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21.
Photosynthetically active vesicles prepared from Chlamydomonas reinhardtii retained a light-dependent glutamate synthase activity which was highly specific for 2-oxoglutarate (Km=2.1 mM) and L-glutamine (Km=0.9 mM) as amido group acceptor and donor respectively. This activity was inhibited by azaserine, p-hydroxymercuribenzoate and 3-(p-chlorophenyl)-1,1-dimethyl urea.Light-dependent synthesis of glutamate was also obtained by coupling Chlamydomonas photosynthetic particles to purified ferredoxin-glutamate synthase, using ascorbate and 2,6-dichlorophenol-indophenol as electron donor. This system was also specific for 2-oxoglutarate (Km=1 mM) and L-glutamine (Km=0.8 mM) as substrates, and was stimulated by dithioerythritol. Azaserine and p-hydroxymercuribenzoate, but not 3-(p-chlorophenyl)-1,1-dimethyl urea, inhibited the reconstituted activity; high concentrations of 2-oxoglutarate were inhibitory.Abbreviations A
Absorbance
- CCP
p-Trichlorometoxi-carbonylcyanide-phenylhydrazone
- Chl
Chlorophyll
- CMU
3-(p-Chlorophenyl)-1,1-dimethyl urea
- DPIP
2,6-Dichlorophenol-indophenol
- DTE
Dithioerythritol
- MSX
L-Methionine, D-L, sulfoximine
- MV
Methyl viologen 相似文献
22.
The phosphate metabolism of Platymonas subcordiformis was investigated by 31P-NMR spectroscopy with special attention on the effect of external pH. Glycolyzing cells and cells energized by respiration or photosynthesis gave spectra dependent upon their metabolic state. The transition from deenergized to energized states is accompanied by a shift of cytoplasmic pH from 7.1–7.4, an increase of ATP level and-in well energized cells-the appearance of a new signal tentatively assigned to phosphoarginine.The spectra remain stable over a wide range of external pH. Cytoplasmic pH is well regulated in respiring cells for external pH in the range 5.3–12.3. The typical 0.4 units difference of internal pH in energized as compared to deenergized cells is not affected by external pH in the range 6–12. The intensity of a signal attributed to PEP is markedly increased at high external pH. pH regulation is less efficient below external pH of 6 in deenergized cells. Below pH 3.8 oxidative phosphorylation ceases. Upon raising cytoplasmic pH to 7.4 in deenergized cells polyphosphate chains start to disintegrate.Abbreviations PEP
Phosphoenolpyruyate
- P
i
inorganic phosphate
- PP
i
inorganic pyrophosphate
- poly P
polyphosphates
- PP-1, PP-2, PP-3
terminal, second, and third phosphate residue of polyphosphates
- PP-4
core phosphate residues of polyphosphates
- pH
i
, pH
o
internal (cytoplasmic) and external pH
- NTP/NDP
nucleotide triphosphate/-diphosphate
- S/N
signal to noise ratio 相似文献
23.
Comparison of the effect of excessive light on chlorophyll fluorescence (77K) and photon yield of O2 evolution in leaves of higher plants 总被引:10,自引:0,他引:10
High-light treatments (1750–2000 mol photons m–2 · s–1) of leaves from a number of higher-plant species invariably resulted in quenching of the maximum 77K chlorophyll fluorescence at both 692 and 734 nm (F
M, 692 and F
M, 734). The response of instantaneous fluorescence at 692 nm (F
O, 692) was complex. In leaves of some species F
O, 692 increased dramatically in others it was quenched, and in others yet it showed no marked, consistent change. Regardless of the response of F
O, 692 an apparently linear relationship was obtained between the ratio of variable to maximum fluorescence (F
V/F
M, 692) and the photon yield of O2 evolution, indicating that photoinhibition affects these two variables to approximately the same extent. Treatment of leaves in a CO2–free gas stream containing 2% O2 and 98% N2 under weak light (100 mol · m–2 · s–1) resulted in a general and fully reversible quenching of 77K fluorescence at 692 and 734 nm. In this case both F
O, 692 and F
M, 692 were invariably quenched, indicating that the quenching was caused by an increased non-radiative energy dissipation in the pigment bed. We propose that high-light treatments can have at least two different, concurrent effects on 77K fluorescence in leaves. One results from damage to the photosystem II (PSII) reaction-center complex and leads to a rise in F
O, 692; the other results from an increased non-radiative energy dissipation and leads to quenching of both F
O, 692 and F
M, 692 This general quenching had a much longer relaxation time than reported for pH-dependent quenching in algae and chloroplasts. Sun leaves, whose F
V/F
M, 692 ratios were little affected by high-light exposure in normal air, suffered pronounced photoinhibition when the exposure was made under conditions that prevent photosynthetic gas exchange (2% O2, 0% CO2). However, they were still less susceptible than shade leaves, indicating that the higher capacity for energy dissipation via photosynthesis is not the only cause of their lower susceptibility. The rate constant for recovery from photoinhibition was much higher in mature sun leaves than in mature shade leaves, indicating that differences in the capacity for continuous repair may in part account for the difference in their susceptibility to photoinhibition.Abbreviations and symbols kDa
kilodalton
- LHC-II
light-harvesting chlorophyll-protein complex
- PFD
photon flux density (photon fluence rate)
- PSI, PSII
photosystem I, II
-
F
O, F
M, F
V
instantaneous, maximum, variable fluorescence emission
-
absorptance
-
a
photon yield of O2 evolution (absorbed light)
C.I.W.-D.P.B. Publication No. 925 相似文献
24.
Measurement of the light response of photosynthetic CO2 uptake is often used as an implement in ecophysiological studies. A method is described to calculate photosynthetic parameters, such as the maximum rate of whole electron transport and dissimilative respiration in the light, from the light response of CO2 uptake. Examples of the light-response curves of flag leaves and ears of wheat (Triticum aestivum cv. ARKAS) are shown.Abbreviations and symbols A
net photosynthesis rate
-
D
1
rate of dissimilative respiration occurring in the light
-
f
loss factor
-
I
incident PPFD
-
I
effective absorbed PPFD
-
J
rate of whole electron transport
-
J
m
maximum rate of whole electron transport
-
p
c
intercellular CO2 partial pressure
- PPFD
photosynthetic photon flux density
-
q
effectivity factor for the use of light (electrons/quanta)
-
absorption coefficient
-
I
*
CO2 compensation point in the absence of dissimilative respiration (bar)
-
II
conversion factor for calculation of CO2 uptake from the rate of whole electron transport
-
convexity factor
Gas-exchange rates relate to the projective area and are given in mol·m-2·s-1. Electron-transport rates are given in mol electrons·m-2·s-1; PPFD is given in mol quanta·m-2·s-1. 相似文献
25.
When detergent-derived photosystem II (PSII) membranes are treated with CaCl2 to remove the three extrinsic proteins associated with the O2-evolving complex, the resulting membranes (CaPSII) can still catalyze water oxidation if sufficient Ca2+ and Cl- are present. When CaPSII membranes are exposed to single turnover flashes on an O2 rate electrode, anomalous O2 is produced by the first two flashes. The addition of catalase to the membrane suspension completely inhibits O2 produced by the first two flashes, but not by subsequent flashes. Exogenous H2O2 stimulates anomalous O2 production by the first few flashes in CaPSII membranes, but not in control PSII membranes. Diuron (DCMU) does not inhibit H2O2-stimulated O2 production by the first flash. However, it does inhibit the O2 yield of all subsequent flashes, indicating that all flash-induced O2 signals in CaPSII membranes are dependent on photosystem II electron transport. H2O2 stimulation of O2 yields is inhibited in Tris-, heat-, and EDTA-(ethylenediaminetetraacetic acid)-treated CaPSII. In the presence of high salt, H2O2 (but not EDTA) treatment of CaPSII, extracts Mn functional in normal photosynthetic O2 evolution. The addition of exogenous Mn2+ reconstitutes anomalous O2 production in Tris-and H2O2/EDTA-treated CaPSII preparations but only in the presence of H2O2. Anomalous H2O2-stimulated O2 production can be observed both with a Clark electrode (steady state) and an O2 rate electrode (flash sequence). The mechanism involves electron donation from H2O2, mediated by free Mn2+, to PSII, and the 33-kDa extrinsic protein under some conditions can block this process. Since H2O2 can remove functional Mn from CaPSII membranes, its presence can convert functional Mn to the Mn2+ mediator state required for anomalous O2 production. EDTA binds Mn in CaPSII disrupted by H2O2 and prevents anomalous O2 evolution.Abbreviations CaPSII
a PSII preparation washed with approximately 1M CaCl2
- Chl
chlorophyll
- DCBQ
2,6-dichloro-p-benzoquinone
- DCMU (diuron)
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- EDTA
ethylenediaminetetraacetic acid
- MES
2-[N-morpholino]-ethanesulfonic acid
- PSII
a detergent-derived photosystem II membrane preparation
- RC
reaction center
- Tris
tris(hydroxymethyl)-aminomethane
- Yn
oxygen rate electrode flash yield resulting from the nth flash of a sequence of single turnover flashes of light
Operated by the Midwest Research Institute for the U.S. Department of Energy under contract DE-AC02-83CH10093. 相似文献
26.
27.
The effects of ultraviolet-B radiation on loblolly pine. I. Growth, photosynthesis and pigment production in greenhouse-grown seedlings 总被引:5,自引:0,他引:5
One-year old loblolly pine ( Pinus taeda L.) seedlings were grown in an unshaded greenhouse for 7 months under 4 levels of ultraviolet-B (UV-B) radiation simulating stratospheric ozone reductions of 16, 25 and 40% and included a control with no UV-B radiation. Periodic measurements were made of growth and gas exchange characteristics and needle chlorophyll and UV-B-absorbing-compound concentrations. The effectiveness of UV-B radiation on seedling growth and physiology varied with the UV-B irradiance level. Seedlings receiving the lowest supplemental UV-B irradiance showed reductions in growth and photosynthetic capacity after only 1 month of irradiation. These reductions persisted and resulted in lower biomass production, while no increases in UV-B-absorbing compounds in needles were observed. Seedlings receiving UV-B radiation which simulated a 25% stratospheric ozone reduction showed an increase in UV-B-absorbing-compound concentrations after 6 months, which paralleled a recovery in photosynthesis and growth after an initial decrease in these characteristics. The seedlings grown at the highest UV-B irradiance (40% stratospheric ozone reduction) showed a more rapid increase in the concentration of UV-B-absorbing compounds and no effects of UV-B radiation on growth or photosynthetic capacity until after 4 months at this irradiance. Changes in photosynthetic capacity were probably the result of direct effects on light-dependent processes, since no effects were observed on either needle chlorophyll concentrations or stomatal conductance. Further studies are necessary to determine whether these responses persist and accumulate over subsequent years. 相似文献
28.
Yuichi Takeuchi Megumi Akizuki Hideyuki Shimizu Noriaki Kondo Kiyoshi Sugahara 《Physiologia plantarum》1989,76(3):425-430
Cucumber ( Cucumis sativus L. cv. Natsusairaku 3) seedlings were grown in a growth cabinet under UV-B (290–320 nm) irradiation (equivalent to the UV-B radiation normally incident at Tokyo, 36°N latitude, during clear sky conditions in mid-april on a weighted daily fluence basis) and a UV-B-free control condition. UV-B irradiation inhibited the growth of the cotyledons, i.e. the increase in area, and increase in fresh and dry weights of the cotyledons. The greatest inhibition rate was observed in the increase in area, causing a significant increase in specific leaf weight (the ratio of weight to area). UV-B irradiation had no significant effect on DNA and RNA contents in the cotyledons, but decreased protein content slightly. In contrast, the irradiation reduced the amounts of organic acids and soluble sugars, indicating that primary carbon metabolism was very sensitive to UV-B radiation. UV-B irradiation lowered the photosynthetic activity in the cotyledons without any effect on chlorophyll content and respiratory activity. These results indicate that UV-B radiation at the ambient level may act as a physiological stress in some UV-sensitive plants. 相似文献
29.
The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention
in recent years. However, insufficient information exists on the coordination of transpiration and CO2 uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration
(E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and
first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas
exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and
fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed
for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf
age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial
leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO2 mmol−1 H2O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in
stomatal conductance (gs·H2O) since decreases in gs·H2O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along
the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these
findings are presented in relation to light competition within the plant canopy during development. 相似文献
30.
Alan Scaife 《Plant and Soil》1989,114(1):139-141
A simple simulation model is described to account for the rates at which plants take up nitrate and reduce it to protein. It is based on the pump and leak principle, with the pump working at a constant rate per unit sap volume provided that there is an adequate concentration of nitrate at the root surface. The rate of leakage is assumed to be proportional to the concentration difference between the inside and the outside of the plant. Nitrogen is removed from the plant nitrate pool (the buffer) at a constant fraction of the photosynthesis rate. When applied to data for the diurnal variation in nitrate uptake by ryegrass, the model predicts an uptake pattern similar to that actually observed, with a time lag of about 5 hours between photosynthesis and uptake. 相似文献