Steady-state Fluorescence Yield Research Articles

Effect of Salicylic Acid and Calcium on Growth, Yield, and Fruit Quality of Pepper (Capsicum annuum L.) Grown Hydroponically

The aim of this study was to investigate the effects of spraying plants with 0.03% salicylic acid (SA), 0.7% calcium nitrate (Ca), and 0.03% salicylic acid together with 0.7% calcium nitrate (SA + Ca) on plant growth, yield, and fruit quality of peppers grown in a mineral wool substrate. The control plants were sprayed with water (C). Two red-fruited sweet pepper cultivars were used in the study: ‘Aifos’, and ‘Palermo’, which produce fruits characterized by different shapes. Biometric measurements of the plants showed a higher growth rate of pepper plants when SA and Ca were applied foliarly compared to the control. Plants treated simultaneously with SA and Ca were characterized by the highest steady-state fluorescence yield [Fs]. The relative chlorophyll content of pepper leaves was also higher in plants sprayed with SA, Ca, and SA + Ca than in plants in the control. The analysis of pepper yield showed in both cultivars the effect of foliar treatment of plants with SA and Ca and SA + Ca on increasing pepper resistance to the occurrence of Ca deficiency on pepper fruit (Blossom end rot). Pepper fruits harvested from plants treated with SA, Ca, and SA + Ca had more juicy flesh.

Canopy structural changes explain reductions in canopy-level solar induced chlorophyll fluorescence in Prunus yedoensis seedlings under a drought stress condition

Drought events have a major impact on vegetation structure and function. Recently, solar-induced chlorophyll fluorescence (SIF) has been widely used to understand the photosynthesis rates of vegetation under drought stress conditions. However, it is still unclear whether the reduction in SIF shown under drought stress conditions is regulated by physiological or structural factors. To understand the underlying reduction mechanism of SIF under drought stress, we conducted an experiment under a drought condition using one-year-old Prunus yedoensis seedlings. We compared the experiment trees with control trees that were not exposed to drought stress. We collected spectral and gas exchange data to monitor physiological changes and scanned the trees with a terrestrial laser scanner to monitor the structural changes. The discrete anisotropic radiative transfer (DART) and Fluspect models were used to simulate canopy-level SIF. We found that drought stress caused leaf-level steady-state fluorescence yield to increase, while maximum photosynthetic rate, stomatal conductance, and the quantum yield of Photosystem II decreased significantly. Regarding the canopy structural changes, the leaf inclination angle distribution of the experiment trees gradually turned toward erectophile over time (55.2 ± 9.3° to 74.7 ± 6.0°; mean ± standard deviation), whereas that of the control trees remained relatively constant (52.9 ± 8.8°). Furthermore, reduction of crown cover of the experiment trees was 3-fold (77.4 ± 9.8%) compared with the control trees (26.0 ± 16.2%). The simulated nadir-view canopy-level SIF of the experiment trees was reduced 2.8-fold compared to the control trees. These findings, obtained specifically from Prunus yedoensis seedlings, indicate that canopy-level SIF reduced due to the canopy structural changes, although leaf-level fluorescence yield increased. Therefore, canopy structural changes should be considered when attempting to understand SIF reduction in drought conditions.

Effects of exogenous NO on the growth and photosynthetic fluorescence characteristics of ryegrass seedlings under B[a]P stress

Benzoapyrene (B[a]P) pollution poses a threat to the environment and the food chain and consequently to human health. However, the alleviation of the harmful effects of B[a]P pollution in perennial ryegrass (Lolium perenne L.) by the application of exogenous nitric oxide (NO) has been ignored. Thus, in this paper the effects of exogenous sodium nitroprusside (SNP, a NO donor) on the growth, photosynthetic fluorescence characteristics, and antioxidant enzyme activity of ryegrass exposed to B[a]P stress are investigated. B[a]P stress induced the reduction of the aboveground and belowground dry weights, chlorophyll (a, b), the total chlorophyll contents, the carotenoid content, the net photosynthetic rate (Pn), the intercellular carbon dioxide concentration (Ci), the water use efficiency (WUE), the photosystem II (PSII) potential activity (Fv/F0), the maximum quantum yield of PSII photochemistry (Fv/Fm), the steady-state fluorescence yield (Fs), and the non-photochemical quenching (qN), while enhancement was recorded in response to the foliar spray of SNP at 200 and 300 μmol·L-1 under B[a]P stress. Gray correlation and principal component analyses show that 200 μmol·L 1 of SNP more drastically alleviated the damage caused by B[a]P stress than 300 μmol·L 1 of SNP. The exogenous NO-mediated alleviation of B[a]P toxicity in ryegrass was associated with preserved photosynthetic characteristics and activation of antioxidant enzymes.

Combining near-infrared radiance of vegetation and fluorescence spectroscopy to detect effects of abiotic changes and stresses

Solar-induced chlorophyll fluorescence (SIF) shows great potential to assess plants physiological state and response to environmental changes. Recently the near-infrared reflectance of vegetation (NIRv) provides a promising way to quantify the confounding effect of canopy structure in SIF, while the difference between SIF and NIRv under varying environmental conditions has not been well explored. Here we developed a simple approach to extract the fluorescence yield (ΦF) by the combined use of SIF and the near-infrared radiance of vegetation (NIRvR). The proposed NIRvR approach was evaluated in multiple ways, including with the seasonal leaf-level steady-state fluorescence yield. Results indicate that NIRvR-derived ΦF well captured the seasonal variation of the fluorescence yield changes, and achieved similar results with the existing approach. Both SIF and NIRvR were derived from the airborne imaging fluorescence spectrometer HyPlant for three case studies to evaluate the impacts of light adaptation, heat stress and water limitation on ΦF. For the light adaptation case study, ΦF over the low-light adapted sugar beet field was about 1.3 times larger compared to an unaffected reference area while the difference in NIRvR was minimal, which clearly shows the short-term photosynthetic light induction effect and the ability of SIF to detect plant physiological responses. For the heat stress experiment, ΦF decreased during a natural heatwave in 2015 in the fields of rapeseed from 0.0150 to 0.0130, barley from 0.0152 to 0.0144, and wheat from 0.0146 to 0.0142 which showed signs of senescence, while slightly increased from 0.0125 to 0.0130 in the corn field which was still in growing. At the water-limited sugar beet field, ΦF first increased towards solar noon and then slightly decreased during the afternoon over the water-limited areas from 0.017 to 0.021 and 0.020, with high temperature and high light at noon. The advantages to use SIF/NIRvR as a proxy of ΦF to detect stress-induced limitations in photosynthesis include that the impacts of canopy structure and sun-sensor geometry on the ΦF estimation are explicitly cancelled, and photosynthetically active radiation (PAR) is not required as input. Finally, our approach is directly applicable to satellite-derived estimates of SIF, enabling the study of variations in ΦF to detect the effects of abiotic changes and stresses at large scale.

Assessing the effects of forest health on sun-induced chlorophyll fluorescence using the FluorFLIGHT 3-D radiative transfer model to account for forest structure

Sun-induced fluorescence (SIF) has been proven to serve as a proxy of photosynthesis activity and therefore, as an early indicator of physiological alterations for global monitoring of vegetation. However, the interpretation of SIF over different spatial resolutions is critical to bridge the existing gap between local and global scales. This study provides insight into the influence of scene components, and forest structure and composition on the quantification of the red and far-red fluorescence signal as an early indicator of forest decline. The experiments were conducted over an oak forest (Quercus ilex) affected by water stress and Phytophthora infection in the southwest of Spain. SIF retrievals through the Fraunhofer Line Depth (FLD) principle with three spectral bands F (FLD3) was assessed using high resolution (60cm) hyperspectral imagery extracting sunlit crown, full crown and aggregated pixels. Results showed the link between F (FLD3) extracted from sunlit crown pixels and the tree physiological condition in this context of disease infection, yielding significant relationships (r2=0.57, p<0.01) for midday xylem water potential (ψ), (r2=0.63, p<0.001) for the de-epoxidation state of the xanthophyll cycle (DEPS), and (r2=0.74, p<0.001) for leaf-level measurements of steady-state fluorescence yield (Fs). In contrast, a poor relationship was obtained when using aggregated pixels at 30m spatial resolution, where the relationship between the image-based F (FLD3) and Fs yielded a non-significant relationship (r2=0.25, p>0.05). These results demonstrate the need for methods to accurately retrieve crown SIF from aggregated pixels in heterogeneous forest canopies with large physiological variability among individual trees. This aspect is critical where structural canopy variations and the direct influence of background and shadows affect the SIF amplitude masking the natural variations caused by physiological condition. FluorFLIGHT, a modified version of the three dimensional (3-D) radiative transfer model FLIGHT was developed for this work, enabling the simulation of canopy radiance and reflectance including fluorescence at different spatial resolutions, such as may be derived from proposed satellite missions such as FLEX, and accounting for canopy structure and varying percentage cover. The 3-D modelling approach proposed here significantly improved the relationship between Fs and F (FLD3) extracted from aggregated pixels (r2=0.70, p<0.001), performing better than when aggregation effects were not considered (r2=0.42, p<0.01). The FluorFLIGHT model used in this study improved the retrieval of SIF from aggregated pixels as a function of fractional cover, Leaf Area Index and chlorophyll content yielding significant relationships between Fs ground-data measurements and fluorescence quantum yield estimated with FluorFLIGHT at p<0.01 (r2=0.79). The methodology presented here using FluorFLIGHT also demonstrated its capabilities for mapping SIF at the tree level for single tree assessment of forest physiological condition in the context of early disease detection.

Photosynthetic acclimation to light in woody and herbaceous species: a comparison of leaf structure, pigment content and chlorophyll fluorescence characteristics measured in the field

Acclimation of foliage photosynthetic properties occurs with varying time kinetics, but structural, chemical and physiological factors controlling the kinetics of acclimation are poorly understood, especially in field environments. We measured chlorophyll fluorescence characteristics, leaf total carotenoid (Car), chlorophyll (Chl) and nitrogen (N) content and leaf dry mass per area (LMA) along vertical light gradients in natural canopies of the herb species, Inula salicina and Centaurea jacea, and tree species, Populus tremula and Tilia cordata, in the middle of the growing season. Presence of stress was assessed on the basis of night measurements of chlorophyll fluorescence. Our aim was to compare the light acclimation of leaf traits, which respond to light availability at long (LMA and N), medium (Chl a/b ratio, Car/Chl ratio) and short time scales (fluorescence characteristics). We found that light acclimation of nitrogen content per unit leaf area (N(area)), chlorophyll content per unit dry mass (Chl(mass)) and Chl/N ratio were related to modifications in LMA. The maximum PSII quantum yield (F(v) /F(m)) increased with increasing growth irradiance in I. salicina and P. tremula but decreased in T. cordata. Leaf growth irradiance, N content and plant species explained the majority of variability in chlorophyll fluorescence characteristics, up to 90% for steady-state fluorescence yield, while the contribution of leaf total carotenoid content was generally not significant. Chlorophyll fluorescence characteristics did not differ strongly between growth forms, but differed among species within a given growth form. These data highlight that foliage acclimation to light is driven by interactions between traits with varying time kinetics.

Near-distance imaging spectroscopy investigating chlorophyll fluorescence and photosynthetic activity of grassland in the daily course.

Detection of grassland canopy chlorophyll fluorescence (Chl-F) conducted with an imaging spectroradiometer provided evidence of potential remote sensing estimation of steady-state Chl-F (Chl-Fs). Daily near-nadir views of extremely high spatial resolution hyperspectral images were acquired from a distance of 4 m for temperate montane grassland in the Czech Republic. Simultaneously, measurements of Chl-F and total chlorophyll content (Chla + b) were made on a single leaf at ground level were collected. A specifically designed 'shade removal' experiment revealed the influence of dynamic physiological plant processes on hyperspectral reflectance of three wavelengths: 532, 686 and 740 nm. Based on this information, the vegetation indexes R686/R630, R740/R800 and PRI calculated as (R532-R570)/(R532+R570) were tested for statistical significance with directly measured Chl-F parameters (maximum fluorescence yield, Fv/Fm; steady-state chlorophyll fluorescence, Chl-Fs and actual quantum yield, ФII). The grassland species under investigation were: Festuca rubra agg. (L.), Hieracium sp., Plantago sp., Nardus stricta (L.) and Jacea pseudophrygia (C.A. Meyer). The coefficients of determination (R2) for best-fit relationships between PRI-ФII and PRI-Chl-Fs, measured in the daily course, show a high variability of 0.23-0.78 and 0.20-0.65, respectively. Similarly, R2 for the R686/R630-ФII and R686/R630-Chl-Fs relationships varied between 0.20-0.73 and 0.41-0.70, respectively. The highest average R2 values were found between PRI and Chla + b (0.63) and R686/R630 and Chla + b (0.72). The ratio R740/R800 did not yield a statistically significant relation with Chl-F parameters.

Detection of water stress in orchard trees with a high-resolution spectrometer through chlorophyll fluorescence in-filling of the O/sub 2/-A band

A high spectral resolution spectrometer with 0.065-nm full-width half-maximum was used for collecting spectral measurements in an orchard field under three water stress treatments. The study was part of the FluorMOD project funded by the European Space Agency to develop a leaf-canopy reflectance model to simulate the effects of fluorescence. Water deficit protocols generated a gradient in solar-induced chlorophyll fluorescence emission and tree physiological measures. Diurnal steady-state chlorophyll fluorescence was measured from leaves in the field between June and November 2004 using the PAM-2100 fluorometer to study the effects of water stress on chlorophyll fluorescence. Spectral measurements of downwelling irradiance and upwelling crown radiance were conducted with the narrow-band spectrometer, enabling the canopy reflectance to be obtained at subnanometer spectral resolution and permitting the evaluation of the fluorescence in-filling effects on reflectance in trees under water stress conditions. Diurnal and seasonal measurements showed consistently lower steady-state fluorescence (Ft) and quantum yield /spl Delta/F/Fm' in water-stressed trees, yielding mean values of Ft=0.38 (well-irrigated) and Ft=0.21 (water-stressed trees). The agreement between Ft and water potential showed that steady-state fluorescence could be used to detect differences in water stress levels, with determination coefficients ranging between r/sup 2/=0.48 and r/sup 2/=0.81 for individual dates. Analysis in the 680-770-nm range showed that the chlorophyll fluorescence in-filling in the O/sub 2/-A band at 760 nm is sensitive to diurnal variations of fluorescence and water stress, yielding r/sup 2/=0.76 (well-watered treatment), r/sup 2/=0.89 (intermediate stress treatment), and r/sup 2/=0.7 (extreme stress treatment), demonstrating the close relationships between Ft and in-filling at the crown level.

The photochemical trapping rate from red spectral states in PSI–LHCI is determined by thermal activation of energy transfer to bulk chlorophylls

The average fluorescence decay lifetimes, due to reaction centre photochemical trapping, were calculated for wavelengths in the 690- to 770-nm interval from the published fluorescence decay-associated emission spectra for Photosystem I (PSI)–light-harvesting complex of Photosystem I (LHCI) [Biochemistry 39 (2000) 6341] at 280 and 170 K. For 280 K, the overall trapping time at 690 nm is 81 ps and increases with wavelength to reach 103 ps at 770 nm. For 170 K, the 690-nm value is 115 ps, increasing to 458 ps at 770 nm. This underlines the presence of kinetically limiting processes in the PSI antenna (diffusion limited). The explanation of these nonconstant values for the overall trapping time band is sought in terms of thermally activated transfer from the red absorbing states to the “bulk” acceptor chlorophyll (chl) states in the framework of the Arrhenius–Eyring theory. It is shown that the wavelength-dependent “activation energies” come out in the range between 1.35 and 2.7 kcal mol −1, increasing with the emission wavelength within the interval 710–770 nm. These values are in good agreement with the Arrhenius activation energy determined for the steady-state fluorescence yield over the range 130–280 K for PSI–LHCI. We conclude that the variable trapping time in PSI–LHCI can be accounted for entirely by thermally activated transfer from the low-energy chl states to the bulk acceptor states and therefore that the position of the various red states in the PSI antenna seems not to be of significant importance. The analysis shows that the bulk antenna acceptor states are on the low-energy side of the bulk antenna absorption band.

Excitation trap approach to analyze size and pigment-pigment coupling: reconstitution of LH1 antenna of Rhodobacter sphaeroides with Ni-substituted bacteriochlorophyll.

Replacement of the central Mg in chlorophylls by Ni opens an ultrafast (tens of femtoseconds time range) radiationless de-excitation path, while the principal ground-state absorption and coordination properties of the pigment are retained. A method has been developed for substituting the native bacteriochlorophyll a by Ni-bacteriochlorophyll a ([Ni]-BChl) in the light harvesting antenna of the core complex (LH1) from the purple bacterium, Rhodobacter (Rb.) sphaeroides, to investigate its unit size and excited state properties. The components of the complex have been extracted with an organic solvent from freeze-dried membranes of an LH1-only strain of Rb. sphaeroides and transferred into the micelles of n-octyl-beta-glucopyranoside (OG). Reconstitution was achieved by solubilization in 3.4% OG, followed by dilution, yielding a complex nearly identical to the native one, in terms of absorption, fluorescence, and circular dichroism spectra as well as energy transfer efficiency from carotenoid to bacteriochlorophyll. By adding increasing amounts of [Ni]-BChl to the reconstitution mixture, a series of LH1 complexes was obtained that contain increasing levels of this efficient excitation trap. In contrast to the nearly unchanged absorption, the presence of [Ni]-BChl in LH1 markedly affects the emission properties. Incorporation of only 3.2 and 20% [Ni]-BChl reduces the emission by 50% and nearly 100%, respectively. The subnanosecond fluorescence kinetics of the complexes were monoexponential, with the lifetime identical to that of the native complex, and its amplitude decreasing in parallel with the steady-state fluorescence yield. Quantitative analysis of the data, based on a Poisson distribution of the modified pigment in the reconstituted complex, suggests that the presence of a single excitation trap per LH1 unit suffices for efficient emission quenching and that this unit contains 20 +/- 1 BChl molecules.

Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory

Photoinduced intermolecular electron transfer between Rhodamine 3B and N,N-dimethylaniline has been studied in a series of seven liquids: acetonitrile, ethanol, propylene glycol, and mixtures of ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol. In each liquid, the donor and acceptors have different diffusion constants and experience distinct dielectric properties. Ps time-dependent fluorescence measurements and steady-state fluorescence yield measurements were made and analyzed using a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants, diffusion constants, and redox potentials, leaving the electronic coupling unknown. Taking the distance-dependence of the coupling to be β=1 Å−1, data were fit to a single parameter, the coupling matrix element at contact, J0. The theory is able to reproduce both the functional form of the time-dependence and the concentration-dependence of the data in all seven liquids by fitting only J0. Despite the substantial differences in the properties of the experimental systems studied, fits to the data are very good and the values for J0 are very similar for all solvents.

Characteristics of Chlorophyll a Fluorescence Induction in Cucumber Cotyledons Treated with Diuron, Norflurazon, and Sulcotrionem

Chlorophyll a fluorescence analysis was carried out to investigate the potential relationship between photosynthetic electron transport and herbicidal action mechanism of sulcotrione, norflurazon, diuron, and two experimental herbicides in cucumber cotyledons. The diuron treatment decreased quantum yield of electron transport and photochemical fluorescence quenching (qP) immediately but increased the steady-state fluorescence yield (Ft) greatly in the light, with a decreased magnitude upon dark adaptation. The profile of changes of qP and Ft in sulcotrione-treated tissues was similar to that of diuron-treated tissues; however, a decline in quantum yield was faster in diuron-treated tissues. Norflurazon-treated tissues also decreased quantum yield as in sulcotrione-treated tissues, but had a slight increase in Ft and a prominent increase in qN in contrast to those of diuron and sulcotrione. Experimental herbicides EK 3651, sulcotrione derivative, and KC 6361, phytoene desaturase inhibitor, also exhibited a similar profile of chlorophyll a fluorescence to that of sulcotrione and norflurazon, respectively. This demonstrates that chlorophyll a fluorescence induction profiles of the chemicals are related to their respective herbicidal activities and can be utilized as a simple way of differentiating the target sites of herbicides in vivo. Based on a correlation between quantum yield inhibition and injury, sulcotrione appears to be closer to diuron than norflurazon. In the combined treatment of herbicides, sulcotrione and diuron had synergistic effect to each other. Our results suggest that sulcotrione inhibits photosynthetic electron transport, in mature cotyledons, through a decrease in plastoquinone pool, which is essential for phytoene desaturase and involved in photosynthetic electron transport as a mediator.

Hg2+, Cu2+, and Pb2+ -induced changes in Photosystem II photochemical yield and energy storage in isolated thylakoid membranes: A study using simultaneous fluorescence and photoacoustic measurements

Simultaneous fluorescence and photoacoustic measurements have been used to study the effects of metal ions (copper, lead, and mercury) during dark incubation of thylakoid membranes. The values of the chlorophyll fluorescence parameters Fo (initial fluorescence yield with the reaction centers in the open state), Fm (maximal fluorescence yield), Ft (steady state fluorescence yield) and the calculated parameters, Φo (maximal quantum yield of Photosystem II photochemistry) and Φt (actual quantum yield of Photosystem II photochemistry), strongly decreased in the presence of the metal ions coinciding with an increase in the non-photochemical deexcitation rate constant k(N). It was observed that photosynthetic energy storage measured by photoacoustic spectroscopy also decreased but a large portion of energy storage remained unaffected even at the highest metal ion concentrations used. A maximal inhibition of photosyntheti c energy storage of 80% and 50% was obtained with Hg2+ and Cu2+-treated thylakoids, respectively, while energy storage was insensitive to Pb2+. The results are consistent with the known predominant inhibition of the donor side of Photosystem II by the metal ions. The insensitive portion of energy storage is attributed to the possible recurrence of cyclic electron transport around Photosystem II that would depend on the extent of inhibition produced on the acceptor side by the metal ion used.

Effects of Molecular Organization on Photophysical Behavior. 1. Steady-State Fluorescence and Fluorescence Quantum Yield Studies of Langmuir−Blodgett Monolayers of Some Surfactant Porphyrins

The surface chemistry of two new groups of surfactant carboxyporphyrins is described. These materials exhibit well-behaved monomolecular films at an air−water interface. In compressed monolayers, the porphyrin ring appears to be oriented so that the plane of the ring is perpendicular to the surface. The surface-pressure−molecular area isotherms change with the length and nature of the side chains in a manner suggesting that a long side chain allows the porphyrin rings to acquire the most ordered packing. A rigid chain structure was found to restrict the orientational flexibility of the porphyrin rings and hence prevented them from acquiring a well-ordered monolayer structure. The solid-state photophysical properties of Langmuir−Blodgett monolayers of these materials are strongly dependent on their degree of order. The absorption, fluorescence, and fluorescence excitation spectra of single monolayer films transferred onto quartz and SnO2 slides using the Langmuir−Blodgett technique indicate that increasing the order in porphyrin monolayers leads to an increased red-shift of the Soret band and to decreased fluorescence quantum yields. On a SnO2 semiconductor surface, the monolayers exhibit enhanced fluorescence quenching. This is interpreted as evidence for isoenergetic electron transfer from the porphyrin to the semiconductor. An approximate interfacial electron-transfer rate (ket) was estimated on the basis of the fluorescence yields on quartz and SnO2 surfaces, respectively.

Spectroscopic and molecular modeling studies of caffeine complexes with DNA intercalators

Recent studies have demonstrated that caffeine can act as an antimutagen and inhibit the cytoxic and/or cytostatic effects of some DNA intercalating agents. It has been suggested that this inhibitory effect may be due to complexation of the DNA intercalator with caffeine. In this study we employ optical absorption, fluorescence, and molecular modeling techniques to probe specific interactions between caffeine and various DNA intercalators. Optical absorption and steady-state fluorescence data demonstrate complexation between caffeine and the planar DNA intercalator acridine orange. The association constant of this complex is determined to be 258.4 +/- 5.1 M-1. In contrast, solutions containing caffeine and the nonplanar DNA intercalator ethidium bromide show optical shifts and steady-state fluorescence spectra indicative of a weaker complex with an association constant of 84.5 +/- 3.5 M-1. Time-resolved fluorescence data indicate that complex formation between caffeine and acridine orange or ethidium bromide results in singlet-state lifetime increases consistent with the observed increase in the steady-state fluorescence yield. In addition, dynamic polarization data indicate that these complexes form with a 1:1 stoichiometry. Molecular modeling studies are also included to examine structural factors that may influence complexation.

CO2 assimilation, respiration and chlorophyll fluorescence in peach leaves infected by Taphrina deformans

Photosynthesis, respiration and chlorophyll fluorescence parameters were determined in peach (Prunus persica L. cv. Dixired) leaves naturally infected by Taphrina deformans (Berk.) Tul. and in healthy leaves (controls), in two successive springs. A drastic decrease in net photosynthesis and an evident increase in respiration in curled leaves were noted. The instantaneous PSII fluorescence yield, with no (F0) and with (F0) quenching component, and steady state fluorescence yield (under actinic light, Fs) were essentially unchanged. Maximal fluorescence in dark‐adapted (Fm) and illuminated (F′m) leaves and the corresponding variable fluorescence (Fv and Fv) clearly decreased. The indicators of PSII quantum yield (Fv/Fm) in dark‐adapted leaves, and the potential PSII excitation capture efficiency (F′v/F′m) and the quantum yield of PSII (qp [F′v/F′m]) in the light were also significantly lower in curled leaves. Decreasing tendencies were also noted for the PSII photochemical yield (photochemical quenching, qp) and in the energy status of the chloroplast (non‐photochemical quenching, qN, and Stern‐Vollmer value, NPQ) although the differences were not always significant. In curled leaves the main alteration documented is the imbalance between the drastic inhibition of CO2 fixation and the moderate decrease in photochemical reactions (i.e. Fv/Fm and ΔF/F′m), indicating changes in the energy flux.

Diurnal changes in chlorophylla fluorescence and carotenoid composition inOpuntia ficus-indica, a CAM plant, and in three C3 species in Portugal during summer.

Diurnal changes in chlorophylla fluorescence were determined in four species, differing in life form, in Portugal during the summer of 1989. These includedOpuntia ficus-indica, a CAM plant, andHelianthus annuus, Ficus carica andArbutus unedo, three C3 species. Steady state fluorescence yield,F S, and maximum fluorescence yield,F M', were determined at different times of the day. Using the model of Genty et al. (1989), the photon use efficiency of photosystem II electron transport,φ e, was calculated from (F M'-F S)/F M'. Diurnal changes in relative rate of non-cyclic electron transport through photosystem II,J e, were derived by multiplyingφ e by the incident photon flux density (PFD). WhenJ e, determined for each species for various points in time throughout the day, was plotted against corresponding values of PFD, the light response curves obtained showed thatJ e was linearly dependent on PFD in low light and approached saturation in high light. The highest values ofJ e were observed inHelianthus annuus, followed byOpuntia ficus-indica, Ficus carica andArbutus unedo. The proportion of the xanthophyll zeaxanthin to total carotenoids, determined around noon, was inversely related to maximum rates ofJ e.

Effects of O2 and CO2 Concentration on the Steady-State Fluorescence Yield of Single Guard Cell Pairs in Intact Leaf Discs of Tradescantia albiflora

A procedure for following changes in the steady-state yield of chlorophyll a fluorescence (F(s)) from single guard cell pairs in variegated leaves of Tradescantia albiflora is described. As an indicator of photosynthetic electron transport, F(s) is a very sensitive indirect measure of the balance of adenosine 5'-triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), producing reactions with the sink reactions that utilize those light-generated products. We found that F(s) under constant light is sensitive to manipulation of ambient CO(2) concentrations, as would be expected if either phosphoenolpyruvate carboxylase or ribulose-1, 5 bisphosphate carboxylase/oxygenase (Rubisco)-dependent CO(2) fixation is the sink for photosynthetic ATP and NADPH in guard cells. However, we also found that changing O(2) concentration had a strong effect on fluorescence yield, and that O(2) sensitivity was only evident when the concentration of CO(2) was low. This finding provides evidence that both O(2) and CO(2) can serve as sinks for ATP and NADPH produced by photosynthetic electron transport in guard cell chloroplasts. Identical responses were observed with mesophyll cell chloroplasts in intact leaves. This finding is difficult to reconcile with the view that guard cell chloroplasts have fundamentally different pathways of photosynthetic metabolism from other chloroplasts in C(3) plants. Indeed, Rubisco has been detected at low levels in guard cell chloroplasts, and our studies indicate that it is active in the pathways for photosynthetic carbon reduction and photorespiration in guard cells.

Analysis of Changes in Minimal and Maximal Fluorescence Yields with Irradiance and O2 Level in Tobacco Leaf Tissue

The responses of minimal and maximal fluorescence yields of chlorophyll a to irradiance of actinic white light were determined by pulse modulated fluorimetry in leaf discs from tobacco, Nicotiana tabacum, at 1.6, 20.5, and 42.0% (v/v) O(2). Steady-state maximal fluorescence yield (F(m)', measured during a saturating light pulse) declined with increasing irradiance at all O(2) levels. In contrast, the steady-state minimal fluorescence yield (F(o)', measured during a brief dark interval) increased with irradiance relative to that recorded for the fully dark-adapted leaf (F(o)) or that observed after 5 minutes of darkness (F(o) (*)). The relative magnitude of this increase was somewhat greater and extended to higher irradiances at the elevated O(2) levels compared with 1.6% O(2). Suppression of F(o)' was only observed consistently at saturating irradiance. The results are interpreted in terms of the occurrence of photosystem II units possessing exceedingly slow turnover times (i.e. "inactive" units). Inactive units play an important role, along with thermal deactivation of excited chlorophyll, in determining the response of in vivo fluorescence yield to changes in irradiance. Also, a significant interactive effect of O(2) concentration and the presence or absence of far red light on oxidation of photosystem II acceptors in the dark was noted.

Relationship between Steady-State Fluorescence Yield and Photosynthetic Efficiency in Spinach Leaf Tissue

The relationship between steady-state photosynthetic efficiency, as moles CO(2) per mole of incident visible photons under 2% O(2), and chlorophyll fluorescence quenching has been investigated in intact leaf tissue of Spinacia oleracia. Fluorescence yield was measured using a pulse amplitude modulation technique that permitted rapid and sensitive resolution and quantitation of photochemical and nonphotochemical quenching coefficients. A highly linear relationship was observed between photosynthetic efficiency and the ratio of photochemical:nonphotochemical quenching coefficients for values of the latter less than 1.6. This relationship applied whether irradiance or CO(2) concentration was varied. The observed relationships between photochemical yield and fluorescence yield were compatible with the photosystem II model proposed by Butler and Kitajima (1975 Biochim Biophys Acta 376: 116-125). The results are discussed with respect to the proposed role of nonphotochemical quenching in regulating radiant energy utilization and also the applicability of fluorescence measurements as a means of estimation of the rate of photosynthetic electron transport.