共查询到20条相似文献,搜索用时 593 毫秒
1.
Gustavo Hernández-Carmona Dennis J. McHugh Francisco López-Gutiérrez 《Journal of applied phycology》1999,11(6):493-502
The effect of temperature (70, 80, 90 °C) and time (1–9 h) during the alkaline extraction step on alginate yield and quality were studied. The alginate yield increased
with time and maximum yield was obtained after 3.5 h treatment, ranging from19.4% at 70 °C to 21.9% at 90 °C. The viscosity of the alginate produced was inversely correlated with the temperature and time. At70 °C the slope of the curve was almost zero(753 to 923 mPa s); at 90 °C the viscosity loss was 154 mPa s per hour during the first two hours, reducing from 523 to 86 mPa s after 5 h; 80 °C yielded values between those for 70 °C and90 °C. The best conditions for alkaline extraction were using pH 10 at 80 °C for two hours. The curves obtained gave useful information for controlling the viscosity of the alginate during production.
It was found that viscosity of the paste formed during alkaline extraction (`process viscosity') was the best parameter to
determine there action rate during extraction. Alginate yield increased during filtration time from 17.6% to 23.7%after 55
min at 70 °C. In this step the viscosity of the alginate obtained remained almost constant (522–610 mPa s), indicating no degradation
of the products during filtration. The best dilution to filter the alginate extract was obtained at 45 mPa s. Diatomaceous
earth (Celite) and expanded lava(Perlite) were tested as filter aids. Expanded lava was the best filter aid, using 1 kg per
kilogram of alginate produced. Three methods were studied to separate the alkaline-insoluble residues after extraction: filtration,
centrifugation, flocculation, and combinations of them. The best system found was filtration with flocculant in a rotary vacuum
filter, with a knife advance of 0.1 mm every 3.5 seconds and drum rotation of 2 rpm, yielding an average filtration flow rate
of 10.5 L min-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
In the autumn of 2007, marine mucilage caused by the diatom Coscinodiscus granii occurred in the central area of Ariake Sound, Japan, and resulted in damage to fishery. To elucidate the mechanism underlying
the outbreak of marine mucilage, we examined the effect of temperature on cell growth and production of transparent exopolymer
particles (TEPs) in a culture of this species. Growth and TEP production of C. granii are influenced by temperature. The maximum growth rate (1.63 divisions day−1) and cell yield (1,280 cells mL−1) at all temperatures were obtained at 30°C. Optimal growth rates (>1.15 divisions day−1: ca. 70% of maximum) and cell yield (>900 cells mL−1: ca. 70% of maximum) were observed at temperatures of 25–30°C. TEP production by C. granii depended on whether volume- or cell-related values were considered. The maximum volume-normalized increase rates and concentrations
of TEP at all temperatures were observed at 25°C. However, when production rates and concentrations of TEP were normalized
to cell numbers, optimal values were measured at 10–15°C. In Ariake Sound, when marine mucilage caused by C. granii occurred, the temperature ranged from 25.0 to 25.4°C. This suggests that growth conditions of C. granii are important factors for production of marine mucilage. 相似文献
3.
Dennis B. Lazof Magaly Rincón Thomas W. Rufty Charles T. Mackown Thomas E. Carter 《Plant and Soil》1994,164(2):291-297
A study was conducted to examine aluminum (Al) exclusion by roots of two differentially tolerant soybean (Glycine max L. Merr.) lines, Pl-416937 (Al-tolerant) and Essex (Al-sensitive). Following exposure to 80μM Al for up to 2 h, roots were rinsed with a 10 mM potassium citrate solution and rapidly dissected to allow estimation of intracellular Al accumulation in morphologically
distinct root regions. Using 10 min exposures to 300μM
15NO3
− and dissection, accompanying effects on NO3
− uptake were measured. With Al exposures of 20 min or 2 h, there was greater Al accumulation in all root regions of Essex
than in those of Pl-416937. The genotypic difference in Al accumulation was particularly apparent at the root apex, both in
the tip and in the adjacent root cap and mucilage. Exposure of roots to Al inhibited the uptake of 15NO3
− to a similar extent in all root regions. The results are consistent with Al exclusion from cells in the root apical region
being an important mechanism of Al tolerance. 相似文献
4.
Some characteristics of the rice (Oryza sativa L.) root were found in the experiment of unilaterally irradiating the roots which were planted in water: (i) All the seminal roots, adventitious roots and their branched roots bent away from light, and their curvatures ranged from 25° to 60°. The curvature of adventitious root of the higher node was often larger than that of the lower node, and even larger than that of the seminal root, (ii) The negative phototropic bending of the rice root was mainly due to the larger growth increment of root-tip cells of the irradiated side compared with that of the shaded side, (iii) Root cap was the site of light perception. If root cap was shaded while the root was irradiated the root showed no negative phototropism, and the root lost the characteristic of negative phototropism when root cap was divested. Rice root could resume the characteristic of negative phototropism when the new root cap grew up, if the original cells of root cap were well protected while root cap was divested, (iv) The growth increment and curvature of rice root were both influenced by light intensity. Within the range of 0–100 μmol · m2 -s−1, the increasing of light intensity resulted in the decreasing of the growth increment and the increasing of the curvature of rice root, (v) The growth increment and the curvature reached the maximum at 30°C with the temperature treatment of 10–40°C. (vi) Blue-violet light could prominently induce the negative phototropism of rice root, while red light had no such effect. (vii) The auxin (IAA) in the solution, as a very prominent influencing factor, inhibited the growth, the negative phototropism and the gravitropism of rice root when the concentration of IAA increased. The response of negative phototropism of rice root disappeared when the concentration of IAA was above 10 mg · L−1 相似文献
5.
Leila Hayashi Eurico C. Oliveira Genevieve Bleicher-Lhonneur Patrick Boulenguer Ricardo T. L. Pereira Roberto von Seckendorff Viviane T. Shimoda André Leflamand Patrick Vallée Alan T. Critchley 《Journal of applied phycology》2007,19(5):505-511
The yield and the quality of carrageenan depend, among other things, on the cultivar or strain and on the cultivation and
processing techniques. This work presents carrageenan yields and some properties of Kappaphycus alvarezii under selected cultivation conditions i.e. cultivation period, depth and planting density. Growth rates (GR) ranged from
5.2–7.2% day−1, with the highest GR at 28 days, at 0–0.5 m depth, and planting density of 12 and 8.4 plants m−2. Highest productivity was observed in samples after 44 and 59 day cultivation period, which were grown at 0–0.5 m depth,
and a planting density of 24 plants m−2. Carrageenan yields, iota fraction, viscosity, molecular weight and gel strength were measured. A cultivation period of 28 days during the winter had
a significant higher carrageenan yield, while samples from 59 days showed a significantly higher iota fraction. Carrageenan also presented an increasing molecular weight under longer cultivation periods. A similar trend was
observed for viscosity and gel strength. All samples cultivated in Brazil gave higher values when compared to a K. alvarezii commercial reference sample, with the exception of carrageenan yield values, which were lower in this study. Taking into
account all parameters, the culture condition which provided the best carrageenan from a commercial perspective were 45 days
of cultivation, growing at the surface, with a planting density of 12 plants m−2. Considering that this study was performed in the least favorable season (winter), these results indicate that the site is
suitable for the implementation of commercial cultivation. 相似文献
6.
Centaurea calcitrapa suspension cultures were grown either in Erlenmeyer flasks or in a mechanically stirred bioreactor. Its rheological behaviour,
when fitted to the Oswald–de Waele model (power law), showed pseudoplastic characteristics in both cases. The flow behaviour
index (n) decreased over the course of a growth cycle and the consistency index (K) increased, reached a value of 1.81 N sn m−2 run on 2 l bioreactor. Bioreactor cultivation of C. calcitrapa cells at different agitation rates (30, 60, 100 and 250 rpm), highlighted the influence of shear forces on cell viability
loss (90–34%) and phenol accumulation (74–140 μg l−1), due to increased stirring speeds. Analysis of these results suggests that this cell line is shear-sensitive. An empirical
exponential correlation was defined between apparent viscosity and biomass concentration, under the studied conditions, giving
the possibility to estimate the prevailing broth regime and to optimize bioreactor design.
Revisions requested 10 October 2005; Revisions received 19 December 2005 相似文献
7.
Jean-Louis Milan Josep A. Planell Damien Lacroix 《Biomechanics and modeling in mechanobiology》2010,9(5):583-596
A computational model of mechanoregulation is proposed to predict bone tissue formation stimulated mechanically by overall
dynamical compression within a porous polymeric scaffold rendered by micro-CT. Dynamic compressions of 0.5–5% at 0.0025–0.025
s−1 were simulated. A force-controlled dynamic compression was also performed by imposing a ramp of force from 1 to 70 N. The
model predicts homogeneous mature bone tissue formation under strain levels of 0.5–1% at strain rates of 0.0025–0.005 s−1. Under higher levels of strain and strain rates, the scaffold shows heterogeneous mechanical behaviour which leads to the
formation of a heterogeneous tissue with a mixture of mature bone and fibrous tissue. A fibrous tissue layer was also predicted
under the force-controlled dynamic compression, although the same force magnitude was found promoting only mature bone during
a strain-controlled compression. The model shows that the mechanical stimulation of bone tissue formation within a porous
scaffold closely depends on the loading history and on the mechanical behaviour of the scaffold at local and global scales. 相似文献
8.
G. E. Zdorovennova 《Aquatic Ecology》2009,43(3):629-639
The thermal structures in the vicinity of the ice–water and water–sediment boundaries of a shallow lake, L. Vendyurskoe (Northwestern
Russia) during four winter seasons are described. The heat flux at the water-ice boundary was 0.1–0.2 W m−2 during winter. The maximal heat flux at the water–sediment boundary was 4.5 W m−2 at the beginning and 0.5 W m−2 at the end of winter. The daily average value of the solar radiation penetrating into the water was 0.5 W m−2 during main part of winter and 2–50 W m−2 during April. During winter, temperature showed an oscillation in the vicinity of the sediment-water interface. Most periods
corresponding to the main oscillation frequencies in the near-bottom water layer (0–0.4 m) and upper layer sediment (0–0.35 m),
identified by FFT analysis, fall within the scale of synoptic variations (3–10 days), and in a number of cases were equal
to 1 day. The theoretical periods of the first baroclinic seiche mode of Lake Vendyurskoe are 4.5–8.5 days that compares well
with identified temperature oscillation periods. The comparison between the rate of heat content change in a water column
and the difference of vertical heat fluxes from sediment to water and from water to ice show that the horizontal heat transport
takes place in the lake during winter as a result of heat advection along the bottom. 相似文献
9.
An enantio-selective d-Phe imprinted P(AA-co-AN) membrane was prepared using the wet-phase inversion method. The membrane not only selectively adsorbed
phenylalanine but also rejected it with a rejection selectivity of 0.82–0.64 and 0.91–0.63 during the filtration of 100 and
10 ppm (g m−3) racemate solutions, respectively. The fluxes of d-Phe and l-Phe during filtration of 10 ppm racemate solution were 0.0077–0.0229 and 0.0064–0.0208 mg m−2 s−1, respectively, and the fluxes of d-Phe and l-Phe during filtration of 100 ppm racemate solution were 0.1287–0.2522 and 0.1174–0.2458 mg m−2 s−1, respectively. The adsorption selectivity was higher at low concentration. The adsorption selectivities varied from 1.11
to 1.65 and from 1.64 to 2.78 during filtration of 100 and 10 ppm racemate solutions, respectively. In respect to desorption,
the fractional difference between d-Phe and l-Phe in the recovered solution from 10 ppm was higher than that from 100 ppm. 相似文献
10.
Li-Hui Sun Zhi-Yuan Song Ya-Qin Sun Zhi-Long Xiu 《World journal of microbiology & biotechnology》2010,26(8):1401-1407
Sustained oscillations have been observed in cell growth and glycerol metabolism by Klebsiella pneumoniae during long-term continuous cultivations under anaerobic conditions. However, the oscillation behavior of glucose–glycerol
co-fermentation under micro-aerobic conditions has yet not been studied. In this study, the unclear mechanism of oscillation
was investigated by using different substrates including glycerol, glucose, and mixtures of glycerol and glucose. A large
perturbation of substrate concentration was operated to study the dynamic behavior of continuous fermentation by K. pneumoniae DSM 2026 under micro-aerobic conditions. Oscillations occurred when 80 g of glycerol l−1 was used as single carbon source or co-substrate with 35 g of glucose l−1, whereas no oscillation was observed when glucose was used alone. During the oscillation phases, parameters periodically
passed maxima and minima at a relatively constant time interval, and the period of oscillation was 10–16 h. The comparison
between glycerol and glucose metabolism revealed that a potential mechanism of oscillation lies in the accumulation of 3-hydroxypropionaldehyde,
which is toxic to cell growth. 相似文献
11.
Asiya Nazir Rohit Soni H. S. Saini R. K. Manhas B. S. Chadha 《World journal of microbiology & biotechnology》2009,25(7):1189-1197
An endoglucanase (1, 4-β-d glucan glucanohydrolase, EC 3.2.1.4) which was catalytically more active and exhibited higher affinity towards barley β-glucan,
xyloglucan and lichenin as compared to carboxymethylcellulose (CMC) was purified from Aspergillus terreus strain AN1 following ion-exchange and hydrophobic interaction chromatography and gel filtration. The purified enzyme (40-fold) that
apparently lacked a cellulose-binding domain showed a specific activity of 60 μmol mg−1 protein−1 against CMC. The purified enzyme had a molecular weight of 78 and 80 KDa as indicated by sodium dodecyl sulphate–polyacrylamide
gel electrophoresis and gel filtration, respectively, and a pI of 3.5. The enzyme was optimally active at temperature 60°C
and pH 4.0, and was stable over a broad range of pH (3.0–5.0) at 50°C. The endoglucanase activity was positively modulated
in the presence of Cu2+, Mg2+, Ca2+, Na+, DTT and mercaptoethanol. Endoglucanase exhibited maximal turn over number (K
cat) and catalytic efficiency (K
cat/km) of 19.11 × 105 min−1 and 29.7 × 105 mM−1 min−1 against barley β-glucan as substrate, respectively. Hydrolysis of CMC and barley β-glucan liberated cellobiose, cellotriose,
cellotetraose and detectable amount of glucose. The hydrolysis of xyloglucan, however, apparently yielded positional isomers
of cellobiose, cellotriose and cellotetraose as well as larger oligosaccharides. 相似文献
12.
Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation 总被引:1,自引:0,他引:1
Cheng Yunhuan Han Youzhi Wang Qingcheng Wang Zhengquan 《Frontiers of Biology in China》2006,1(3):310-317
Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive
to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics
and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes
associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen
are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch
and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the
pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length
(SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource
availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective
of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource
availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics
in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October
in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter
60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate
fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates)
at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live
and dead) was 189.1 g·m−2·a−1, 50% (95.4 g·m−2·a−1) in the surface soil layer (0–10 cm), 33% (61.5 g·m−2·a−1), 17% (32.2 g·m−2·a−1) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May
to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased
during the growing season. Mean RLD (7,411.56 m·m−3·a−1) and SRL (10.83 m·g−1·a−1) in the surface layer were higher than RLD (1 474.68 m·m−3·a−1) and SRL (8.56 m·g−1·a−1) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m−3 and 14.83m·g−1) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m−3) and SRL in October (3.77 m·g−1). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature,
and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the
upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture
uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer
was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the
seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic
activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate
to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability.
__________
Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410] 相似文献
13.
We have used current/voltage (I/V) analysis to investigate the role played by extracellular mucilage in the cellular response to osmotic shock in Lamprothamnium papulosum. Cells lacking extracellular mucilage originated in a brackish environment (1/3 seawater). These were compared, first with
cells coated with thick (∼50 μm) extracellular mucilage, collected from a marine lake, and second, with equivalent mucilaginous
marine cells, treated with heparinase enzyme to disrupt the mucilage layer. Histochemical stains Toluidine Blue and Alcian
Blue at low pH identified the major component of the extracellular mucilage as sulfated polysaccharides. Treating mucilage
with heparinase removed the capacity for staining with cationic dyes at low pH, although the mucilage was not removed, and
remained as a substantial unstirred layer. Cells lacking mucilage responded to hypotonic shock with depolarization (by ∼95
mV), cessation of cyclosis, due to transient opening of Ca2+ channels, and opening of Ca2+-activated Cl− channels and K+ channels. Cell conductance transiently increased tenfold, but after 60 min was restored to the conductance prior to hypotonic
shock. Mucilaginous cells depolarized by a small amount (∼18 mV), but Ca2+ channels failed to open in large enough numbers for cyclosis to cease. Likewise most Ca2+-activated Cl− channels failed to open and conductance increased only ∼1.2-fold above the prehypotonic level. After 60 min conductance was
less than the conductance prior to hypotonic shock. Heparinased mucilaginous cells recovered several aspects of the hypotonic
response in cells lacking mucilage. These cells depolarized (by ∼103 mV); cyclosis ceased, indicating that Ca2+ channels had opened, and conductance increased to ∼4 times the value prior to hypotonic shock, indicating that Ca2+-activated Cl− channels opened. However, after 60 min, these cells had neither restored membrane potential (and remained at positive values),
nor decreased their conductance. It was not possible to determine whether K+ channels had opened. The heparinased cells recovered the normal hypotonic response of mucilaginous cells when heparinase
was washed out. Apical seawater cells, which lacked mucilage, were unaffected by heparinase treatment. The results demonstrate
that the presence of extracellular sulfated polysaccharide mucilage impacts upon the electrophysiology of the response to
osmotic shock in Lamprothamnium cells. The role of such sulfated mucilages in marine algae and animal cells is compared and discussed.
Received: 24 March 1998/Revised: 28 April 1999 相似文献
14.
The conventional view of root-cap mucilage as an expanded blob of mucilage is characteristic only of root tips in contact with free water. In soil, the mucilage is almost always a dry coating over the tip to which soil particles adhere. The kinetics of expansion of root-cap mucilage of Zea mays roots grown in field soil, in soil in pots, and axenically on agar, were determined when the mucilage was exposed to water. On the soil-grown roots the increase in mucilage volume was linear with time, sometimes reaching a constant volume during the 6 h of measurement, but sometimes not. This linear expansion is interpreted as limited by the rate at which the condensed mucilage in the periplasmic and intercellular spaces of the root cap passes to the exterior of the cap, expanding as fast as it arrives outside in the water. The height of the plateau is interpreted as a measure of the amount of mucilage initially present in the interior spaces. Because of the greater availability of water in the axenic roots grown on 1% agar, the mucilage was already outside the root cap, and it expanded more rapidly. It reached a final volume about 10-fold greater than that on the soil-grown roots. The volume increase was curvilinear with time. An analysis of these curves suggested that this swelling on axenic roots was a diffusion of mucilage outwards from the flanks of the root cap, and the diffusivity of the mucilage was estimated as 4 × 10?8 cm2 s?1. The molecular radius derived from this diffusivity was 34 nm, and the estimated molecular weight was 1.6 × 108 Da. 相似文献
15.
A. I. Bozhkov Yu. A. Kuznetsova N. G. Menzyanova 《Russian Journal of Plant Physiology》2009,56(4):480-487
The number of border (scaled off) cells (BCs) was determined in the root apex of 1-day-old wheat (Triticum aestivum L.) seedlings. Microscopic examination of cytological root preparations showed that in 24 h the number of BCs in the gel
sheath of the root apex was 30–40 per root. When the gel sheath was preparatively removed, their number per root increased
twice. It is assumed that the subpopulation of BCs directly associated with the root apex differs from the subpopulation of
BCs freely accommodated in the gel sheath. The number of BCs was the same in the roots with low and high natural growth rates.
NaF (1–20 mM) suppressed growth of wheat seedling roots; the viscosity of the gel sheath increased (by 3–5 times), and the
number of BC rose with the most pronounced increment in the size of the BC subpopulation directly associated with the root
apex.
Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 530–538. 相似文献
16.
Manabu Fukui Jungin Suh Yoshitaka Yonezawa Yoshikuni Urushigawa 《Ecological Research》1997,12(2):201-209
To clarify the anaerobic microbial interactions in the process of carbon mineralization in marine eutrophic environments,
the microbial sulfate reduction and methane production rates were examined in coastal marine sediments of Ise Bay, Japan,
in autumn 1990. Sulfate reduction rates (51–210 nmol ml−1 day−1 at 24°C) were much higher than the methane production ones (<1.78 nmol ml−1 day−1) in the surface sediments (top 2 cm) at the six stations surveyed (water depth: 10.7–23.3 m). Substrates for sulfate-reducing
bacteria (SRB) were estimated after the addition of a specific inhibitor for SRB (20 mmol l−1 molybdate) into the sediment slurry, from the substrate accumulation rates. In the presence of the inhibitor, sulfate reduction
was completely stopped and volatile fatty acids (mainly acetate) were accumulated, although hydrogen was not. Methane production
occurred markedly accompanied by consumption of the accumulated acetate from the third day after the addition of molybdate.
The maximum rate of methane production was 1.2–1.9 μmol ml−1 day−1, which was similar to those in highly polluted freshwater sediments such as the Tama River, Tokyo, Japan. These results show
that acetate is a common major substrate for sulfate reduction and methane production, and SRB competitively inhibit potential
acetoclastic methanogenesis in coastal sediments. Methanogens may potentially inhabit the sediments at low levels of population
density and activity. 相似文献
17.
Characterizing Pathways by Which Gravitropic Effectors Could Move from the Root Cap to the Root of Primary Roots of Zea mays 总被引:1,自引:0,他引:1
Plasmodesmata linking the root cap and root in primary rootsZea mays are restricted to approx. 400 protodermal cells borderingapprox. 110000 µm2 of the calyptrogen of the root cap.This area is less than 10% of the cross-sectional area of theroot-tip at the cap junction. Therefore, gravitropic effectorsmoving from the root cap to the root can move symplasticallyonly through a relatively small area in the centre of the root.Decapped roots are non-responsive to gravity. However, decappedroots whose caps are replaced immediately after decapping arestrongly graviresponsive. Thus, gravicurvature occurs only whenthe root cap contacts the root, and symplastic continuity betweenthe cap and root is not required for gravicurvature. Completelyremoving mucilage from the root tip renders the root non-responsiveto gravity. Taken together, these data suggest that gravitropiceffectors move apoplastically through mucilage from the capto the root. Calyptrogen, open meristem, protoderm, root cap, root gravitropism, Zea mays 相似文献
18.
B B Nepple J Kessi R Bachofen 《Journal of industrial microbiology & biotechnology》2000,25(4):198-203
Rhodobacter sphaeroides grew in the presence of up to 43 μM chromate and reduced hexavalent chromium to the trivalent form under both aerobic and
anaerobic conditions. Reduced chromium remained in the external medium. Reductase activity was present in cells of R. sphaeroides independent of whether chromate was present or not in the growth medium. The reducing activity was found in the cytoplasmic
cell fraction and was dependent on NADH. The chromate-reducing enzyme was purified by anion exchange, hydroxyapatite and hydrophobic
interaction chromatography, and gel filtration. The molecular weight of the enzyme was 42 kDa as determined by gel filtration.
The optimum of the reaction is at pH 7.0 and 30°C. The enzyme activity showed a hyperbolic dependence on the concentrations
of both substrates, NADH and chromate, with a maximum velocity at 0.15 mM NADH. A K
m of 15±1.3 μM CrO4
2− and a V
max of 420±50 μmol min−1 mg protein−1 was determined for the enzyme isolated from anaerobically grown cells and 29±6.4 μM CrO4
2− and 100±9.6 μmol CrO4
2− min−1 mg protein−1 for the one from aerobically grown ones. Journal of Industrial Microbiology & Biotechnology (2000) 25, 198–203.
Received 05 January 2000/ Accepted in revised form 27 May 2000 相似文献
19.
The growth behavior of Clostridium thermobutyricum JW171K and its production of butyric acid were investigated under continuous cultivation in a recently developed rotary fermentor.
Using low dilution rates (up to 40 times the shortest doubling time), the continuous culture conditions caused metabolic shifts
from butyrate formation to the production of acetate. Using an 18-h volumetric retention time, no true steady state in butyrate
formation was achieved after 22 days, although the optical density was stable. Acetate and butyrate were formed in an oscillatory
mode with an alternating predominance between these two products, indicating an oscillation between the less exergonic acetate-forming
but higher ATP (4ATP mol−1 glucose) forming mode, and the more exergonic butyrate and 3ATP mol−1 glucose forming mode. During the continuous culture drastic changes in cell morphology occurred and, at the lower dilution
rates, long, granulose-containing, filamentous cells with rounded protuberances and swellings were observed. A maximal butyrate
concentration of 18.4 g L−1 and a productivity of about 2.4 g L−1 per h (at 25–27 mM concentration in the broth) were obtained. Journal of Industrial Microbiology & Biotechnology (2000) 24, 7–13.
Received 26 April 1999/ Accepted in revised form 16 August 1999 相似文献
20.
Phytoremediation is emerging as an alternative agriculture-based technology because remediation of metalpolluted sites can
be brought about utilizing the ability of plants to uptake and store contaminants in them. A field study was conducted to
assess the role of Indian mustard in phytoremediation of chromium-contaminated substrata. Uptake parameters, namely, bio-concentration
factor, translocation index, Cr distribution within plant, and tolerance index were used in determining the remediation potential
of the crop. A significant increase in Cr accumulation (0.64–4.19 mg g−1 DW, stem; and 0.77–1.1 mg Cr g−1 DW, root), coupled with high tolerance indices, was observed in response to Cr stress, thus showing that Indian mustard is
a potential hyperaccumulator. Movement and subsequent distribution of metal ions in the plant were assessed by studying the
translocation index which showed a consistent increase (27–87% at T5) with time, and bioconcentration factor, where also an
increase over a time period was observed in stem (1.3–11.4, T1) and root (1.96–5.56, T1), thereby, depicting the strong ability
of Indian mustard for phytoextraction. A significant decline, however, was observed in the bioconcentration factor with increase
in the dose of Cr application. 相似文献