Monitoring Of Chlorophyll Fluorescence Research Articles

Hyperspectral and Photodiode Retrievals of Nighttime LED‐Induced Chlorophyll Fluorescence (LEDIF) for Tracking Photosynthetic Phenology in a Vineyard

AbstractThe magnitude of chlorophyll fluorescence emission represents both chlorophyll content and energy quenching processes enabling its application to serve as a proxy of photosynthetic activity. Thus, there is interest in advancing methods for canopy‐scale monitoring of chlorophyll fluorescence. Remotely sensed solar‐induced fluorescence (SIF) retrievals offer daytime monitoring of chlorophyll fluorescence, which can serve as an indicator of photosynthesis. However, it represents an instantaneous measurement during the day, which is strongly influenced by incoming radiation, solar angle, and sun/shade fraction—making it difficult to tease out baseline information on plant health and potential photosynthetic capacity—which could be tracked by changes in fluorescence yield (independent of sunlight). Recent advances have demonstrated the potential for inducing nighttime chlorophyll fluorescence via LED light sources at the canopy‐scale, which can be retrieved as LED‐induced chlorophyll fluorescence (LEDIF), potentially serving as a baseline indicator of plant health and photochemical capacity, independent of daytime conditions. In this study, we explored two methods of LEDIF retrievals: (a) hyperspectral sensor (1.33 nm full‐width half max) and (b) low‐cost Red‐Far‐Red photodiode sensor. LEDIF retrieved by the hyperspectral sensor demonstrated strong correlations with daytime SIF and gross primary productivity during mid to end of season phenology (R2 > 0.70). In contrast, phenological dynamics of LEDIF retrieved by the photodiode sensor was more subtle, likely due to weaker signal‐to‐noise ratio, but still demonstrated some potential. Overall, LEDIF offers a technique to monitor nighttime chlorophyll fluorescence emissions (and changes in its spectral shape with a hyperspectral sensor) to assess canopy‐scale phenology of photosynthetic potential.

Exploring the Potential of Solar-Induced Chlorophyll Fluorescence Monitoring Drought-Induced Net Primary Productivity Dynamics in the Huang-Huai-Hai Plain Based on the SIF/NPP Ratio

Drought causes significant losses in vegetation net primary productivity (NPP). However, the lack of real-time, large-scale NPP data poses challenges in analyzing the relationship between drought and NPP. Solar-induced chlorophyll fluorescence (SIF) offers a real-time approach to monitoring drought-induced NPP dynamics. Using two drought events in the Huang–Huai–Hai Plain from 2010 to 2020 as examples, we propose a new SIF/NPP ratio index to quantify and evaluate SIF’s capability in monitoring drought-induced NPP dynamics. The findings reveal distinct seasonal changes in the SIF/NPP ratio across different drought events, intensities, and time scales. SIF demonstrates high sensitivity to commonly used vegetation greenness parameters for NPP estimation (R2 > 0.8, p < 0.01 for SIF vs NDVI and SIF vs LAI), as well as moderate sensitivity to land surface temperature (LST) and a fraction of absorbed photosynthetically active radiation (FAPAR) (R2 > 0.5, p < 0.01 for SIF vs FAPAR and R2 > 0.6, p < 0.01 for SIF vs LST). However, SIF shows limited sensitivity to precipitation (PRE). Our study suggests that SIF has potential for monitoring drought-induced NPP dynamics, offering a new approach for real-time monitoring and enhancing understanding of the drought–vegetation productivity relationship.

Continuous Wavelet Transform and Back Propagation Neural Network for Condition Monitoring Chlorophyll Fluorescence Parameters Fv/Fm of Rice Leaves

The chlorophyll fluorescence parameter Fv/Fm (maximum photosynthetic efficiency of optical system II) is an intrinsic index for exploring plant photosynthesis. Hyperspectral remote sensing technology can be used for rapid nondestructive detection of chlorophyll fluorescence parameters. Existing studies show that there is a good correlation between the vegetation index and Fv/Fm. However, due to the limited hyperspectral information reflected by the vegetation index, the established model often cannot reach the ideal accuracy. Therefore, this study took rice as the research object and explored the internal relationship between chlorophyll fluorescence parameters and spectral reflectance by setting different fertilization treatments. Spectral sensitive information was extracted by vegetation index and continuous wavelet transform (CWT) to explore a more suitable method for Fv/Fm hyperspectral estimation at the rice leaf scale. Then a monitoring model of Fv/Fm in rice leaves was established by the back propagation neural network (BPNN) algorithm. The results showed that: (1) the accuracy of univariate models constructed by Fv/Fm inversion based on 10 commonly used vegetation indices constructed by traditional methods was low; (2) The correlation between leaf hyperspectral reflectance and Fv/Fm could be effectively improved by using CWT, and the accuracy of the univariate model constructed by using the best wavelet coefficients could reach the level of rough evaluation of Fv/Fm; (3) The effect of wavelet transform using different mother wavelet functions as the basis function was different, and bior3.3 function was the best; R2, RMSE and RPD of the BPNN model constructed by using the first 10 best wavelet coefficients decomposed by the bior3.3 was 0.823 6, 0.013 2 and 2.304 3. In conclusion, this study proves that CWT can effectively extract sensitive bands of rice leaves for Fv/Fm monitoring, providing a reference for the follow-up rapid and nondestructive monitoring of chlorophyll fluorescence.

Integration of biophysical photosynthetic parameters into one photochemical index for early detection of Tobacco Mosaic Virus infection in pepper plants

Photosynthesis in host plants is significantly reduced by many virus families. The early detection of viral infection before the onset of visual symptoms in both directly and systemically infected leaves is critical in crop protection. Viral pathogens cause a variety of symptoms through modifications of chloroplast structure and function and the response of the photochemistry process is immediate. Therefore, chlorophyll fluorescence monitoring has been extensively investigated the last two decades as a tool for timely assessment of pathogenic threats. Alternatively, the analysis of Chla fluorescence transients offers several interlinked parameters which describe the fate of excitation energy round and through the photosystems. Additionally, OJIP fluorescence transients and leaf reflectance spectra methodologies serve for rapid screening of large number of samples. The objective of the present study was to achieve early detection of viral infection, integrating the multiparametric information of the Chla fluorescence transients and of the leaf reflectance spectra into one photochemical performance index. Infection decreased the maximum quantum yield of PSII (FV/FM), the effective quantum yield of PSII (ΦPSII), the CO2 assimilation rate (A) and the stomatal conductance (gs) in the studied TMV-pepper plant pathosystem, while non-photochemical quenching (NPQ) increased. Some parameters from the OJIP transients and the leaf reflectance spectra were significantly affected 24 h after infection, while others modified three to five days later. Similar results were obtained from systemically infected leaves but with one to three days hysteresis compared to inoculated leaves. Differences between healthy and infected leaves were marginal during the first 24 h post infection. The Integrated Biomarker Response tool was used to create a photochemical infection index (PINFI) which integrates the partial effects of infection on each fluorescence and reflectance index. The PINFI, which to the best of our knowledge is the first photochemical infection index created by the IBR method, discriminated reliably between the infected and healthy leaves of pepper plants from the first 24 h after infection with the TMV.

Deficiency in flavodiiron protein Flv3 promotes cyclic electron flow and state transition under high light in the cyanobacterium Synechocystis sp. PCC 6803

Photosynthetic organisms adjust their activity to changes in irradiance by different ways, including the operation of cyclic electron flow around photosystem I (PSI) and state transitions that redistribute amounts of light energy absorbed by PSI and PSII. In dark-acclimated wild type cells of Synechocystis PCC 6803, linear electron transport was activated after the first 500 ms of illumination, while cyclic electron flow around PSI was long predominant in the mutant deficient in flavodiiron protein Flv3. Chlorophyll P700 oxidation associated with activation of linear electron flow extended in the Flv3− mutant to several tens of seconds and included a P700+ re-reduction phase. Parallel monitoring of chlorophyll fluorescence and the redox state of P700 indicated that, at low light intensity both in wild type and in the Flv3− mutant, the transient re-reduction step coincided in time with S-M fluorescence rise, which reflected state 2–state 1 transition (Kaňa et al., 2012). Despite variations in the initial redox state of plastoquinone pool, the oxidases-deficient mutant, succinate dehydrogenase-deficient mutant, and wild type cells did not show the S-M rise under high-intensity light until additional Flv3− mutation was introduced in these strains. Thus, the lack of available electron acceptor for PSI was the main cause for the appearance of S-M fluorescence rise under high light. It is concluded that the lack of Flv3 protein promotes cyclic electron flow around PSI and facilitates the subsequent state 2–state 1 transition in the absence of strict relation to the dark-operated pathways of plastoquinone reduction or oxidation.

Photochemical Characterization of Greenhouse-grown Lettuce (Lactuca sativa L. ‘Green Towers’) with Applications for Supplemental Lighting Control

Plant light use efficiency decreases as light intensity is increased, and a better understanding of crop-specific light responses can contribute to the development of more energy-efficient supplemental lighting control strategies for greenhouses. In this study, diurnal chlorophyll fluorescence monitoring was used to characterize the photochemical responses of ‘Green Towers’ lettuce (Lactuca sativa L.) to photosynthetic photon flux density (PPFD) and daily light integral (DLI) in a greenhouse during a production cycle. Plants were monitored continuously for 35 days, with chlorophyll fluorescence measurements collected once every 15 minutes. Quantum yield of photosystem II (ΦPSII) decreased exponentially with PPFD, whereas electron transport rate (ETR) increased asymptotically to 121 µmol·m–2·s–1. Daily photochemical integral (DPI) is defined as the integral of ETR over a 24-hour period; DPI increased asymptotically to 3.29 mol·m–2·d–1 with increasing DLI. No effects of plant age or prior day’s DLI and a negligible effect of PPFDs 15 or 30 minutes before measurements within days were observed. Simulations were conducted using the regression equation of ETR as a function of PPFD {ETR = 121[1 – exp(–0.00277PPFD)]} to illustrate methods of increasing photochemical light use efficiency for improved supplemental lighting control strategies. For a given DLI, DPI can be increased by providing light at lower PPFDs for a longer period of time, and can be maximized by providing light with a uniform PPFD throughout the entire photoperiod. Similarly, the DLI required to achieve a given DPI is reduced using these same methods.

Fluorescencia de la clorofila <i>a</i> en plantas de piña sometidas a aplicación de herbicidas

El manejo químico de malezas con herbicidas es una actividad recomendada en cultivos, estrategia que permite un control eficaz para el cultivo de piña, que puede afectar su crecimiento y fisiología. De acuerdo a esto, el objetivo de este trabajo es evaluar el efecto de herbicidas de post-emergencia en parámetros de fluorescencia de la clorofila y tasa de transporte de electrones, relacionando la fluorescencia de la clorofila a en plantas de piña, variedad Imperial, así como, comprobar la intoxicación causada por estos productos. El experimento se realizó en campo en bloques aleatorizados en esquema factorial 5×2, siendo cuatro herbicidas (ametym, diuron, fluazifop y sulfentrazona) y el control (sin herbicida) y dos tiempos de evaluación (7 y 21 días después de la aplicación). El monitoreo de la fluorescencia de clorofila y las tasas de transporte de electrones también se llevaron a cabo a los 7 y 21 días después de la aplicación del tratamiento, siendo las variables: 1) fluorescencia inicial; 2) fluorescencia máxima; 3) relación de fluorescencia variable y fluorescencia total y 4) tasa de transporte de electrones. Los herbicidas evaluados afectaron negativamente el aparato fotosintético de las plantas de piña, el herbicida diuron seguido del ametrym fueron los productos que provocaron mayor estrés fisiológico en el cultivo. En la segunda época de evaluación, los efectos sobre el aparato fotosintético de las plantas se fueron intensificando, donde los productos probados redujeron los valores de la relación fluorescencia variable y máxima, indicando aumento del estrés causado por los herbicidas evaluados.

Electrochemical Regulation of the Cyanobacterial Circadian Oscillation

There has been a growing awareness of a close relationship between circadian oscillation and intracellular redox state in diverse species ranging from cyanobacteria to mammals [1]. The elucidation of this relationship is of physiological importance since malfunction and disruption of the circadian clock can threaten the wellbeing of living organisms. Here we report that the circadian oscillation of the cyanobacterium Synechococcus elongatus PCC7942, the simplest organism found to exhibit circadian oscillation,can be entrained by periodical modulation of the intracellular redox state via electrochemically controlled-extracellular electron transfer (EC-EET), a process in which intracellular electrons are exchanged with extracellular electrodes [2].In-vivo monitoring of chlorophyll fluorescence revealed that the redox state of plastoquionone pool could be controlled by EC-EET with simply changing the electrode potential in the presence of biocompatible electron mediators. As a result, the endogenous circadian clock of S. elongatuscells was successfully entrained through periodically modulated EC-EET by emulating the natural light-and-dark cycle, even under constant illumination conditions. This represents the first example of regulating the biological oscillation via intracellular redox state by electrochemical technique.[1] S. Edgar et al., PNAS10.1073. (2012).[2] Y. Lu et al., Angew. Chem. Int. Ed., 53, 2208-2211 (2014).

Regulation of the Cyanobacterial Circadian Clock by Electrochemically Controlled Extracellular Electron Transfer

AbstractThere is growing awareness that circadian clocks are closely related to the intracellular redox state across a range of species. As the redox state is determined by the exchange of the redox species, electrochemically controlled extracellular electron transfer (EC‐EET), a process in which intracellular electrons are exchanged with extracellular electrodes, is a promising approach for the external regulation of circadian clocks. Herein, we discuss whether the circadian clock can be regulated by EC‐EET using the cyanobacterium Synechococcus elongatus PCC7942 as a model system. In vivo monitoring of chlorophyll fluorescence revealed that the redox state of the plastoquionone pool could be controlled with EC‐EET by simply changing the electrode potential. As a result, the endogenous circadian clock of S. elongatus cells was successfully entrained through periodically modulated EC‐EET by emulating the natural light/dark cycle, even under constant illumination conditions. This is the first example of regulating the biological clock by electrochemistry.

Use of in vivo chlorophyll fluorescence to estimate photosynthetic activity and biomass productivity in microalgae grown in different culture systems

In vivo chlorophyll fluorescence associated to Photosystem II is being used to evaluate photosynthetic activity of microalgae grown in different types of photobioreactors; however, controversy on methodology is usual. Several recommendations on the use of chlorophyll fluorescence to estimate electron transport rate and productivity of microalgae grown in thin-layer cascade cultivators and methacrylate cylindrical vessels are included. Different methodologies related to the measure of photosynthetic activity in microalgae are discussed: (1) measurement of light absorption, (2) determination of electron transport rates versus irradiance and (3) use of simplified devices based on pulse amplitude modulated (PAM) fluorescence as Junior PAM or Pocket PAM with optical fiber and optical head as measuring units, respectively. Data comparisons of in vivo chlorophyll fluorescence by using these devices and other PAM fluorometers as Water- PAM in the microalga Chlorella sp. (Chlorophyta) are presented. Estimations of carbon production and productivity by transforming electron transport rate to gross photosynthetic rate (as oxygen evolution) using reported oxygen produced per photons absorbed values and carbon photosynthetic yield based on reported oxygen/carbon ratio are also shown. The limitation of ETR as estimator of photosynthetic and biomass productivity is discussed. Low cost:quality PAMs can promote monitoring of chlorophyll fluorescence in algal biotechnology to estimate the photosynthetic activity and biomass productivity.

Intelligent lighting system for plant growth and development

A smart illumination system (ILSys) to study the growth process of green plants was developed. This system can control commercial LED lamps that can be turned on to emit continuous or pulsed light. ILSys was applied to determine the effect of pulsed light on the fluorescence emission in tomato plants (Lycopersicon esculentum). The fluorescence emission was measured when the plants were radiated with continuous light and light pulsed at different frequencies (0.1Hz, 1Hz, 10Hz, 50Hz, 100Hz, 500Hz, 1kHz, 5kHz, 10kHz, 50kHz and 100kHz). For the experiment three red and blue-LEDs lamps and a Pulse Modulated Chlorophyll Fluorescence Monitoring System were connected to the ILSys. Results showed the highest quantum efficiencies in the Photosystem II (φPSII) was obtained when applying pulse frequency of 0.1Hz and 1Hz with 50% light pulse width. ILSys allowed the finding of a significant difference in the response of the quantum efficiency in the Photosystem II between pulsed light at a number of frequencies and continuous light.

Composition of photosynthetic organisms and diurnal changes of photosynthetic efficiency in algae and moss crusts

In Dalateqi region of Inner Mongolia (at eastern edge of Qubqi Desert), man-made algae crusts were constructed with two filamentous cyanobacteria. Two to three years later, the algae crusts began to succeed to moss crusts under some microterrain conditions. In order to characterize the community structure and compare the photosynthetic characteristics in different successional stages of biological soil crusts (BSCs). This paper studied composition of photosynthetic organisms and diurnal changes of photosynthetic efficiency, with microscopic observation and chlorophyll fluorescence monitoring techniques. Compared with the early successional algae crusts, later moss crusts had a higher photosynthetic efficiency, which was closely related with the different community structure of photosynthetic organisms. Further, moss crusts had a higher total photosynthetic biomass, although the algal biomass decreased along the successional sequence. Similar to higher vascular plants, a midday depression of photosynthetic efficiency was detected in BSCs, although the depression extents were different in different successional stages. Analysis demonstrated the depression was mainly caused by non-stomata limitations, and photosynthetically active radiation (PAR) was a significant influencing factor in the down-regulation of photosynthetic efficiency. We conclude, cyanobacterial inoculation effectively promotes the formation, development and seccession of BSCs. Furthermore, the later successional BSCs have a better photosynthetic performance and thus are expected to play a more effective role in desertification control.

Impact of Innovative Controlled Atmosphere Storage Technologies and Postharvest Treatments on Volatile Compound Production in Cv. Pinova Apples

Organically grown apples cv. Pinova harvested at two different dates were stored at 1.3 degrees C for up to 4 months in air, up to 7 months in ULO (1.5 kPa of O(2) and 1.3 kPa of CO(2)) and in dynamic controlled atmosphere (DCA) conditions (0.4-0.6 kPa of O(2) and 0.6-0.8 kPa of CO(2)); the DCA storage method involved the use of a chlorophyll fluorescence monitoring system in order to detect low-O(2) stress in apples and to allow for the dynamic adaptation of storage atmosphere to O(2) levels that were lower than in ULO but still tolerated by fruits. A postharvest 1-MCP treatment (for 24 h at 1.3 degrees C) and a hot water treatment (for 180 s at 50 degrees C) were also tested on apples stored afterward in ULO and air, respectively. Volatile compounds isolated from the pulp of fruits were measured after 4 and 7 months, just upon removal from storage and after 11 days at 22 degrees C. Total amount of aroma compounds detected in apples stored in DCA was markedly higher (from 2- to 4-fold) than in fruits exposed to 1-MCP + ULO but, at most sampling times, significantly lower than in ULO fruits. Moderate differences in storage atmosphere composition between ULO and DCA significantly affected both total amount and profile of volatile esters. Analogous effects were observed on the alcohol precursors of the main esters. Exposure to 1-MCP inhibited biosynthesis of straight-chain esters more than that of branched-chain esters. The hot water treatment did not seem to produce marked changes in volatile composition after four months of air storage, except for a sharp accumulation of aldehydes during the shelf-life time. DCA storage technology, besides avoiding any chemical treatment, can preserve apple aroma compounds better than 1-MCP + ULO during long-term storage.

Remote monitoring of chlorophyll fluorescence in two reef corals during the 2005 bleaching event at Lee Stocking Island, Bahamas

Zooxanthellae fluorescence was measured in situ, remotely, and in near real-time with a pulse amplitude modulated (PAM) fluorometer for a colony of Siderastrea siderea and Agaricia tenuifolia at Lee Stocking Island, Bahamas during the Caribbean-wide 2005 bleaching event. These colonies displayed evidence of photosystem II (PS II) inactivation coincident with thermal stress and seasonally high doses of solar radiation. Hurricane-associated declines in temperature and light appear to have facilitated the recovery of maximum quantum yield of PS II within these two colonies, although both corals responded differently to individual storms. PAM fluorometry, coupled with long-term measurement of in situ light and temperature, provides much more detail of coral photobiology on a seasonal time scale and during possible bleaching conditions than sporadic, subjective, and qualitative observations. S. siderea displayed evidence of PS II inactivation over a month prior to the issuing of a satellite-based, sea surface temperature (SST) bleaching alert by the National Oceanic and Atmospheric Administration (NOAA). In fact, recovery had already begun in S. siderea when the bleaching alert was issued. Fluorescence data for A. tenuifolia were difficult to interpret because the shaded parts of a colony were monitored and thus did not perfectly coincide with thermal stress and seasonally high doses of solar radiation as in S. siderea. These results further emphasize the limitations of solely monitoring SST (satellite or in situ) as a bleaching indicator without considering the physiological status of coral-zooxanthellae symbioses.

Large-Scale Analysis of Chlorophyll Fluorescence Kinetics in Synechocystis sp. PCC 6803: Identification of the Factors Involved in the Modulation of Photosystem Stoichiometry

Since chlorophyll fluorescence reflects the redox state of photosynthetic electron transport chain, monitoring of chlorophyll fluorescence has been successfully applied for the screening of photosynthesis-related genes. Here we report that the mutants having a defect in the regulation of photosystem stoichiometry could be identified through the simple comparison of the induction kinetics of chlorophyll fluorescence. We made a library containing 500 mutants in the cyanobacterium Synechocystis sp. PCC 6803 with transposon-mediated gene disruption, and the mutants were used for the measurement of chlorophyll fluorescence kinetics for 45 s. We picked up two genes, pmgA and sll1961, which are involved in the modulation of photosystem stoichiometry. The disruptants of the two genes share common characteristics in their fluorescence kinetics, and we searched for mutants that showed such characteristics. Out of six mutants identified so far, five showed a different photosystem stoichiometry under high-light conditions. Thus, categorization based on the similarity of fluorescence kinetics is an excellent way to identify the function of genes.

Photoinhibition of photosynthesis is reduced by water flow in the reef-building coral Acropora digitifera

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 301:109-118 (2005) - doi:10.3354/meps301109 Photoinhibition of photosynthesis is reduced by water flow in the reef-building coral Acropora digitifera T. Nakamura1, R. van Woesik2,*, H. Yamasaki1 1Center of Molecular Biosciences, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-0213, Japan2Department of Biological Sciences, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901-6988, USA *Corresponding author. Email: rvw@fit.edu ABSTRACT: While photosynthesis of symbiotic algae is essential for reef-building corals, excess irradiance inhibits photosynthesis through photoinhibition, which can lead to coral bleaching under elevated temperature conditions. Here we show that water flow reduces photoinhibition of in hospite endosymbionts in the coral Acropora digitifera. Diurnal monitoring of chlorophyll fluorescence, under 2 different flow regimes (<3 and 20 cm s–1 flow rates) in an outdoor aquarium, showed reduced photoinhibition, but only under moderate flow conditions (20 cm s–1). Experimental (laboratory) measurements, on time scales ranging from minutes to hours, showed that flow-mediated reductions in photoinhibition occurred not by enhancing recovery of the damaged photosystem, but rather through inducing differential photodamage. Moreover, experiments involving sequential light oscillations (500/20 and 1000/20 µmol photons m–2 s–1) at 3 flow regimes, <3, 10, and 20 cm s–1, on a time scale ranging from hours to days, revealed water-velocity-dependent reductions of dynamic photoinhibition. These results, on time scales ranging from minutes to weeks, confirm that reduced water flow amplifies photodamage of algal photosynthesis under strong irradiance, which in turn affects coral tolerance to strong irradiance and temperature. KEY WORDS: Coral bleaching · Photoinhibition · Water-flow rates · Passive diffusion Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 301. Online publication date: October 11, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Optimal Growth Conditions for the Two Euryhaline Cyanobacterial Clones, Anabaena sp. CB-MAL21 and CB-MAL22 Isolated from Mankyeong Estuary, Korea

As a result of the 2-year monthly monitoring of the phytoplankton community at 3 stations in Mankyeong Estuary, Korea, we learned that cyan bacterial species of the genus Anabaena occurred at most sampling points with huge salinity differences (0.1-32.5 psu). We isolated several clones of Anabaena spp. from the monitoring stations, and screen out two euryhaline and nitrogen-fixing Anabaena clones, CB-MAL21 and CB-MAL22. The two clones were grown under various environmental gradients such as temperature (20, 30, 35 and 40), salinity (0, 2, 5, 15 and 30psu), and -P concentration (0, 1.6, 8.0, 40 and 200 M). Growth of CB-MAL21 and CB-MAL22 was measured by daily monitoring of chlorophyll fluorescence from each experimental culture for more than three serial transfers. Both the two experimental clones did not grow at 0psu. Maximal growth rates of the two clones were markedly reduced at lower -P concentrations showing negligible growth at 0 and 1.6 M. However, growth of CB-MAL21 was not affected by low concentration in culture media, showing the nitrogen-fixing ability. Maximum biomass yields of the two clones decreased dramatically at 35 and 40. Optimal growth conditions for the two experimental clones were determined to be 20-30, 40 M -P, and wide salinity range from 5.0 to over 30psu. Best growth of CB-MAL21 was shown at (20-15psu), which is less saline and cooler condition than those (i.e., 30-30psu) for the best growth of CB-MAL22. The euryhaline and nitrogen-fixing CB-MAL21 strain thus can be a candidate laboratory culture for the future cyan bacterial marine biotechnology in temperate coastal waters.

In situ monitoring of chlorophyll fluorescence to assess the synergistic effect of low temperature and high irradiance stresses inSpirulina cultures grown outdoors in photobioreactors

A chlorophyll fluorescence technique was applied to an in situ study on the effects of low temperature and high light stresses on Spirulina cultures grown outdoors in controlled tubular photobioreactors at high (1.1 g L- 1 ) and low (0.44 g L -1 ) biomass concentrations. Diurnal changes in PSII photochemistry (F v /F m ) after 15 min of darkness, or in the light (dF/F' m ), and non-photochemical (qN) quenching were measured using a portable, pulse-amplitude-modulated fluorometer. The depression of the F v /F m ratio of Spirulina cultures grown outdoors at 25°C (i.e. 10°C below optimum for growth) and 0.44 g L -1 , reached 30% at the middle of the day. At the same time of the day the dF/F' m ratio showed a reduction of up to 52%. The depression of both F v /F m and dF/F' m was lower in the cultures grown at 1.1 g L -1 . Photoinhibition reduced the daily productivity of the culture grown at 0.44 g L -1 and 25°C by 33% with respect to that grown at 35°C. Changes in the growth yields of the cultures grown under different temperatures and growth rates correlate well with analogous changes in photon yield (dF/F' m ). Simple measurements of photochemical yield (F v /F m ) can be used to test the physiological status of Spirulina cultures. The results indicate that the saturating pulse fluorescence technique, when used in situ, is a powerful tool for assessment of the photosynthetic characteristics of outdoor cultures of Spirulina.

Ozone-induced changes in chlorophyll fluorescence kinetics and CO 2 assimilation in Vicia faba

Summary After subsymptomatic exposure to 150ppb of ozone for a single 3-h period, a significant reduction in photosynthetic activity coupled with a reduction in stomatal conductance and transpiration was rapidly induced in two cultivars of broad bean, Vicia faba cvs. Reina blanca and Gigante d'Ingegnoli. The two cultivars behaved quite differently in the post-fumigation stages. Reina blanca recovered quickly, its photosynthetic rate returning to pre-fumigation values within 48 h. In Gigante d'Ingegnoli the recovery process took much longer; 72 h after ozonization the net photosynthesis was only 59% that of the unfumigated controls. The chlorophyll fluorescence kinetics also showed significant alterations following the treatment, reflecting a perturbation in the photochemical functioning of the thylakoids, and specifically disturbances of the water-splitting enzyme system of the PSII. Such effects proved to be reversible in both cultivars, but the response of Reina blanca was much quicker, so that 72 h after the treatment normal kinetics had been restored. At the end of this same period the fluorescence behaviour of Gigante d'Ingegnoli was still altered, complete recovery taking 1 week. The contributions of stomatal conductance and photochemical quantum conversion to the observed reductions in photosynthetic rates also differed between the two cultivars. Thus, the monitoring of chlorophyll fluorescence is a simple and informative tool for the investigation of the subsymptomatic (latent) phytotoxic effects of the air pollutant ozone.

Chlorophyll fluorescence monitoring of freezing point exotherms in leaves

Following supercooling prompt chlorophyll fluorescence and delayed fluorescence from leaves undergo transients simultaneous with the freezing point exotherm. The degree of supercooling and, hence, the temperature at which the exotherm occurs is dependent upon the leaf water content. Winter wheat leaves ( Triticum aestivum L.) that had the lowest water content (hardened “Kharkov”) supercooled to a greater degree than those leaves with a higher water content (hardened “Rescue” and unhardened “Kharkov” or “Rescue”). Seeding the leaves with ice increased the temperature at which the exotherm occurred and decreased the difference between varities but not between hardened and unhardened material. Our results suggest that freeze-avoidance via supercooling may be one mechanism in winter wheat for withstanding subfreezing temperatures.