Chlorophyll Fluorescence Emission Research Articles

Chlorophyll fluorescence characterization of the action of photosystem II electron transport inhibitors

The action of substituted 9, 10-anthraquinones on the room-temperature chlorophyll fluorescence emission from photosystem II in plant chloroplasts is consistent with the inhibition of electron transport. Previous fluorescence measurements suggest that anthraquinones competitively displace the electron acceptor Q B from its binding sites on the D1 protein. Competition studies and molecular orbital calculations led to a hypothesis whereby the substituents on the 9, 10-anthraquinone ring dictate whether an anthraquinone hydrogen bonds to one or both of the domains of the D1 polypeptide suggested as sites of Q B binding. This study seeks to confirm our binding site predictions for substituted anthraquinones using Stern-Volmer investigations of the chlorophyll fluorescence emission of spinach chloroplasts treated to alter the Q B function. Anthraquinone-induced fluorescence quenching is measured for chloroplasts depleted of Q B and the associated plastoquinone pool and for chloroplasts treated with additional inhibitors which are ascribed to different binding regions of the D1 protein. Comparisons of Stern-Volmer parameters, particularly ƒ a values, for anthraquinones in normal, Q B-depleted, and inhibitor-treated chloroplasts reveal variations in the accessibility of anthraquinones in normal, Q B site. The preferred anthraquinone binding sites supported by these findings are in excellent agreement with our previous predictions.

Dynamics of electron transfer within and between PS II reaction center complexes indicated by the light-saturation curve of in vivo variable chlorophyll fluorescence emission

The dynamics of light-induced closure of the PS II reaction centers was studied in intact, dark-adapted leaves by measuring the light-irradiance (I) dependence of the relative variable chlorophyll fluorescence V which is the ratio between the amplitude of the variable fluorescence induced by a pulse of actinic light and the maximal variable fluorescence amplitude obtained with an intense, supersaturating light pulse. It is shown that the light-saturation curve of V is a hyperbola of order n. The experimental values of n ranged from around 0.75 to around 2, depending on the plant material and the environmental conditions. A simple theoretical analysis confirmed this hyperbolic relationship between V and I and suggested that n could represent the apparent number of photons necessary to close one reaction center. Thus, experimental conditions leading to n values higher than 1 could indicate that, from a macroscopic viewpoint, more than one photon is necessary to close one PS II center, possibly due to changes in the relative concentrations of the different redox states of the PS II reaction center complexes at the quasi-steady state induced by the actinic light. On the other hand, the existence of environmental conditions resulting in n noticeably lower than 1 suggests the possibility of an electron flow between PS II reaction center complexes.

Effect of Phosphlnothricin (Glufosinate) on Photosynthesis and Chlorophyll Fluorescence Emission by Barley Leaves Illuminated Under Photorespiratory and Non-Photorespiratory Conditions

The aim of this work was to concentrate on the effect of the inhibitor on CO2 assimilation and other aspects of photosynthesis. The changes in quantum requirement and in the characteristics of chlorophyll fluorescence emission brought about by feeding phosphinothricin to primary leaves were reported. The methods employed provide indirect information on the redox state of the photosynthetic electron transport and on chloroplast energization

Changes in the Blue-Green and Red Fluorescence-Emission Spectra of Beech Leaves during the Autumnal Chlorophyll Breakdown

The UV-light (337 nm) induced complete fluorescence-emission spectra of sun and shade leaves of the beech were measured between 400 to 800 nm and during the autumnal chlorophyll breakdown. The fluorescence-emission spectra are characterized by maxima in the blue region at 450 nm (blue fluorescence BF), near 530 nm (green fluorescence GF) and the two red chlorophyll fluorescence maxima near 690 and 735 nm. Lower leaf sides exhibit a higher BF, GF and red chlorophyll fluorescence (RF) emission than the upper leaf sides. The differences and changes in the fluorescence ratios BF/GF and BF/RF as well as in the chlorophyll fluorescence ratio F690/F735 between sun and shade leaves and during autumnal chlorophyll breakdown are presented. It is assumed that BF and GF emission emanate from at least two different blue-green-fluorescing substances and sites in the leaf. The possible nature of blue fluorescence-emitting plant substances is discussed.

Laser-induced time-resolved fluorescence of vegetation

Time-resolved measurements of the laser-induced chlorophyll fluorescence emission of vegetation detected by two different techniques are described. Fluorescence decay time measurements using single photon counting and picosecond laser pulse excitation have been used to analyze the fluorescence heterogeneity of plant leaves. The fluorescence is described by lifetimes of 10-40, 80-150, 400-500, and 700-1000 ps. By closing the reaction centers via application of the herbicide DCMU, the lifetimes of the two slowest components increase by a factor of about three. Another possible method to monitor the fluorescence after picosecond excitation could be a streak camera detection system. Measurements performed on the slow decay component of stressed and unstressed plants are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of incident light intensity on the yield of steady-state chlorophyll fluorescence in intact leaves. An example of bioenergetic homeostasis

The emission of modulated 685-nm chlorophyll fluorescence from intact leaves was measured using a pulsed (yellow) exciting light of very low intensity combined with various non-modulated lights of sub- and supersaturating intensities. It was found that, whereas the “extreme” (initial and maximal) fluorescence levels were drastically quenched by high light intensities, the level of steady-state modulated fluorescence in light-adapted leaves was virtually constant and independent of the intensity and the quality of the continuous light used to drive photosynthesis. These results provided an example of biological homeostasis. For instance, the modulated fluorescence emission from a dark-adapted leaf with all photosystem II reaction centers in the open configuration was similar to the steady-state modulated fluorescence emission measured in leaves illuminated with an additional strong, photosynthetically saturating light with all photosystem II traps closed. This homeostatic behavior was characteristic of only healthy and mature leaves. It was strongly perturbed in young leaves and also in leaves exposed to unfavorable environmental conditions. In some stress situations (e.g. leaf dehydration), noticeable deviations from homeostasis were detected before any significant changes in the familiar photochemical ( q p) and non-photochemical ( q NP) fluorescence quenching coefficients could be observed, suggesting that the analysis of this “bio-energetic homeostasis”, revealed by the examination of raw fluorescence data, could be a useful approach for early detection of subtle changes in the physiological state of plants.

Chlorophyll fluorescence measurements to assess the competition of substituted anthraquinones for the Q B binding site

As analogs of the Photosystem II plastoquinone electron acceptor, Q B, substituted quinones compete with Q B for a common binding domain and thereby inhibit Q B function. Substituted quinones interact with the Q B binding niche via hydrogen bonds, and the extent of hydrogen bond formation is determined by quinone structure. We have previously shown that the quinone inhibitory activity can be quantitated using measurements of chlorophyll fluorescence quenching. To assess competition for the Q B binding site, we report here measurements of the action of various pairs of substituted anthraquinones on the chlorophyll fluorescence emission of barley chloroplasts. The degree of competition between quinones for the Q B binding site is classified as competition, partial competition, or no competition. Two quinones were classified as undergoing competition, i.e., interacting for the same or overlapping sites, if the chlorophyll fluorescence level in the presence of the two quinones was not as low as that achieved in the presence of either one of the quinones individually. Non-competitive quinones with different binding sites quenched chlorophyll fluorescence to the level expected if the quenching effects of the individual quinones were additive. Partial competition, or some interaction for the same or overlapping sites, was characterized by an extent of fluorescence quenching in the presence of two quinones that was more effective than either quinone alone but not as sizable as that expected when the two quinones act independently. These results reflect an interesting situation whereby substitution patterns can alter the binding characteristics within a single class of inhibitors. In an accompanying manuscript we report the results of CNDO molecular orbital calculations to demonstrate that the π charge distribution in substituted quinones governs their binding properties.

The chlorophyll fluorescence ratio F690/F730 in leaves of different chlorophyll content

The red laser-induced chlorophyll-fluorescence induction kinetics of predarkened leaf samples were registered simultaneously in the 690 and 730 nm regions i.e., in the region of the two chlorophyll fluorescence emission maxima. From the induction kinetics the chlorophyll fluorescence ratio F690/F730 was calculated. The ratio F690/F730 shows to be dependent on the chlorophyll content of leaves. It is significantly higher in needles of damaged spruces (values of 0.45-0.9) than in normal green needles of healthy trees (values of 0.35-0.5). During development and greening of maple leaves the ratio F690/F730 decreases with increasing chlorophyll content. Determination of the ratio F690/F730 can be a suitable method of monitoring changes in chlorophyll content in a non-destructive way in the same leaves during development or the yellowish-green discolouration of needles of damaged spruces in the Black Forest with the typical tree decline symptoms.

Analysis of the Molecular Organization of Photosystem I During Light‐Dependent Chloroplast Differentiation in Mutant C‐6D of Scenedesmus obliquus*

AbstractCells of pigment mutant C‐6D of the green alga Scenedesmus obliquus synthesize only Chl a and precursors of carotenoids during heterotrophic growth in the dark. These cells exhibit high PSI‐activity per Chl and a low Chl/P700‐ratio. After transfer to light, Chl a, Chl b and carotenoids are formed with different kinetics.Analysis of chlorophyll fluorescence emission and excitation spectra revealed a sevenfold increase in the amount of the long wavelength antenna of PSI (720 nm) resulting in an increase in the absorption cross section of PSI during illumination. The underlying changes in molecular organization of PSI were investigated by sucrose density centrifugation of solubilized thylakoids after digitonin treatment and subsequent identification of the components by gel electrophoresis, HPLC and fluorescence. In dark grown cells one blue‐green band (0‐II) could be resolved. This band contained only Chl a and the reaction center complex of PSI, CPI.After 24 hours of illumination three pigmented zones and a small amount of free pigment were observed. One of the zones (24‐I) was identified as a light‐harvesting fraction containing the pigment‐protein complexes LHCP1 and LHCP3. In the second fraction (24‐II) the reaction center complexes of PSI and PSII were found. The highest molecular weight fraction (24‐III) was enriched in PSI‐complexes of higher molecular weight and contained a high amount of long wavelength fluorescence antenna (720 nm) attributed to PSI. In contrast to band 24‐II which contained a high percentage of β‐carotene and a high Chl a/b‐ratio, the Chl a/b‐ratio of fraction 24‐III was lower and the xanthophyll content increased.Our data demonstrate an increase in the PSI‐unit size during chloroplast development in mutant C‐6D of Scenedesmus obliquus. Dark‐grown cultures have small functional PSI‐units composed of the chlorophylls involved in charge separation and the core antenna. This unit contains only Chl a and no carotenoids. After transfer to light Chl b and carotenoids are formed. Simultaneously with the appearance of carotenoids and Chl b, PSI‐complexes of higher molecular weight are synthesized indicating the addition of a LHC to the reaction center complex of PSI.

Mapping of phytoplankton by solar-stimulated fluorescence using an imaging spectrometer

Abstract We present here the first example of a remote sensing image of the solar-stimulated fluorescence emission from marine phytoplankton. The measurements were made with a prototype imaging spectrometer (the Fluorescence Line Imager, FLI) designed to have sufficient sensitivity and spectral resolution to detect and map the relatively narrow band solar-stimulated chlorophyll fluorescence emission at 685 nm. The narrow band fluorescence signal can be relatively easily separated from other components of the backscattered radiance and can give information on the physiological state of the phytoplankton. Successful imaging using this technique demonstrates a new capability in remote sensing of the oceans.

Comparative ultrastructural and fluorescence studies of grapevine ( Vitis vinifera L.) chloroplasts isolated from stem and leaf tissues

Ultrastructural observations of chlorophyll-containing stem tissues (woody shoots) of Vitis vinifera L. show that the chloroplasts in mature sieve elements (phloem and xylem) contain preferentially a large number of appressed (granal) thylakoids. This finding is in close relation with the extremely low chlorophyll a/ b ratios in the stem tissues, which characterizes the photosystem II (PSII)-containing granal membranes. These structural differences are accompanied also by differences in the properties of the low temperature (77K) chlorophyll fluorescence emission. In both phloem and xylem chloroplasts the peak at 735 nm originating from photosystem I (PSI) is strongly reduced and the F 735 F 695 ratio is much more lower than in leaf chloroplasts. Furthermore, the value of the F 735 F 695 ratio in stem tissues depends to a lower extent on the presence of Mg 2+, i.e.,the cation control of excitation energy distribution between PSII and PSI (spillover) is considerably restricted in both phloem and xylem thylakoid membranes.

Flux determinations and physiological response in the exposure of red spruce to gaseous hydrogen peroxide, ozone, and sulfur dioxide

We report on the 3-week exposure of a branch of a forest-grown red spruce (Picea rubens) sapling to the combination of gaseous hydrogen peroxide, ozone, and sulphur dioxide. The exposure was conducted continuously using concentrations of H2O2, O3, and SO2 that have been observed during the summertime on the summit of Whiteface Mountain, New York. Fluxes of H2O, CO2, and the three pollutants were determined throughout the exposure. At weekly intervals, measurements of chlorophyll fluorescence, stomatal conductance, and hydrocarbon emissions were made. The response of the branch was compared to an equivalent branch of the same tree which received no pollutants but was otherwise treated identically. The exposure produced no visible injury symptoms but did produce an increase in dark respiration; the respiration rate more than doubled during the 21-day exposure period. Net photosynthesis was unaffected for both the experimental and the control branches. Nighttime fluxes of SO2 and H2O2 to external plant surfaces were significant. The stomatal component of O3 uptake by the branch displayed a linear increase during the experiment, and showed no evidence of saturating. Daytime and nighttime fluxes of H2O2 were increasing at the end of the experiment. We observed that isoprene is emitted from red spruce, but saw no clear-cut change in emission rate in response to the exposure experiment. Possible relationships between our experimental results and observations of red spruce decline in the forests of the northeastern United States are suggested for further investigation.

An integrated portable apparatus for the simultaneous field measurement of photosynthetic CO2 and water vapour exchange, light absorption and chlorophyll fluorescence emission of attached leaves

Abstract. A portable apparatus has been constructed to measure simultaneously the quantum yield of CO2 assimilation, light absorption, chlorophyll fluorescence emission and water vapour exchange of attached intact leaves in the field. The core of the instrument is a light‐integrating spherical leaf chamber which includes ports for a light source, photosynthetically active radiation sensor, fluorescence probes and gas inlet and outlet manifolds. Measurement of the quantum flux inside the empty chamber and with a leaf present allows determination of leaf absorptance. An open gas exchange system is employed using an infra‐red analyser to measure leaf CO2 exchange. Using a DC white light source the quantum yield of CO2 assimilation based on absorbed light (φabs) may be determined rapidly in either ambient air or artificial gas mixtures. Inclusion of capacitance humidity probes into the gas inlet and outlet ports allows simultaneous determination of water vapour exchange and subsequent estimation of stomatal conductance to CO2 and intercellular CO2 concentration. Measurement of fluorescence emission by the sample leaf exposed to white light is achieved by a modulated fluorescence detection system. In addition to determination of the minimal, maximal and variable fluorescence levels, a further analysis allows the photochemical and non‐photochemical components of fluorescence quenching, to be estimated. The theory and design of this apparatus is described in detail. The use of the apparatus in the field is demonstrated through a study of the photosynthetic performance of a maize and bean crop during the growing season and by analysis of the photosynthetic performance of crops subjected to nitrogen‐stress and a herbicide treatment.

Assessment of photosynthetic activity of nursery-grown Piceaglauca seedlings using an integrating fluorometer to monitor variable chlorophyll fluorescence

Photosynthetic activity of intact nursery-grown white spruce (Piceaglauca (Moench) Voss) seedlings was assessed by measuring CO2 exchange (apparent photosynthesis) and normalized, integrated variable chlorophyll fluorescence emission. Agreement between fluorescence and apparent photosynthesis indicated that photosynthetic inactivation of seedlings from selected seedlots began in mid-August and approached completion in late October. Inactivation occurred somewhat earlier in northern seedlot seedlings than in those from a more southerly provenance. Seedlings tested in late October showed significant photosynthetic inactivation, as indicated by both fluorescence and apparent photosynthesis. These seedlings also had passed the −18 °C frost hardiness test currently used in British Columbia as an indicator for safe lifting. On removal from −2 °C storage, seedlings lifted and stored according to nursery practises showed fluorescence emission indicative of photosynthetic reactivation and also had high root growth capacity scores. Low root growth capacity scores were associated with delayed or incomplete photosynthetic reactivation. These results show that fluorescence assessment provides information about the physiological status of white spruce seedlings. Variable fluorescence assays are nondestructive and can be made and interpreted within minutes. As an indicator of shoot metabolic activity, fluorescence assessment provides information useful in selecting lifting dates and in evaluating the effects of dark cold storage on white spruce seedlings.

Regulation of the distribution of excitation energy in Ochromonas danica, an organism containing a chlorophyll-A/C/carotenoid light harvesting antenna

A chlorophyll a, c-fucoxanthin pigment-protein complex8 functions as the major light harvesting antenna in the Chrysophyte Ochromonas danica. The regulated distribution of excitation energy between the two photosystems was investigated in these organisms and was shown to be strongly wavelength dependent. A light state transition was induced by pre-illumination of cells using light 2 (640 nm) and light 1 (700 nm) of equal absorbed intensity, and detected by reversible changes in the 77 K chlorophyll fluorescence emission spectra. Peaks at ∼ 690 nm and ∼ 720 nm in the low temperature spectra are most likely associated with PS2 and PS1 respectively. A room temperature fluorescence emission at 680 nm induced by modulated light 2 (500 nm) was strongly quenched in the presence of background light 1 (720 nm). Removal of light 1 led to an increase in fluorescence followed by a slow quenching. The room temperature fluorescence changes were directly correlated with changes in the 77 K emission spectra that indicated a change in the distribution of excitation energy between the two photosystems. It was established that DCMU (1 μmol) prevented the state 2. The conversion to state 1 followed a simple photochemical dose dependence and had a half-time of 20 s-1.5 min at 6 W m(-2). In contrast, the conversion to state 2 was independent of light intensity. These data indicate that O. danica undergoes a light state transition in response to the preferential excitation of PS2 or PS1.

Photoinhibition at Low Temperature in Chilling-Sensitive and -Resistant Plants

Photoinhibition resulting from exposure at 7 degrees C to a moderate photon flux density (300 micromoles per square meter per second, 400-700 nanometers) for 20 hours was measured in leaves of annual crops differing widely in chilling tolerance. The incidence of photoinhibition, determined as the decrease in the ratio of induced to total chlorophyll fluorescence emission at 693 nanometers (F(v)/F(max)) measured at 77 Kelvin, was not confined to chilling-sensitive species. The extent of photoinhibition in leaves of all chilling-resistant plants tested (barley [Hordeum vulgare L.], broad bean [Vicia faba L.], pea [Pisum sativum L.], and wheat [Triticum aestivum L.]) was about half of that measured in chilling-sensitive plants (bean [Phaseolus vulgaris L.], cucumber [Cucumis sativus L.], lablab [Lablab purpureus L.], maize [Zea mays L.], pearl millet [Pennisetum typhoides (Burm. f.) Stapf & Hubbard], pigeon pea [Cajanus cajun (L.) Millsp.], sesame [Sesamum indicum L.], sorghum [Sorghum bicolor L. Moench], and tomato [Lycopersicon esculentum Mill.]). Rice (Oryza sativa L.) leaves of the indica type were more susceptible to photoinhibition at 7 degrees C than leaves of the japonica type. Photoinhibition was dependent both on temperature and light, increasing nonlinearly with decreasing temperature and linearly with increasing light intensity. In contrast to photoinhibition during chilling, large differences, up to 166-fold, were found in the relative susceptibility of the different species to chilling injury in the dark. It was concluded that chilling temperatures increased the likelihood of photoinhibition in leaves of both chilling-sensitive and -resistant plants. Further, while the photoinhibition during chilling generally occurred more rapidly in chilling-sensitive plants, this was not related directly to chilling sensitivity.

Monitoring chilling injury: A comparison of chlorophyll fluorescence measurements, post‐chilling growth and visible symptoms of injury in Zea mays

Changes in chlorophyll fluorescence emission from maize (Zea mays L. cv. Northern Belle) seedlings chilled at 1.5°C in the dark for 3–30 h were compared with the ability of plants to resume growth in the immediate post‐chilling period and with the development of visible symptoms of injury to the leaves. During chilling, the maximal rate of increase of the induced chlorophyll fluorescence rise. FR, was measured on secondary leaf tissue. FR decreased exponentially, at approximately the same rate in plants grown and chilled in hydroponic pots, in leaves detached from similar plants and in plants that were removed from the hydroponic pots and laid on wet filter paper adjacent to the detached leaves. The half‐fall time for FR in the 3 treatments was 7.8 ± 1.3 h, 8.6 ± 0.6 h and 8.8 ± 1.0 h, respectively. Following seedling removal from 1.5°C and return to 25/15°C, relative growth rates were determined from daily measurements of plant fresh weight gain. Compared with non‐chilled seedlings, plants chilled for 3 h and longer showed depressed rates of growth. Inhibition of growth in the immediate post‐chilling period (0–27 h) was linearly related to the duration of the chilling period and had a high positive correlation with the decrease in chlorophyll fluorescence (linearly related to log FR) sustained during the chilling exposure. Visible symptoms of chilling injury developed during the post‐chilling period on seedlings chilled for longer than 3 h. The decrease in log FR during chilling was also linearly correlated with the severity of visual symptoms of chilling injury expressed in the post‐chilling period. It is concluded that the extent of chilling injury in maize can be rapidly and non‐destructively assessed from measurements of chlorophyll fluorescence.

Molecular Events of Photoinhibitory Inactivation in the Reaction Centre of Photosystem II

The events of photoinhibition were examined at the molecular level. The evidence presented here suggests that the primary event of photoinhibition involves inactivation of photosystem II reaction centre function. Chlorophyll fluorescence emission and excitation spectra and fluorescence induction transients were suppressed after photoinhibitory treatment. Such fluorescence is directly dependent on photosystem II photochemistry. In addition, photoinhibition caused a decline in charge separation measured by the absorbance change at 320 nm arising from the light-induced reduction of the primary acceptor of photosystem II, QA. Inhibition of this parameter is indicative of damage to a component involved in primary photochemistry. That the effect of high light treatment could not be correlated with any loss of the D1 protein supports the suggestion that a cofactor involved in primary photochemistry is the initial site of photoinhibition. It is possible that D1 may eventually be lost as a result of such damage. The reaction centre chlorophyll of photosystem II, P680, is suggested to be the cofactor involved. Possible mechanisms of damage are discussed with reference to the prosthetic components of the reaction centre of photosynthetic bacteria.

Photoinhibition, 77K chlorophyll fluorescence quenching and phosphorylation of the light-harvesting chlorophyll-protein complex of photosystem II in soybean leaves

When the capacity of leaves for orderly dissipation of excitation energy in photosynthesis is exceeded, one mechanism by which the excess energy appears to be dissipated is through a nonradiative decay process. This process is observed as a reversible quenching of chlorophyll fluorescence emission (77K) from both photosystem II and photosystem I which persists in darkness (Demmig and Björkman 1987, Planta 171, 171-184). Fluorescence quenching was induced in soybean (Glycine max (L.) Merr.) leaves by two methods: 1) changing the composition of the gas surrounding the leaf from normal air to 2% O2, 0% CO2 at a low, constant photon flux density (PFD=photon fluence rate), and 2) increasing the PFD in the presence of normal air. In either case the quenching was fully reversible after return to the original condition (low PFD, normal air). The half-time of the relaxation of the quenching was in the order of 30 min. Both treatments resulted in reversible dephosphorylation of the light-harvesting chlorophyll-protein complex of photosystem II (LHC-II). Treatment under photoinhibitory conditions (high PFD plus chloramphenicol) also caused dephosphorylation of LHC-II. Therefore, phosphorylation of LHC-II cannot account for the observed fluorescence quenching. In addition, our results indicate that in vivo a factor other than the redox state of the plastoquinone pool controls LHC-II phosphorylation. This factor may be ΔpH, the pH gradient across the thylakoid membranes.

Chlorophyll Fluorescence Signatures of Leaves during the Autumnal Chlorophyll Breakdown

Summary The change of the in situ chlorophyll fluorescence spectra, the fluorescence induction kinetics (Kautsky effect: slow component) and the content of photosynthetic pigments were determined in green and yellowish-green leaves of wild vine ( Parthenocissus tricuspidata Veitchii ) during the autumnal senescence. Lower values for the ratio chlorophylls/carotenoids indicate a faster breakdown of chlorophylls than carotenoids. The intensity of the chlorophyll fluorescence of leaves rises with the decline of photosynthesis during increasing senescence and chlorophyll breakdown. The fluorescence intensity decreases again only in yellow leaves at a progressed stage of chlorophyll breakdown. The beginning decline of photosynthesis is visible in the variable fluorescence induction kinetics by a very low fluorescence decrease (fd) from the maximum (fmax) before changes in the pigment content are detectable. This is indicated by very low values of the fluorescence ratio Rfd. The chlorophyll fluorescence emission spectra of green Parthenocissus leaves exhibit two maxima near 690 and 735 nm. During the autumnal senescence the ratio of fluorescence at these wavelengths (ratio F 690/F 735) increases from values of ca. 1 to 8. The possibility of remote sensing of the decline of broadleaf vegetation via the changing chlorophyll fluorescence ratio F 690/F 735 is discussed.