Protection of Photosystem II by Light in Heat-Stressed Pea Leaves

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1133-1141 ◽  
Author(s):  
Michel Havaux ◽  
Reto J. Strasser
Keyword(s):  
Steady State ◽  
Reaction Centers ◽  
Thermal Dissipation ◽  
Short Exposure ◽  
Variable Fluorescence ◽  
Ps Ii ◽  
Heat Injury ◽  
Actinic Light ◽  
Main Effect

Modulated 685-nm chlorophyll fluorescence was measured under steady-state conditions in pea leaves adapted to moderate actinic light. When the measurements were performed after a short exposure to heat (42 °C) in darkness, the maximal (Fm) and steady-state (Fs) fluorescence levels were dramatically and irreversibly quenched whereas the basic fluorescence Fo remained unchanged. Concomitantly , photo synthetic O2 evolution was irreversibly inhibited. Analysis of the fluorescence data suggested that the heat treatment affected primarily the PS II reaction center, with the main effect being presumably an increased thermal dissipation of the excita­tion energy transferred to the reaction centers. In contrast, when heat stress was imposed in the presence of light, the loss of variable fluorescence (Fm-Fo) was much less marked and was fully reversible. In addition , no inhibition of in vivo O2 : evolution was observed when the samples heated in the light were recooled at 25 °C. The results indicate that light acted as an efficient protector of PS II against heat injury.

Chlorophyll fluorescence quenching by oxygen in plants

1981 ◽  
Vol 59 (2) ◽  
pp. 190-198 ◽  
Author(s):  
William Vidaver ◽  
Konrad Colbow ◽  
Gordon Hall ◽  
Silvia Wessel
Keyword(s):  
Fluorescence Quenching ◽  
Fluorescence Yield ◽  
Reaction Centers ◽  
Variable Fluorescence ◽  
Chlorophyll Fluorescence Quenching ◽  
Sensitive Phase ◽  
Feedback Regulator ◽  
Quenching By Oxygen ◽  
Bean Leaves

Three distinct phases of chlorophyll a fluorescence quenching were observed in green plants by applying O2 pressures of up to 400 atm. These phases are interpreted as indications of three different mechanisms of O2 quenching. The most sensitive phase is dependent on intersystem electron transport. For dark-adapted bean leaves this fluorescence was quenched to half the initial yield with an O2 pressure of about 3 atm. The second mechanism was observed with 3-(3,4)dichlorophenyl)-1,1-dimethylurea (DCMU), namely the quenching of variable fluorescence in leaves, chloroplasts, and green algae cells. This effect of O2 is thought to be closely associated with the photochemical system II reaction centers. Half of the variable fluorescence was quenched with about 40 atm of O2. Finally, the antennae pigments are quenched, as observed by the effect of O2 on the O-level fluorescence yield, when all photochemical system II reaction center traps are presumably open. The O2 pressure required for half-quenching in this case was about 400 atm.The possibility that the quenching of fluorescence occurs with O2 concentrations low enough for endogenous O2 to have an effect on in vivo fluorescence was investigated. We suggest that O2 quenches by competing with photochemical system I for electrons derived from water splitting, and may thus function as a feedback regulator of photosynthesis.

scholarly journals Evidence for variable chlorophyll fluorescence of photosystem I in vivo

2021 ◽  
Author(s):  
Ulrich Schreiber ◽  
Christof Klughammer
Keyword(s):  
Photosystem I ◽  
Variable Fluorescence ◽  
Pam Fluorometer ◽  
Actinic Light ◽  
Synechococcus Leopoliensis ◽  
Variable Chlorophyll Fluorescence ◽  
Fluorescence Rise ◽  
Induced Changes ◽  
Light Green

AbstractRoom temperature fluorescence in vivo and its light-induced changes are dominated by chlorophyll a fluorescence excited in photosystem II, F(II), peaking around 685 nm. Photosystem I fluorescence, F(I), peaking around 730 nm, so far has been assumed to be constant in vivo. Here, we present evidence for significant contributions of F(I) to variable fluorescence in the green unicellular alga Chlorella vulgaris, the cyanobacterium Synechococcus leopoliensis and a light-green ivy leaf. A Multi-Color-PAM fluorometer was applied for measurements of the polyphasic fluorescence rise (O-I1-I2-P) induced by strong 440 nm light in a dilute suspension of Chlorella, with detection alternating between emission above 700 nm (F > 700) and below 710 nm (F < 710). By averaging 10 curves each of the F > 700 and F < 710 recordings even small differences could be reliably evaluated. After equalizing the amplitudes of the O-I1 phase, which constitutes a specific F(II) response, the O-I1-I2 parts of the two recordings were close to identical, whereas the I2-P phase was larger in F > 700 than in F < 710 by a factor of 1.42. In analogous measurements with Synechococcus carried out in the dark state 2 using strong 625 nm actinic light, after O-I1 equalization the I2-P phase in F > 700 exceeded that in F < 710 even by a factor of 1.99. In measurements with Chlorella, the I2-P phase and with it the apparent variable fluorescence of PS I, Fv(I), were suppressed by moderate actinic background light and by the plastoquinone antagonist DBMIB. Analogous measurements with leaves are rendered problematic by unavoidable light intensity gradients and the resulting heterogenic origins of F > 700 and F < 710. However, a light-green young ivy leaf gave qualitatively similar results as those obtained with the suspensions, thus strongly suggesting the existence of Fv(I) also in leaves.

Further Studies on Quantifying Photosystem II in vivo by Flash-Induced Oxygen Yield From Leaf Discs

1991 ◽  
Vol 18 (4) ◽  
pp. 397 ◽  
Author(s):  
WS Chow ◽  
AB Hope ◽  
JM Anderson
Keyword(s):  
Steady State ◽  
Photosystem Ii ◽  
Red Light ◽  
Light Activation ◽  
Ps Ii ◽  
Dark Incubation ◽  
Leaf Discs ◽  
Reaction Centres ◽  
Oxygen Yield

It was shown briefly [W. S. Chow, A. B. Hope and J. M. Anderson (1989), Biochirnica et Biophysics Acta, 973, 105-8] that the oxygen evolved per flash from leaf discs, under steady-state flashing conditions and in the presence of background far-red light, gave a valid measure of the number of functional photosystem II (PS II) reaction centres. Further work on this direct and convenient method has been done to optimise conditions for making reliable measurements. It is found that, to obtain the higher estimates of [PS II], corresponding to functionality of practically all PS II reaction centres that bind herbicides, a form of 'light activation' is necessary after a prolonged dark pre-incubation. Without a sufficient number of flashes being given following a long dark incubation, the number of functional PS II reaction centres was underestimated. Provided light activation had occurred, the measured number of functional PS II reaction centres was independent of flash frequencies up to at least 40 Hz. The results strongly suggest that, in steady-state, light-limited photosynthesis, there does not exist any sub- stantial fraction of non-functional or 'slow' PS II reaction centres.

Phosphate Deficiency Increases the Rate Constant of Thermal Dissipation of Excitation Energy by Photosystem II in Intact Leaves of Sunflower and Maize.

1995 ◽  
Vol 22 (3) ◽  
pp. 417 ◽  
Author(s):  
J Jacob
Keyword(s):  
Excitation Energy ◽  
Rate Constant ◽  
Thermal Dissipation ◽  
Phosphate Deficiency ◽  
Photon Flux ◽  
Photochemical Quenching ◽  
Variable Fluorescence ◽  
Psii Photochemistry ◽  
Non Photochemical Quenching

Sunflower (Helianthus annuus L.) and maize (Zea mays L.) plants were grown in controlled environment chambers either with adequate supply or no external supply of inorganic phosphate. On the third fully-expanded leaves, chlorophyll fluorescence from photosystem II (PSII) was measured using a modulated fluorescence measuring system at various photon flux densities at room temperature. Phosphate deficiency resulted in an increase in the coefficient of non-photochemical quenching and a decrease in the coefficient of photochemical quenching of variable fluorescence. The efficiency of excitation energy capture by open PSII reaction centres and quantum yield of PSII photochemistry were decreased with phosphate deficiency. There was a significant effect of phosphate deficiency on in vivo PSII photochemistry which was independent of changes in thylakoid membrane energisation induced by the actinic light. An increase in the non-photochemical quenching of variable fluorescence with phosphate deficiency was due to an increased rate constant of thermal dissipation of excitation energy by PSII. Analyses of fluorescence signals suggest that phosphate deficiency decreased the rate constant of PSII photochemistry as well as the probability of excitation energy transfer from PSII antenna to PSII reaction centre. These effects were more apparent at low photon flux densities than at high photon flux densities. Regulation of energy transduction in the thylakoid and in vivo PSII activity in response to the physical environment of the plant are important aspects of environmental regulation of photosynthesis.

Isolierung von PS II-Partikeln mit in vivo Eigenschaften aus Euglena gracilis, Stamm Z / Isolation of PS II-Particels with in vivo Characteristics from Euglena gracilis, Stamm Z

1982 ◽  
Vol 37 (3-4) ◽  
pp. 256-259 ◽  
Author(s):  
F. Schuler ◽  
P. Brandt ◽  
W. Wießner
Keyword(s):  
Euglena Gracilis ◽  
Fluorescence Emission ◽  
Improved Method ◽  
Ps Ii ◽  
Ps I ◽  
Emission And Absorption Spectra ◽  
Chlorophyll Protein ◽  
Ps Ii Activity ◽  
Photosystem Ii Particles

Abstract An improved method for isolation of (photosystem II)-particles from Euglena gracilis, strain Z was established. PS II-particles isolated by ultrasonic treatment and following differential centrifugation show fluorescence emission and absorption spectra identical with in vivo properties of Euglena gracilis. These PS II-particles have only PS II-activity and contain CP a, the typical chlorophyll-protein-complex of PS II. No contamination of PS I-components are detectable.

scholarly journals Inducible ablation of mouse Langerhans cells diminishes but fails to abrogate contact hypersensitivity

2005 ◽  
Vol 169 (4) ◽  
pp. 569-576 ◽  
Author(s):  
Clare L. Bennett ◽  
Erwin van Rijn ◽  
Steffen Jung ◽  
Kayo Inaba ◽  
Ralph M. Steinman ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
Steady State ◽  
Diphtheria Toxin ◽  
Langerhans Cells ◽  
Contact Hypersensitivity ◽  
Relative Importance ◽  
Skin Immunity

Langerhans cells (LC) form a unique subset of dendritic cells (DC) in the epidermis but so far their in vivo functions in skin immunity and tolerance could not be determined, in particular in relation to dermal DC (dDC). Here, we exploit a novel diphtheria toxin (DT) receptor (DTR)/DT-based system to achieve inducible ablation of LC without affecting the skin environment. Within 24 h after intra-peritoneal injection of DT into Langerin-DTR mice LC are completely depleted from the epidermis and only begin to return 4 wk later. LC deletion occurs by apoptosis in the absence of inflammation and, in particular, the dDC compartment is not affected. In LC-depleted mice contact hypersensitivity (CHS) responses are significantly decreased, although ear swelling still occurs indicating that dDC can mediate CHS when necessary. Our results establish Langerin-DTR mice as a unique tool to study LC function in the steady state and to explore their relative importance compared with dDC in orchestrating skin immunity and tolerance.

Noradrenaline-induced calorigenesis in warm- or cold-acclimated rats. In vivo estimation of adrenoceptor concentration of noradrenaline effecting half-maximal response

1980 ◽  
Vol 58 (9) ◽  
pp. 1072-1077 ◽  
Author(s):  
Florent Depocas ◽  
Gloria Zaror-Behrens ◽  
Suzanne Lacelle
Keyword(s):  
Adipose Tissue ◽  
Steady State ◽  
Brown Adipose Tissue ◽  
Maximal Response ◽  
Brown Adipose ◽  
Acclimation Group ◽  
Arterial Plasma ◽  
State Concentration ◽  
Na Uptake

Desmethylimipramine (DMI, 1 mg DMI∙HCl kg−1) and normetanephrine (NMN, 1 μg min−1 g−0.74) were used to inhibit, respectively, neuronal and extraneuronal uptakes of noradrenaline (NA) during calorigenesis induced in barbital-sedated warm-acclimated (WA) or cold-acclimated (CA) rats by infusion of NA, a procedure which mimics the effects of NA released within calorigenic tissues in response to cold exposure. The doses of the inhibitors were selected for maximal effectiveness in potentiating calorigenic response and for minimal side effects. For rats of either acclimation group treated with DMI and NMN, with DMI only, or with neither inhibitor the doses of NA required to evoke approximately half-maximal calorigenic responses were, respectively, 0.5, 1.0, and 3.5 ng min−1 g−0.74. The corresponding steady-state concentrations of NA in arterial plasma averaged 14.3, 21.7, and 43.2 nM in the three groups of WA rats and 10.0, 14.8, and 31.9 nM in the three groups of CA rats. Reduction by NA uptake inhibitors of the circulating levels of NA necessary to stimulate calorigenesis, half-maximally, presumably in brown adipose tissue, indicates a reduction in the steepness of the NA concentration gradient between capillary plasma and synaptic clefts in that tissue. The steady-state concentration of NA in blood plasma of rats treated with DMI and NMN and infused with NA at a dose of 0.5 ng min−1 g−0.74 (~1 × 10−8 M) is a good estimate of the NA concentration required at calorigenic adrenoceptors to effect half-maximal activation. Presumably, this concentration is also an estimate of that resulting from NA released at nerve endings during cold-induced activation of nonshivering thermogenesis at half-maximal rates in brown adipose tissue.

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