Chlorophyll Fluorescence Induction Research Articles

A T-DNA insertion mutant of AtHMA1 gene encoding a Cu transporting ATPase in Arabidopsis thaliana has a defect in the water–water cycle of photosynthesis

The water–water cycle is the electron flow through scavenging enzymes for the reactive species of oxygen in chloroplasts, and is proposed to play a role in alternative electron sink in photosynthesis. Here we showed that the water–water cycle is impaired in the T-DNA insertion mutant of AtHMA1 gene encoding a Cu transporting ATPase in chloroplasts. Chlorophyll fluorescence under steady state was not affected in hma1, indicating that photosynthetic electron transport under normal condition was not impaired. Under electron acceptor limited conditions, however, hma1 showed distinguished phenotype in chlorophyll fluorescence characteristics. The most severe phenotype of hma1 could be observed in high (0.1%) CO 2 concentrations, indicating that hma1 has the defect other than photorespiration. The transient increase of chlorophyll fluorescence upon the cessation of the actinic light as well as the NPQ induction of chlorophyll fluorescence revealed that the two pathways of cyclic electron flow around PSI, NDH-pathway and FQR-pathway, are both intact in hma1. Based on the NPQ induction under 0% oxygen condition, we conclude that the water–water cycle is impaired in hma1, presumably due to the decreased level of Cu/Zn SOD in the mutant. Under high CO 2 condition, hma1 exhibited slightly higher NPQ induction than wild type plants, while this increase of NPQ in hma1 was suppressed when hma1 was crossed with crr2 having a defect in NDH-mediated PSI cyclic electron flow. We propose that the water–water cycle and NDH-mediated pathways might be regulated compensationally with each other especially when photorespiration is suppressed.

Enhanced protection against oxidative stress in an astaxanthin-overproduction Haematococcus mutant (Chlorophyceae)

Many unicellular green algae can become yellow or red in various natural habitats due to mass accumulation of a secondary carotenoid, such as lutein, or astaxanthin. The accumulation of secondary carotenoids is generally thought to be a survival strategy of the algae under photo-oxidative stress or other adverse environmental conditions. The physiological role of the carotenoids in stress response is less well understood at the subcellular or molecular level. In this study, a stable astaxanthin overproduction mutant (MT 2877) was isolated by chemical mutagenesis of a wild type (WT) of the green microalga Haematococcus pluvialis Flotow NIES-144. MT 2877 was identical to the WT with respect to morphology, pigment composition, and growth kinetics during the early vegetative stage of the life cycle. However, it had the ability to synthesize and accumulate about twice the astaxanthin content of the WT under high light, or under high light in the presence of excess amounts of ferrous sulphate and sodium acetate. Under stress, the mutant exhibited higher photosynthetic activities than the WT, based on considerably higher chlorophyll fluorescence induction, chlorophyll autofluorescence intensities, and oxygen evolution rates. Cell mortality caused by stress was reduced by half in the mutant culture compared with the WT. Enhanced protection of the mutant against stress is attributed to its accelerated carotenogenesis and accumulation of astaxanthin. Our results suggest that MT 2877, or other astaxanthin overproduction Haematococcus mutants, may offer dual benefits, as compared with the wild type, by increasing cellular astaxanthin content while reducing cell mortality during stress-induced carotenogenesis.

Retrieving quantum yield of sun-induced chlorophyll fluorescence near surface from hyperspectral in-situ measurement in productive water

Magnitude and quantum yield (eta) of sun induced chlorophyll fluorescence are determined in widely varying productive waters with chlorophyll concentrations from 2- 200 mg/m(3). Fluorescence was estimated using linear fitting of in-situ measured surface reflectance with elastic and inelastic reflectance spectra. Elastic reflectance spectra were obtained from Hydrolight simulations with measured absorption and attenuation spectra as inputs. Eta is then computed based on a depth integrated fluorescence model and compared with Hydrolight calculation results. Despite the large variability of coastal environments examined the ? values are found to vary over a relatively narrow range 0.1%-1% with mean values of 0.33%+/-0.17%.

Accumulation of overproduced ferritin in the chloroplast provides protection against photoinhibition induced by low temperature in tobacco plants

Wild-type tobacco plants (Nicotiana tabacum L. cv. Petit Havanna line SR1) and plants transformed with full-length alfalfa ferritin cDNA with the chloroplast transit peptide under the control of a Rubisco small subunit gene promoter (C3 and C8) were cold-treated at 0 degrees C with continuous light (250 micromol m(-2)s(-1)). These transgenic plants had higher chlorophyll content and higher F(v)/F(m) chlorophyll-a fluorescence induction parameters than wild-type plants after 2 or 3d of cold treatment in C3 and C8 transgenic plants, respectively. Thermoluminescence studies on the high-temperature bands suggest that these plants suffered less oxidative damage in comparison to the wild-type genotype. The present experiments provide evidence that transgenic tobacco lines overexpressing alfalfa ferritin, which is accumulated in the chloroplasts, may show higher tolerance to various stress factors, generating ROS including low temperature-induced photoinhibition.

Effects of heat stress on PSII photochemistry in a cyanobacterium Spirulina platensis

The effects of heat stress (30–50 °C) on photosystem II (PSII) photochemistry in a cyanobacterium Spirulina platensis grown at 30 °C were studied by measuring chlorophyll fluorescence induction kinetics and thermoluminescence. Heat stress inhibited significantly the maximum efficiency of PSII photochemistry. An investigation of the kinetics of flash-induced fluorescence yield decay revealed that heat stress caused a shift of the equilibrium towards Q A but showed no effect on the kinetics of flash-induced fluorescence yield decay in the presence of DCMU. An analysis of polyphasic rise of fluorescence transients indicated that heat stress induced a decrease in the total number of PSII active reaction centers. Thermoluminescence measurements demonstrated that the B band in Spirulina cells corresponding to the S 2Q B − state consisted of two different components, the B 32 and the B 24 bands with the peak temperatures at 32 and 24 °C, respectively. The intensity of the B 32 band and the B 24 band decreased significantly with increasing temperature but the decrease of the intensity of the B 24 band was much greater than that of the B 32 band. There were no significant changes in the peak temperatures of the B 24 and B 32 bands. The intensity of the Q band corresponding to the recombination of the S 2Q A − charge pair decreased significantly with increasing temperature. The period-four oscillation of the B band was significantly damped at temperatures higher than 45 °C. The contents of D1 and PsbO proteins decreased with increasing temperature. The results in this study suggest that heat stress shows no effects on the stability of the S 2Q A − and S 2Q B − states and that the different populations of the active PSII reaction centers show different sensitivity to heat stress in S. platensis cells.

Temporal characteristics of chlorophyll fluorescence quenching and dissolved oxygen concentration as indicators of photosynthetic activity in Chlorella emersonii

A simple chlorophyll fluorescence (CF) measuring system has been implemented to study temporal characteristics of chlorophyll fluorescence induction (CFI) in dark-adapted freshwater algal cultures of Chlorella emersonii. There were two different decay time constants describing the CF quenching: τ0 (the faster) and τ1 (the slower) with amplitudes A0 and A1, respectively. The relative amplitude of the faster quenching component decreased once the sample was subject to deprivation from dissolved oxygen (DO). The DO concentration of samples was monitored to validate the effects of deprivation from air contact for up to 7 d and to the effect of adding DCMU to the culture (herbicide for blocking electron transport of photosystem 2). CFI analysis and DO measurements showed that the relative amplitude of A0 to (A0 + A1) and the DO concentration can be used as an indication of relative photosynthetic activity, thus allowing for the possibility to classify the physiological state of algal blooms into active and inactive states.

In vivo target sites of nitric oxide in photosynthetic electron transport as studied by chlorophyll fluorescence in pea leaves.

The role of nitric oxide (NO) in photosynthesis is poorly understood as indicated by a number of studies in this field with often conflicting results. As various NO donors may be the primary source of discrepancies, the aim of this study was to apply a set of NO donors and its scavengers, and examine the effect of exogenous NO on photosynthetic electron transport in vivo as determined by chlorophyll fluorescence of pea (Pisum sativum) leaves. Sodium nitroprusside-induced changes were shown to be mediated partly by cyanide, and S-nitroso-N-acetylpenicillinamine provided low yields of NO. However, the effects of S-nitrosoglutathione are inferred exclusively by NO, which made it an ideal choice for this study. Q(A)(-) reoxidation kinetics show that NO slows down electron transfer between Q(A) and Q(B), and inhibits charge recombination reactions of Q(A)(-) with the S(2) state of the water-oxidizing complex in photosystem II. Consistent with these results, chlorophyll fluorescence induction suggests that NO also inhibits steady-state photochemical and nonphotochemical quenching processes. NO also appears to modulate reaction-center-associated nonphotochemical quenching.

Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genusInga

Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga, Lx levels were high in shade leaves (mostly above 20 mmol mol(-1) chlorophyll) and low in sun leaves. In Virola surinamensis, both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol(-1) chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, Q(A), and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection.

Analysis of initial chlorophyll fluorescence induction kinetics in chloroplasts in terms of rate constants of donor side quenching release and electron trapping in photosystem II

The fluorescence induction F(t) of dark-adapted chloroplasts has been studied in multi-turnover 1 s light flashes (MTFs). A theoretical expression for the initial fluorescence rise is derived from a set of rate equations that describes the sequence of transfer steps associated with the reduction of the primary quinone acceptor Q (A) and the release of photochemical fluorescence quenching of photosystem II (PSII). The initial F(t) rise in the hundreds of mus time range is shown to follow the theoretical function dictated by the rate constants of light excitation (k (L)) and release of donor side quenching (k ( si )). The bi-exponential function shows sigmoidicity when one of the two rate constants differs by less than one order of magnitude from the other. It is shown, in agreement with the theory, that the sigmoidicity of the fluorescence rise is variable with light intensity and mainly, if not exclusively, determined by the ratio between rate of light excitation and the rate constant of donor side quenching release.

Potential impacts of nonalgal materials on water-leaving Sun induced chlorophyll fluorescence signals in coastal waters

It has been suggested that Sun induced chlorophyll fluorescence (SICF) signals could be used to estimate phytoplankton chlorophyll concentration and to investigate algal physiology from space. However, water-leaving SICF is also a product of the ambient light field. In coastal waters both algal and nonalgal materials affect the underwater light field. In this study we examine the independent impacts of varying loads of mineral suspended solids (MSS) and colored dissolved organic materials (CDOM) on water-leaving SICF signals using Hydrolight radiative transfer simulations. We show that SICF signals in coastal waters are strongly influenced by nonalgal materials. Increasing concentrations of CDOM and minerals can reduce the water-leaving SICF per unit chlorophyll by over 50% for the concentration ranges explored here (CDOM = 0 to 1 m(-1) at 440 nm, MSS=0 to 10 g m(-3)). The moderate-resolution imaging spectroradiometer (MODIS) fluorescence line height algorithm is shown to be relatively unaffected by increasing CDOM, but performance is significantly degraded by mineral concentrations greater than 5 g m(-3) owing to increased background radiance levels. The combination of these two effects means that caution is required for the interpretation of SICF signals from coastal waters.

Responses of photosynthetic activity in the drought-tolerant cyanobacterium, Nostoc flagelliforme to rehydration at different temperature

Photosynthetic activity during rehydration at four temperatures (5, 15, 25, 35 °C) was studied in a terrestrial, highly drought-tolerant cyanobacterium, Nostoc flagelliforme. At all the temperatures, the optimum quantum yield F v/ F m increased rapidly within 1 h and then increased slowly during the process of rehydration. The increase in F v/ F m at 25 and 35 °C was larger than that at 5 and 15 °C. In addition, the changes of initial intensity of fluorescence ( F 0) and variable fluorescence ( F v) were more significant at 25 and 35 °C than those at 5 and 15 °C. Chlorophyll a content increased with the increase of temperature during the course of rehydration, with this being more pronounced at 25 and 35 °C. The photosynthetic rates at 25 and 35 °C were higher than those at 5 and 15 °C. Induction of chlorophyll fluorescence with sustained rewetting at 5 and 15 °C had two phases of transformation, whereas at 25 and 35 °C it had a third peak kinetic phase and showed typical chlorophyll fluorescence steps on rewetting for 24 h, representing a normal physiological state. A comparison of the chlorophyll fluorescence parameters, chlorophyll a content, and the chlorophyll fluorescence induction led to the conclusion that N. flagelliforme had a more rapid and complete recovery at 25 and 35 °C than that at 5 and 15 °C, although it could recover its photosynthetic activity at any of the four temperatures.

The PsbP Protein Is Required for Photosystem II Complex Assembly/Stability and Photoautotrophy in Arabidopsis thaliana

Interfering RNA was used to suppress the expression of the genes At1g06680 and At2g30790 in Arabidopsis thaliana, which encode the PsbP-1 and PsbP-2 proteins, respectively, of photosystem II (PS II). A phenotypic series of transgenic plants was recovered that expressed intermediate and low amounts of PsbP. Chlorophyll fluorescence induction and Q(A)(-) decay kinetics analyses were performed. Decreasing amounts of expressed PsbP protein led to the progressive loss of variable fluorescence and a marked decrease in the fluorescence quantum yield (F(V)/F(M)). This was primarily due to the loss of the J to I transition. Analysis of the fast fluorescence rise kinetics indicated no significant change in the number of PS II(beta) centers present in the mutants. Analysis of Q(A)(-) decay kinetics in the absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea indicated a defect in electron transfer from Q(A)(-) to Q(B), whereas experiments performed in the presence of this herbicide indicated that charge recombination between Q(A)(-) and the oxygen-evolving complex was seriously retarded in the plants that expressed low amounts of the PsbP protein. These results demonstrate that the amount of functional PS II reaction centers is compromised in the plants that exhibited intermediate and low amounts of the PsbP protein. Plants that lacked detectable PsbP were unable to survive in the absence of sucrose, indicating that the PsbP protein is required for photoautotrophy. Immunological analysis of the PS II protein complement indicated that significant losses of the CP47 and D2 proteins, and intermediate losses of the CP43 and D1 proteins, occurred in the absence of the PsbP protein. This demonstrates that the extrinsic protein PsbP is required for PS II core assembly/stability.

Validation of photosynthetic-fluorescence parameters as biomarkers for isoproturon toxic effect on alga Scenedesmus obliquus

Photosynthetic-fluorescence parameters were investigated to be used as valid biomarkers of toxicity when alga Scenedesmus obliquus was exposed to isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] effect. Chlorophyll fluorescence induction of algal cells treated with isoproturon showed inactivation of photosystem II (PSII) reaction centers and strong inhibition of PSII electron transport. A linear correlation was found ( R 2 ≥ 0.861) between the change of cells density affected by isoproturon and the change of effective PSII quantum yield ( Φ M′), photochemical quenching ( q P) and relative photochemical quenching ( q P(rel)) values. The cells density was also linearly dependent ( R 2 = 0.838) on the relative unquenched fluorescence parameter (UQF (rel)). Non-linear correlation was found ( R 2 = 0.937) only between cells density and the energy transfer efficiency from absorbed light to PSII reaction center (ABS/RC). The order of sensitivity determined by the EC-50% was: UQF (rel) > Φ M′ > q P > q P(rel) > ABS/RC. Correlations between cells density and those photosynthetic-fluorescence parameters provide supporting evidence to use them as biomarkers of toxicity for environmental pollutants.

Effect of selenate on growth and photosynthesis of Chlamydomonas reinhardtii

Algal communities play a crucial role in aquatic food webs by facilitating the transfer of dissolved inorganic selenium (both an essential trace element and a toxic compound for a wide variety of organisms) to higher trophic levels. The dominant inorganic chemical species of selenium in freshwaters are selenite (SeO 3 2−) and selenate (SeO 4 2−). At environmental concentrations, selenite is not likely to have direct toxic effects on phytoplankton growth [Morlon, H., Fortin, C., Floriani, M., Adam, C., Garnier-Laplace, J., Boudou, A., 2005a. Toxicity of selenite in the unicellular green alga Chlamydomonas reinharditii: comparison between effects at the population and sub-cellular level. Aquat. Toxicol. 73(1), 65–78]. The effects of selenate, on the other hand, are poorly documented. We studied the effects of selenate on Chlamydomonas reinhardtii growth (a common parameter in phytotoxicity tests). Growth inhibition (96-h IC 50) was observed at 4.5 ± 0.2 μM selenate ( p < 0.001), an effective concentration which is low compared to environmental concentrations. Growth inhibition at high selenium concentrations may result from impaired photosynthesis. This is why we also studied the effects of selenate on the photosynthetic process (not previously assessed in this species to our knowledge) as well as selenate's effects on cell ultrastructure. The observed ultrastructural damage (chloroplast alterations, loss of appressed domains) confirmed that chloroplasts are important targets in the mechanism of selenium toxicity. Furthermore, the inhibition of photosynthetic electron transport evaluated by chlorophyll fluorescence induction confirmed this hypothesis and demonstrated that selenate disrupts the photosynthetic electron chain. Compared to the classical ‘growth inhibition’ parameter used in phytotoxicity tests, cell diameter and operational photosynthetic yield were more sensitive and may be convenient tools for selenate toxicity assessment in non-target plants.

Bioenergetic strategy of microalgae for the biodegradation of phenolic compounds—Exogenously supplied energy and carbon sources adjust the level of biodegradation

The biodegradation of phenolic compounds by microalgae seems to be not a simple feature of a particular organism, but mostly a bioenergetic process depending on the growth conditions, especially on the exogenously supplied energy (carbon and light) sources. By using chlorophyll fluorescence induction measurements to estimate the molecular structure and function of the photosynthetic apparatus and therefore the tolerance/sensitivity of microalgae incubated with phenols, it can be assumed that, at least in low concentrations, phenol have no toxic effects on the cultures and can be used as alternative carbon source in them. Halophenols (chlorophenols, bromophenols and iodophenols) are quite toxic for the microalgal cultures. In halophenols the first step of the biodegradation is the split of the halogen substituent (dehalogenation). This is strongly determined by the bond dissociation energy of the corresponding substituent and therefore the energetic requirement for the biodegradation of halophenols increases following the sequence: iodophenol<bromophenol<chlorophenol. Additionally, the meta-position of the halogen on the phenol ring needs more energy than the ortho- and the para-one. These are possible explanations of the fact that the biodegradation of halophenols needs additional energy sources that can be exogenously supplied as organic carbon (glucose) or inorganic carbon (CO(2)).

Radiative and non-radiative charge recombination pathways in Photosystem II studied by thermoluminescence and chlorophyll fluorescence in the cyanobacterium Synechocystis 6803

The mechanism of charge recombination was studied in Photosystem II by using flash induced chlorophyll fluorescence and thermoluminescence measurements. The experiments were performed in intact cells of the cyanobacterium Synechocystis 6803 in which the redox properties of the primary pheophytin electron acceptor, Phe, the primary electron donor, P 680, and the first quinone electron acceptor, Q A, were modified. In the D1Gln130Glu or D1His198Ala mutants, which shift the free energy of the primary radical pair to more positive values, charge recombination from the S 2Q A − and S 2Q B − states was accelerated relative to the wild type as shown by the faster decay of chlorophyll fluorescence yield, and the downshifted peak temperature of the thermoluminescence Q and B bands. The opposite effect, i.e. strong stabilization of charge recombination from both the S 2Q A − and S 2Q B − states was observed in the D1Gln130Leu or D1His198Lys mutants, which shift the free energy level of the primary radical pair to more negative values, as shown by the retarded decay of flash induced chlorophyll fluorescence and upshifted thermoluminescence peak temperatures. Importantly, these mutations caused a drastic change in the intensity of thermoluminescence, manifested by 8- and 22-fold increase in the D1Gln130Leu and D1His198Lys mutants, respectively, as well as by a 4- and 2.5-fold decrease in the D1Gln130Glu and D1His198Ala mutants, relative to the wild type, respectively. In the presence of the electron transport inhibitor bromoxynil, which decreases the redox potential of Q A/Q A − relative to that observed in the presence of DCMU, charge recombination from the S 2Q A − state was accelerated in the wild type and all mutant strains. Our data confirm that in PSII the dominant pathway of charge recombination goes through the P 680 +Phe − radical pair. This indirect recombination is branched into radiative and non-radiative pathways, which proceed via repopulation of P 680 * from 1[P 680 +Ph −] and direct recombination of the 3[P 680 +Ph −] and 1[P 680 +Ph −] radical states, respectively. An additional non-radiative pathway involves direct recombination of P 680 +Q A −. The yield of these charge recombination pathways is affected by the free energy gaps between the Photosystem II electron transfer components in a complex way: Increase of Δ G(P 680 * ↔ P 680 +Phe −) decreases the yield of the indirect radiative pathway (in the 22–0.2% range). On the other hand, increase of Δ G(P 680 +Phe − ↔ P 680 +Q A −) increases the yield of the direct pathway (in the 2–50% range) and decreases the yield of the indirect non-radiative pathway (in the 97–37% range).

Field screening for heat tolerant common bean cultivars (Phaseolus vulgaris L.) by measuring of chlorophyll fluorescence induction parameters

Abstract The temperature induced changes in chlorophyll fluorescence induction parameters (F0, Fm, Fv and their ratios) measured by a PEA analyzer were used to screen for heat-tolerance 12 cultivars and lines of common bean (Phaseolus vulgaris L.) available in the germplasm collections of Maritsa Vegetable Crops Research Institute, Plovdiv, and Institute of Plant Genetic Resources, Sadovo, Bulgaria. The experiments were carried out in a selection field of Maritsa Institute. The measurements were made on six different dates during the bean reproductive period (in June–July) when the temperatures were approximately 26 °C in the morning to and 42 °C at noon. Two lines, known earlier as heat-tolerant were used as controls. We found that most of studied cultivars and lines were heat-sensitive because upon day-course increase of temperatures from 26 °C to 42 °C they revealed statistically significant increase in initial fluorescence (F0), simultaneous decreases in maximum fluorescence (Fm), and in Fv/F0 ratio. Only two cultivars: Ranit and Nerine RS like the heat-tolerant lines preserved F0, Fm and Fv values and Fv/F0 ratio at 42 °C similar to those values at 26 °C. We have considered these two cultivars as heat-tolerant. They have good productivity and been quality and will be used as parental lines in bean breeding program.

Non-Invasive Monitoring of the Light-Induced Cyclic Photosynthetic Electron Flow during Cold Hardening in Wheat Leaves

The effect of irradiance during low temperature hardening was studied in a winter wheat variety. Ten-day-old winter wheat plants were cold-hardened at 5 degrees C for 11 days under light (250 micromol m(-2) S(-1)) or dark (20 micromol m(-2) s(-1)) conditions. The effectiveness of hardening was significantly lower in the dark, in spite of a slight decrease in the Fv/Fm chlorophyll fluorescence induction parameter, indicating the occurrence of photoinhibition during the hardening period in the light. Hardening in the light caused a downshift in the far-red induced AG (afterglow) thermoluminescence band. The faster dark re-reduction of P700+, monitored by 820-nm absorbance, could also be observed in these plants. These results suggest that the induction of cyclic photosynthetic electron flow may also contribute to the advantage of frost hardening under light conditions in wheat plants.

Quantitative analysis of the experimental O–J–I–P chlorophyll fluorescence induction kinetics

Fluorescence induction has been studied for a long time, but there are still questions concerning what the O-J-I-P kinetic steps represent. Most studies agree that the O-J rise is related to photosystem II primary acceptor (Q(A)) reduction, but several contradictory theories exist for the J-I and I-P rises. One problem with fluorescence induction analysis is that most work done to date has used only qualitative or semiquantitative data analysis by visually comparing traces to observe the effects of different chemicals or treatments. Although this method is useful to observe major changes, a quantitative method must be used to detect more subtle, yet important, differences in the fluorescence induction trace. To achieve this, we used a relatively simple mathematical approach to extract the amplitudes and half-times of the three major fluorescence induction phases obtained from traces measured in thylakoid membranes kept at various temperatures. Apparent activation energies (E(A)) were also obtained for each kinetic step. Our results show that each phase has a different E(A), with E(A O-J) <E(A J-I) < E(A I-P), and thus a different origin. The effects of two well-known chemicals, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, which blocks electron transfer to the photosystem II secondary electron acceptor (Q(B)), and decylplastoquinone, which acts similarly to endogenous reducible plastoquinones, on the quantitative parameters are discussed in terms of the origin of each kinetic phase.

Effects of sulfur limitation on photosystem II functioning in Chlamydomonas reinhardtii as probed by chlorophyll a fluorescence

Chlorophyll fluorescence methods were applied to probe in vivo photosystem II (PSII) function in Chlamydomonas reinhardtii grown in sulfur‐depleted media under aerobic conditions. The rates of oxygen evolution and dark reduction decreased during a 24‐h incubation in sulfur‐deficient medium, while the respiration rate increased. The analysis of chlorophyll fluorescence induction curves suggests that electron transport was perturbed on both the acceptor and donor sides of PSII. Light‐induced violaxanthin de‐epoxidation and non‐photochemical fluorescence quenching were suppressed, owing to dark accumulation of zeaxanthin. Also sulfur‐deprived cells showed elevated concentrations of violaxanthin and lutein. Sulfur deprivation stimulated a pronounced (three‐ to four‐fold) increase in chlorophyll a fluorescence intensity (parameters Fo and Fm), probably due to greater light absorption by carotenoids and changes in the excitation energy transfer and deactivation in PSII of C. reinhardtii.