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41.
The photosynthetic behaviour ofDunaliella viridis has been studied under a combination of three variables: irradiance (0–900 mol m–2 s–1), temperature (15, 23, 31, 38, 42 °C) and nitrogen concentration (0.05, 0.5, 1.5, 5, 10 mM NO
3
-
) at a salinity of 2 M NaCl.The highest rates of photosynthesis have been found at 31 °C and a nitrate concentration of 10 mM. There exists a synergistic effect between temperature and nitrogen availability on the photosynthesis ofD. viridis; under nitrogen deficiency oxygen evolution is low, even null at high temperature. The interaction between these two variables of control occurs in a multiplicative way. There is also a general increase in photosynthetic pigments following the increase in nitrogen concentration in the culture medium. The normalization of net photosynthesis data in relation to chlorophylla shows that nitrogen concentration makes an indirect control of the photosynthetic rate ofD. viridis through the variation of pigment concentration. 相似文献
42.
Valerio Vidotto Giuseppe Picerno Stefano Caramello Giovanna Paniate 《Mycopathologia》1988,104(3):129-135
The passage between the yeast and mycelial forms of Candida albicans B 311-10 was studied by using the minimal syntehtic medium of Shepherd et al. [19] modified without biotin and with low glucose concentrations. It was observed that biotin, aminoacids and particularly pH are not important factors in the dimorphism of C. albicans. The only factor of notable importance in the passage of yeast form to mycelial form in C. albicans was glucose concentration. 相似文献
43.
Abstract. Portulacaria afra (L.) Jacq. is a perennial facultative CAM species showing a seasonal shift from C3 to CAM photosynthesis. The shift to CAM during the summer occurs despite continued irrigation of the plants. The authors examined the hypothesis that the seasonal shift to CAM occurred because of low transient water potentials. They measured changes in whole leaf water, osmotic and pressure potentials over the course of the shift. They also studied changes in enzyme activity to ascertain if PEP carboxylase and PEP carboxykinase were induced during the seasonal shift to CAM. Water potentials were high, from -0.1 to -0.5 MPa, predawn and midday, when the C3 pathway of photosynthesis was utilized. Osmotic potentials were constant, from -0.7 to - 0.8 MPa, indicating very little change in turgor. P. afra shifted to CAM indicated by large diurnal acid fluctuations (300 400 meq m−2 ) despite C3 -like predawn water potentials. Midday water potentials usually decreased 0.2-0.7 MPa, while the osmotic potential remained unchanged or decreased slightly. Thus, a midday loss of turgor was associated with the use of the CAM pathway. The results support the hypothesis that the induction of CAM occurred due to low transient water potentials and may be partially mediated through the loss of turgor. The shift to CAM is only a partial induction with PEP carboxykinase showing high activity all year round while PEP carboxylase increases three-to five-fold over C3 levels. Relatively high levels of CAM enzyme activity enables the utilization of the CAM pathway in the winter and spring in response to high daytime temperatures and increased evaporative demand. These results would lead to an increase in water use efficiency during such periods when compared to other inducible CAM species. 相似文献
44.
Ilhan Olmez M. Cetin Gulovali Glen E. Gordon Robert I. Henkin 《Biological trace element research》1988,17(1):259-270
Although various proteins and some electrolytes have been measured in human saliva, little systematic data about the major
and minor elemental components of this body fluid have been obtained. In order to obtain such data, concentrations of C, Na,
P, Cl, K, Ca, Sc, Cr, Fe, Co, Zn, Se, Br, Rb, Sb, I, and Cs in human parotid saliva were measured by instrumental nuclear
methods. The data obtained confirmed the relative lack of Zn in saliva of patients with hypogeusia (decreased taste acuity)
and suggested that concentrations of Na, Cl, Br, and Ca followed the order: normals > hypogeusia > hyposmia (decreased smell
acuity). To compare concentrations of elements in saliva with those in blood and urine, absolute concentrations were normalized
to that of Na through the use of a concept called an enrichment factor. On this basis, parotid saliva is relatively depleted
in Se, Zn, and Fe and enriched for most other elements relative to blood plasma indicating that the fluid is not simply a
transudate of blood plasma. Using this same technique, saliva composition was found more similar to urine than blood plasma,
being relatively depleted in Se, Cs, and Co, being enriched in I, Br, and Cr and having about the same relative concentrations
of P, Cl, Zn, Fe, Ca, K, and Rb. As the total body concentrations of many of the enriched elements in saliva are extremely
small, their enrichment in saliva suggests special roles for these elements in the oral cavity. Because of its accessibility,
ease of collection, and interaction with some body constituents, saliva represents a useful, albeit neglected, tool in the
diagnosis of some physiological and pathological changes in body function and in understanding important aspects of trace
metal metabolism. 相似文献
45.
Mark L. Paddock Scott H. Rongey Edward C. Abresch George Feher Melvin Y. Okamura 《Photosynthesis research》1988,17(1-2):75-96
Many herbicides that inhibit photosynthesis in plants also inhibit photosynthesis in bacteria. We have isolated three mutants of the photosynthetic bacterium Rhodobacter sphaeroides that were selected for increased resistance to the herbicide terbutryne. All three mutants also showed increased resistance to the known electron transfer inhibitor o-phenanthroline. The primary structures of the mutants were determined by recombinant DNA techniques. All mutations were located on the gene coding for the L-subunit resulting in these changes Ile229 Met, Ser223 Pro and Tyr222 Gly. The mutations of Ser223 is analogous to the mutation of Ser264 in the D1 subunit of photosystem II in green plants, strengthening the functional analogy between D1 and the bacterial L-subunit. The changed amino acids of the mutant strains form part of the binding pocket for the secondary quinone, Q
b
. This is consistent with the idea that the herbicides are competitive inhibitors for the Q
b
binding site. The reaction centers of the mutants were characterized with respect to electron transfer rates, inhibition constants of terbutryne and o-phenanthroline, and binding constants of the quinone UQ0 and the inhibitors. By correlating these results with the three-dimensional structure obtained from x-ray analysis by Allen et al. (1987a, 1987b), the likely positions of o-phenanthroline and terbutryne were deduced. These correspond to the positions deduced by Michel et al. (1986a) for Rhodopseudomonas viridis.Abbreviations ATP
adenosine 5-triphosphate
- Bchl
bacteriochlorophyll
- Bphe
bacteriopheophytin
- bp
basepair
- cyt c2+
reduced form of cytochrome c
- DEAE
diethylami-noethyl
- EDTA
ethylenediamine tetraacetic acid
- Fe2+
non-heme iron atom
- LDAO
lauryl dimethylamine oxide
- Pipes
piperazine-N,N-bis-2-ethane-sulfonic acid
- PSII
photosystem II
- RC
reaction center
- SDS
sodium dodecylsulfate
- Tris
tris(hydroxy-methyl)aminomethane
- UQ0
2,3-dimethoxy-5-methyl benzoquinone
- UQ10
ubiquinone 50 相似文献
46.
Gas exchange and abscisic acid content of Digitalis lanata EHRH. have been examined at different levels of plant water stress. Net photosynthesis, transpiration and conductance of attached leaves declined rapidly at first, then more slowly following the withholding of irrigation. The intercellular partial pressure of CO2 decreased slightly. The concentration of 2-cis(S)ABA increased about eight-fold in the leaves of non-irrigated plants as compared with well-watered controls. A close linear correlation was found between the ABA content of the leaves and their conductance on a leaf area basis. In contrast, the plot of net assimilation versus ABA concentration was curvilinear, leading to an increased efficiency of water use during stress. After rewatering, photosynthesis reached control values earlier than transpiration, leaf conductance and ABA content. From these data it is concluded that transpiration through the stomata is directly controlled by the ABA content, whereas net photosynthesis is influenced additionally by other factors.Possible reasons for the responses of photosynthesis and water use efficiency to different stress and ABA levels are discussed.Abbreviations A
net CO2 assimilation
- ABA
abscisic acid
- Ci
intercellular CO2 concentration
- g
stomatal conductance
- T
transpiration
- WUE
water use efficiency 相似文献
47.
The light-harvesting complex of photosystem II (LHC II) contains one major (LHC IIb) and at least three minor chlorophyll-protein components. The apoproteins of LHC IIb (LHCP) are encoded by nuclear genes and synthesized in the cytoplasm as a higher molecular weight precursor(s) (pLHCP). Several genes coding for pLHCP have been cloned from various higher plant species. The expression of these genes is dependent upon a variety of factors such as light, the developmental stage of the plastids and the plant. After its synthesis in the cytoplasm, pLHCP is imported into plastids, inserted into thylakoids, processed to its mature form, and assembled into LHC IIb. The pathway of assembly of LHC IIb in the thylakoid membranes is currently being investigated in several laboratories. We present a model that gives some details of the steps in the assembly process. Many of the steps involved in the synthesis and assembly are dependent on light and the stage of plastid development.Abbreviations PS
Photosystem
- LHC II
Light-harvesting complex of PS II
- LHCP
Apoproteins of LHC IIb
- pLHCP
Precursor of LHCP
- PAGE
Polyacrylamide gel electrophoresis 相似文献
48.
49.
Since the thylakoid membranes of an active chloroplast are constantly exposed to the electric fields generated by the electron transport system inside the membranes, we have studied the effects of pretreating chloroplasts of spinach ( Spinacia oleracea L.) leaves with an external AC (alternating current) electric field on their electron transport system. It was found that a few minutes electric field pretreatment (333 V cm-1 across chloroplast samples), especially at low frequency, irreversibly inhibited the activity of photosystem II (PSII), but under certain conditions, stimulated that of photosystem I (PSI). From the measurements of fluorescence from PSII, we ascribe the inhibition to a lesion close to its reaction center P680, leading to increased dissipation of excitation energy to heat. The effect on PSI was investigated by the reduction of its reaction center, P700 by various artificial donors. We suggest that the stimulative effect can be attributed to a positive shift of the surface charge density of thylakoid membranes that brings about an increase in the accessibility of exogenous electronegative donors. 相似文献
50.
While diurnal cycles in nitrogen fixation rates are sometimes assumed to result from diurnal variation in photosynthetically active radiation, contradicting evidence exists that indicate soil temperature is the primary environmental influence. These studies assessed the significance of temperature on soybean nitrogen fixation under field conditions. Two groups of intact field-grown soybean plants, one at ambient and the other exposed to a 10°C diurnal variation in soil temperature, were nondestructively assayed for acetylene reduction rates. Activity was closely associated with soil temperature (R2=0.85), even when temperature was 12 h out of phase with ambient. Data were also obtained to determine if the effects of rhizosphere temperature on nitrogen fixation are mediated through an effect on the nodule oxygen permeability. Nodule oxygen permeability of intact, aeroponically grown soybean was closely correlated with the diurnal changes in temperature (R2=0.90). 相似文献