Chromium uptake,retention and reduction in photosynthetic <Emphasis Type="Italic">Euglena gracilis</Emphasis>

Photosynthetic Euglena gracilis grown with different K₂CrO₄ concentrations was analyzed for its ability to take up, retain and reduce Cr(VI). For comparison, cells were also exposed to CrCl₃. Cellular Cr(VI) uptake at pH 7.2 showed a hyperbolic saturation pattern with K _m of 1.1 mM, V _m of 16 nmol (h × 10⁷ cells)⁻¹, and K _i sulfate of 0.4 mM. Kinetic parameters for sulfate uptake were similar, K _m = 0.83 mM, V _m = 15.9 nmol (h × 10⁷cells)⁻¹ and K _i chromate = 0.3 mM. The capacity to accumulate chromium depended on the ionic species, external concentration and pH of the incubation medium. Cr(VI) or Cr(III) accumulation was negligible in the acidic (pH 3.5) culture medium, in which Cr(VI) was abiotically reduced to Cr(III). At pH 7.2 Cr(VI) was fully stable and high accumulation (>170 nmol/1 × 10⁷ cells at 1 mM K₂CrO₄) was achieved; surprisingly, Cr(III) accumulation was also significant (>35 nmol/1 × 10⁷ cells at 1 mM CrCl₃). Cr(VI) was reduced by cells at pH 7.2, suggesting the presence of an external reductive activity. Cr(VI) induced an increased cysteine and glutathione content, but not in phytochelatins suggesting that chromium accumulation was mediated by monothiol compounds.     

Structural requirements for cellular uptake of α‐helical amphipathic peptides

The structure of the cell‐permeable α‐helical amphipathic model peptide FLUOS‐KLALKLALKALKAALKLA‐NH₂ ( I ) was modified stepwise with respect to its helix parameters hydrophobicity, hydrophobic moment and hydrophilic face as well as molecular size and charge. Cellular uptake and membrane destabilizing activity of the resulting peptides were studied using aortic endothelial cells and HPLC combined with CLSM. With the exceptions that a reduction of molecule size below 16 amino acid residues and the introduction of a negative net charge abolished uptake, none of the investigated structural parameters proved to be essential for the passage of these peptides across the plasma membrane. Membrane toxicity also showed no correlation to any of the parameters investigated and could be detected only at concentrations higher than 2 μm . These results implicate helical amphipathicity as the only essential structural requirement for the entry of such peptides into the cell interior, in accord with earlier studies. The pivotal role of helical amphipathicity was confirmed by uptake results obtained with two further pairs of amphipathic/non‐amphipathic 18‐mer peptides with different primary structure, net charge and helix parameters from I . The amphipathic counterparts were internalized into the cells to a comparable extent as I , whereas no cellular uptake could be detected for the non‐amphipathic analogues. The mode of uptake remains unclear and involves both temperature‐sensitive and ‐insensitive processes, indicating non‐endocytic contributions. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

Metabolism of (±) 2-[14C]-abscisic acid in Lactuca sativa achenes

Achenes ofLactuca sativa L. cv. Grand Rapids were treated with (±) 2-[¹⁴C]-abscisic acid (ABA) at 10⁵ - or 2-10⁶ M for 6, 12, 24, 48 or 96 h in darkness at 24°C. They were then extracted in 80% ethanol. Two acidic diethyl ether phases which contained the free acids and the acids released after mild alkaline hydrolysis respectively, were analyzed as well as the radioactivity which remained in the final aqueous phase. For treatment durations between 6 and 96 h, the major part of the radioactivity was found in the free phase, in the form of ABA. For treatment durations up to 48 h, no radioactivity was detected at the Rf of phaseic acid or dihydrophaseic acid (free and hydrolysed phases). After 96 h culture on 10⁵ M ABA, dihydrophaseic acid was present, but only in very small quantities. Two ABA metabolites were detected. One was characterized as β-d -glucopyranosyl abscisate since its Rf was the same as that of an authentic sample in three different solvent systems and also since it released ABA on mild alkaline hydrolysis. It increased steadily with time and represented the main metabolite. The other metabolite found in the aqueous phase after mild alkaline hydrolysis and extraction with ether at pH 3 was a very polar compound, resistant to alkaline hydrolysis in the presence of concentrated ammonia and to methylation. It was, however, metabolized by apple embryo, yielding essentially dihydrophaseic acid and an ester which released dihydrophaseic acid on mild alkaline hydrolysis. These results indicate that under the conditions tried, the metabolism of [¹⁴C]-ABA by lettuce achenes leads almost exclusively to the formation of conjugates, oxidative metabolism of ABA being almost non-existent. Separate analysis of the integuments and of the endosperm plus embryo after culture of whole achenes for 48 h in the presence of 10⁵ M [¹⁴C]-ABA showed that ABA metabolism occurred only in the endospermembryo tissue.     

Chemical Characterization,Crossfeeding and Uptake Studies on Hydroxamate Siderophore of <Emphasis Type="Italic">Alcaligenes faecalis</Emphasis>

We report the production of two types of siderophores namely catecholate and hydroxamate in modified succinic acid medium (SM) from Alcaligenes faecalis. Two fractions of siderophores were purified on amberlite XAD, major fraction was hydroxamate type having a λ_max at 224 nm and minor fraction appeared as catecholate with a λ_max of 264 nm. The recovery yield obtained from major and minor fractions was 297 and 50 mg ml⁻¹ respectively. The IEF pattern of XAD-4 purified siderophore suggested the pI value of 6.5. Cross feeding studies revealed that A. faecalis accepts heterologous as well as self (hydroxamate) siderophore in both free and iron complexed forms however; the rate of siderophore uptake was more in case of siderophores complexed to iron. Siderophore iron uptake studies indicated the differences between hydroxamate siderophore of A. faecalis and Alc E, a siderophore of Alcaligenes eutrophus.     

Improved Tolerance of Three Saudi Pearl Millet Cultivars (<i>Pennisetum spicatum</i>) to Salt Stress by Mycorrhiza

Seeds of three Saudi pearl millet cultivars (Pennisetum spicatum) from three regions (Madinah, Khulais and Jaizan) were inoculated with arbuscular mycorrhizal fungus Glomus mosseae obtained from the Agriculture Research Center of Giza, Egypt to enhance their salt tolerance. Five different NaCl concentrations (0, 30, 60, 90, and 120 mM) were used for treating cultivars with and without mycorrhiza. Growth rates, chlorophyll content, chlorophyll fluorescence (Fv/Fm), proline content and gas exchange were measured to determine the effect of salinity on these cultivars. The results indicated that compared to cultivars without mycorrhiza, all cultivars with mycorrhiza had enhanced growth and physiological parameters including shoot and root length, area and number of leaves, fresh and dry weights of shoots and roots, chlorophyll contents and gas exchanges at 0 and 30 mM of salinity. In addition, the measurements of the different growth rates showed higher growth performance of the cultivars from Madinah and Khulais than the cultivar from Jaizan. However, all cultivars with and without mycorrhiza showed significant reductions in growth rates, chlorophyll contents and gas exchanges at a salinity of 60 mM than those grown at 0 and 30 mM. Moreover, the values of Fv/Fm were significantly reduced in all cultivars with and without mycorrhiza grown at 60 mM than in those grown at 0 mM and 30 mM. Proline contents indicated a progressive increase with the elevation of NaCl concentration stress. The proline contents in the mycorrhiza-inoculated cultivars were significantly higher than those in the non-inoculated cultivars. On the other hand, all cultivars with and without mycorrhiza underwent senescence within four weeks of growth at salinity concentrations of 90 mM and 120 mM. Therefore, relatively low salinity must be maintained to achieve high growth rates and gas exchanges of these inoculated cultivars.     

Biochar Application Enhanced Post-Heading Radiation Use Efficiency in Field-Grown Rice (<i>Oryza sativa</i> L.)

It has been shown that adding biochar to soil can improve nitrogen (N) uptake and utilization in rice (Oryza sativa L.). However, there is a lack of research on the physiological alterations of rice as a result of the changes in nitrogen uptake due to the addition of biochar. This study conducted field experiments in 2015 and 2016 with the goal of testing the hypothesis that the application of biochar would enhance radiation use efficiency (RUE) of rice by improving the plant’s ability to take in and utilize nitrogen. Our results demonstrated that the application of biochar (20 t ha⁻¹ ) induced no significant effects on pre-heading specific leaf weight (SLW), nitrogen uptake (NUpre), and leaf area index (LAI) at heading, the ratios of LAI/NUpre and SLW/Nupre, or pre-heading RUE. However, biochar application significantly increased post-heading nitrogen uptake (NUpost), ratios of NUpost/SLW and NUpost/LAI, and post-heading RUE. These results indicate that the application of biochar can improve the plant’s nitrogen uptake and RUE in field-grown rice during the post-heading period, which con- firms our hypothesis.     

Bacterial Uptake by the Marine Sponge <Emphasis Type="Italic">Aplysina aerophoba</Emphasis>

Sponges (Porifera) are filter feeders that take up microorganisms from seawater and digest them by phagocytosis. At the same time, many sponges are known to harbor massive consortia of symbiotic microorganisms, which are phylogenetically distinct from those in seawater, within the mesohyl matrix. In the present study, feeding experiments were performed to investigate whether phylogenetically different bacterial isolates, hereafter termed “food bacteria,” microbial seawater consortia, and sponge symbiont consortia are taken up and processed differently by the host sponge. Aplysina aerophoba retained high numbers of bacterial isolates and microbial seawater consortia with rates of up to 2.76 × 10⁶ bacteria (g sponge wet weight)^–1 h^–1, whereas the retention of sponge symbionts was lower by nearly two orders of magnitude [5.37 × 10⁴ bacteria (g sponge wet weight)⁻¹ h^–1]. In order to visualize the processing of a food bacterium within sponge tissues, the green fluorescent protein-labeled Vibrio strain MMW1, which had originally been isolated from A. aerophoba, was constructed. Incubation of this strain with A. aerophoba and subsequent visualization in tissue cryosections showed its presence in the choanocytes and/or endopinacocytes lining the canals but, unlike latex beads, not in deeper regions of the mesohyl, which suggests digestion of the bacteria upon contact with the host. Denaturing gradient gel electrophoresis (DGGE) was performed on the incubation seawater to monitor the changes in phylogenetic composition after incubation of the sponge with either seawater or sponge symbiont consortia. However, the DGGE experiment provided no evidence for selective processing of individual lineages by the host sponge. In conclusion, this study extends early studies by Wilkinson et al. (Proc R Soc London B 220:519–528, 1984) that sponges, here A. aerophoba, are able to differentiate between food bacteria and their own bacterial symbionts.     

SIDEROPHORE‐INDEPENDENT IRON UPTAKE BY IRON‐LIMITED CELLS OF THE CYANOBACTERIUM ANABAENA FLOS‐AQUAE1

Iron acquisition by iron‐limited cyanobacteria is typically considered to be mediated mainly by siderophores, iron‐chelating molecules released by iron‐limited cyanobacteria into the environment. In this set of experiments, iron uptake by iron‐limited cells of the cyanobacterium Anabaena flos‐aquae (L.) Bory was investigated in cells resuspended in siderophore‐free medium. Removal of siderophores decreased iron‐uptake rates by ～60% compared to siderophore‐replete conditions; however, substantial rates of iron uptake remained. In the absence of siderophores, Fe(III) uptake was much more rapid from a weaker synthetic chelator [N‐(2‐hydroxyethyl)ethylenediamine‐N,N′,N′‐triacetic acid (HEDTA); log K_cond = 28.64 for Fe(III)HEDTA(OH)^?] than from a very strong chelator [N,N′‐bis(2‐hydroxybenzyl)‐ethylenediamine‐N,N′‐diacetic acid (HBED); log K_cond = 31.40 for Fe(III)HBED^?], and increasing chelator:Fe(III) ratios decreased the Fe(III)‐uptake rate; these results were evident in both short‐term (4 h; absence of siderophores) and long‐term (116 h; presence of siderophores) experiments. However, free (nonchelated) Fe(III) provided the most rapid iron uptake in siderophore‐free conditions. The results of the short‐term experiments are consistent with an Fe(III)‐binding/uptake mechanism associated with the cyanobacterial outer membrane that operates independently of extracellular siderophores. Iron uptake was inhibited by temperature‐shock treatments of the cells and by metabolically compromising the cells with diphenyleneiodonium; this finding indicates that the process is dependent on active metabolism to operate and is not simply a passive Fe(III)‐binding mechanism. Overall, these results point to an important, siderophore‐independent iron‐acquisition mechanism by iron‐limited cyanobacterial cells.     

Trypanosoma cruzi Proline Transport Presents a Cell Density‐dependent Regulation

Trypanosoma cruzi, the etiological agent of Chagas disease, uses proline as its main carbon source, essential for parasite growth and stage differentiation in epimastigotes and amastigotes. Since proline is mainly obtained from extracellular medium by transport proteins, in this work we studied the regulation of the T. cruzi proline transporter TcAAAP069. Proline uptake and intracellular concentration presented oscillations during epimastigote growth phases, increasing during the early exponential phase (322 pmol/min) and decreasing to undetectable levels during the late exponential phase. Transporter expression rate correlated with proline uptake, and its subcellular localization alternated from both, the plasma membrane and close to the flagellar pocket, when the transport is higher, to only the flagellar pocket region, when the transport decreased until proline uptake and TcAAAP069 protein became undetectable at the end of the growth curve. Interestingly, when parasites were treated with conditioned medium or were concentrated to artificially increase the culture density, the proline transport was completely abolished resembling the effects observed in late exponential phase. These data highlight for the first time the existence of a density‐associated regulation of relevant physiological processes such as proline metabolism.     

Effects of mycorrhizal colonisation on<Emphasis Type="Italic"> Thymus polytrichus</Emphasis> from heavy-metal-contaminated sites in northern England

A study was performed to establish whether colonisation with arbuscular mycorrhizal (AM) fungi is beneficial to wild thyme [Thymus polytrichus A. Kerner ex Borbás ssp. britannicus (Ronn.) Kerguelen (Lamiaceae)] growing in the heavy-metal-contaminated soils along the River South Tyne, United Kingdom. T. polytrichus plants of the same genotype were grown under controlled conditions with and without Zn contamination, and differences between AM-colonised and -uncolonised plants in mean shoot and root growth (dry weight) and Zn concentration were assessed. When grown in the heavy-metal-contaminated, low-P soil from one of the South Tyne sites, AM-colonised plants grew significantly larger than uncolonised plants; however, there was no significant difference in growth between AM and non-AM plants grown in an artificial substrate with a larger available P concentration, with or without Zn contamination. Mycorrhizal colonisation increased tissue Zn concentrations during the experiments. It is concluded that AM fungi are beneficial, if not essential, to T. polytrichus growing in the low-nutrient soils along the River South Tyne, because of their role in enhancing plant uptake of P (and possibly other nutrients). There was no evidence from this study that the fungi reduce plant uptake of heavy metals at these sites, but rather increase Zn uptake. However, the resulting tissue metal concentrations do not appear to be large enough to be detrimental to plant growth.     

Scaling Vo2 Peak in Obese and Non‐obese Girls

Objective: The conventional ratio method (milliliters O₂ per mass) typically is used to express Vo ₂ peak. The goal of the current study was to compare Vo ₂ peak of obese girls with normal‐weight girls by ratio and allometric scaling methods. Research Methods and Procedures: We compared Vo ₂ peak by ratio and allometric methods in 46 obese and 47 normal‐weight girls. Indirect calorimetry was used to measure Vo ₂ peak during either treadmill running or walking. Regression analysis was used to determine coefficients for mass and stature for each group with ANOVA used to compare data between groups. Results: The obese girls were taller and had higher values of body fatness (p ≤ 0.05). Absolute Vo ₂ peak (liters per minute) was similar between groups ; however Vo ₂ peak relative to mass was 50% lower (p ≤ 0.05) in the obese girls. When Vo ₂ peak (milliliters per minute per kilogram) and mass were correlated, r = ?0.48 was found in the obese group. Allometric scaling of logarithmic transformed stature and mass reduced this to r = ?0.002, thus eliminating the bias associated with the ratio method. Adjusting Vo ₂ peak allometrically scaled for mass, stature, and the combination of mass and stature reduced the difference between groups from 50% (ratio method) to 10% to 11% (p ≤ 0.05) with higher values found in the normal‐weight girls. Discussion: These results demonstrate the bias associated with the ratio method when comparing Vo ₂ peak in obese girls with Vo ₂ peak in normal‐weight girls. Allometric scaling eliminated the bias and thus may reflect a truer comparative response.     

Kinetics of nitrate uptake by New Zealand marine macroalgae and evidence for two nitrate transporters in <Emphasis Type="Italic">Ulva intestinalis</Emphasis> L.

Kinetic constants were determined for nitrate uptake in three species, Pterocladiella capillacea (S.G. Gmelin) Santelices et Hommersand (Rhodophyceae, Gelidiales), Ulva intestinalis L. (Chlorophyceae, Ulvales) and Xiphophora chondrophylla (Turner) Montagne ex Harvey (Phaeophyceae, Fucales), of New Zealand macroalgae, with K _m values ranging from 10 to 17 μM and V _max values from 3 to 65 μmole g⁻¹ dry weight h⁻¹. There was no effect of ammonium on nitrate uptake by Pterocladiella capillacea or Xiphophora chondrophylla. Ammonium inhibited nitrate uptake by 40% in Ulva intestinalis from a site with relatively low seawater ammonium concentrations. In contrast, U. intestinalis from an ammonium-enriched site had lower rates of nitrate uptake that were insensitive to inhibition by ammonium. It is suggested that there are (at least) two transport systems for nitrate in U. intestinalis; a constitutive transporter, which is insensitive to ammonium, and a transporter that is sensitive to ammonium inhibition and down-regulation by ammonium; the implications of this for our understanding of macroalgal blooms is discussed. Handling editor: K. Martens     

Nod factor enhances calcium uptake by soybean

Inoculation with rhizobia or application of Nod factors (lipo-chitooligosaccharides, LCOs) causes transient increases in cytosolic calcium concentration in root hairs of legume plants. We conducted experiments to evaluate whether application of LCO and inoculation with rhizobia improved (45)CaCl(2) uptake into soybean (Glycine max [L.] Merr.) leaves. Roots of soybean seedlings with one developing trifoliolate were immersed in Murashige and Skoog (MS) basal liquid medium containing treatment solutions and (45)CaCl(2), and the plants were incubated under continuous light. After 24 h, leaf samples were taken, and their radioactivity levels were determined. Addition of NodBj-V (C18:1 MeFuc) at a concentration of 10(-7) M increased (45)Ca(2+) uptake. Inoculation with genistein-induced Bradyrhizobium japonicum strain 532C and USDA3 also increased (45)Ca(2+) uptake; whereas, inoculation with strain Bj-168, a nodC-mutant incapable of producing LCO, did not. Rhizobia that do not normally nodulate soybean, i.e. Rhizobium leguminosarum, and Sinorhizobium meliloti did not affect calcium uptake, nor did the tetramer or pentamer of chitosan, or lumichrome. Surprisingly, Rhizobium sp. NGR234, which can nodulate some types of soybean, although without effective N(2)-fixation, also did not affect calcium uptake. This work suggests that the rhizobial symbiosis, in addition to its known role in provision of nitrogen fixation, also improves early calcium uptake into soybean plants.     

Oxygen uptake through water during early life in Channa punctatus (Bloch) (Pisces; Ophicephaliformes)

Oxygen uptake in relation to body size during the early life of the fish Channa punctatus shows a significant two-component curve: one related to the fully aquatic phase and the other to the bimodal phase of respiration. The onset of the air-breathing habit around the 18–20th day after hatching brings about a 45% drop in O₂ uptake through the gill/skin in water.     

Measuring Nitrogen and Phosphorus Uptake by Intact Roots of Mature Acer saccharum Marsh., Pinus resinosa Ait., and Picea abies (L.) Karst

A common method for measuring uptake by intact roots in situ is the depletion method, wherein intact fine roots are separated from soil and placed in nutrient solution. The difference between initial and final amounts of nutrient in solution is attributed to root uptake. Variations on this method include applying pretreatment solutions, training roots to grow into bags or trays, and varying concentrations of nutrient solution. We tested whether variations in methods affected measured net uptake rates of NH ₄ ⁺ , NO ₃ ⁻ , and PO ₄ ³⁻ . Intact roots of 60 year-old sugar maple (Acer saccharum Marsh.), red pine (Pinus resinosa Ait.), and Norway spruce (Picea abies (L.) Karst.) were given one of four treatments prior to measuring net uptake. “Trained” roots were grown in a sand-soil mixture. “Recovered” roots were excavated and allowed to recover in nutrient solution for two or four days (“two-day recovery” and “four-day recovery”, respectively). “No recovery” roots were excavated and used immediately in experiments. We exposed roots to three concentrations of nutrient solutions to observe the effects of initial nutrient solution concentration. Initial nutrient solution concentration was an important source of variation in measured uptake rates, and N uptake was stimulated by low antecedent concentrations. We found no significant differences in net uptake rates between pretreatments for any of the species studied, indicating that our pretreatments were not effective in improving measurement of uptake. Such pretreatments may not be necessary for measuring net uptake and may not hinder the comparison of rates measured using variations of the depletion method.     

Estimation of Growth and Photosynthetic Performance of Two C₄ Species (<i>Pennisetum spicatum</i> (L.) Körn. and <i>Zea mays</i> L.) under a Low Temperature Treatment

Pearl millet (Pennisetum spicatum (L.) Körn.) and maize (Zea mays L.) are C₄ grass species grown for feeding humans and animals in Almadinah Almunawwarah, which is in the western part of Saudi Arabia. During the winter, the mean temperature, which drops to 14°C, represents a major problem for the growth of these species in this region. Therefore, the objectives of this research were to investigate the growth response and the photosynthetic performance of P. spicatum and Z. mays under a low temperature stress. The treatments involved daytime and nighttime temperatures of 14/12°C (low temperature) and 24/22°C (optimum temperature). The results indicated that low temperature significantly reduced all growth and physiological parameters, including seed germination, leaf expansion, leaf area, shoot length and root length of the two species compared to those of the control. Additionally, the low temperature significantly decreased the light-saturated assimilation rate (A_sat), quantum yield (ϕ), saturated rate of carbon dioxide uptake (A_max) and efficiency of carboxylation on both species compared to those of the control. Moreover, the values of Fv/Fm and the chlorophyll contents of both species were significantly reduced by low temperature compared to those of the control. It can be concluded that both species had little tolerance to low temperatures.