Chlorophyll Fluorescence Of Photosystem Research Articles

Effects of sodium hypochlorite treatment on the chlorophyll fluorescence in photosystem II of microalgae

Chlorophyll fluorescence-based method shows great potentials for on-site assessing the vitality of algae in treated ship's ballast water. However, there is very limited information on the mechanism of chlorophyll fluorescence in photosystem II (PSII) after the NaClO treatment. In this paper, the effects of NaClO treatments with five concentrations (0.01, 0.04, 0.08, 0.12 and 0.15 mg/L) and treating periods (6, 24 and 48 h) on the chlorophyll fluorescence kinetics and spectra of Chlorella vulgaris (C. vulgaris) and Platymonas helgolandica (P. helgolandica) were investigated. Experimental results showed that both exposure time and dose were important factors that affect the toxicity of NaClO to microalgae. Further analyses showed that the maximum photochemical quantum yield of PSII, photochemical quenching and yield decreased rapidly with the increase in NaClO concentrations in the range of 0.04 mg/L to 0.15 mg/L, suggesting that NaClO seriously inhibited PSII reaction centers of algae. In addition, the maxima value of fluorescence at excitation wavelength still appeared near 437 nm and 468 nm under NaClO stress, pointing to the pigments for fluorescence produced by algae were mainly chlorophyll a and chlorophyll b antenna. As compared to chlorophyll a, the relative fluorescence intensity of chlorophyll b decreased significantly in the all of NaClO treatments. According to the fluorescence emission spectra, treatment of NaClO resulted in a shift of the maximum peak of C. vulgaris and P. helgolandica from 685.2 nm to 681.9 nm and 685.2 nm to 680.5 within 6 h, respectively. This indicates that the structure of antenna light-absorbing pigments of PSII changed under NaClO stress. These results revealed that the chlorophyll fluorescence mechanism in PSII of damaged microalgae occurred variation, which was important for the reliable application of on-site analysis of ballast water indicator based on chlorophyll fluorescence detection.

Responses of photorespiration and thermal dissipation in PSII to soil water in cotton bracts

Aims Photorespiration and non-photochemical quenching of chlorophyll fluorescence in photosystem II (PSII) were studied in bracts and leaves of cotton (Gossypium hirsutum) plants, in order to investigate the photoprotective mechanisms and drought tolerance in cotton bracts under field conditions of water-saving drip irrigations. Methods Gas exchange and chlorophyll fluorescence parameters of PSII were analyzed in bracts and leaves of cotton plants after anthesis. The study was conducted with two treatments comprising normal drip irrigation (5 228.5 m 3 ·hm -2 ) and water-saving drip irrigation (3 874.1 m 3 ·hm -2 ) under field conditions. Important findings The actual photochemical efficiency of PSII (ΦPSII) decreased in both bracts and leaves of cotton plants after anthesis under water-saving drip irrigation, but the magnitude of decrease was less in bracts than in leaves. Results showed the bracts experienced less severe photoinhibition than leaves. The rate of net pho- tosynthesis (Pn), ΦPSII, net photorespiration (Pr), photochemical quenching (qP), and non-photochemical quench- ing (NPQ) decreased in the leaves of cotton plants under water-saving drip irrigation, but no significant difference was observed in the bracts. With decreasing water supply, the Pr/Pn in bracts was much higher than that in leaves and water deficit had no significant effect on the Pr/Pn in bracts. The results of chlorophyll fluorescence parame- ters showed that the quantum yield of regulated energy dissipation (Y(NPQ)) was higher in bracts than in leaves under high irradiance and temperature conditions, and that the thermal dissipation in bracts was not susceptible to water deficit, thus protecting the photosynthetic apparatus against photodamage. Overall, both photorespiration and energy dissipation in bracts were found to alleviate photoinhibition and played important roles in protecting

Tolerance of chufa (Cyperus esculentus L.) plants, representing the higher plant compartment in bioregenerative life support systems, to super-optimal air temperatures

Plants intended to be included in the photosynthesizing compartment of the bioregenerative life support system (BLSS) need to be studied in terms of both their production parameters under optimal conditions and their tolerance to stress factors that might be caused by emergency situations. The purpose of this study was to investigate tolerance of chufa (Cyperus esculentus L.) plants to the super-optimal air temperature of 45±1°C as dependent upon PAR (photosynthetically active radiation) intensity and the duration of the exposure to the stress factor. Chufa plants were grown hydroponically, on expanded clay, under artificial light. The nutrient solution was Knop’s mineral medium. Until the plants were 30days old, they had been grown at 690μmolm−2s−1 PAR and air temperature 25°C. Thirty-day-old plants were exposed to the temperature 45°C for 6h, 20h, and 44h at PAR intensities 690μmolm−2s−1 and 1150μmolm−2s−1. The exposure to the damaging air temperature for 44h at 690μmolm−2s−1 PAR caused irreversible damage to PSA, resulting in leaf mortality. In chufa plants exposed to heat shock treatment at 690μmolm−2s−1 PAR for 6h and 20h, respiration exceeded photosynthesis, and CO2 release in the light was recorded. Functional activity of photosynthetic apparatus, estimated from parameters of pulse-modulated chlorophyll fluorescence in Photosystem 2 (PS 2), decreased 40% to 50%. After the exposure to the stress factor was finished, functional activity of PSA recovered its initial values, and apparent photosynthesis (Papparent) rate after a 20-h exposure to the stress factor was 2.6 times lower than before the elevation of the temperature. During the first hours of plant exposure to the temperature 45°C at 1150μmolm−2s−1 PAR, respiration rate was higher than photosynthesis rate, but after 3–4h of the exposure, photosynthetic processes exceeded oxidative ones and CO2 absorption in the light was recorded. At the end of the 6-h exposure, Papparent rate was close to that recorded prior to the exposure, and no significant changes were observed in the functional activity of PSA. At the end of the 20-h exposure, Papparent rate was close to its initial value, but certain parameters of the functional activity of PSA decreased 25% vs. their initial values. During the repair period, the parameters of external gas exchange recovered their initial values, and parameters of pulse-modulated chlorophyll fluorescence were 20–30% higher than their initial values. Thus, exposure of chufa plants to the damaging temperature of the air for 20h did not cause any irreversible damage to the photosynthetic apparatus of plants at either 690μmolm−2s−1 or 1150μmolm−2s−1 PAR, and higher PAR intensity during the heat shock treatment enhanced heat tolerance of the plants.

Photochemical and photoelectrochemical quenching of chlorophyll fluorescence in photosystem II

This paper deals with kinetics and properties of variable fluorescence in leaves and thylakoids upon excitation with low intensity multi-turnover actinic light pulses corresponding with an excitation rate of about 10 Hz. These show a relatively small and amply documented rise in the sub-s time range towards the plateau level Fpl followed by a delayed and S-shaped rise towards a steady state level Fm which is between three and four fold the initial dark fluorescence level Fo. Properties of this retarded slow rise are i) rate of dark recovery is (1–6 s)−1, ii) suppression by low concentration of protonophores, iii) responsiveness to complementary single turnover flash excitation with transient amplitude towards a level Fm which is between five and six fold the initial dark fluorescence level Fo and iv) in harmony with and quantitatively interpretable in terms of a release of photoelectrochemical quenching controlled by the trans-thylakoid proton pump powered by the light-driven Q cycle. Data show evidence for a sizeable fluorescence increase upon release of (photo) electrochemical quenching, defined as qPE. Release of qPE occurs independent of photochemical quenching defined here as qPP even under conditions at which qPP=1. The term photochemical quenching, hitherto symbolized by qP, will require a new definition, because it incorporates in its present form a sizeable photoelectrochemical component. The same is likely to be true for definition and use of qN as an indicator of non photochemical quenching.

Comparative study of the water oxidizing reactions and the millisecond delayed chlorophyll fluorescence in photosystem II at different pH

Water splitting activity, the multiline EPR signal associated with S 2-state of the CaMn 4-cluster and the fast and slow phases of the induction curve of the millisecond delayed chlorophyll fluorescence from photosystem II (PSII) in the pH range of 4.5–8.5 were studied in the thylakoid membranes and purified PSII particles. It has been found that O 2 evolution and the multiline EPR signal were inhibited at acidic (p K ∼ 5.3) and alkaline (p K ∼ 8.1) pH values, and were maximal at pH 6.0–7.0. Our results indicate that the loss of O 2 evolution and the S 2-state multiline EPR signal associated with the decrease of the millisecond delayed chlorophyll fluorescence only in alkaline region (pH 7.0–8.5). Possible correlations of the millisecond delayed chlorophyll fluorescence components with the donor side reactions in PSII are discussed.

Carbonic anhydrase in subchloroplast particles of pea plants

The partitioning of carbonic anhydrase (CA) activity in chloroplasts isolated from 10–14-day-old pea (Pisum sativum L.) seedlings was investigated. The effect of CA inhibitors on the kinetics of chlorophyll fluorescence in photosystem II (PSII) preparations was also studied. The activity of CA was detected in fractions of soluble proteins and in the polypeptide complexes of the PSI and PSII. Isolated particles of photosystems retained a high photochemical activity similar to that of intact chloroplasts and the high level of polyunsaturated fatty acids. The association of CA with the particles of PSII (PSII-CA) was also tested by Western-blot analysis using antibodies against PSII-CA (Cah3) from Chlamydomonas reinhardtii. The PSII particles isolated with Triton X-100 (T-20) showed a higher activity of the enzyme as calculated on a protein basis than the DT-20 particles isolated with digitonin and Triton X-100. This difference seems to be related to the higher degree of nativity of the chloroplast T-20 fragments as compared to DT-20 particles. The higher level of chlorophyll per reaction center as well as the higher content of chlorophyll b and lipid fatty acids as calculated on protein basis, in particular of E-16:1ω13 acid, which stabilizes the oligomeric structure of the light-harvesting complex of the PSII, also confirms this suggestion. The activity of CA was not detected in the DT-20 preparations treated with Tris–HCl to eliminate manganese ions. This is likely to indicate that one of the extrinsic polypeptides of PSII exhibits CA activity. Specific inhibitors of CA (acetazolamide and imidazole) inhibited the photoinduced yield of chlorophyll fluorescence (ΔF). This might be determined by damaging the water-oxidizing system or its interaction with the PSII reaction centers. The functional role of PSII-CA for СО2-concentrating in carboxylation sites as well as its role in the coupling of light and dark reactions in chloroplasts is discussed.

Chilling-Induced Photoinhibition in Two Oak Species: Are Evergreen Leaves Inherently Better Protected Than Deciduous Leaves?

We compared the sensitivity to cold stress, in terms of photosynthetic capacity and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern United States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than the deciduous species, Quercus michauxii. Short-term cold stress in both species lead to greater than 50 % reduction in maximum photosynthetic rates, 60-70 % reduction in electron transport, and irreversible quenching of PS2 fluorescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 µmol m-2 s-1) and chilling (5 °C) showed that the evergreen Q. virginiana exhibited more protective qE and less irreversible quenching (qI) than the deciduous Q. michauxii. The large qE which we observed in Q. virginiana suggests that the capacity for photoprotection at low temperatures is not induced by a long-term acclimation to cold but preexists in evergreen leaves. This capacity may contribute to the ability of this species to maintain leaves during the winter.

Gas Exchange and Chlorophyll Fluorescence of C3 and C4 Saltmarsh Species

Spartina maritima (Curtis) Fernald, Spartina densiflora Brong, Arthrocnemum perenne (Miller) Moss, and Arthrocnemum fruticosum (L.) Moq are very frequent halophytes on the coasts of SW Europe. The first two are perennial Gramineae with C4 metabolism; the last two are perennial Chenopodiaceae with C3 metabolism. Controlled garden experiments were carried out with the four species to compare their physiological response, i.e., water potential (Ψ), net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), and chlorophyll fluorescence of photosystem (PS) 2 under saline and non-saline conditions. S. maritima behaves as an osmoconformer species, the other three as osmoregulators. In the four species, PN, E, and gs improved following freshwater irrigation. The variations in PN might be related with biochemical changes (which appear not to affect PS2), but not with significant stomatal fluctuations, which are associated with a lower water use efficiency in the case of Arthrocnemum. The species were segregated into two groups (not depending on their C3 or C4 photosynthetic pathway), in relation with the topographic level of this species in natural conditions: the relative responses of PN in S. maritima and A. perenne were lower than those of S. densiflora and A. fruticosum. The salt-tolerance index supports such segregation. S. densiflora demonstrated the best competitive possibilities against salt-tolerant glycophytes, with its more flexible response in saline or brackish environments, which explains its spreading along the rivers draining into the estuaries of the SW Iberian Peninsula.