces is to create beautiful and pleasant scenes and consequently creating mental relaxation; turfs are the most important plants for this purpose. One factor which affects the growth of plants in arid and semi-arid regions is the salinity of the water and soil; therefore, using some types of turfgrasses which are tolerant to salinity is a key factor for culturing them more in the city landscapes in such regions. The aim of this study was to investigate the physio-morphological and structural changes in common bermudagrass (Cynodon dactylon [L.] Pers., as more tolerant species) and Kentucky bluegrass (Poa pratensis L., as less tolerant species) under salt stress condition. The salt stress treatments were applied by seven concentrations of NaCl + CaCl₂ (1:1 proportion based on the final EC) including: 0.0, 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 dS m^?1. This study was conducted in a completely randomized design with factorial arrangements, each treatment with four replications. Data were analyzed and means were compared using LSD test at 5 % level. Results showed that with increasing salinity levels Kentucky bluegrass started to decrease in visual quality at 2.5 dS m^?1, but bermudagrass’ visual quality was still acceptable at 5.0 dS m^?1. Furthermore, increasing the salinity level caused a reduction in the following indices in both species: shoot height, shoot fresh and dry weight, root fresh and dry weight, leaf area, photosynthetic rate, total chlorophyll, and starch level. However, the reducing sugar levels and indices of proline, and catalase and superoxide dismutase enzymes had shown an increasing trend while salinity increased. However, reducing sugar levels, and catalase and superoxide dismutase activities decreased at salinity levels higher than 10 dS m^?1. Structural studies showed that bermudagrass, with help of bulliform cells, could prevent water loss and tolerate the higher salinity levels. Based on these results, it can be concluded that under the no salinity condition Kentucky bluegrass has more folded leaves than common bermudagrass, however, bermudagrass is more tolerant because of thicker epidermis. Under high salinity conditions, bermudagrass kept their leaves folded, whereas the leaf structure was drastically damaged in bluegrass and no folded leaf was seen at 15 dS m^?1. Further ultrastructural studies are needed to clarify more the changes occurring in leaves under salinity stress condition.     

High tolerance of aluminum in the grass species Cynodon aethiopicus

Concentrations of aluminum (Al) were determined in leaves of native terrestrial plants, macrophytes and fruit parts (watermelon and tomato) using inductively coupled plasma mass spectrometry. Al concentrations in water and soil were determined by inductively coupled plasma optical emission spectrometry. Potamogeton thunbergii (macrophyte) and Cynodon aethiopicus (terrestrial grass) had the highest leaf Al concentrations (2 and 1 g kg^?1 dw, respectively). Transfer factors (mg kg^?1 dw plants/mg kg^?1 dw soil) based on total Al concentrations in soil varied from 2 × 10^?3 to 0.05 and from 1.9 to 78 based on mobile Al concentrations determined after sequential extraction. Bioconcentration factors (mg kg^?1 dw plants/mg L^?1 water) varied from 19 to 9.5 × 10³ L kg^?1 dw. Plants can accumulate high concentrations of Al when growing in neutral pH soils and slightly alkaline lakes in the Ethiopian Rift Valley. Controlled experiments showed that C. aethiopicus can accumulate high levels of Al both in root and shoot. Compared to Arabidopsis thaliana, C. aethiopicus was more tolerant to Al exposure as ≥400 μM AlCl₃ was needed to inhibit root growth compared to 200 μM in A. thaliana. After exposing C. aethiopicus and A. thaliana in 800 μM AlCl_3, alkaline comet assay indicates significant DNA (deoxyribonucleic acid) damage in A. thaliana while C. aethiopicus was unaffected. No significant induction of reactive oxygen species (ROS), in terms of leaf H₂O₂ levels, could be observed in C. aethiopicus. C. aethiopicus has mechanisms to suppress both Al-induced ROS and DNA damage, thereby increasing tolerance of the species to high Al concentrations.     

The influence of salinity on cell ultrastructures and photosynthetic apparatus of barley genotypes differing in salt stress tolerance

A hydroponic experiment was conducted to elucidate the difference in growth and cell ultrastructure between Tibetan wild and cultivated barley genotypes under moderate (150 mM NaCl) and high (300 mM NaCl) salt stress. The growth of three barley genotypes was reduced significantly under salt stress, but the wild barley XZ16 (tolerant) was less affected relative to cultivated barley Yerong (moderate tolerant) and Gairdner (sensitive). Meanwhile, XZ16 had lower Na⁺ and higher K⁺ concentrations in leaves than other two genotypes. In terms of photosynthetic and chlorophyll fluorescence parameters, salt stress reduced maximal photochemical efficiency (F _v/F _m), net photosynthetic rate (Pn), stomatal conductance (Gs), and intracellular CO₂ concentration (Ci). XZ16 showed relatively smaller reduction in comparison with the two cultivated barley genotypes. The observation of transmission electron microscopy found that fundamental cell ultrastructure changes happened in both leaves and roots of all barley genotypes under salt NaCl stress, with chloroplasts being most changed. Moreover, obvious difference could be detected among the three genotypes in the damage of cell ultrastructure under salt stress, with XZ16 and Gairdner being least and most affected, respectively. It may be concluded that high salt tolerance in XZ16 is attributed to less Na⁺ accumulation and K⁺ reduction in leaves, more slight damage in cell ultrastructure, which in turn caused less influence on chloroplast function and photosynthesis.     

Compartmentalization and ultrastructural alterations induced by chromium in aquatic macrophytes

The aim of the present study was to identify the sites of accumulation of Cr in the species of macrophytes that are abundant in the Cachoeira river, namely, Alternanthera philoxeroides, Borreria scabiosoides, Polygonum ferrugineum and Eichhornia crassipes. Plants were grown in nutritive solution supplemented with 0.25 and 50 mg l^?1 of CrCl₃·6H₂O. Samples of plant tissues were digested with HNO₃/HCl in a closed-vessel microwave system and the concentrations of Cr determined using inductively-coupled plasma mass spectrometry (ICP-MS). The ultrastructure of root, stem and leaf tissue was examined using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) in order to determine the sites of accumulation of Cr and to detect possible alterations in cell organelles induced by the presence of the metal. Chromium accumulated principally in the roots of the four macrophytes (8.6?C30 mg kg^?1 dw), with much lower concentrations present in the stems and leaves (3.8?C8.6 and 0.01?C9.0 mg kg^?1 dw, respectively). Within root tissue, Cr was present mainly in the vacuoles of parenchyma cells and cell walls of xylem and parenchyma. Alterations in the shape of the chloroplasts and nuclei were detected in A. philoxeroides and B. scabiosoides, suggesting a possible application of these aquatic plants as biomarkers from Cr contamination.