Pulse Amplitude Modulated Chlorophyll Fluorescence Research Articles

Key stress indicators from chlorophyll fluorescence in five desert plant species

Pulse-amplitude modulated chlorophyll fluorescence (ChlF) is widely used to measure environmental stress in plants. Yet, its continuous, long-term usage in situ is challenged due to the lack of appropriate daytime indicators. We investigated the prospect of creating new daytime indicators based on an application of linear regression on daily measurements of photochemical efficiency (ФPSII) and photosynthetically active radiation acquired in situ at 30-minute intervals. Daily regression parameters, thus generated, were subsequently used in a broader context of desert-plant response to environmental change. Here, we compared parametric and non-parametric methods to test the feasibility of daytime-based regression parameters, i.e., maximal quantum yield of photosystem II photochemistry (Fv/Fm) and daily mean ФPSII, in gauging physiological response in three shrub and two herb species as influenced by eight environmental variables. Results demonstrated that: (i) Random Forest (RF; a non-parametric method) provided the best assessment of interaction between ChlF-based parameters and environmental variables, compared with multiple linear regression (MLR; a conventional parametric method); (ii) variable importance and partial dependence plots indicated that the daily regression parameters of the ФPSII-to- photosynthetic photon flux density relationship (y-intercept and slope) were superior to those of ФPSII and Fv/Fm; and (iii) compared with Fv/Fm, the y-intercept and slope improved discrimination of interspecific differences (p < 0.05). Our research showed that the regression y-intercept and slope can serve as practical daytime indicators of desert-plant photosynthetic physiology in field applications of continuous ChlF measurements. RF is extremely skilled at capturing nonlinearities in eco-environmental interactions compared with standard parametric methods. This new method provides a basis for the collection of key ecological information in assessing desert-plant physiological response to environmental variability.

Problems in estimation of photosynthesis in cyanobacteria by pulseamplitude modulation chlorophyll fluorescence

Problems in estimation of photosynthesis in cyanobacteria by pulseamplitude modulation chlorophyll fluorescence

Photosynthetic fluctuation accompanied by translocation of chloroplasts in Ulva conglobata (Ulvophyceae) grown under a low irradiance regime

SUMMARYFluctuations in photosynthetic characteristics related to chloroplast translocation have been known in the foliose green algae Ulva lactuca var. latissima and var. rigida and U. mutabilis according to photoperiod. In Ulva, the single parietal chloroplast is found along the thallus surface wall and exhibits high photosynthetic activity during the light period; the chloroplast then moves towards the side walls and shows low photosynthetic activity during the dark period. In this study, we re‐investigated whether the photosynthetic ability is dependent on chloroplast location in a unialgal culture of U. conglobata grown and maintained under low irradiance regime by analyzing in vivo absorption spectra, oxygen evolution, and pulse amplitude modulation chlorophyll fluorescence. The light absorbance of the thallus was higher when chloroplast was along the thallus surface wall than when along the side walls and, therefore, the thallus absorbance at 680 nm was used as an index of chloroplast position. Some photosynthetic parameters such as maximum net photosynthetic rate per thallus area and effective quantum yield of photosystem II correlated with the thallus absorbance. The highest rate and absorption were reached 3 to 9 h after the beginning of light period (12 h), which gradually decreased at 10 to 15 h after the beginning of light or dark period. The lowest rate and absorption was observed after the beginning of the dark period. The chloroplast movement was inhibited for 12 h by colchicine, and photosynthetic parameters were found to be dependent on various chloroplast positions in the thallus. Interestingly, the chloroplast moved to the surface and the side walls of the cells under continuous dark and light conditions, respectively, at approximately 48 to 72 h. However, decreased maximum quantum yield was observed under both continuous dark and light conditions.

Optimal temporal-spatial fluorescence techniques for phenotyping nitrogen status in oilseed rape.

Nitrogen (N) fertilizer maximizes the growth of oilseed rape (Brassica napus L.) by improving photosynthetic performance. Elucidating the dynamic relationship between fluorescence and plant N status could provide a non-destructive diagnosis of N status and the breeding of N-efficient cultivars. The aim of this study was to explore the impacts of different N treatments on photosynthesis at a spatial-temporal scale and to evaluate the performance of three fluorescence techniques for the diagnosis of N status. One-way ANOVA and linear discriminant analysis were applied to analyze fluorescence data acquired by a continuous excitation chlorophyll fluorimeter (OJIP transient analysis), pulse amplitude-modulated chlorophyll fluorescence (PAM-ChlF), and multicolor fluorescence (MCF) imaging. The results showed that the maximum quantum efficiency of PSII photochemistry (Fv/Fm) and performance index for photosynthesis (PIABS) of bottom leaves were sensitive to N status at the bolting stage, whereas the red fluorescence/far-red fluorescence ratio of top leaves was sensitive at the early seedling stage. Although the classification of N treatments by the three techniques achieved comparable accuracies, MCF imaging showed the best potential for early diagnosis of N status in field phenotyping because it had the highest sensitivity in the top leaves, at the early seedling stage. The findings of this study could facilitate research on N management and the breeding of N-efficient cultivars.

Influence of Foliar Kaolin Application and Irrigation on Photosynthetic Activity of Grape Berries

Climate changes may cause severe impacts both on grapevine and berry development. Foliar application of kaolin has been suggested as a mitigation strategy to cope with stress caused by excessive heat/radiation absorbed by leaves and grape berry clusters. However, its effect on the light micro-environment inside the canopy and clusters, as well as on the acclimation status and physiological responses of the grape berries, is unclear. The main objective of this work was to evaluate the effect of foliar kaolin application on the photosynthetic activity of the exocarp and seeds, which are the main photosynthetically active berry tissues. For this purpose, berries from high light (HL) and low light (LL) microclimates in the canopy, from kaolin-treated and non-treated, irrigated and non-irrigated plants, were collected at three developmental stages. Photochemical and non-photochemical efficiencies of both tissues were obtained by a pulse amplitude modulated chlorophyll fluorescence imaging analysis. The maximum quantum efficiency (Fv/Fm) data for green HL-grown berries suggest that kaolin application can protect the berry exocarp from light stress. At the mature stage, exocarps of LL grapes from irrigated plants treated with kaolin presented higher Fv/Fm and relative electron transport rates (rETR200) than those without kaolin. However, for the seeds, a negative interaction between kaolin and irrigation were observed especially in HL grapes. These results highlight the impact of foliar kaolin application on the photosynthetic performance of grape berries growing under different light microclimates and irrigation regimes, throughout the season. This provides insights for a more case-oriented application of this mitigation strategy on grapevines.

Noninvasive Phenotyping of Plant-Pathogen Interaction: Consecutive In Situ Imaging of Fluorescing Pseudomonas syringae, Plant Phenolic Fluorescence, and Chlorophyll Fluorescence in Arabidopsis Leaves.

Plant–pathogen interactions have been widely studied, but mostly from the site of the plant secondary defense. Less is known about the effects of pathogen infection on plant primary metabolism. The possibility to transform a fluorescing protein into prokaryotes is a promising phenotyping tool to follow a bacterial infection in plants in a noninvasive manner. In the present study, virulent and avirulent Pseudomonas syringae strains were transformed with green fluorescent protein (GFP) to follow the spread of bacteria in vivo by imaging Pulse-Amplitude-Modulation (PAM) fluorescence and conventional binocular microscopy. The combination of various wavelengths and filters allowed simultaneous detection of GFP-transformed bacteria, PAM chlorophyll fluorescence, and phenolic fluorescence from pathogen-infected plant leaves. The results show that fluorescence imaging allows spatiotemporal monitoring of pathogen spread as well as phenolic and chlorophyll fluorescence in situ, thus providing a novel means to study complex plant–pathogen interactions and relate the responses of primary and secondary metabolism to pathogen spread and multiplication. The study establishes a deeper understanding of imaging data and their implementation into disease screening.

Improvement of the rice photosynthetic apparatus defence under cadmium stress modulated by salicylic acid supply to roots

The present study was conducted to investigate the effect of exogenous salicylic acid (SA) added to the nutrient solution on the growth parameters and the functions of the photosynthetic apparatus of rice plants under cadmium (Cd) stress. Our investigations have shown that 10 µM SA has an optimal effect in rice plants grown hydroponically. Pulse amplitude modulated chlorophyll fluorescence, low-temperature chlorophyll fluorescence, oxygen evolution (measured with Clark-type and Joliot-type electrodes) and P700 photo-oxidation measurements were carried out to assess the effect of SA on the activity of the photosynthetic apparatus. The levels of three important parameters associated with oxidative stress (hydrogen peroxide, lipid peroxidation and proline content) were measured. The application of low concentration of SA significantly decreased the levels of hydrogen peroxide, lipid peroxidation and proline under Cd stress. The results revealed that low concentration of SA, applied in plants exposed to 150 µM CdCl2, significantly improves plant growth, photochemical activities of both photosystems, the electron flow from QA to plastoquinone, energetic distribution between pigment-protein complexes and the kinetic parameters of oxygen-evolving reactions. This study suggests that exogenous application of 10 µM SA through the rooting medium has a protective effect against Cd toxicity in rice plants. The possible molecular mechanisms involved in the defence effect of SA on the function of photosynthetic apparatus are discussed.

Linking chloroplast relocation to different responses of photosynthesis to blue and red radiation in low and high light-acclimated leaves of Arabidopsis thaliana (L.).

Low light (LL) and high light (HL)-acclimated plants of A. thaliana were exposed to blue (BB) or red (RR) light or to a mixture of blue and red light (BR) of incrementally increasing intensities. The light response of photosystem II was measured by pulse amplitude-modulated chlorophyll fluorescence and that of photosystem I by near infrared difference spectroscopy. The LL but not HL leaves exhibited blue light-specific responses which were assigned to relocation of chloroplasts from the dark to the light-avoidance arrangement. Blue light (BB and BR) decreased the minimum fluorescence ([Formula: see text]) more than RR light. This extra reduction of the [Formula: see text] was stronger than theoretically predicted for [Formula: see text] quenching by energy dissipation but actual measurement and theory agreed in RR treatments. The extra [Formula: see text] reduction was assigned to decreased light absorption of chloroplasts in the avoidance position. A maximum reduction of 30% was calculated. Increasing intensities of blue light affected the fluorescence parameters NPQ and qP to a lesser degree than red light. After correcting for the optical effects of chloroplast relocation, the NPQ responded similarly to blue and red light. The same correction method diminished the color-specific variations in qP but did not abolish it; thus strongly indicating the presence of another blue light effect which also moderates excitation pressure in PSII but cannot be ascribed to absorption variations. Only after RR exposure, a post-illumination overshoot of [Formula: see text] and fast oxidation of PSI electron acceptors occurred, thus, suggesting an electron flow from stromal reductants to the plastoquinone pool.

Quantifying the efficiency of photoprotection.

A novel emerging technology for the assessment of the photoprotective ‘power’ of non-photochemical fluorescence quenching (NPQ) has been reviewed and its insightful outcomes are explained using several examples. The principles of the method are described in detail as well as the work undertaken for its justification. This pulse amplitude modulated chlorophyll fluorescence approach has been applied for the past 5 years to quantify the photoprotective effectiveness of the NPQ and the light tolerance in Arabidopsis plants grown under various light conditions, during ontogenetic development as well as in a range of mutants impaired in carotenoid and protein biosynthesis. The future applications of this approach for the assessment of crop plant light tolerance are outlined. The perspective of obtaining detailed information about how the extent of photoinhibition and photoprotection can affect plant development, growth and productivity is highlighted, including the potential for us to predict the influence of environmental elements on plant performance and yield of crops. The novel methodology can be used to build up comprehensive light tolerance databases for various current and emerging varieties of crops that are grown outdoors as well as in artificial light environments, in order to optimize for the best environmental conditions that enable high crop productivity.This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.

Effect of high light intensity on the photosynthetic apparatus of two hybrid lines of Paulownia grown on soils with different salinity

The objective of this investigation was to evaluate the simultaneous action of light stress and salinity. Pulse amplitude modulated chlorophyll fluorescence, P700 redox state, and pigment analysis were used to assess the impact of high light intensity on Paulownia tomentosa × fortunei and Paulownia elongata × elongata grown on soils with different salinity. It was found that light stress reduced the amount of pigments and the efficiency of photochemical energy conversion, inhibited the maximum and the effective quantum yields of PSII photochemistry, decreased photochemical quenching and photosynthetic rate. Data also showed influence on the primary quinone acceptor (QA) reoxidation, which led to the restriction of the electron flow from QA to plastoquinone and stimulation of the cyclic electron flow. The possible reasons for the increased effects of the light stress under conditions of high salt concentration in soil for Paulownia tomentosa × fortunei are discussed.

Estimation of photosynthesis in cyanobacteria by pulse-amplitude modulation chlorophyll fluorescence: problems and solutions.

Cyanobacteria are photosynthetic prokaryotes and widely used for photosynthetic research as model organisms. Partly due to their prokaryotic nature, however, estimation of photosynthesis by chlorophyll fluorescence measurements is sometimes problematic in cyanobacteria. For example, plastoquinone pool is reduced in the dark-acclimated samples in many cyanobacterial species so that conventional protocol developed for land plants cannot be directly applied for cyanobacteria. Even for the estimation of the simplest chlorophyll fluorescence parameter, F v/F m, some additional protocol such as addition of DCMU or illumination of weak blue light is necessary. In this review, those problems in the measurements of chlorophyll fluorescence in cyanobacteria are introduced, and solutions to those problems are given.

Microalgal consortia differentially modulate progressive adsorption of hexavalent chromium.

A set of experiments was conducted to provide significant insights of micro-algal consortia regarding chromium adsorption. Four monocultures; Scenedesmus dimorphus, Chlorella sp., Oscillatoria sp., and Lyngbya sp., and their synthetic consortia were evaluated initially for chromium bio-adsorption at four different regimes of hexavalent chromium i.e. 0.5, 1.0, 3.0 and 5.0ppm. Based on findings, only 1.0 and 5.0ppm were considered for future experiments. Consequently, three different types of monoculture and consortia cells namely; live cells, heat-killed cells, and pre-treated cells were prepared to enhance their adsorption potential. Maximal adsorption of 112% was obtained at the dose of 1.0ppm with 0.1% SDS pre-treated consortia cells over live consortia cells. In support, atomic absorption spectroscopy, laser induced breakdown spectroscopy, pulse amplitude modulated chlorophyll fluorescence, and scanning electron microscopy were performed to assess the structural and functional changes within consortia and their utilization in mitigation of elevated chromium levels.

Diurnal Solar Energy Conversion and Photoprotection in Rice Canopies.

Genetic improvement of photosynthetic performance of cereal crops and increasing the efficiency with which solar radiation is converted into biomass has recently become a major focus for crop physiologists and breeders. The pulse amplitude modulated chlorophyll fluorescence technique (PAM) allows quantitative leaf level monitoring of the utilization of energy for photochemical light conversion and photoprotection in natural environments, potentially over the entire crop lifecycle. Here, the diurnal relationship between electron transport rate (ETR) and irradiance was measured in five cultivars of rice (Oryza sativa) in canopy conditions with PAM fluorescence under natural solar radiation. This relationship differed substantially from that observed for conventional short term light response curves measured under controlled actinic light with the same leaves. This difference was characterized by a reduced curvature factor when curve fitting was used to model this diurnal response. The engagement of photoprotective processes in chloroplast electron transport in leaves under canopy solar radiation was shown to be a major contributor to this difference. Genotypic variation in the irradiance at which energy flux into photoprotective dissipation became greater than ETR was observed. Cultivars capable of higher ETR at midrange light intensities were shown to produce greater leaf area over time, estimated by noninvasive imaging.

Influence of the sanosil-induced oxidative stress on the photosynthetic apparatus of different strains of green algae and cyanobacteria

Photosynthetic oxygen evolution (measured by polarographic oxygen rate electrode) and pulse amplitude modulated chlorophyll fluorescence were used to assess the effect of sanosil-induced oxidative stress on photosystem II (PSII) in the green alga Chlorella vulgaris and the cyanobacterium Synechocystis salina isolated from Antarctic and mesophilic environments. This study revealed a relatively stronger influence of sanosil (especially its main component, hydrogen peroxide) on the donor site (oxygen evolving complex) compared to the acceptor side of the PSII in both green algae and cyanobacteria. The inhibition of the oxygen evolution results mainly from a decrease in the fast operating PSII centers. In addition, the obtained data showed that the effects of the oxidative stress on the cyanobacterium and the green alga strongly depend on the antenna size of PSII.

Factors influencing the distribution of coastal lichens Hydropunctaria maura and Wahlenbergiella mucosa

AbstractResponses to abiotic and biotic stresses that potentially drive the vertical zonation of the intertidal lichens Hydropunctaria maura, an upper littoral lichen, and Wahlenbergiella mucosa, a lower littoral lichen, were investigated in field and laboratory experiments. When transplanted, both lichens exhibited an inability to survive outside their normal vertical distribution range. W. mucosa appeared to be unable to tolerate prolonged periods of desiccation following translocation from lower to upper littoral regions, whereas H. maura was unable to survive in lower littoral zones possibly owing to increased grazing pressure. The effect of desiccation in both lichens was compared using pulse amplitude modulated chlorophyll fluorescence and infra‐red gas analysis; results indicated a more hydration‐dependent nature of W. mucosa. Photosynthetic (algal) pigments and phenolic compounds were determined in both lichen thalli, and a range of additional coastal lichens occupying a natural gradient from upper to lower shore levels. Pigment composition and concentration in both lichen thalli were similar whereas levels of phenolic compounds were up to three times higher in W. mucosa than H. maura. Pigment and phenolic concentration and composition exhibited some seasonality across 13 different lichens originating from different shore levels. Phenolic concentration increased towards the lower shore, suggesting a potential anti‐herbivory function. This marks the first study of pigments and phenolics in coastal lichen communities, and prompts further investigations on the particular physiological features of marine and maritime lichens that enable them to thrive in this extreme environment.

Effect of UV-B radiation on photosystem II functions in Antarctic and mesophilic strains of a green alga Chlorella vulgaris and a cyanobacterium Synechocystis salina

The green alga Chlorella vulgaris and the cyanobacterium Synechocystis salina cells isolated from Antarctic and mesophilic environments, grown in batch cultures under continuous visible light, were used to assess the effect of the UV-B radiation on the photosystem II (PSII). UV-induced changes in its functional activity were estimated by Pulse Amplitude Modulated chlorophyll fluorescence and oxygen evolution (measured with oxygen rate electrode). The data reveal a relatively stronger UV-B-induced inhibition of oxygen evolution in comparison to that of the primary photochemistry of the PSII in both green algae and cyanobacteria. The inhibition of oxygen evolution was a result of the decrease in the number of functionally active PSII centers. The modification of active reaction centers was also recorded through the relatively more effect on fast operating PSII centers than that of the slow operating PSII centers. On the other hand, the PSII activity of cyanobacteria was more vulnerable to UV-B radiation than that of green algae. Likewise, the mesophilic strain of S. salina was more susceptible to UV-B radiation than the Antarctic isolates.

Mapping Grape Berry Photosynthesis by Chlorophyll Fluorescence Imaging: The Effect of Saturating Pulse Intensity in Different Tissues

Grape berry development and ripening depends mainly on imported photosynthates from leaves, however, fruit photosynthesis may also contribute to the carbon economy of the fruit. In this study pulse amplitude modulated chlorophyll fluorescence imaging (imaging-PAM) was used to assess photosynthetic properties of tissues of green grape berries. In particular, the effect of the saturation pulse (SP) intensity was investigated. A clear tissue-specific distribution pattern of photosynthetic competence was observed. The exocarp revealed the highest photosynthetic capacity and the lowest susceptibility to photoinhibition, and the mesocarp exhibited very low fluorescence signals and photochemical competence. Remarkably, the seed outer integument revealed a photosynthetic ability similar to that of the exocarp. At a SP intensity of 5000 μmol m(-2) s(-1) several photochemical parameters were decreased, including maximum fluorescence in dark-adapted (F(m)) and light-adapted (F'(m)) samples and effective quantum yield of PSII (Φ(II)), but the inner tissues were susceptible to a SP intensity as low as 3200 μmol m(-2) s(-1) under light-adapted conditions, indicating a photoinhibitory interaction between SP and actinic light intensities and repetitive exposure to SP. These results open the way to further studies concerning the involvement of tissue-specific photosynthesis in the highly compartmentalized production and accumulation of organic compounds during grape berry development.

高浓度CO2引起的海水酸化对小珊瑚藻光合作用和钙化作用的影响

Increasing atmospheric CO2 is causing global public concern and seabed sequestration is one possible method of carbon reduction.However,studies on the potential risk of CO2 leakage and its possible effects on the marine environment are still very limited.To investigate such possible effects on sensitive marine organisms,coralline algae,Corallina pilulifera,were cultured under controlled conditions: 20℃,100μmol photons m-2 s-1 and a light period of 12h.Three treatments were set at acidities of pH 8.1,6.8 and 5.5,by aerating natural seawater with pure gaseous CO2.After 24 hours,photosynthesis and calcification rates of C.pilulifera cultured at different pH levels were determined.The rate of photosynthetic carbon fixation was enhanced at the pH of 6.8 and was inhibited at the pH of 5.5,compared with the algae grown in the seawater control(pH 8.1).The rate of calcified carbon fixation was depressed with decreasing pH,and even exhibited a negative value [(-2.53±0.57) mg C(g DW)-1 h-1] at pH 5.5.Additionally,with the decrease in pH,the ratio of particulate inorganic carbon(PIC) to particulate organic carbon(POC) content in the algae,measured with a vario TOC cube,decreased remarkably,which reflected the comprehensive effects of CO2-induced seawater acidification on photosynthesis and calcification.Rapid light curves of algae cultured at different pH levels,which indicated the responses of electron transport rates(ETR) in photosystem II(PS II) to irradiance,were determined by pulse amplitude modulated chlorophyll fluorescence(PAM).The results showed that the photoinhibition term(a) increased with the decrease in pH,indicating that algae grown at lower pH levels experience greater photoinhibition.The light saturation point(Ik) decreased significantly under the CO2-induced acidification conditions,though a significant difference was not found between pH of 6.8 and 5.5.The initial slope of the rapid light curve(α),reflecting the efficiency of the electron transport rate at low irradiance,was lower at pH 5.5 than at the other two levels,while there was no significant difference between pH 8.1 and 6.8 levels.The maximum relative electron transport rate(rETRmax) exhibited the highest value in algae cultured at pH 6.8 and the lowest at pH 5.5.According to these results,we concluded that CO2-induced seawater acidification noticeably affected the photosynthesis and calcification of C.pilulifera,and different degrees of acidification caused different responses of photosynthesis and calcification.At the lowest pH level(pH 5.5),both the photosynthesis and calcification of C.pilulifera were significantly inhibited.These results provide a reference for studies on the risk of CO2 leakage from seabed sequestration methods on the physiology and ecology of marine coralline algae.

Metal accumulation and toxicity measured by PAM—Chlorophyll fluorescence in seven species of marine macroalgae

The effects of five metals, copper (Cu), chromium (Cr), Zinc (Zn), cadmium (Cd) and lead (Pb), on photosynthetic activity, measured as pulse amplitude modulation (PAM) chlorophyll fluorescence yield, was monitored in seven species of green, red and brown macroalgae over a 14 d period. The 10 μmol l −1 of Cr and Zn reduced chlorophyll fluorescence of all species by day 4, and 10 μmol l −1 of Cu and Cd reduced the fluorescence of some species; however, fluorescence yields of all species were unaffected by 10 μmol l −1 of Pb. Metals were generally accumulated in the order of Cu>Pb>Zn>Cr>Cd. Ulva intestinalis accumulated the highest amounts of all metals, and Cladophora rupestris the lowest. A relationship between internal metal concentration and fluorescence was not always evident as in some cases fluorescence was reduced at low metal contents. In the case of Zn, fluorescence was lowest in plants which contained lowest concentrations after 14 d-exposure, possibly because plants had died and Zn leached out of the algal cells. The relationship between internal metal concentration and fluorescence was algal species and metal-specific.

Detection of Heterodera schachtii infestation in sugar beet by means of laser-induced and pulse amplitude modulated chlorophyll fluorescence

AbstractTwo glasshouse experiments with sugar beet cvs Penta and Macarena inoculated, respectively, with 0 or 1500 and 0, 500, 1000 or 1500 juveniles of Heterodera schachtii, were conducted to estimate the capability of laser-induced chlorophyll fluorescence (LIF) and pulse amplitude modulated (PAM) chlorophyll fluorescence techniques to detect H. schachtii infestation and to differentiate between infestation levels. Fluorescence and gas exchange parameters, nitrogen and chlorophyll content of sugar beet leaves were measured weekly after nematode inoculation. Sugar beet plants responded to H. schachtii infestation initially with a decrease in photosynthesis rate and later with a reduction in nitrogen uptake and chlorophyll concentration. At the early stages of nematode infestation, before visual symptoms were evident, infested sugar beet plants displayed increased fluorescence (F680, F740). Later stages of infection were accompanied by an increase in the F686/F740 ratio, ground fluorescence (Fo) and a decrease in photochemical efficiency (Fv/Fm) induced by degradation of leaf chlorophyll. Sugar beet plants infested with 500, 1000 or 1500 juveniles per 100 cm3 of soil did not differ either in their nitrogen and chlorophyll content or in photosynthesis and transpiration rate. The linear discrimination analysis based on the combination of PAM and LIF parameters resulted in 100% correct classification of control plants and high classification rates (60-100%) of the infested treatments on all the sampling dates. Whether the fluorescence technique will differentiate nematode densities under field conditions needs further study.