Crystal structures and chemical composition of leaf surface wax depositions on the desert moss Syntrichia caninervis

The structures and composition of cuticular waxes deposited on the leaves of a typical desert moss, Syntrichia caninervis, were investigated. The wax crystals deposited on leaves shifted with leaf aging. The results of chemical analysis showed the main chemical components of the moss wax were fatty acids, alcohols and alkanes. Leaf aging increased the content of cuticular wax and the percentage of very long chain components, from 1150 μg g⁻¹ DW and 13.6% in younger leaves to 2640 μg g⁻¹ DW and 37.2% in aged leaves, respectively. Dehydration/hydration also augmented the wax content by 35.17% in juvenile leaves and by 1900% in lab-cultivated leaves after three-cycle treatments. Synthesis of hexadecanoic acid and tetracosane were predicted to be the first step of wax accumulation. The responses of cuticular waxes in crystal structure and chemical composition were recommended as a biomonitor for assessing the shift of ecological and environmental quality.     

Variations in leaf epicuticular n-alkanes in some Broussonetia,Ficus and Humulus species

n-Alkanes are biosynthesized from very long-chain fatty acid wax precursors and its distribution grants the most useful taxonomic contribution for plant species. In current study, five species from three genera of Moraceae family were sampled separately from three areas (Mountain Jin-yun, Mountain Jin-fo and Bei-bei) in Chongqing, China, namely, Broussonetia papyrifera, Broussonetia kazinoki, Ficus virens, Ficus tikoua, and Humulus scandens. The amounts of n-alkanes in epicuticular wax enabled discrimination among areas, varying from 4.9 μg cm⁻² to 16.9 μg cm⁻² in Mountain Jin-yun, 6.9 μg cm⁻² to 20.5 μg cm⁻² in Bei–bei, and 4.7 μg cm⁻² to 61.7 μg cm⁻² in Mountain Jin-fo, respectively. Among the five species, the amount of n-alkanes was the highest in B. papyrifera and the lowest in F. tikoua for all areas, showing high species variation. The most abundant n-alkanes in all investigated species were two odd-numbered n-alkanes, i.e., C₂₉ and C₃₁. The epicuticular waxes of H. scandens from Bei-bei had a higher relative abundance of C₂₉ than other species from Mountain Jin-yun and Mountain Jin-fo. The chain length of n-alkanes from Bei-bei was longer than that from other areas. The even/odd predominance (EOP) or odd/even predominance (OEP) occurred in short-chain n-alkanes of plant epicuticular wax might be correlated with their growing environments. All Carbon Preference Index (CPIs) and Average Chain Length (ACLs) from Bei-bei were lower than those from other sampling areas, mainly attributing to the higher numbers of short- and mid-chain n-alkanes in plants from Bei-bei. Cluster analysis revealed that H. scandens from Bei-bei and F. virens from Mountain Jin-yun were different from other species. Based on these findings, it seems that environmental conditions contribute to the complex patterns and variation of n-alkanes and different plant species had different responses to environment changes. The distribution of n-alkanes could be a good indicator to distinguish plant species under different growing conditions before other obvious morphological changes could be observed.     

Taxonomic significance of the epicuticular wax composition in species of the genus Clusia from Panama

We attempted to separate species of the genus Clusia according to the concentration of linear alkanes (C25 and C35), and the presence and diversity of terpenes in epicuticular wax extracts. We collected leaves of 15 Clusia species growing in mountain forests of Panama (Cerro Jefe 1007 m and Altos de Campana 800 m a.s.l.) and from cultivated plants at two lowland sites. Leaf surfaces were washed gently with hexane to extract epicuticular waxes, which were analyzed using gas chromatography and mass spectrometry. The predominant alkanes were C29, C31, and C33. In the extract the ratio C31/C29 was ≤1 in 6 of the 15 species analyzed: Clusia multiflora, Clusia peninsulae (Hammel ined.), Clusia stenophylla, Clusia liesneri, Clusia coclensis, and Clusia triflora. The concentrations of C29 and C33 were inversely related, the latter being above 10% in Clusia divaricata, Clusia pratensis, Clusia rosea, Clusia uvitana, and Clusia valerioi. Proportion of triterpenes was less than 5% in the species C. minor, C. pratensis, C. uvitana, C. rosea, Clusia cylindrica, C. divaricata, and C. valerioi. The rest contained squalene, and specific triterpenes such as β-amyrine in C. liesneri, betuline in Clusia osseocarpa, taraxerol in C. stenophylla, and lupeol in C. multiflora. The variety of triterpenes was higher in Clusia liesneri (5) and C. multiflora (3). The results suggest that groups of species can be distinguished within the genus according to the presence of terpenes and ratios of linear alkanes. These groups overlap with those generated by other classifications using morphology and nuclear ribosomal DNA.     

核盘菌侵染对拟南芥表皮蜡质结构及化学组成的影响

以野生型拟南芥与蜡质突变体cer1、cer4为试验材料,通过研究核盘菌胁迫对拟南芥茎表皮蜡质结构及组分含量的影响,揭示核盘菌侵染与表皮蜡质的关系。扫描电镜结果显示,野生型拟南芥蜡质晶体以垂直于表面的杆状、块状结构为主;突变体cer1晶体类型以水平的松针状、块状结构为主;突变体cer4蜡质晶体以垂直片层结构为主。核盘菌胁迫下,拟南芥蜡质晶体结构及分布形态发生变化。蜡质层结构在核盘菌胁迫下表现为:杆状、松针状蜡质晶体减少—蜡质晶体熔融—表皮"囊状凸起"—表皮膜层破裂。这些结构变化有利于病菌突破角质层屏障而侵入到植株体内。色质谱分析结果显示:与野生型相比,cer1突变体烷、次级醇、酮类显著减少;cer4突变体表现为一级醇含量减少。接种核盘菌后,野生型拟南芥与蜡质突变体一级醇类显著增加(cer1增加不显著);烷类、次级醇类、酮类含量与蜡质总量均显著减少,表明蜡质前体物质在受到核盘菌胁迫后更多地通过酰基还原途径生成一级醇,从而减少了由脱羰基途径所生成的蜡质组分。核盘菌通过改变表皮蜡质晶体结构与化学组分分泌量来促进侵染。     

Sorgoleone,a sorghum root exudate: Algicidal activity and acute toxicity to the ricefish Oryzias latipes

The discovery of natural and natural-based compounds has resulted in its application as an alternative to synthetic algicides to control harmful algae in aquatic systems. Of the many natural-product-based algicides, sorgoleone, a natural plant product from Sorghum bicolor root exudates has been investigated for its controlling effect on different algal species and its acute fish toxicity. Growth of the blue green algal species Microcystis aeruginosa Kützing was completely inhibited by the crude methanol extract of sorghum root at 20 μg mL⁻¹. The most noticeable inhibition was observed in the bioassay of n-hexane soluble extract, where 98% growth inhibition occurred in M. aeruginosa at the concentration of 1.25 μg mL⁻¹. Sorgoleone very effectively controlled blue green algae inhibiting 97% of M. aeruginosa at 0.5 μg mL⁻¹ and 99% of Anabaena affinis Lemmermann at 4 μg mL⁻¹. In contrast, inhibition of the green algae species Chlorella vulgaris Beijerinck and Scenedensmus spp. at 16 μg mL⁻¹ sorgoleone was 87 and 68%, respectively. There were no mortalities or adverse effects observed in any of the fish exposed to water control, solvent control, and a nominal concentration of 1 μg mL⁻¹ during the test period. The no observed effect concentration (NOEC) value was 1.5 μg mL⁻¹ for the tested fish (O. latipes). Sorgoleone can be considered as an effective and an ecologically and environmentally sustainable approach to controlling harmful algae.     

Primary production,respiration and calcification of the temperate free-living coralline alga Lithothamnion corallioides

Calcification and primary production responses to irradiance in the temperate coralline alga Lithothamnion corallioides were measured in summer 2004 and winter 2005 in the Bay of Brest. Coralline algae were incubated in dark and clear bottles exposed to different irradiances. Net primary production reached 1.5 μmol C g⁻¹ dry wt h⁻¹ in August and was twice as high as in January–February. Dark respiration showed significant seasonal variations, being three-fold higher in summer. Maximum calcification varied from 0.6 μmol g⁻¹ dry wt h⁻¹ in summer 2004 to 0.4 μmol g⁻¹ dry wt h⁻¹ in winter 2005. According to P–E curves and the daily course of irradiance, estimated daily net production and calcification reached 131 μg C g⁻¹ dry wt and 970 μg CaCO₃ g⁻¹ dry wt in summer 2004, and 36 μg C g⁻¹ dry wt and 336 μg CaCO₃ g⁻¹ dry wt in winter 2005. The net primary production of natural L. corallioides populations in shallow waters was estimated at 10–600 g C m⁻² y⁻¹, depending on depth and algal biomass. The mean annual calcification of L. corallioides populations varied from 300 to 3000 g CaCO₃ m⁻². These results are similar to those reported for tropical coralline algae in terms of carbon and carbonate productivity. Therefore, L. corallioides can be considered as a key element of carbon and carbonate cycles in the shallow coastal waters where they live.     

Ontogenetic variation in chemical and physical characteristics of adaxial apple leaf surfaces

The reaction of plants to environmental factors often varies with developmental stage. It was hypothesized, that also the cuticle, the outer surface layer of plants is modified during ontogenesis. Apple plantlets, cv. Golden Delicious, were grown under controlled conditions avoiding biotic and abiotic stress factors. The cuticular wax surface of adaxial apple leaves was analyzed for its chemical composition as well as for its micromorphology and hydrophobicity just after unfolding of leaves ending in the seventh leaf insertion. The outer surface of apple leaves was formed by a thin amorphous layer of epicuticular waxes. Epidermal cells of young leaves exhibited a distinctive curvature of the periclinal cell walls resulting in an undulated surface of the cuticle including pronounced lamellae, with the highest density at the centre of cells. As epidermal cells expanded during ontogenesis, the upper surface showed only minor surface sculpturing and a decrease in lamellae. With increasing leaf age the hydrophobicity of adaxial leaf side decreased significantly indicated by a decrease in contact angle. Extracted from plants, the amount of apolar cuticular wax per area unit ranged from only 0.9 microgcm(-2) for the oldest studied leaf to 1.5 microgcm(-2) for the youngest studied leaf. Differences in the total amount of cuticular waxes per leaf were not significant for older leaves. For young leaves, triterpenes (ursolic acid and oleanolic acid), esters and alcohols were the main wax components. During ontogenesis, the proportion of triterpenes in total mass of apolar waxes decreased from 32% (leaf 1) to 13% (leaf 7); absolute amounts decreased by more than 50%. The proportion of wax alcohols and esters, and alkanes to a lesser degree, increased with leaf age, whereas the proportion of acids decreased. The epicuticular wax layer also contained alpha-tocopherol described for the first time to be present also in the epicuticular wax. The modifications in the chemical composition of cuticular waxes are discussed in relation to the varying physical characteristics of the cuticle during ontogenesis of apple leaves.     

Composition of the epicuticular and intracuticular wax layers on Kalanchoe daigremontiana (Hamet et Perr. de la Bathie) leaves

Epicuticular and intracuticular waxes from both adaxial and abaxial surfaces of the leaves of Kalanchoe daigremontiana were analyzed. All wax mixtures were found to contain approximately equal amounts of triterpenoids and very long chain fatty acid (VLCFA) derivatives. The triterpenoid fraction consisted of glutinol (8-19% of the total wax) and friedelin (4-9%), together with smaller amounts of glutanol, glutinol acetate, epifriedelanol, germanicol and β-amyrin. The VLCFA derivatives comprised C₂₇-C₃₅ alkanes (19-37% of the total wax), C₃₂-C₃₄ aldehydes (3-7%), C₃₂ and C₃₄ fatty acids (0.2-3%), C₂₆-C₃₆ primary alcohols (4-8%), and C₄₂-C₅₂ alkyl esters (2-9%). The wax layers were found to differ in triterpenoid amounts, with the intracuticular wax containing higher percentages of most triterpenoids than the epicuticular wax. Friedelin, the only triterpenoid ketone present, showed the opposite distribution with higher proportions in the epicuticular wax. VLCFA derivatives also accumulated to higher percentages in the epicuticular than in the intracuticular wax layer. Epicuticular wax crystals were observed on both the adaxial and abaxial leaf surfaces.     

Foliar cuticular waxes of cultivated species and varieties of Coffea

The cuticular waxes of leaves of Coffea arabica cv. ‘Catuaí Vermelho’, C. arabica cv. ‘Obatã’, Coffea canephora cv. ‘Apoatã’, Coffea racemosa and two hybrids between C. arabica and C. racemosa were extracted by rapid washing of the surface with chloroform. The waxes were fractionated by thin layer chromatography over silicagel. The fractions of the constituent classes were characterized by infrared spectroscopy and the distribution of the homologs of the n-alkanes and n-primary alcohols was determined by GC/MS and GC/FID. Among the samples analyzed, leaves of C. racemosa have the highest content of foliar wax (22.9 μg cm⁻²). Most samples contain either n-alkanes (C. canephora and C. racemosa) or n-primary alcohols (C. arabica) as predominant wax constituents. The distribution of n-alkanes allowed the distinction of C. racemosa from the other samples; the distribution of alcohols allowed the distinction of the three species. The two hybrids have waxes similar to the wax of C. arabica.     

Effects of UV radiation and nitrate limitation on the production of biogenic sulfur compounds by marine phytoplankton

We tested the effects of UV radiation (UVR) and nitrate limitation on the production of dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSPp), and particulate dimethylsulfoxide (DMSOp) in natural seawater from the Gulf of Mexico and in phytoplankton cultures. DMS/Chl a ratios in PAR-only and PAR + UV-exposed seawater were 0.44–2.0 and 0.46–1.9 nmol DMS μg⁻¹ Chl a, respectively, whereas the ratios in cultures of Amphidinium carterae were 1.0–2.2 nmol μg⁻¹ in PAR-exposed samples and 0.91–2.1 nmol μg⁻¹ in PAR + UV-exposed samples. These results suggested that UVR did not substantially affect DMS/Chl a ratios in seawater and A. carterae culture samples. Similarly, UVR had no significant effect on DMSOp/Chl a in seawater samples (0.83–1.6 nmol DMSO μg⁻¹ Chl a for PAR + UV vs. 0.70–1.5 nmol μg⁻¹ for PAR-exposed seawater samples, respectively) or in A. carterae cultures (0.20–1.3 and 0.19–0.88 nmol DMSO μg⁻¹ Chl a in PAR + UV- and PAR-exposed cultures, respectively). In an experiment with the diatom, Thalassiosira oceanica, the culture was grown in high nitrate (30 μM) or low nitrate (6 μM) media and exposed to PAR-only or PAR + UV. The low nitrate, PAR-only samples showed an increase of intracellular dimethylsulfoniopropionate (DMSP) concentration from 2.1 to 15 mmol L⁻¹ in 60 h, but the increase occurred only after cultures reached the stationary phase. Cultures of T. oceanica grown under UVR had lower growth rates than those under PAR-only (μ′ = 0.17 and 0.32 d⁻¹, respectively) and perhaps did not experience severe nitrate limitation even in the low nitrate treatment. These results suggest that the elevated UVR in low nitrate environments could result in reduction of DMSP in some species, whereas DMSP concentrations would not be affected in eutrophic areas.     

Leaf cuticular waxes are arranged in chemically and mechanically distinct layers: evidence from Prunus laurocerasus L.

The composition and spatial arrangement of cuticular waxes on the leaves of Prunus laurocerasus were investigated. In the wax mixture, the triterpenoids ursolic acid and oleanolic acid as well as alkanes, fatty acids, aldehydes, primary alcohols and alcohol acetates were identified. The surface extraction of upper and lower leaf surfaces yielded 280 mg m ^{? 2} and 830 mg m ^{? 2}, respectively. Protocols for the mechanical removal of waxes from the outermost layers of the cuticle were devised and evaluated. With the most selective of these methods, 130 mg m ^{? 2} of cuticular waxes could be removed from the adaxial surface before a sharp, physically resistant boundary was reached. Compounds thus obtained are interpreted as ‘epicuticular waxes’ with respect to their localization in a distinct layer on the surface of the cutin matrix. The epicuticular wax film can be transferred onto glass and visualized by scanning electron microscopy. Prunus laurocerasus epicuticular waxes consisted entirely of aliphatic compounds, whereas the remaining intracuticular waxes comprised 63% of triterpenoids. The ecological relevance of this layered structure for recognition by phytotrophic fungi and herbivorous insects that probe the surface composition for sign stimuli is discussed.     

Cultivation of microalgae for oil production with a cultivation strategy of urea limitation

The microalgae, Chlorella sp., were cultivated in various culture modes to assess biomass and lipid productivity in this study. In the batch mode, the biomass concentrations and lipid content of Chlorella sp. cultivated in a medium containing 0.025–0.200 g L⁻¹ urea were 0.464–2.027 g L⁻¹ and 0.661–0.326 g g⁻¹, respectively. The maximum lipid productivity of 0.124 g d⁻¹ L⁻¹ occurred in a medium containing 0.100 g L⁻¹ urea. In the fed-batch cultivation, the highest lipid content was obtained by feeding 0.025 g L⁻¹ of urea during the stationary phase, but the lipid productivity was not significantly increased. However, a semi-continuous process was carried out by harvesting the culture and renewing urea at 0.025 g L⁻¹ each time when the cultivation achieved the early stationary phase. The maximum lipid productivity of 0.139 g d⁻¹ L⁻¹ in the semi-continuous culture was highest in comparison with those in the batch and fed-batch cultivations.     

Surface wax of Andreaea and Pogonatum species

The mosses Andreaea rupestris, Pogonatum aloides and P. urnigerum contain surface waxes in amounts of 0.05–0.12% dry wt. The waxes consisted of esters (C₃₈-C₅₄), primary alcohols (C₂₀-C₃₂), free fatty acids (C₁₆-C₃₀), and alkanes (C₂₁-C₃₁). Additionally, aldehydes (C₂₂-C₃₀) were major constituents in the wax of P. urnigerum. The classes and their chain length distributions in the surface waxes of these mosses are comparable to those of epicuticular waxes of higher plants.     

Termiticidal activity of lectins from Myracrodruon urundeuva against Nasutitermes corniger and its mechanisms

The isolation of lectins from Myracrodruon urundeuva bark (MuBL) and heartwood (MuHL) as well as the termiticidal activity of MuHL against Nasutitermes corniger has already been described. This work reports on the purification of a leaf lectin (MuLL) and the characterization of MuBL, MuHL, and MuLL; also described are the resistance of hemagglutinating activity of the three lectins to trypsin activity from N. corniger gut and the termiticidal activity on N. corniger of MuBL (LC₅₀ of 0.974 mg ml⁻¹ on workers and 0.787 mg ml⁻¹ on soldiers) and MuLL (LC₅₀ of 0.374 mg ml⁻¹ on workers and 0.432 mg ml⁻¹ on soldiers). The antibacterial effect of MuBL, MuHL, and MuLL on bacteria from gut of N. corniger was also investigated and lectins showed similar bacteriostatic activity (MIC of 62.5 ??g ml⁻¹ for workers and 125 ??g ml⁻¹ for soldiers). MuBL and MuHL were more efficient bactericidal agents on bacteria in the workers’ gut (MBC of 125 ??g ml⁻¹) than MuLL (MBC of 250 ??g ml⁻¹) and similar bactericidal activity was detected on bacteria in the gut of soldiers (MBC of 250 ??g ml⁻¹). The termiticidal activity of M. urundeuva lectins can be explained by the chitin-binding property, resistance to termite digestive enzyme, and the antibacterial effect on symbiotic bacteria of N. corniger gut.     

Substrate-inhibitory analysis of the cholinesterase in the freshwater oligochaete Lumbriculus variegatus (O.F. Műller, 1773; Lumbriculidae,Oligochaeta)

The substrate-inhibitory analysis has shown that single “atypical” cholinesterase (ChE) presents in tissues of freshwater oligochaete Lumbriculus variegatus (O.F. M?ller). This enzyme differs both from “typical” acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Specific activity of oligochaete ChE ranges 55–100 μmol ATCh g⁻¹ tissue min⁻¹ or 0.7–1 μmol ATCh mg⁻¹ protein min⁻¹, ratio of maximal rates (V) of substrate hydrolysises is 100:72:71:83 for acetyl-, propionyl-, butyryl- and acetyl-β-metylthiocholine respectively. Values of Michaelis constant (K_m) for these substrates are (1.9–2.5) × 10⁻⁴ M. The bimolecular enzyme inhibition rate constants (k_II) for organophosphorus inhibitors paraoxon, DDVP, and iso-OMPA are 10⁷, 10⁶ и 10³ mol⁻¹ | min⁻¹. ATCh and BuTCh exhibit the effect of substrate inhibition of ChE activity, while PrTCh and MeTCh do not.     

Inter-population variability of leaf morpho-anatomical and terpenoid patterns of Pistacia atlantica Desf. ssp. atlantica growing along an aridity gradient in Algeria

Three Algerian populations of female Pistacia atlantica shrubs were investigated in order to check whether their terpenoid contents and morpho-anatomical parameters may characterize the infraspecific variability. The populations were sampled along a gradient of increasing aridity from the Atlas mountains into the northwestern Central Sahara.As evidenced by Scanning Electron Microscopy, tufted hairs could be found only on seedling leaves from the low aridity site as a population-specific trait preserved also in culture. Under common garden cultivation seedlings of the high aridity site showed a three times higher density of glandular trichomes compared to the low aridity site. Increased aridity resulted also in reduction of leaf sizes while their thickness increased. Palisade parenchyma thickness also increases with aridity, being the best variable that discriminates the three populations of P. atlantica.Analysis of terpenoids from the leaves carried out by GC-MS reveals the presence of 65 compounds. The major compounds identified were spathulenol (23 μg g⁻¹ dw), α-pinene (10 μg g⁻¹ dw), verbenone (7 μg g⁻¹ dw) and β-pinene (6 μg g⁻¹ dw) in leaves from the low aridity site; spathulenol (73 μg g⁻¹ dw), α-pinene (25 μg g⁻¹ dw), β-pinene (18 μg g⁻¹ dw) and γ-amorphene (16 μg g⁻¹ dw) in those from medium aridity and spathulenol (114 μg g⁻¹ dw), α-pinene (49 μg g⁻¹ dw), germacrene D (29 μg g⁻¹ dw) and camphene (23 μg g⁻¹ dw) in leaves from the high aridity site. Terpene concentrations increased with the degree of aridity: the highest mean concentration of monoterpenes (136 μg g⁻¹ dw), sesquiterpenes (290 μg g⁻¹ dw) and total terpenes (427 μg g⁻¹ dw) were observed in the highest arid site and are, respectively, 3-, 5- and 4-fold higher compared to the lower arid site. Spathulenol and α-pinene can be taken as chemical markers of aridity. Drought discriminating compounds in low, but detectable concentrations are δ-cadinene and β-copaene. The functional roles of the terpenoids found in P. atlantica leaves and principles of their biosynthesis are discussed with emphasis on the mechanisms of plant resistance to drought conditions.     

pH-control modes in a 5-L stirred-tank bioreactor for cell biomass and exopolysaccharide production by Tremella fuciformis spore

The effect of pH-control modes on cell growth and exopolysaccharide production by Tremella fuciformis was evaluated in a 5-L bioreactor. The results show that the maximal dry cell weight (DCW) and exopolysaccharide production were 23.57 and 4.48 g L⁻¹ in pH-stat fermentation, where the maximal specific growth rate (μ_max) and specific production rate of exopolysaccharide (P_P/X) were 1.03 and 0.24 d⁻¹, respectively; under pH-shift cultivation, the maximal DCW and exopolysaccharide production were 30.57 and 3.90 g L⁻¹, where the μ_max and P_P/X were 1.21 and 0.06 d⁻¹. Unlike batch fermentation, maximal DCW and exopolysaccharide production merely reached 15.04 and 2.0 g L⁻¹, where the μ_max and P_P/X were 0.86 and 0.05 d⁻¹, respectively. These results suggest that a pH-stat strategy is a more efficient way of performing the fermentation process to increase exopolysaccharide production. Furthermore, this research has also proved that the three-stage pH-control mode is effective for cell growth.     

Optimization, purification, characterization and antioxidant activity of an extracellular polysaccharide produced by Paenibacillus polymyxa SQR-21

The optimization, purification and characterization of an extracellular polysaccharide (EPS) from a bacterium Paenibacillus polymyxa SQR-21 (SQR-21) were investigated. The results showed that SQR-21 produced one kind of EPS having molecular weight of 8.96 × 10⁵ Da. The EPS was comprised of mannose, galactose and glucose in a ratio of 1.23:1.14:1. The ratio of monosaccharides and glucuronic acid was 7.5:1. The preferable culture conditions for EPS production were pH 6.5, temperature 30 °C for 96 h with yeast extract and galactose as best N and C sources, respectively. The maximum EPS production (3.44 g L⁻¹) was achieved with galactose 48.5 g L⁻¹, Fe³⁺ 242 μM and Ca²⁺ 441 μM. In addition, the EPS showed good superoxide scavenging, flocculating and metal chelating activities while moderate inhibition of lipid peroxidation and reducing activities were determined. These results showed the great potential of EPS produced by SQR-21 to be used in industry in place of synthetic compounds.     

Effect of deltamethrin on the gills of Aphanius dispar: a microscopic study

Aphanius dispar, a freshwater fish (mean total length ± sd, 3.42 ± 0.33 cm) was exposed to different concentrations of deltamethrin (2.25, 2.50 and 3.00 μg L⁻¹), an insecticide used to control Dubas bug, Ommatissus lybicus in Oman. The histopathological changes in the structure of the gills in fish exposed to deltamethrin was studied using light, transmission and scanning electron microscopy. In light microscopy, the fish exposed to 2.25 μg L⁻¹ deltamethrin, showed hypertrophy and hyperplasia of chloride cells, while in 2.50 μg L⁻¹, additional changes like vacuolization, lifting of the lamellar epithelium and fusion of secondary lamellae were observed. The most severe alteration including vacuolization, desquamation of cells and dilation of intercellular space was recorded at 3.00 μg L⁻¹. Transmission and scanning electron microscopy, supports the findings of light microscopy and further document the ultrastructural damage caused, especially in exposure to 2.50 and 3.00 μg L⁻¹. Al l changes observed are described in detail. The deltamethrin exposure concentration of 2.25 μg L⁻¹ seems to be a threshold above which any small increase in concentration results in severe damage. All present results have been compared with those of previous studies on gill damage caused by various chemical substances. The impacts of the damage on the functioning of gills as a respiratory organ are discussed.     

Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth,morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate

In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO₃⁻, NH₄⁺, or both at equimolar concentrations (500 μM). Plants supplied with only NO₃⁻ had lower growth rates (0.17 ± 0.01 g g⁻¹ d⁻¹), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH₄⁺ alone or in combination with NO₃⁻ (RGR = 0.28 ± 0.01 g g⁻¹ d⁻¹). Ammonium was the preferred form of N taken up. The maximal rate of NH₄⁺ uptake (V_max) was 6–14 times higher than the maximal uptake rate of NO₃⁻ and the minimum concentration for uptake (C_min) was lower for NH₄⁺ than for NO₃⁻. Plants supplied with NO₃⁻ had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO₃⁻ was primarily reduced in the roots, but NRA levels were generally low (<4 μmol NO₂⁻ g⁻¹ DW h⁻¹). Under natural growth conditions NH₄⁺ is probably the main N source for S. natans, but plants probably also exploit NO₃⁻ when NH₄⁺ concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH₄⁺ levels in the water, even though the uptake capacity for NO₃⁻ is reduced under these conditions.