Fusicoccin, an inhibitor of brassinosteroid-induced ethylene production

Fusicoccin was evaluated for its effects on brassinosteroid (BR), indole-3-acetic acid (IAA) and BR + IAA-induced ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC-synthase production by etiolated mung bean ( Vigna radiata L. Rwilez cv. Berken) hypocotyl segments. Fusicoccin inhibition of ethylene and ACC production induced by 2 μ M BR started at concentrations as low as 0.05 μ M . Maximum inhibition occurred at a 1 μ M concentration with no further inhibition at higher concentrations tested. Fusicoccin (1 μ M ) was effective in the inhibition of BR-induced ethylene, ACC and ACC-synthase production at low and high concentrations of BR.
Fusicoccin at concentrations as high as 2 μ M had no effect on ethylene and ACC production promoted by low concentrations of IAA (1 to 10 μ M ). When higher concentrations (100–1000 μ M ) of IAA were used, fusicoccin (1 μ M ) had an inhibitory effect on ethylene and ACC production. Interestingly, fusicoccin (1 μ M ) had little or no effect on ACC-synthase promoted by high concentrations of IAA (1000 μ M ).
When BR and IAA were used in combination, fusicoccin inhibited ethylene and ACC production at concentrations as low as 0.05 μ M with maximum inhibition occurring at 0.5 μ M . At a 1 μ M concentration, fusicoccin was effective in inhibiting the synergistic stimulation of ACC-synthase promoted by BR and IAA.     

Retardation of abscission of citrus leaf and fruitlet explants by brassinolide

Brassinolide (BR), a novel plant growth-regulating steroidal lactone, markedly retarded the abscission of leaf explants of Calamondin (Citrus madurensis Lour.), when dissolved in water and fed through the petiole. BR was effective at concentrations as low as 0.021 M, and showed a stronger effect than IAA which also retarded abscission. Trifluoperazine (TFP), an inhibitor of the calmodulin-calcium complex, accelerated abscission, and this acceleration could be counteracted by a simultaneous addition of IAA or BR, the effect of IAA being stronger. BR in lanolin applied to the cut surface of the leaf blade of the explant showed a weaker abscission-retarding effect than that applied in water via the petiole. BR and IAA also markedly retarded the abscission of fruitlet explants of Calamondin.     

Effects of a brassinosteroid on growth and on H+-extrusion in isolated radish cotyledons: comparison with the effects of benzyladenine

We investigated the effect of 24-epibrassinolide (BR) on the cytokinin-bioassay based on growth of isolated radish ( Raphanus sativus L. cv. Tondo Rosso Quarantino) cotyledons. BR stimulated growth of the cotyledons by about 50% when applied at saturating concentrations (3 μ M ). This effect was much lower than that of saturating concentrations of benzyladenine (BA) which was about 150% at 10 μ M BA. The effects of saturating concentrations of BR and BA were additive. BR, but not BA, stimulated H⁺-secretion by the cotyledons (measured as acidification of the incubation medium) slightly but reproducibly. These results indicate that the modes of action of the two phytoregulators are at least partially different.
BR-induced stimulation of H⁺-secretion was of similar amplitude to that induced by a concentration of fusicoccin (30 n M ) such as to stimulate growth to the same extent as BR. These results suggest that BR-induced stimulation of radish cotyledon growth might depend, at least in part, on BR-induced acidification of the wall space, similar to that observed on Azuki bean epicotyls and maize roots.     

Isolation and identification of a potent allelopathic substance in Bangladesh rice

Aqueous methanol extracts of Bangladesh rice (Oryza sativa L. cv. BR17) inhibited the growth of roots and shoots of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), timothy (Phleum pratense), Digitaria sanguinalis, Echinochloa crus-galli and Echinochloa colonum. Increasing the extract concentration increased the inhibition, suggesting that the BR17 may have growth inhibitory substances and possess allelopathic potential. The aqueous methanol extract of the BR17 was purified and a main inhibitory substance was isolated and determined by spectral data as 2,9-dihydroxy-4-megastigmen-3-one. This substance inhibited root and shoot growth of cress and E. crus-galli seedlings at concentrations greater than 0.03 and 3 μM, respectively. The concentrations required for 50% growth inhibition on cress roots and shoots were 0.22 and 0.47 μM, respectively, and on E. crus-galli roots and shoots were 36 and 133 μM, respectively. These results suggest that 2,9-dihydroxy-4-megastigmen-3-one may contribute to the growth inhibitory effect of BR17 and may play an important role in the allelopathy of BR17. Thus, Bangladesh rice BR17 may be potentially useful for weed management in a field setting. An erratum to this article can be found at     

Albumin domain II mutant with high bilirubin binding affinity has a great potential as serum bilirubin excretion enhancer for hyperbilirubinemia treatment

Background

4Z,15Z-bilirubin-IXα (BR), an endogenous toxic compound that is sparingly soluble in water, binds human serum albumin (HSA) with high affinity in a flexible manner. Our previous findings suggest that both Lys195 and Lys199 in subdomain IIA are important for the high-affinity binding of BR, and especially Lys199 in stand-alone domain II plays a prominent role in the renal elimination of BR. Our hypothesis is that HSA-domain II with high BR binding would be a useful therapeutic agent to treat hyperbilirubinemia in patients with impaired liver function.

Methods

Unbound BR concentrations were determined using a modified HRP assay. To evaluate the effect of pan3_3-13 domain II mutant in promoting urinary BR excretion, the serum concentration and urinary excretion amount of BR were determined using bile duct ligation mice.

Results

After three or six rounds of panning, pan3_3-13 and pan6_4 were found to have a significantly higher affinity for BR than wild-type domain II. Administration of pan3_3-13 significantly reduced serum BR level and increased its urinary excretion in the disease model mice as compared to wild-type domain II treatment.

Conclusions

These results suggest that pan3_3-13 has great potential as a therapeutic agent that promotes urinary BR excretion in hyperbilirubinemia.

General significance

This is the first study to be applied to other HSA bound toxic compounds that are responsible for the progression of disease, thereby paving the way for the development of non-invasive and cost effective blood purification treatment methods.     

Ethylene and rooting of mung bean cuttings. The role of auxin induced ethylene synthesis and phase-dependent effects

We have re-examined the role of ethylene during rooting of mung bean cuttings. Cuttings were treated for 5 days with a low or a high concentration of NAA (naphthaleneacetic acid). During this 5 days period, we also applied STS (silverthiosulfate, an inhibitor of ethylene action) or ACC (1-aminocyclo-propane-l-carboxylic acid, a direct precursor of ethylene). At high NAA concentration, STS promoted and ACC inhibited rooting, respectively. At low NAA concentration, the effects were opposite, STS being inhibitory and ACC promotive. AVG (aminoethoxyvinylglycine, an inhibitor of ethylene synthesis) gave similar results as STS. Together, these data suggest supraoptimal and suboptimal ethylene levels in the tissue at high and low NAA concentration, respectively. We also examined whether the effect of ethylene varied during the successive phases of the rooting process. Thus, we gave 24 h pulses with either STS or ACC during the rooting treatment. During the first two days (0–48 h), ACC-pulses were promotive and STS-pulses inhibitory. Later on (48–168 h), the ACC-pulses were inhibitory and the STS-pulses promotive. Whether this effect was observed or not was dependent on the NAA concentration. These data indicate that ethylene promotes or inhibits rooting depending on the stage in the rooting process. When ACC was added only during the initial period, rooting was increased at all NAA concentrations in a NAA dose-response curve and the optimal NAA concentration remained the same. This suggests that ethylene renders more cells responsive to NAA.     

A brassinosteroid-cytokinin interaction on ethylene production by etiolated mung bean segments

Three cytokinins and their ribosides were tested in conjunction with brassinosteroid (BR) for their effects on ethylene production in etiolated mung bean ( Vigna radiata L. Rwilcz cv. Berken) hypocotyl segments. When varying concentrations of BR were tried in combination with a fixed amount of kinetin (10 μ M ), there was an increase in ethylene production with increasing concentrations of BR up to 3 μ M , and a decline beyond. A stimulation in ethylene production was observed with increasing concentrations of each of the cytokinins used. However, when applied in conjunction with 3 μ M BR, all cytokinin concentrations produced similar stimulatory patterns. When 3 μ M BR or 10 μ M 6-benzylaminopurine (BAP) was applied in conjunction with increasing concentrations of IAA, there was a stimulation in ethylene production with increasing concentrations of IAA. However, 3 μ M BR and 10 μ M BAP together with varying concentrations of IAA failed to alter the level of ethylene production.     

Effects of brassinosteroid on cotton regeneration via somatic embryogenesis

Brassinolide (BR), which is the most biologically active brassinosteroid, was used to examine the potential effect of hormone on cotton somatic embryogenesis. Ten-day-old cotton (Gossypium hirsutum L., cv. Cooker) seedlings were used for explant source and hypocotyls were removed and cultured on MS basal medium with B₅ vitamins supplemented with 1 mg/L 6-benzylaminopurine + 0.5 mg/L kinetin for callus induction. After one month proliferating calli pieces were collected and cultured on MS basal medium containing various concentrations of BR (0.1, 0.5, 1.0 μM) with their controls. BR treatments were negatively effective on the fresh weight of calli when compared to control. Differential somatic embryogenesis maturation rates due to BR treatment were observed. Somatic embryogenesis was stimulated especially for transition to cotyledonary phase at 0.5 mg/L BR. Histological preparations from embryogenic calli and somatic embryos at different stages of development revealed the spontaneous polyploidisation during early somatic embryogenesis on BR-treated calli. Present results suggest that BR negatively effected calli growth, however, had a stimulating role in maturation of somatic embryos.     

Influence of the Charge at D85 on the Initial Steps in the Photocycle of Bacteriorhodopsin

Studies have shown that trans-cis isomerization of retinal is the primary photoreaction in the photocycle of the light-driven proton pump bacteriorhodopsin (BR) from Halobacterium salinarum, as well as in the photocycle of the chloride pump halorhodopsin (HR). The transmembrane proteins HR and BR show extensive structural similarities, but differ in the electrostatic surroundings of the retinal chromophore near the protonated Schiff base. Point mutation of BR of the negatively charged aspartate D85 to a threonine T (D85T) in combination with variation of the pH value and anion concentration is used to study the ultrafast photoisomerization of BR and HR for well-defined electrostatic surroundings of the retinal chromophore. Variations of the pH value and salt concentration allow a switch in the isomerization dynamics of the BR mutant D85T between BR-like and HR-like behaviors. At low salt concentrations or a high pH value (pH 8), the mutant D85T shows a biexponential initial reaction similar to that of HR. The combination of high salt concentration and a low pH value (pH 6) leads to a subpopulation of 25% of the mutant D85T whose stationary and dynamic absorption properties are similar to those of native BR. In this sample, the combination of low pH and high salt concentration reestablishes the electrostatic surroundings originally present in native BR, but only a minor fraction of the D85T molecules have the charge located exactly at the position required for the BR-like fast isomerization reaction. The results suggest that the electrostatics in the native BR protein is optimized by evolution. The accurate location of the fixed charge at the aspartate D85 near the Schiff base in BR is essential for the high efficiency of the primary reaction.     

Increased heme catabolism in critically ill patients: correlation among exhaled carbon monoxide, arterial carboxyhemoglobin, and serum bilirubin IXalpha concentrations

It has been reported that exhaled carbon monoxide (CO) concentrations and arterial carboxyhemoglobin (CO-Hb) concentration in blood may be increased in critically ill patients. However, there was no study that examined correlation among amount of CO in exhaled air, CO-Hb concentrations in erythrocytes, and bilirubin IXalpha (BR) in serum, i.e., the three major indexes of heme catabolism, within the same subject. Here, we examined CO concentrations in exhaled air, CO-Hb concentrations in arterial blood, and BR levels in serum in 29 critically ill patients. Measurements of exhaled CO, arterial CO-Hb, and serum total BR have been done in the intensive care unit. As control, exhaled CO concentration was also measured in eight healthy volunteers. A median exhaled CO concentration was significantly higher in critically ill patients compared with control. There was significant correlation between CO and CO-Hb and CO and total BR level. We also found CO concentrations correlated with indirect BR but not direct BR. Multivariate linear regression analysis for amount of exhaled CO concentrations also showed significant correlation with CO-Hb and total BR, despite the fact that respiratory variables of study subjects were markedly heterogeneous. We found no correlation among exhaled CO, patients' severity, and degree of inflammation, but we found a strong trend of a higher exhaled CO concentration in survivors than in nonsurvivors. These findings suggest there is an increased heme breakdown in critically ill patients and that exhaled CO concentration, arterial CO-Hb, and serum total BR concentrations may be useful markers in critically ill conditions.     

Effect of Tilemsi phosphate rock-solubilizing microorganisms on phosphorus uptake and yield of field-grown wheat (Triticum aestivum L.) in Mali

With the broad aim of biologically improving P uptake by wheat fertilized with Tilemsi phosphate rock (TPR), we investigated the effect of inoculation with TPR-solubilizing microorganisms isolated from Malian soils and with a commercial isolate of the arbuscular mycorrhizal (AM) fungus Glomus intraradices (Gi). AM root length colonization, and growth yield and P concentration of the cultivar Tetra of wheat were measured under field conditions in Mali. Experimental plots were established in Koygour (Diré) during the 2001–2002 cropping season. Inoculation treatments included two fungal isolates, Aspergillus awamori (C1) and Penicillium chrysogenum (C13), and an isolate of Pseudomonas sp. (BR2), used alone or in fungus-bacterium combinations in the presence or absence of the AM fungus Gi. In fertilized treatments, 0 or 30 kg P ha⁻¹ was applied as TPR or diammonium phosphate (DAP). In 45-day-old wheat plants, the highest root length AM colonization (62%) was observed with TPR fertilized wheat inoculated with Gi and BR2. Our results suggest that BR2 is a mycorrhizal-helper bacteria and a good plant growth-promoting rhizobacteria. In fact, inoculation of wheat Tetra fertilized with TPR with a combination of Gi, BR2 and C1 produced the best grain yield with the highest P concentration. This work shows that by inoculating seeds with TPR-solubilizing microorganisms and AM fungi under field conditions in Mali it is possible to obtain wheat grain yields comparable to those produced by using the expensive DAP fertilizer.     

Higher order structure of Balbiani ring premessenger RNP particles depends on certain RNase A sensitive sites

Specific premessenger ribonucleoprotein (RNP) particles, the Balbiani ring (BR) granules from Chironomus tentans salivary glands, were treated with RNase A to study the effect of RNA strand breaks on the higher order structure of the particles. Isolated, radioactively labeled BR granules, known to sediment at 300 S, were digested with RNase A and centrifuged in sucrose gradients. The fractionated particles were subsequently analyzed using electron microscopy and caesium chloride centrifugation. At a low RNase concentration, most of the 300 S particles disintegrated completely, and no metastable degradation products were observed. At intermediate RNase concentrations, no 300 S particles were left, but a minor fraction of the BR granules had unfolded and sedimented at 160 S. These granules could represent particles modified during the RNase treatment or represent a more slowly degrading subfraction of the particles. At a high RNase concentration, no RNP particles at all remained in the gradient. The rapid disintegration of the majority of the BR granules was investigated further by electrophoretic analysis of RNA in the remaining particles. During the RNase treatment BR granules, still sedimenting at 300 S, accumulated strand breaks; in fact, as many as 50 to 100 nicks in the 37 kb RNA could be tolerated. It was concluded from RNA analyses that the disintegration of the BR granules was not dependent on any single nick in the RNA, nor on the accumulation of a certain number of nicks, but rather on one or a few critical strand breaks. We propose that there are organizing sequences essential for particle integrity; once these sequences are nicked, the premessenger RNP particles are rapidly and completely degraded.     

Is bromodeoxyuridine resistance a consequence of cytokinin habituation in Nicotiana tabacum?

Cytokinin-habituated, as compared to nonhabituated Nicotiana tabacum cv. Havana 425 callus was shown to tolerate higher concentrations of 5-bromodeoxyuridine (BUdR) if cytokinin was added to the medium [Meins, Planta 129, 239–244 (1976)].Our aim was to clarify whether or not BUdR-resistance and cytokinin-habituation are linked characters in callus cultures of our BUdR-resistant tobacco mutant BR 37/21, obtained from Nicotiana tabacum cv. Ottawa.It is demonstrated that BUdR-resistance and cytokinin-habituation are independent characters in the case of this mutant. Non-habituated BR 37/21 callus grows as a resistant line on a medium containing BUdR at a selective concentration (30 mg/l) whereas cytokinin-habituated callus, not selected for BUdR-resistance, behaves as a sensitive line, i.e. turns brown and dies, on the same medium.     

Kinetics of growth and leukotoxin production by <Emphasis Type="Italic">Mannheimia haemolytica</Emphasis> in continuous culture

The growth and product formation kinetics of the bovine pathogen Mannheimia (Pasteurella) haemolytica strain OVI-1 in continuous culture were investigated. The leukotoxin (LKT) concentration and yield on biomass could substantially be enhanced by supplementation of a carbon-limited medium with an amino acid mixture or a mixture of cysteine and glutamine. Acetic acid was a major product, increasing to 1.66 g l(-1) in carbon-limited chemostat culture at intermediate dilution rates and accounting for more than 80% of the glucose carbon, whereas in amino acid-limited cultures high acetic acid concentrations were produced at low dilution rates, suggesting a carbon-overflow metabolism. The maintenance coefficients of carbon-limited and carbon-sufficient cultures were 0.07 and 0.88 mmol glucose g(-1) h(-1), respectively. LKT production was partially growth-associated and the LKT concentration was maximised to 0.15 g l(-1) and acetic acid production minimised by using a carbon-limited medium and a low dilution rate.     

Foliar Application of Brassinolide Induced Regulation of Grain Yield and Quality,Antioxidant Responses and Aroma in Fragrant Rice

Brassinolide (BR) is a new green plant growth regulator. The present field study was conducted on two fragrant rice cultivars (i.e., Meixiangzhan-2 and Xiangyaxiangzhan) to study the effects of foliar application of BR on fragrant rice performance. At the heading stage, BR solutions at 0.05, 0.15, 0.25 and 0.50 mg L-1 were sprayed on fragrant rice at 600 liters per hectare; these treatments were named as BR1, BR2, BR3 and BR4, respectively. The treatment sprayed with distilled water was taken as a control (CK). Compared with CK, the BR2 treatment significantly enhanced the chlorophyll concentration and net photosynthetic rate for Meixiangzhan-2, and Xiangyaxiangzhan. The BR3 and BR4 treatments increased the concentrations of chlorophyll a, chlorophyll b and carotenoid, and also enhanced net photosynthetic rate by 31.91% and 40.43%, respectively. Higher grain yields were recorded in the BR2 treatment than on CK on Meixiangzhan-2, while on Xiangyaxiangzhan, the BR3 and BR4 treatments increased grain yield compared with CK. In relation to CK, higher head rice rates were recorded in the BR2 treatment for Meixiangzhan-2, and in the BR3 and BR4 treatments for Xiangyaxiangzhan. BR treatments (BR2 for Meixiangzhan-2, BR3 and BR4 for Xiangyaxiangzhan) also significantly enhanced the activities of GPX, SOD and CAT by 10.22% to 23.00%, and reduced the malonaldehyde concentration. In addition, we observed that some BR treatments (BR2 for Meixiangzhan-2, BR3 and BR4 for Xiangyaxiangzhan) decreased the grain 2-acetyl-1-pyrroline concentration of fragrant rice.     

Brassinolide alleviated the adverse effect of water deficits on photosynthesis and the antioxidant of soybean (<Emphasis Type="Italic">Glycine max</Emphasis> L.)

Brassinolide (BR) is a relatively new plant growth regulator. To test whether BR could be used to increase tolerance to water deficits in soybean, the effects of BR application on photosynthesis, assimilate distribution, antioxidant enzymes and seed yield were studied. BR at 0.1 mg l⁻¹ was foliar applied at the beginning of bloom. Two levels of soil moisture (80% field capacity for well-watered control and 35% for drought-stressed treatment) were applied at pod initiation. BR treatment increased biomass accumulation and seed yield for both treatments. Drought stress inhibited translocation of assimilated ¹⁴C from the labeled leaf, but BR increased the translocation for both treatments. Drought stress depressed chlorophyll content and assimilation rate (A), while chlorophyll content and A of BR-treated plants were greater than that of drought-stressed plants. BR treatment increased maximum quantum yield of PS II, the activity of ribulose-1,5-bisphosphate carboxylase, and the leaf water potential of drought-stressed plants. Treatment with BR also increased the concentration of soluble sugars and proline, and the activities of peroxidase and superoxide dismutase of soybean leaves when drought-stressed. However, it decreased the malondialdehyde concentration and electrical conductivity of leaves under drought stress. This study show that BR can be used as a plant growth regulator to enhance drought tolerance and minimize the yield loss of soybean caused by water deficits.     

The effect of brassinosteroid on auxin-induced ethylene production by etiolated mung bean segments

Brassinosteroid, an analogue of brassinolide, (BR) (2α, 3α, 22β, 23β-tetrahydroxy-24β-methyl-B-homo-7-oxa-5α-cholestan-6-one), was tested in conjunction with indole-3-acetic acid (IAA), naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), indole-3-butyric acid (IBA), indole-3-propionic acid (IPA), indole-3-pyruvic acid (IPyA), indole-3-aldehyde (IAld), indole-3-carbinol (ICB) or tryptophan (TRP) for its effects on ethylene production by etiolated mung bean (Vigna radiata (L.) Rwilcz cv. Berken) hypocotyl segements. The enhancement of ethylene production due to BR was greatest in conjunction with 1 μM IBA, 2,4-D, IAA, or NAA (these increases were 2580, 2070, 890, and 300%, respectively). When increasing concentrations of IBA, 2,4-D, IAA, or NAA were used, there was a decrease in the percentage stimulation by BR. Both IPyA and IPA had different optimal concentrations than the other auxins tested. Their BR-enhanced maximum percentage stimulations (1430 and 1580%) were greatest with 5 μM IPya and 10 μM IPA, respectively. There was a marked reduction in the percentage stimulation by BR with either 100 μM IPyA or IPA. The inactive indoles (IAld, ICB, or TRP) did not synergize with BR at any of the concentrations tested. Four hours following treatment those segments in contact with 1 μM BR with or without the addition of 10 μM IAA began to show a stimulation in ethylene production above the control and this stimulation became greater over the following 20 h. It was necessary for BR to be in continual contact with the tissue to have a stimulatory effect on auxin-induced ethylene production. When segments excised from greater distances below the hypocotyl hook, were treated with either IAA alone or in combination with BR, there was a decrease in ethylene production with increasing distance. There was no effect of hypocotyl length on BR stimulation of auxin-induced ethylene production; however, there was a definite decrease in ethylene production when IAA was applied alone.     

The extremely high Al resistance of Penicillium janthineleum F-13 is not caused by internal or external sequestration of Al

Penicillium janthinellum F-13 has been isolated in previous work as a fungus tolerating the presence of high concentrations of Al (as high as 100 mM AlCl₃). Here its growth rate and yield in three acidic (pH 3.0) media of different composition with varying concentrations of Al are reported. The presence of Al did not affect these parameters, except that the growth yield was somewhat lower in GM (a glucose/peptone/yeast extract-containing medium) with the highest concentration tested (100 mM AlCl₃). The amount of Al found in the mycelium was so low that it cannot lead to a significant decrease in the medium for the higher Al concentrations applied. Although citric acid was excreted at growth on GM, and the presence of Al even promoted this, the concentration of this was far too low to diminish (by chelation) the high Al concentrations in the medium to a non-toxic level, i.e. the level (of approx. 1 mM) that is tolerated by low-resistance fungi. At growth on SLBM (a peptone/yeast extract/soil extract-containing medium), a rise in pH occurred. The same was found for SM (a glucose/mineral salts-containing medium), although in this case the picture was more complicated because the initial rise in pH was followed by a lowering due to the excretion of oxalic acid. Although both phenomena can diminish Al toxicity (by decreasing the external concentration of monomeric Al, regarded to be the toxic species), again the decrease is far too low to attain a non-toxic level when high Al concentrations are applied. Therefore, although in principal the metabolic phenomena observed for P. janthinellum F-13 at growth on different media can diminish Al toxicity, the tolerance of this organism for high external Al concentrations must be caused by another mechanism.     

Removal of hexavalent chromium by fungal biomass of <Emphasis Type="Italic">Mucor racemosus</Emphasis>: influencing factors and removal mechanism

This study reported the hexavalent chromium removal by untreated Mucor racemosus biomass and the possible mechanism of Cr (VI) removal to the biomass. The optimum pH, biomass dose, initial Cr (VI) concentration and contact time were investigated thoroughly to optimize the removal condition. The metal removal by the biomass was strongly affected by pH and the optimum pH ranged from 0.5 to 1.0. The residual total Cr was determined. It was found that dichromate reduction occurred at a low very low pH value. At biomass dose 6 g/l, almost all the Cr (VI) ions were removed in the optimum condition. Higher removal percentage was observed at lower initial concentrations of Cr (VI) ions, while the removal capacity of the biomass linearly depended on the initial Cr (VI) concentration. More than half of Cr (VI) ions were diminished within 1 h of contact and removal process reached a relative equilibrium in approximately 8 h. Almost all of the Cr (VI) ions were removed in 24 h when initial concentrations were below 100 mg/l. The equilibrium data were fitted in to the Langmuir and the Freundlich isotherm models and the correlated coefficients were gained from the models. A Fourier transform infrared spectra was employed to elucidate clearly the possible biosorption mechanism as well.     

Phytotoxicity of iron in relation to its solubility conditions and the effect of ionic strength

The effect of iron on root elongation and seed germination of Lactuca sativa was investigated within the limits of the plant's sensitivity to an acidic environment and iron solubility under experimental conditions. Because ionic strength was found to have phytotoxic effects, the same pH and ionic strength conditions were kept constant over the entire iron concentration range, so as to evaluate solely the effect of iron. 0.14 mM Fe³⁺ was found to be the lowest effective concentration inhibiting root elongation. The low solubility of iron at a pH of 3 (the lowest value which could be applied for root elongation) excluded the testing of higher iron concentrations. Due to the lower sensitivity of seed germination to acidity, a pH of 2.6 could be applied in this case. The lowest effective iron concentration (the lowest applied concentration causing a significant decrease in germination as compared to the control, P < 0.05), EC50 (the concentration at which germination was 50% of that of the control specimens) and the completely effective iron concentration (the concentration that completely inhibited seed germination) were 0.6, 0.92 and 2.0 mM, respectively.