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1.
The influence of temperature ( T) and water activity ( a
w) on the growth rate ( μ) of seven moulds ( Alternaria alternata, Aspergillus flavus, Cladosporium cladosporioides, Mucor racemosus, Penicillium chrysogenum, Rhizopus oryzae and Trichoderma harzianum) was assessed in suboptimal conditions. Firstly, the dependence of fungal growth on temperature, at a
w 0.99, was modelled through an approach described previously for bacteria. A dimensionless growth rate variable: μ
dimα= μ/ μ
optα depended on the following normalised temperature: T
dim=( T− T
min)/( T
opt− T
min) according to a power function: μ
dimα=[ T
dim]
α
, where α was an exponent to be estimated. Secondly, the same approach was used to describe the influence of a
w on fungal growth, at the respective optimum temperatures for each mould. Similarly, μ
dimβ= μ/ μ
optβ depended on the following normalised water activity: a
wdim=( a
w− a
wmin)/( a
wopt− a
wmin) according to a power function: μ
dimβ=[ a
wdim] β. Results show: (i) for each mould, the α-value is significantly less than the β-value, confirming that water activity has a greater influence than temperature on fungal development; (ii) the α-values and the β-values depend on the mould; (iii) the α-value is less than 1 for the mesophilic mould A. flavus, whereas the other moulds are characterised by higher α-values ranging from 1.10 to 1.54; (iv) the mesophilic A. flavus exhibits a low β-value, 1.50, compared to the hydrophilic T. harzianum, β=2.44, while β-values are within the range (1.71–2.37) for the other moulds. Journal of Industrial Microbiology & Biotechnology (2002) 28, 311–315 DOI: 10.1038/sj/jim/7000248
Received 27 June 2001/ Accepted in revised form 04 February 2002 相似文献
2.
Pollution of terrestrial surfaces and aquatic systems by hexavalent chromium, Cr(VI), is a worldwide public health problem.
A chromium resistant bacterial isolate identified as Exiguobacterium sp. GS1 by 16S rRNA gene sequencing displayed high rate of removal of Cr(VI) from water. Exiguobacterium sp. GS1 is 99% identical to Exiguobacterium acetylicum. The isolate significantly removed Cr(VI) at both high and low concentrations (1–200 μg mL −1) within 12 h. The Michaelis–Menten K
m
and V
max for Cr(VI) bioremoval were calculated to be 141.92 μg mL −1 and 13.22 μg mL −1 h −1, respectively. Growth of Exiguobacterium sp. GS1 was indifferent at 1–75 μg mL −1 Cr(VI) in 12 h. At initial concentration of 8,000 μg L −1, Exiguobacterium sp. GS1 displayed rapid bioremoval of Cr(VI) with over 50% bioremoval in 3 h and 91% bioremoval in 8 h. Kinetic analysis
of Cr(VI) bioremoval rate revealed zero-order in 8 h. Exiguobacterium sp. GS1 grew and significantly reduced Cr(VI) in cultures containing 1–9% salt indicating high salt tolerance. Similarly
the isolate substantially reduced Cr(VI) over a wide range of temperature (18–45 °C) and initial pH (6.0–9.0). The T
opt and initial pH opt were 35–40 °C and 7–8, respectively. Exiguobacterium sp. GS1 displayed a great potential for bioremediation of Cr(VI) in diverse complex environments. 相似文献
3.
In cystic fibrosis airway epithelia, mutation of the CFTR protein causes a reduced response of Cl − secretion to secretagogues acting via cAMP. Using a Ca 2+ imaging system, the hypothesis that CFTR activation may permit ATP release and regulate [Ca 2+]
i
via a receptor-mediated mechanism, is tested in this study. Application of external nucleotides produced a significant increase
in [Ca 2+]
i
in normal (16HBE14o − cell line and primary lung culture) and in cystic fibrosis (CFTE29o − cell line) human airway epithelia. The potency order of nucleotides on [Ca 2+]
i
variation was UTP ≫ ATP > UDP > ADP > AMP > adenosine in both cell types. The nucleotide [Ca 2+]
i
response could be mimicked by activation of CFTR with forskolin (20 μ m) in a temperature-dependent manner. In 16HBE14o − cells, the forskolin-induced [Ca 2+]
i
response increased with increasing temperature. In CFTE29o − cells, forskolin had no effect on [Ca 2+]
i
at body temperature-forskolin-induced [Ca 2+]
i
response in CF cells could only be observed at low experimental temperature (14°C) or when cells were cultured at 26°C instead
of 37°C. Pretreatment with CFTR channel blockers glibenclamide (100 μ m) and DPC (100 μ m), with hexokinase (0.5 U/mg), and with the purinoceptor antagonist suramin (100 μ m), inhibited the forskolin [Ca 2+]
i
response. Together, these results demonstrate that once activated, CFTR regulates [Ca 2+]
i
by mediating nucleotide release and activating cell surface purinoceptors in normal and CF human airway epithelia.
Received: 3 April 2000/Revised: 30 June 2000 相似文献
4.
Ambient temperatures are major factors regulating the growth rates, yields, and geographical distribution of crop species. The cultivation of sesame (Sesamum indicum L.) is expanding with the rising demand in regions where it is not traditionally grown, and sub-optimal yields due to extremely low or high temperatures could occur. Currently literature lacks information on the temperature responses of sesame growth. An experiment was conducted to quantify the effects of different temperatures on vegetative growth and reproductive development of sesame, and to estimate its cardinal temperature limits (Topt; Tmin; Tmax). Plants were subjected to six different day/night temperature treatments of 40/32, 36/28, 32/24, 28/20, and 20/12 °C using walk-in growth chambers. Vegetative growth of sesame was sensitive to low temperatures (<?15 °C), but tolerant of high temperatures. The cardinal temperature limits of 15.7 °C (Tmin), 27.3 °C (Topt), and 44.6 °C (Tmax) were observed for rate of biomass accumulation. Sesame reached the flowering stage under moderate to high temperature conditions; however, reproductive yields progressively declined above 25 °C, and no seed yields were obtained beyond 33 °C. The estimated temperature limits could be employed to develop crop models for simulating management and adaptation strategies of sesame under current and future climate scenarios, and adaptation to regions where the crop is not currently grown. Future research should focus on understanding factors controlling the temperature tolerance of reproductive development in sesame, to provide a broader geographical adaptation. 相似文献
5.
Although some anaerobic and aerobic mesophiles have long been known to grow at alkaline pH (above 9.5), little was known
until recently about thermophilic alkaliphiles, termed now alkalithermophiles. This minireview describes presently known and
recently validly described anaerobic alkalithermophilic bacteria (pH opt
55C > 8.5; T opt > 55°C) and alkalitolerant thermophiles (pH opt
55C < 8.5 but pH max
55C above 9.0). Some of these are widely distributed, but others have been isolated (thus far) only from one specific location.
This novel group of anaerobic bacteria is comprised of physiologically different genera and species which, so far, all belong
to the Gram-type positive Bacillus-Clostridium phylogenetic subbranch. An interesting feature of these anaerobic alkalithermophiles is that most of the isolates have short
doubling times. The fastest growing among them are strains of Thermobrachium celere, with doubling times as short as 10 min while growing above pH 9.0 and above 55°C.
Received: January 22, 1998 / Accepted: February 16, 1998 相似文献
6.
We report here the finding of a highly significant inverse correlation of the uracil content of 16S rRNA and the optimum growth temperature ( Topt) of cultured thermophilic and psychrophilic prokaryotes. This correlation was significantly different from the weaker correlations between the contents of other nucleotides and Topt. Analysis of the 16S rRNA secondary structure regions revealed a fall in the A:U base-pair content in step with the increase in Topt that was much steeper than that of mismatched base-pairs, which are thermodynamically less stable. These findings indicate that the 16S rRNA sequences of thermophiles and psychrophiles are under a strong thermo-adaptive pressure, and that structure–function constraints play a crucial role in determining their 16S rRNA nucleotide composition. The derived relationship between uracil content and Topt was used to develop an algorithm to predict the Topt values of uncultured prokaryotes lacking cultured close relatives and belonging to the phyla predominantly containing thermophiles. This algorithm may be useful in guiding the design of cultivation conditions for hitherto uncultured microbes. 相似文献
7.
In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization
(branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates ( P
N) were observed in T1 [13.2±1.0 μmol(CO 2) m −2 s −1] compared to T2 [8.0±1.8 μmol(CO 2) m −2 s −1] and T0 [4.8±1.3 μmol(CO 2) m −2 s −1]. Stomatal conductance ( g
s), transpiration rate ( E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and
63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (F v), performance index (P.I.) and total chlorophyll [Chl ( a+ b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants
of B. excelsa in young phase. 相似文献
8.
The initial rate of d-glucosamine uptake by the non-halotolerant yeast Saccharomyces cerevisiae was approximately halved as the apparent half saturation constant (K m) and the apparent maximum velocity (V max) changed from 6.6 mm to 16.4 mm and from 22 μmol · g −1 · min −1 to 16 μmol · g −1 · min −1, respectively, when the salinity in the medium was increased from zero m to 0.68 m NaCl. Corresponding changes in a high affinity transport system in the halotolerant yeast Debaryomyces hansenii were from 1.1 mm to 4.6 mm and from 3.1 μmol · g −1 · min −1 to 4.5 μmol · g −1 · min −1, implying a practically unchanged transport capacity. In 2.7 m NaCl, K m and V max in this system were 24.5 mm and 1.1 μmol · g −1 · min −1, respectively, representing a marked decrease in transport capability. Nevertheless, the degree of affinity in this extreme
salinity must still be regarded as noteworthy. In addition to the high affinity transport system in D. hansenii, a low affinity system, presumably without relevance in d-glucosamine transport, was observed. 相似文献
9.
Siebold’s beech ( Fagus crenata) is a common species in the cool temperate forests of Japan. As the natural regeneration of beech forests is expected to
contribute to forest conservation in the future, we investigated the effects of different CO 2 concentrations ([CO 2]) on the growth of beech seedlings in relation to morphological and physiological changes. Acorns collected from beech forest
in Minakami, central Japan were germinated and grown during a first growing season of 6 months under four [CO 2] levels (200, 350, 550, and 750 μL L −1). Stem mass increased with increasing [CO 2]; however, root mass did not change significantly among the treatments. As [CO 2] increased, net photosynthetic rate ( P
n) and leaf area increased, whereas transpiration ( T
r), stomatal conductance, leaf chlorophyll content, and leaf longevity decreased. Although water-use efficiency (WUE; i.e.,
P
n/ T
r) improved with increasing [CO 2], the density of stomata did not significantly change. Increases in the number of buds and the terminal bud length with increasing
[CO 2] indicated accelerated formation of additional branches and leaves in the next season. The enhanced WUE levels seen in beech
saplings growing under the higher environmental [CO 2] levels that are expected in the future may be advantageous for their survival, considering that beech saplings prefer mesic
conditions. 相似文献
10.
A quantitative study of indole-3-acetic acid (IAA) turnover, and the contribution of tryptophan-dependent and tryptophan-independent
IAA-biosynthesis pathways, was carried out using protoplast preparations and shoot apices obtained from wild-type and transgenic,
IAA-overproducing tobacco ( Nicotiana tabacum L.) plants, during a phase of growth when the level of endogenous IAA was stable. Based on the rate of disappearance of [ 13C 6]IAA, the half-life of the IAA pool was calculated to be 1.1 h in wild-type protoplasts and 0.8 h in protoplasts from the
IAA-overproducing line, corresponding to metabolic rates of 59 and 160 pg IAA (μg Chl) −1 h −1, respectively. The rate of conversion of tryptophan to IAA was 15 pg IAA (μg Chl) −1 h −1 in wild-type protoplasts and 101 pg IAA (μg Chl) −1 h −1 in protoplasts from IAA-overproducing plants. In both instances, IAA was metabolised more rapidly than it was synthesised
from tryptophan. As the endogenous IAA pools were in a steady state, these findings indicate that IAA biosynthesis via the
tryptophan-independent pathway was 44 pg IAA (μg Chl) −1 h −1 and 59 pg IAA (μg Chl) −1 h −1, respectively, in the wild-type and transformed protoplast preparations. In a parallel study with apical shoot tissue, the
presumed site of IAA biosynthesis, the rate of tryptophan-dependent IAA biosynthesis exceeded the rate of metabolism of [ 13C 6]IAA despite the steady state of the endogenous IAA pool. The most likely explanation for this anomaly is that, unlike the
protoplast system, injection of substrates into the apical tissues did not result in uniform distribution of label, and that
at least some of the [ 2H 5]tryptophan was metabolised in compartments not normally active in IAA biosynthesis. This demonstrates the importance of using
experimental systems where labelling of the precursor pool can be strictly controlled.
Received: 18 January 2000 / Accepted 24 February 2000 相似文献
11.
Summary We have developed optimum culture conditions for the large-scale propagation of chrysanthemum in balloon-type bioreactors
to achieve vigorous growth and quality. The effects of NH
4
+
/NO
3
−
ratio, air volume, air temperature, photosynthetic photo flux, and an inoculation density on the growth and quality of plantlets
were investigated. The best production conditions were an NH
4
+
:NO
3
−
ratio of 20∶40 m M, air exchange of 0.1 vvm min −1, air temperature 25°C, photosynthetic photo flux (PPF) at 100 μmol m −2 s −1, and an inoculation density of 40 nodes Chrysanthemum grandiflorum. Under each of these conditions, the maximum growth rate reached 279.0, 260,0, 20.0, 23.3, and 94.5 (g-fresh weight per plantlet
d −1), respectively, at 12 wk of culture. These results specify the key environmental factors that can be regulated to improve
the quality and quantity of flowers and increase yield in large-scale bioreactor cultures of chrysanthemum. 相似文献
12.
This combined study of patch-clamp and intracellular Ca 2+ ([Ca 2+]
i
) measurement was undertaken in order to identify signaling pathways that lead to activation of Ca 2+-dependent Cl − channels in cultured rat retinal pigment epithelial (RPE) cells. Intracellular application of InsP3 (10 μ m) led to an increase in [Ca 2+]
i
and activation of Cl − currents. In contrast, intracellular application of Ca 2+ (10 μ m) only induced transient activation of Cl − currents. After full activation by InsP3, currents were insensitive to removal of extracellular Ca 2+ and to the blocker of I
CRAC, La 3+ (10 μ m), despite the fact that both maneuvers led to a decline in [Ca 2+]
i
. The InsP3-induced rise in Cl − conductance could be prevented either by thapsigargin-induced (1 μ m) depletion of intracellular Ca 2+ stores or by removal of Ca 2+ prior to the experiment. The effect of InsP3 could be mimicked by intracellular application of the Ca 2+-chelator BAPTA (10 m m). Block of PKC (chelerythrine, 1 μ m) had no effect. Inhibition of Ca 2+/calmodulin kinase (KN-63, KN-92; 5 μ m) reduced Cl −-conductance in 50% of the cells investigated without affecting [Ca 2+]
i
. Inhibition of protein tyrosine kinase (50 μ m tyrphostin 51, 5 μ m genistein, 5 μ m lavendustin) reduced an increase in [Ca 2+]
i
and Cl − conductance. In summary, elevation of [Ca]
i
by InsP3 leads to activation of Cl − channels involving cytosolic Ca 2+ stores and Ca 2+ influx from extracellular space. Tyrosine kinases are essential for the Ca 2+-independent maintenance of this conductance.
Received: 15 October 1998/Revised: 3 March 1999 相似文献
13.
Plant traits of Malcolmia littorea growing at the Botanic Garden of Rome and transplanted from the wild population developing along the Latium coast (Italy) were analyzed. The highest photosynthetic rates [ P
N, 22.5 ± 0.5 μmol(CO 2) m −2 s −1], associated to the highest chlorophyll content (Chl, 60 ± 5 SPAD units), and respiration rates [ R, 11.1 ± 0.2 μmol(CO 2) m −2 s −1] were reached in spring, when mean air temperature ( T
m) was in the range 17°C to 23°C. P
N, Chl, and R decreased by 86, 38, and 59% in summer when mean maximum air temperature ( T
max) was 30.3 ± 2.6°C. Leaf water potential decreased by 34% in summer compared to the spring value, and it was associated to
a relative water content (RWC) of 74 ± 4%, and to a water-use efficiency (WUE) of 2.15 ± 0.81 μmol(CO 2) mmol −1(H 2O). Moreover, also low air temperatures determined a significant P
N and R decreases (by 52 and 40% compared to the maximum, respectively). Responsiveness of gross photosynthetic rate ( P
g) to R was higher than that to P
N as underlined by the slope of the regression line between the two variables. The results underlined a low tolerance to both
high- and low air temperatures of M. littorea. The selected key traits ( R, WUE, Chl) by the discriminant analysis might be used to monitor the M. littorea wild population in the long time. The ex situ cultivated plants could be propagated and used to increase the individuals number of the wild population. 相似文献
14.
The eco-physiological responses of three nitrogen-fixing cyanobacteria (N-fixing cyanobacteria), Aphanizomenon gracile, Anabaena minderi, and Ana. torques-reginae, to light were assessed under nutrient saturation. The N-fixing cyanobacteria were isolated into monocultures from a natural
bloom in a shallow colored lake and their growth irradiance parameters and pigment composition were assessed. The different
ecological traits related to light use (μ max, α, I
k) suggest that these N-fixing cyanobacteria are well adapted to low light conditions at sufficient nutrients, yet interspecific
differences were observed. Aphanizomenon gracile and Anabaena minderi had high relative growth rates at low irradiances (ca. 70% of those in high light), low half saturation constant for light-limited
growth ( I
k < 9.09 μmol photon m −2 s −1) and high efficiency ( α < 0.11 day −1 μmol photon −1 m 2 s). Conversely, Ana. torques-reginae showed poorer light competitiveness: low relative growth rates at low irradiances (ca. 40% of those in high light), low α
(0.009 day −1 μmol photon −1 m 2 s) and higher I
k (35.5 μmol photon m −2 s −1). Final densities in Aphanizomenon gracile and Anabaena minderi reached bloom densities at irradiances above 30 μmol photon m −2 s −1 with different hierarchy depending on irradiance, whereas Ana. torques-reginae never achieved bloom densities. All species had very low densities at irradiances ≤17 μmol photon m −2 s −1, thus no N-fixing blooms would be expected at these irradiances. Also, under prolonged darkness and at lowest irradiance
(0 and 3 μmol photon m −2 s −1) akinetes were degraded, suggesting that in ecosystems with permanently dark sediments, the prevalence of N-fixing cyanobacteria
should not be favored. All species displayed peaks of phycocyanin, but no phycoeritrin, probably due to the prevailing red
light in the ecosystem from which they were isolated. 相似文献
15.
The effects of elevated [CO 2] (700 μl l −1 [CO 2]) and temperature increase (+3 °C) on carbon accumulation in a grassland soil were studied at two N-fertiliser supplies (160
and 530 kgN ha −1 year −1) in a long-term experiment (2.5 years) on well established ryegrass swards (Lolium perenne L.,) supplied with the same amounts
of irrigation water. For all experimental treatments, the C:N ratio of the top soil organic matter fractions increased with
their particle size. Elevated CO 2 concentration increased the C:N ratios of the below-ground phytomass and of the macro-organic matter. A supplemental fertiliser
N or a 3 °C increase in elevated [CO 2] reduced it. At the last sampling date, elevated [CO 2] did not affect the C:N ratio of the soil organic matter fractions, but increased significantly the accumulation of roots
and of macro-organic matter above 200 μm (MOM). An increased N-fertiliser supply stimulated the accumulation of the non harvested
plant phytomass and of the OM between 2 and 50 μm, without positive effect on the macro-organic matter >200 μm. Elevated [CO 22] increased C accumulation in the OM fractions above 50 μm by +2.1 tC ha −1, on average, whereas increasing the fertiliser N supply led to an average supplemental accumulation of +0.8 tC ha −1. There was no significant effect of a 3 °C temperature increase under elevated [CO 2] on C accumulation in the OM fractions above 50 μm.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
Formate oxidase was found in cell-free extracts of Debaryomyces vanrijiae MH201, a soil isolate. After purification by column chromatography, the preparation showed a protein band corresponding to
a molecular mass (MM) of 64 kDa on sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The MM, estimated by a gel filtration,
was 99 kDa. The preparation showed two and three bands on isoelectric focusing under denaturing and native conditions, respectively.
These results suggest that the preparation contained three isoforms, each of which might be composed of αα, αβ, and ββ subunits
with apparently similar MM. The preparation acted on formate with K
m and V
max values of 11.7 mM and 262 μmol min −1 mg −1, respectively, at pH 4.5 and 25°C, but showed no evidence of activity on the other compounds tested. The optimum pH and temperature
were pH 4.0 and 35°C, respectively. The preparation showed activities of 85% of the initial activity after storage at pH 6.0
and 4°C for 8 weeks. When 10 mM formaldehyde was reacted with 2.0 U ml −1 of the enzyme preparation at pH 5.5 and room temperature in the presence of 2.0 U ml −1 of a microbial aldehyde oxidase and 100 U ml −1 of catalase for 180 min, neither of formate nor formaldehyde was detected, suggesting that the reaction involved the quantitative
conversion of formaldehyde to carbon dioxide. 相似文献
17.
Quasi steady state growth of Lactococcus
lactis IL 1403 was studied in glucose-limited A-stat cultivation experiments with acceleration rates ( a) from 0.003 to 0.06 h −2 after initial stabilization of the cultures in chemostat at D = 0.2–0.3 h −1. It was shown that the high limit of quasi steady state growth rate depended on the acceleration rate used—at an acceleration
rate 0.003 h −2 the quasi steady state growth was observed until μ
crit = 0.59 h −1, which is also the μ
max value for the culture. Lower values of μ
crit were observed at higher acceleration rates. The steady state growth of bacteria stabilized at dilution rate 0.2 h −1 was immediately disrupted after initiating acceleration at the highest acceleration rate studied—0.06 h −2. Observation was made that differences [Δ( μ − D)] of the specific growth rates from pre-programmed dilution rates were the lowest using an acceleration rate of 0.003 h −2 (< 4% of preset changing growth rate). The adaptability of cells to follow preprogrammed growth rate was found to decrease
with increasing dilution rate—it was shown that lower acceleration rates should be applied at higher growth rates to maintain
the culture in the quasi steady state. The critical specific growth rate and the biomass yields based on glucose consumption
were higher if the medium contained S
0 = 5 g L −1 glucose instead of S
0 = 10 g L −1. It was assumed that this was due to the inhibitory effect of lactate accumulating at higher concentrations in the latter
cultures. Parallel A-stat experiments at the same acceleration and dilution rates showed good reproducibility—Δ( μ − D) was less than 5%, standard deviations of biomass yields per ATP produced ( Y
ATP), and biomass yields per glucose consumed ( Y
XS) were less than 15%. 相似文献
18.
The present study examined the effects of plant growth hormones, incubation period, biotic ( Trametes versicolor, Mucor sp., Penicillium notatum, Rhizopus stolonifer, and Fusarium oxysporum) and abiotic (NaCl, MgSO 4, FeSO 4, ZnSO 4, and FeCl 3) elicitors on cell growth and α-tocopherol and pigment (red and yellow) productions in Carthamus tinctorius cell cultures. The cell growth and α-tocopherol and pigment contents improved significantly on Murashige and Skoog (MS) liquid
medium containing 50.0 μM α-naphthalene acetic acid (NAA) and 2.5 μM 6-Benzyladenine (BA) at 28 days of incubation period.
Incorporation of T. versicolor (50 mg l −1) significantly enhanced the production of α-tocopherol (12.7-fold) and red pigment (4.24-fold). Similarly, supplementation
of 30 mg l −1
T. versicolor (7.54-fold) and 70 mg l −1
Mucor sp. (7.40-fold) significantly increased the production of yellow pigment. Among abiotic elicitors, NaCl (50–70 mg l −1) and MgSO 4 (10–30 mg l −1) significantly improved production of α-tocopherol (1.24-fold) and red pigment (20-fold), whereas yellow pigment content
increased considerably by all the abiotic elicitor treatments. Taken together, the present study reports improved productions
of α-tocopherol and the pigment as a stress response of safflower cell cultures exposed to these elicitors. 相似文献
19.
Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska,
were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates
of maximum quantum efficiency ( F
v/ F
m), maximum relative electron transport rate (rETR max), photosynthetic efficiency (α), and the photoadaptive index ( E
k). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical
resolution for the first time. Bottom ice algae (0–5 cm from ice–water interface) expressed low F
v/ F
m (0.331–0.426) and low α (0.098–0.130 (μmol photons m −2s −1) −1) in December. F
v/ F
m and α increased in March and May (0.468–0.588 and 0.141–0.438 (μmol photons m −2s −1) −1, respectively) indicating increased photosynthetic activity. In addition, increases in rETR max (3.3–16.4 a.u.) and E
k (20–88 μmol photons m −2 s −1) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to
under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly
linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen). 相似文献
20.
The response of barley ( Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO 2] [700 μmol (CO 2) mol −1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO 2] [350 μmol (CO 2) mol −1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total
Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol
m −2 s −1 (PPFD 730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for
all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD 730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as F V/F M) for EC plants grown at 730 and 1 200 μmol m −2 s −1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin
in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly
PPFD 730) to the photoinactivation of PS2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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