共查询到20条相似文献,搜索用时 15 毫秒
1.
Size-fractionated chlorophyll a (Chla)-specific productivity (μgC μgChla
−1 h−1) was measured at 11 stations off the northern coast of the South Shetland Islands during summer. The Chla-specific productivity of the 2- to 10 or 10- to 330-μm fraction was highest at 100% and 23% light depths. The Chla-specific productivity of the 2- to 10-μm fraction was generally highest, and that of the <2 or 10- to 330-μm fraction was
sometimes highest at 12% and 1% light depths. Temperature was less than 3°C within the euphotic zone at all stations. The
hypothesis of Shiomoto et al., according to which Chla-specific productivity of picophytoplankton (<2 μm) is not significantly higher than that of larger phytoplankton (>2 μm)
in water colder than 10°C, was supported on condition that light is not limited for larger phytoplankton.
Received: 16 September 1997 / Accepted: 8 December 1997 相似文献
2.
M. Aubele Horst Zitzelsberger Sandor Szücs Martin Werner Herbert Braselmann Peter Hutzler Karsten Rodenacker Lars Lehmann Günter Minkus Heinz Höfler 《Histochemistry and cell biology》1997,107(2):121-126
Interphase fluorescence in situ hybridization (FISH) was performed on 15-μm-thick paraffin sections from prostatic carcinomas
using a chromosome 7-specific α-satellite DNA probe. A confocal laser scanning microscope (CLSM) was used for optical sectioning
of the thick sections and reconstruction of 3D images. The number of FISH signals was determined by a gallery of optical sections
evaluating only complete nuclei. To investiate the influence of section thickness and truncation and nuclei on scoring results,
we compared the FISH data from 15-μm sections with signal counts obtained from 5-μm sections. The latter were evaluated by
conventional fluorescence microscopy in the same tumor regions previously defined and marked on the slides. After statistical
analysis of spot frequencies in tumor and non-tumorous cells (χ2 test), we transferred the signal frequencies into a cytogenetic classification (−7, +7, polysomy 7). Based on this classification,
most cases showed more than one chromosome 7 aberration type. Trisomy 7 (+7) became apparent in 15-μm-thick sections in all
19 tumors, polysomy 7 (>3 spots) in 18/19 cases, and monosomy 7 (−7) in 13/19 cases. In 5-μm sections, however, trisomy 7
and polysomy 7 were found in only 7/19 and 13/19 cases, respectively, and monosomy 7 in 7/19 cases. When comparing the classification
results of tumor cells of the same tumor regions originating either from 5-μm or 15-μm sections, the following discrepancies
were noted: in 15-μm sections exclusively, in 12/19 tumors, trisomy 7 was found; in 6/19 cases, polysomy 7; in 8/19 cases,
monosomy 7. The high proportion of cases with tumor nuclei expressing only one hybridization signal of chromosome 7 in 15-μm
sections could be confirmed as monosomy 7 in five selected cases by double-hybridization using centromere-specific probes
for chromosomes 7 and 12. These results demonstrate that numerical chromosome 7 aberrations are more frequently observed in
thick (15-μm) paraffin-embedded tissue sections by evaluating only complete nuclei. The use of routine sections (5-μm) for
interphase cytogenetic analyses is compromised by a remarkable underestimation of the real chromosome copy numbers.
Accepted: 7 November 1996 相似文献
3.
Oze H Hirao M Ebina K Shi K Kawato Y Kaneshiro S Yoshikawa H Hashimoto J 《In vitro cellular & developmental biology. Animal》2012,48(2):123-130
Previous studies have demonstrated that oxygen environment is an important determinate factor of cell phenotypes and differentiation,
although factors which affect pericellular oxygen concentration (POC) in murine chondrogenic cell culture remain unidentified.
Oxygen concentrations in vivo were measured in rabbit musculoskeletal tissues, which were by far hypoxic compared to 20% O2 (ranging from 2.29 ± 1.16 to 4.36 ± 0.51%). Oxygen concentrations in murine chondrogenic cell (C3H10T1/2) culture medium
were monitored in different oxygen concentrations (20% or 5%) in the incubator and in different medium volumes (3,700 or 7,400 μl)
within 25-cm2 flasks. Chondrogenic differentiation was assessed by glycosaminoglycan production with quantitative evaluation of Alcian
blue staining in 12-well culture dishes. Expression of chondrogenic genes, aggrecan, and type II collagen α1, was examined
by quantitative real-time polymerase chain reaction. Oxygen concentrations in medium decreased accordingly with the depth
from medium surface, and POC at Day 6 was 18.99 ± 0.81% in 3,700-μl medium (1,480-μm depth) and 13.26 ± 0.23% in 7,400-μl
medium (2,960-μm depth) at 20% O2 in the incubator, which was 4.96 ± 0.08% (1,480-μm depth) and 2.83 ± 0.42% (2,960-μm depth) at 5% O2, respectively. The differences of POC compared by medium volume were statistically significant (p = 0.0003 at 20% and p = 0.001 at 5%). Glycosaminoglycan production and aggrecan gene expression were most promoted when cultured in moderately
low POC, 1,000 μl (2,960-μm depth) at 20% O2 and 500 μl (1,480-μm depth) at 5% O2 in 12-well culture dishes. We demonstrate that medium volume and oxygen concentration in the incubator affect not only POC
but also chondrogenic differentiation. 相似文献
4.
Toshi Nagata 《Ecological Research》1986,1(2):207-221
The seasonal changes in the size-fractionated chlorophylla concentrations (<3 μm, 3 to 25 μm, and >25 μm) were investigated at a pelagic site of the north basin of Lake Biwa during
June to December 1985. Autofluorescing plankton cells in the <3-μm fractions were also examined using the fluorescein isothiocyanate
staining epifluorescence microscopic technique. The <3-μm phytoplankton (usually dominated by chroococcoid cyanobacteria except
for a few cases dominated by small eukaryotes) showed a clearly different pattern of seasonal change compared with the larger
fractions. That is, from August to early September, chlorophylla of the larger fractions declined considerably, while the <3-μm chlorophylla did not decrease significantly. Moreover, cyanobacterial cell density in the <3-μm fraction showed a maximum value (2–3.5×105 cells·ml−1) during this period. The relative contribution of the <3-μm chlorophylla to the total chlorophylla increased from <5% to 45% during the course of this change. No clear vertical trend in the distribution and composition of
the <3-μm phytoplankton was found, except that relatively large cyanobacteria (>4 μm3) appeared at a depth of 15m but not at 0,5 and 10 m from late July to August. These large cells were also found in November
and December. The drastic seasonal change of phytoplankton size structure occurring in this basin was discussed in relation
to grazing, nutrient depletion and sinking.
Contribution from Otsu Hydrobiological Station, Kyoto Univeristy (No. 308, foreign language series). 相似文献
5.
Katherine Cilwa Shannon Teeters-Kennedy Keith A. Ramsey James V. Coe 《Plasmonics (Norwell, Mass.)》2013,8(2):349-355
The high fractional open area of metal thin film coatings, with two dimensional, hexagonally ordered, close packed arrays of holes, makes them of interest for the incorporation of plasmonic effects into a variety of optical devices. Gold films with hexagonal patterns of circular holes have been created on ZnSe infrared windows. The films have 2.50 μm diameter holes and a hexagonal lattice parameter of 3.06 μm which places the primary transmission resonances of the ZnSe/gold interface at ~1,400 cm?1 (7.14 μm) and that of the air/gold interface at ~3,800 cm?1 (2.63 μm). This geometry produces useful transmission across the whole traditional mid-infrared range. The dispersion of these resonances has been measured by changing the angle of incident light. The data is modeled with explicit momentum matching equations in two different, high symmetry geometries, allowing the effective index of refraction to vary with wavelength. The response of these resonances to the addition of an acetaldehyde coating is described. 相似文献
6.
Three types of microprojectile particles, 1.0-μm gold, 1.3-μm tungsten, and 1.6-μm gold, were studied for their effectiveness
on genetic transformation of black spruce via bombardment with somatic embryos as the target tissue. Different particles resulted
in different levels of transient expression of theGUS reporter gene; 1.0-μm gold particles produced the highest level of expression, and 1.6-μm gold particles produced the lowest
level. Particle type also affected stable transformation; 1.0-μm gold particles had a 10-fold higher stable transformation
efficiency than did 1.6-μm gold particles and a 2-fold higher efficiency than did 1.3-μm tungsten particles. This study indicates
that microprojectile particle type and size are important in bombardment-mediated plant transformation. 相似文献
7.
The collection efficiency and sample retention of a batch-type wetted wall bioaerosol sampling cyclone (BWWC) were experimentally
characterized. The BWWC is designed to sample air at 400 l/min and concentrate the particles into 12 ml of water. Aerosol
is transported into a cylindrically-shaped axial flow cyclone through a tangential slot and the particles are impacted on
the inner wall, which is wetted by air shear acting on a liquid pool at the base of the cyclone. The retention of collected
particles and the aerosol collection efficiency of the BWWC were evaluated with polystyrene latex beads (PSL), sodium fluorescein/oleic
acid droplets, and Bacillus atrophaeus (aka BG) spores. The retention of particles was determined by adding hydrosol directly into the device, running the BWWC
for a pre-set period of time, and then determining the amount of particulate matter recovered relative to the initial amount.
For 1-μm diameter PSL, 90% of the particles were recoverable from the cyclone body immediately after their introduction; however,
only 10% were retained in the collection liquid after 8 h of operation. The aerosol sampling efficiency was determined by
comparing the amount of particulate matter collected in the liquid with that collected by a reference filter. The collection
efficiency was 50–60% for 1- and 3-μm polystyrene (PSL) particles, and 1.5% for 10-μm oleic acid particles. The efficiency
for 3-μm oleic acid droplets was 35%. Explanations are provided for the difference between liquid and solid particle behavior,
and for the low efficiency for the large liquid particles. The collection efficiency for single spore BG was slightly lower
than that for 1-μm PSL. 相似文献
8.
V. B. Meyer-Rochow 《Polar Biology》1999,21(3):166-170
The ultrastructure of the nauplius eye of the tiny Antarctic ostracode Acetabulastoma sp. is described and conclusions about its possible function are drawn. Each of the three eye-cups measures approximately
20 μm in diameter and is optically isolated from its neighbour by screening pigments, which are contained in pigment cells
behind a tapetum of concentrically arranged, ca. 1-μm-long and 0.1-μm-thick, crystals. Three and sometimes four separate rhabdoms
with microvilli measuring 50–60 nm in diameter project from the concave side of the tapetum up to 5 μm deep into the eye-cup
interior, which is filled by the retinula cell bodies with their spherical nuclei and various organelles. Desmosomes and microtubules
are seen and light-induced cell or membrane damage was minimal. The observations suggest that the Acetabulastoma eye has photoreceptors that can tolerate an exposure to bright light and it may be used to inform its owner of the approach
of danger, the depth of water, and/or the season.
Accepted: 27 August 1998 相似文献
9.
Summary The three-dimensional architecture of a filamentous nucleolar structure, called the “nucleolonema”, was investigated in onion
root-tip cells by applying a silver impregnation technique to air-dried cells and serial ultrathin sections. The entire configuration
of the nucleolonema was revealed when silver staining was applied to air-dried cells. The nucleolonema was knobbly or segmented
along its entire length and showed great variation in thickness. Three categories of nucleolonema were discriminated depending
on thickness; each had an average value of 0.5, 1.0, and 1.3 μm, respectively. Some root tips were embedded in Lowicryl K4M
resin and cut into serial ultrathin sections about 100 nm thick. When these sections were subjected to silver impregnation,
segments of nucleolonema were visualized. Most of them were found to contain achromatic holes. These holes apparently corresponded
to the fibrillar centres seen with the electron microscope. According to the profiles of the holes, nucleolonema structures
were classified into three types: (1) nucleolonema with no distinct holes, (2) those with beaded holes, and (3) those with
cylindrical holes. The thicknesses were 0.7–0.8, 0.9–1.2, or 1.2–1.4 μm for nucleolonemata with no holes, beaded holes, or
cylindrical holes, respectively. The argyrophilic wall of nucleolonemata with holes was about 0.4 μm thick, roughly compatible
with the thinnest nucleolonema seen in air-dried specimens. The crescent-shaped segments were sometimes observed when the
nucleolonema was sectioned transversely, suggesting that the achromatic holes are exposed to the nucleoplasm, in other words,
the nucleolonema is partially degraded. Thus, the nucleolonema was not always structurally stable during interphase. The results
suggest that the nucleolonemata gradually become knobbly and increase their thickness, with concomitant expansion of the fibrillar
centres sometimes degrading into approximately 0.5 μm thick strands. 相似文献
10.
We present a new style extraordinary optical transmission (EOT) nano optical filter combined by two kinds of subwavelength holes array on a gold film. In the design, a square array of non-penetrating holes (hollow holes) inlays into another square array of penetrating holes ordered by a central arrange mode. We numerically calculated the transmission spectra of the patterned gold films by finite-difference time-domain (FDTD) method. Results show that the transmission of the filter can be manipulated by changing the depth of non-penetrating holes. The (1, 1) peak can be enhanced when the incident light normally illuminates one side of the filter with the hollow holes, yet the (1, 1) peak can be suppressed when the light illuminates the other side without hollow holes. It also depicts that the hollow hole array results in energy level splitting of (1, 0) mode propagating on the surface of the filter. What’s more, the splitting can be eliminated by modulating the depth of the hollow holes. Our study further reveals the role of suface plasmon effect in the EOT. 相似文献
11.
This study evaluates food supply for copepods, highlighting the trophic relationship between copepods and protozooplankton.
To test the hypotheses that protozooplankton prey are capable of sustaining the copepod standing stock in the western Irish
Sea, the taxonomic and size composition of these two groups and the size-specific predation of copepods on protozooplankton
were investigated. Protozooplankton and copepod samples were collected off the southwest coast of the Isle of Man using 1.7 l
Niskin water bottles and two nets (64 and 280 μm meshes), respectively. Copepod predation on protozooplankton was calculated
using weight-specific clearance rates from the literature, considering the availability of prey that was accessible to a given
size of copepod. Low protozooplankton biomass was dominated by small cells (<60 μm), and high copepod biomass was dominated
by small species, which were more efficiently collected by a 64-μm mesh net. However, large copepods were only collected by
a 280-μm mesh net, suggesting that the combination of the two nets provided a better estimate of copepod biomass. Predation
by the copepod assemblage in the Irish Sea removed 1–47% and 0.5–22% of ciliates and dinoflagellates standing stock, respectively,
resulting in 1–40% of the copepod feeding requirement per day. Contrary to our hypothesis, copepods could not meet their feeding
requirements by grazing only on the microzooplankton prey (15–200 μm), and other food sources (i.e. nanoplankton) must be
important additional dietary components to copepods in the Irish Sea.
Handling editor: S. M. Thomaz 相似文献
12.
The survival and persistence of growing and starved cells of Enterococcus faecalis in untreated and differentially filtered (20 μm, 5 μm, 3 μm, 1.2 μm, and 0.1 μm) seawater was analyzed in samples taken at
different times over a 1-year period by plate counts and scanning electron microscopy. Whereas seawater filtered through a
0.1-μm mesh was not at all or only slightly bactericidal during incubation at 16°C in the dark, culturability of E. faecalis in the other systems decreased as a function of increasing pore size of the filters. Recovery of culturable, glucose pre-starved
cells was always higher than that of cells harvested from the exponential growth phase. Electron microscopic analysis showed
that the disappearance of enterococci appeared related to the presence and multiplication of various zooflagellates.
Received: 25 July 2001 / Accepted: 27 August 2001 相似文献
13.
Thomas S. Vates Garry L. Brake S. K. Majumdar Gail L. Ferguson 《In vitro cellular & developmental biology. Plant》1986,22(6):305-310
Summary Cis-diamminedichloroplatinum II (cis-DDP), an antitumor drug and the inactive trans-isomer were studied to evaluate their
effects on cell multiplication, DNA synthesis, and surface morphology of the murine erythroleukemia cells (clone 6A11A). Short-term
treatment of cells (1h) with 5 and 10μg/ml of cis-DDP resulted in a significant inhibition of cell multiplication. Continuous
treatment with cis-DDP (up to 144 h) significantly arrested cell growth at 1,5, and 10μg/ml. The cells exposed to 10 μg/ml
trans-DDP exhibited a slight decrease in cell multiplication; however, the 25-μg/ml treatments showed a modest inhibition
of cell growth. Continuous treatment with cis-DDP resulted in a concentrationdependent decrease in DNA synthesis, although
low-dose treatment (0.05 and 0.1 μg/ml), with a few exceptions, had no relative inhibitory effect. Likewise, trans-DDP treatments
decreased tritiated thymidine incorporation; however, this inhibitory effect was not as drastic as with corresponding concentrations
of cis-DDP. Scanning electron microscope studies revealed the formation of many giant cells and blebs at all short-term treatment
concentrations of cis-DDP past the 48 h interval. Continuous treatment of cis-DDP at 1 μg/ml concentration produced giant
cells with minute holes, whereas the 5 and 10 μg/ml exposure resulted in the formation of blebs and large holes and reduction
of microvilli past the 48-h treatment period. At higher concentrations the continuous treatment of cis-DDP completely destroyed
the cells. The surface morphology of trans-isomer treated cells, in most instances, resembled the corresponding untreated
control cells. 相似文献
14.
Replicon spacing was measured during the S-phase of the cell cycle in shoot meristems of Silene coeli-rosa L., a long-day (LD) plant, and Pharbitis nil Chois, a short-day (SD) plant to examine the hypothesis that activation of latent origins of DNA replication is a feature
of floral determination. Silene coeli-rosa was germinated and grown in SD for 28 d and then exposed to either a florally inductive combination of 7 LD + 2 SD, the last
day of which coincides with determination of the sepal and stamen whorls, or was germinated and grown in 37 non-inductive
SD. Pharbitis nil was germinated and grown in continuous light (CL) for 5 d and then given either 48 h of inductive darkness followed by 1 d
of CL, the last day of which coincides with determination of the sepal, petal and stamen whorls, or given one of two independent
non-inductive treatments: 48 h dark interrupted by red light (R) + 1 d of CL, or 8 d of CL. Following these treatments, each
batch of plants was exposed to tritiated [methyl-3H]thymidine for 30, 60, 90 or 120 min. Apical domes were dissected, nuclei lysed and prepared as fibre autoradiographs from
which replicon size was recorded. In S. coeli-rosa, replicon size was in the range 10–15 μm in SD (non-inductive) and 0–5 μm in LD (inductive) while in P. nil it was 10–15 μm in the 48 h dark interrupted by R, 5–10 μm in CL (both non-inductive) but was reduced to 0–5 μm in the 48 h
dark treatment (inductive). Therefore, the recruitment of additional initiation points for DNA replication occurred in both
a LD and a SD plant immediately before the appearance of floral organs. The data are consistent in showing that a shortening
of S-phase, which is a characteristic feature of florally determined shoot meristems for both species, is brought about by
the activation of latent origins of DNA replication.
Received: 14 May 1998 / Accepted: 20 August 1998 相似文献
15.
Berg R Königer M Schjeide BM Dikmak G Kohler S Harris GC 《Photosynthesis research》2006,87(3):303-311
A new microcontroller-based photometric instrument for monitoring blue light dependent changes in leaf transmission (chloroplast movement) was developed based on a modification of the double-beam technique developed by Walzcak and Gabrys [(1980) Photosynthetica 14: 65–72]. A blue and red bicolor light emitting diode (LED) provided both a variable intensity blue actinic light and a low intensity red measuring beam. A phototransistor detected the intensity of the transmitted measuring light. An inexpensive microcontroller independently and precisely controlled the light emission of the bicolor LED. A typical measurement event involved turning off the blue actinic light for 100 μs to create a narrow temporal window for turning on and measuring the transmittance of the red light. The microcontroller was programmed using LogoChip Logo (http://www.wellesley.edu/Physics/Rberg/logochip/) to record fluence rate response curves. Laser scanning confocal microscopy was utilized to correlate the changes in leaf transmission with intercellular chloroplast position. In the dark, the chloroplasts in the spongy mesophyll exhibited no evident asymmetries in their distribution, however, in the palisade layer the cell surface in contact with the overlying epidermis was devoid of chloroplasts. The low light dependent decrease in leaf transmittance in dark acclimated leaves was correlated with the movement of chloroplasts within the palisade layer into the regions previously devoid of chloroplasts. Changes in leaf transmittance were evident within one minute following the onset of illumination. Minimal leaf transmittance was correlated with chloroplasts having retreated from cell surfaces perpendicular to the incident light (avoidance reaction) in both spongy and palisade layers.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
16.
Christofer J. Clemente Jan-Henning Dirks David R. Barbero Ullrich Steiner Walter Federle 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(9):805-814
The contact of adhesive structures to rough surfaces has been difficult to investigate as rough surfaces are usually irregular
and opaque. Here we use transparent, microstructured surfaces to investigate the performance of tarsal euplantulae in cockroaches
(Nauphoeta cinerea). These pads are mainly used for generating pushing forces away from the body. Despite this biological function, shear stress
(force per unit area) measurements in immobilized pads showed no significant difference between pushing and pulling on smooth
surfaces and on 1-μm high microstructured substrates, where pads made full contact. In contrast, on 4-μm high microstructured
substrates, where pads made contact only to the top of the microstructures, shear stress was maximal during a push. This specific
direction dependence is explained by the interlocking of the microstructures with nanometre-sized “friction ridges” on the
euplantulae. Scanning electron microscopy and atomic force microscopy revealed that these ridges are anisotropic, with steep
slopes facing distally and shallow slopes proximally. The absence of a significant direction dependence on smooth and 1-μm
high microstructured surfaces suggests the effect of interlocking is masked by the stronger influence of adhesion on friction,
which acts equally in both directions. Our findings show that cockroach euplantulae generate friction using both interlocking
and adhesion. 相似文献
17.
I. L. Lisovskaya R. I. Volkova V. M. Nesterenko I. M. Shcherbachenko F. I. Ataullakhanov 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2011,5(1):37-44
This study is focused on the effect of the antifungal drug clotrimazole (CLT), also possessing anti-malarial and anticancer
activities, on hemin-induced hemolysis and changes in ion permeability and filter-ability of human erythrocytes. In the presence
of 10 μM clotrimazole, the hemolytic response of erythrocytes to exogenous hemin at concentrations as low as 2–8 μM was considerably
potentiated and their filterability, as measured by passing them through a 5-μm nuclepore filter, dropped sharply. Flavonoids
quercetin (Q) and taxifolin (DHQ), unlike the standard antioxidant Trolox, abolished the effects of clotrimazole, suggesting
that protection of hemin-treated erythrocytes by flavonoids is not related to their antioxidant properties. 相似文献
18.
Hizikia fusiformis thalli experience dynamic incident light conditions during the period of growth. The present study was designed to examine
how changing photon irradiance affects the photosynthesis both in the short and long terms by culturing H. fusiformis under three different light levels: 35 μmol photons m-2 s-1 (low light, LL), 85 μmol photons m-2 s-1 (intermediate light, IL), and 165 μmol photons m-2 s-1 (high light, HL). A similar relative growth rate was observed between IL- and HL-grown algae, but the growth rate was significantly
reduced in LL-grown algae. The photosynthetic rates (P
n) measured at their respective growth light levels were found to be lowest in the thalli grown at LL and highest at HL. However,
LL-grown algae exhibited much higher P
n in comparison with IL- and the HL-grown thalli at the same measuring photosynthetic photon flux density, indicating the photosynthetic
acclimation to low growth light in H. fusiformis. The photosynthesis–light curves showed that LL-grown algae had a highest light-saturating maximum P
n (P
max) in comparison with IL- or HL-grown algae when the photosynthetic rates were expressed on the biomass basis. However, P
max was highest in HL-grown algae compared to IL- or LL-grown algae when the rates were normalized to chlorophyll a. The photosynthesis–inorganic carbon (Ci) response curves were also significantly affected by the growth light conditions.
The highest value of apparent photosynthetic conductance occurred in LL-grown algae while the lowest value in HL-grown algae.
Additionally, the activity of external carbonic anhydrase (CA) tended to increase while the total CA activity inclined to
decrease in H. fusiformis thalli when the growth light level altered from 35 to 165 μmol photons per square meter per second. The external CA inhibitors
showed a higher inhibition in HL-grown algae compared with LL-grown algae. It was proposed that photosynthetic acclimation
to low light condition in H. fusiformis was achieved through an increase in the number of reaction centers and increased capacities of electron transport and of
Ci transport within cells. The ability of photosynthetic acclimation to low light confers H. fusiformis thalli to overcome the environmental low light condition as a result of the attenuation of seawater or self-shading through
enhancing its photosynthetic performance and carbon assimilation necessary for growth. 相似文献
19.
Photosynthesis-light response curves of Gelidium sesquipedale from the west coast of Portugal (Cape Espichel) were determined
at four different depths, 3, 10, 15 and 22 m. Data acquisition using chlorophyll a fluorescence methodology and oxygen electrode
measurements were compared. Response curves were determined over an increasing range of irradiance values (I), from darkness
to 900 μmol photon m-2 s-1 PAR. In general, light response curves obtained for G. sesquipedale showed a similar pattern whether
determined by the chlorophyll fluorescence method or by oxygen evolution. The photosynthetic capacity of G. sesquipedale decreased
with depth, as expected, revealing a ‘sun’ and ‘shade’ acclimation pattern, between shallow and deeper waters.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
Cytoplasmic streaming plays an important role in cell processes since it promotes solute exchange between the cytoplasm and
organelles and enables lateral transport for extensive distances. The role of cyclosis in chloroplast functioning should be
most conspicuous under conditions mimicking natural mosaic illumination and consequent alternation of cell regions with dominant
dark and photosynthetic metabolism. Based on this assumption, we examined the light response curves and the induction kinetics
of fluorescence-based parameters of chloroplast photosynthetic activity on small regions (d ∼ 100 μm) of Chara corallina Klein ex Willd. internodal cells exposed to local and overall illumination under conditions of normal cytoplasmic streaming
and after suppression of cyclosis by cytochalasin B, an inhibitor of actin microfilaments. Under control conditions, the whole
cell illumination caused non-photochemical quenching (NPQ) of chlorophyll fluorescence, which approached the saturation at
a photon flux density of about 40 μmol/(m2 s). By contrast, illumination of a small (2 mm wide) cell part did not cause significant NPQ at light intensities up to 100
μmol/(m2 s), indicating that the chloroplast photosynthetic activity was substantially higher under conditions of localized illumination.
After the inhibition of cyclosis by cytochalasin B, the light response curves were represented by nearly identical sigmoid
curves, irrespective of the illumination pattern. When the cyclosis was restored in the cells washed from the inhibitor, the
light response curves measured under overall and localized illumination returned to their original divergent shapes. These
and other data indicate that different photosynthetic activities of chloroplasts in cells exposed to entire and partial illumination
are directly related to the flow of compositionally nonuniform cytoplasm between the cell parts with prevalent photosynthetic
and respiratory metabolism. 相似文献