Chlorophyll Fluorescence Transients Research Articles

Genotype Specific Photosynthesis x Environment Interactions Captured by Automated Fluorescence Canopy Scans Over Two Fluctuating Growing Seasons.

Photosynthesis reacts dynamic and in different time scales to changing conditions. Light and temperature acclimation balance photosynthetic processes in a complex interplay with the fluctuating environment. However, due to limitations in the measurements techniques, these acclimations are often described under steady-state conditions leading to inaccurate photosynthesis estimates in the field. Here we analyze the photosynthetic interaction with the fluctuating environment and canopy architecture over two seasons using a fully automated phenotyping system. We acquired over 700,000 chlorophyll fluorescence transients and spectral measurements under semi-field conditions in four crop species including 28 genotypes. As expected, the quantum efficiency of the photosystem II (Fv/Fm in the dark and Fq'/Fm' in the light) was determined by light intensity. It was further significantly affected by spectral indices representing canopy structure effects. In contrast, a newly established parameter, monitoring the efficiency of electron transport (Fr2/Fv in the dark respective Fr2'/Fq' in the light), was highly responsive to temperature (R2 up to 0.75). This parameter decreased with temperature and enabled the detection of cold tolerant species and genotypes. We demonstrated the ability to capture and model the dynamic photosynthesis response to the environment over entire growth seasons. The improved linkage of photosynthetic performance to canopy structure, temperature and cold tolerance offers great potential for plant breeding and crop growth modeling.

Chlorophyll fluorescence as a tool to select salinity-tolerant cowpea genotypes

The use of saline water reduces the growth and productivity of crops, so the need for techniques that make possible the use of this resource such as the use of salinity tolerant genotypes and efficient selection methods are of great importance. Thus, this study aimed to evaluate the tolerance of cowpea (Vigna unguiculata L. Walp.) genotypes to salt stress, through the chlorophyll fluorescence analysis. The experiment was conducted in a protected environment at the Federal University of Campina Grande, Paraíba, Brazil, using a completely randomized design in a 2 x 10 factorial arrangement, with three replications, consisting of two levels of irrigation water salinity (0.6 and 5.1 dS m-1) and ten cowpea genotypes: (G1: MNCO1-649F-2-1, G2: MNCO3-736F-2, G3: PINGO DE OURO-1-2, G4: BRS GURGUÉIA, G5: BRS MARATAOÃ, G6: MNCO2-676F-3, G7: MNCO2-683F-1, G8: MNCO3-737F-5-4, G9: MNCO3-737F-5-9, and G10: BRS TUMUCUMAQUE). The stem length, stem diameter, SPAD index, and chlorophyll fluorescence transients were evaluated. The G2 and G4 genotypes had the lowest reductions in the growth, stem diameter, initial fluorescence, and primary and maximum photochemical efficiency of PSII, proving to be tolerant to salinity. Chlorophyll fluorescence is a tool that can be used in the selection of salinity-tolerant cowpea genotypes.

Photosystem II of Ligustrum lucidum in response to different levels of manganese exposure

The toxic effect of excessive manganese (Mn) on photosystem II (PSII) of woody species remains largely unexplored. In this study, five Mn concentrations (0, 12, 24, 36, and 48 mM) were used, and the toxicity of Mn on PSII behavior in leaves of Ligustrum lucidum was investigated using in vivo chlorophyll fluorescence transients. Results showed that excessive Mn levels induced positive L- and K- bands. Variable fluorescence at 2 ms (VJ) and 30 ms (VI), absorption flux (ABS/RC), trapped energy flux (TRo/RC), and dissipated energy flux (DIo/RC) increased in Mn-treated leaves, whereas the performance index (PIABS), electron transport flux (ETo/RC), maximum quantum yield (φPo), quantum yield of electron transport (φEo), and probability that an electron moves further than QA− (ψo) decreased. Also, excessive Mn significantly decreased the net photosynthesis rate and increased intercellular CO2 concentration. The results indicated that Mn blocked the electron transfer from the donor side to the acceptor side in PSII, which might be associated with the accumulation of QA−, hence limiting the net photosynthetic rate.

Different response of photosynthetic apparatus to high-light stress in sporotrophophyll and nest leaves of Platycerium bifurcatum

Tropical forest deforestation leads to sudden changes in light conditions, which is a problem for the development of epiphytes, such as Platycerium bifurcatum. High light (HL) results in disturbances of the light phase of photosynthesis and changes in leaf pigment composition. The current study determined differences in fast chlorophyll fluorescence transients and changes in radiation reflectance in sporotrophophylls and nest leaves after one and seven days of HL. In addition, a spectral range was identified with the largest change in reflectance induced by HL. Sporotrophophylls exhibited a stronger response of the photosynthetic apparatus to photoinhibition than that of the nest leaves. Moreover, in sporotrophophylls, disorders of electron transport were visible in the whole O-P phase, and in the nest leaves mainly in the O-J phase. Higher accumulation of photoprotective compounds in sporotrophophylls underlined a different reaction to HL.

Size- and shape-dependent toxicity of silver nanomaterials in green alga Chlorococcum infusionum

Silver nanomaterials (AgNMs) of different shapes and sizes are potentially toxic to aquatic organisms. However, studies on the toxicity of AgNMs and on their shape-dependent effects on algae are scarce. The present study evaluated the effects of three AgNMs (silver nanospheres, AgNPs; silver nanowires, AgNWs; silver nanoplates, AgPLs) with different shapes coated with polyvinylpyrrolidone on the growth and photosynthetic performance of an alga, Chlorococcum infusionum. We used growth measurements and determined the photosynthetic parameters based on chlorophyll fluorescence transients in the algal cells exposed to different concentrations of the three AgNMs. The effective concentrations at 50% (EC50) of AgNPs, AgNWs, and AgPLs were calculated to be 0.1, 0.045, and 0.021 mg/L, respectively. The results showed that the toxicity of AgNMs in C. infusionum was in the order, AgPLs (40 nm diameter) > AgNWs (21,000 nm length × 42 nm diameter) > AgNPs (57 nm diameter), based on the decrease in growth and three photosynthetic activities. We propose that the toxic potential of AgNMs is primarily dependent on their diameter and secondarily on their shape. Overall, this study provides, for the first time, a comparison of the growth and photosynthetic activities of C. infusionum exposed to AgNMs of three different shapes.

Control of Microcystis (Cyanobacteria) using the fruit of Macleaya cordata: from laboratory experiment to in situ field test

:Biologically derived algicidal substances are regarded as environmentally friendly in the control of harmful cyanobacterial blooms. To evaluate the possible control of Microcystis-based water blooms using fruit from Macleaya cordata (MC-fruit), the effects of MC-fruit on the growth, polyphasic chlorophyll fluorescence transients, microcystin production and efficacy of in situ cyanobacterial bloom removal were investigated. The results showed that MC-fruit could effectively inhibit the growth of M. aeruginosa PCC7806 at a concentration of 1 mg l−1. MC-fruit stress caused severe damage to photosynthesis of M. aeruginosa and decreased the content of cellular microcystin-LR. The results of an in situ field test showed that MC-fruit effectively reduced the biomass of Microcystis and improved water quality. Accordingly, MC-fruit may be a useful biologically derived algicide for cyanobacterial bloom control.

Effects of short-term low temperature stress on chlorophyll fluorescence transients in Antarctic lichen species

Chlorophyll fluorescence is an effective tool for investigating characteristics of any photosynthesizing organisms and its responses due to different stressors. Here, we have studied a short-term temperature response on two Antarctic green algal lichen species: Umbilicaria antarctica, and Physconia muscigena. We measured slow chlorophyll fluorescence transients in the species during slow a cooling of thallus temperature from 20°C to 5°C with a 10 min. acclimation at each temperature in dark. The measurements were supplemented with saturation pulses for the analysis of chlorophyll fluorescence parameters: maximum yield of PS II photochemistry (FV/FM), effective quantum yield of PS II photochemistry (FPSII) and non-photochemical quenching (NPQ). In response to decreasing thallus temperature, we observed species-specific changes in chlorophyll fluorescence levels P, S, M, T reached during chlorophyll fluorescence transient as well as in the shape of the chlorophyll fluorescence transients. With a decrease in temperature, the time at which M and T chlorophyll fluorescence levels were reached, increased. These changes were attributed to redox state of plastoquinon pool, changes in Calvin-Benson cycle activity, non-photochemical quenching components, state transition in particular. In this study, we present some chlorophyll fluorescence ratios (P/M, M/T, P/T) and chlorophyll fluorescence increase rates (FR1, i.e. O to P, and FR2 - i.e. S to M) as the parameters reflecting direct temperature effects on chloroplastic apparatus of lichen alga sensitively. We proposed that species-specific changes in the slow phase of chlorophyll fluorescence transients could be potentially used as indicators of low temperature effects in photosynthetic apparatus of lichen algal photobionts. Interspecific differences in response to low temperature might be evaluated using the approach as well.

Features of chlorophyll fluorescence transients can be used to investigate low temperature induced effects on photosystem II of algal lichens from polar regions ( Short Communication )

Chlorophyll fluorescence is an effective tool for investigating characteristics of any photosynthesizing organisms and its responses due to different stressors. Here, we have studied a short-term temperature response on three Antarctic green algal lichen species: Umbilicaria antarctica, Xanthoria elegans, and Rhizoplaca melanophtalma. We measured slow chlorophyll fluorescence transients in these Antarctic lichen species during slowely cooling of thallus temperature from 20°C to 5, 0 and -5°C with 20 minute acclimation at each temperature. The measurements were supplemented with saturation pulses for the analysis of chlorophyll fluorescence parameters: maximum yield of PS II photochemistry (FV/FM), effective quantum yield of PS II photochemistry (FPSII) and quenching parameters. In response to decreasing thallus temperature, we observed species-specific changes in chlorophyll fluorescence parameters as well as in the shape of the chlorophyll fluorescence transients. We propose that species-specific changes in the slow phase of chlorophyll fluorescence transients can be potentially used as indicators of freezing stress in photosynthetic apparatus of lichen algal photobionts.

Use of O-J-I-P Chlorophyll Fluorescence Transients to Probe Multiple Effects of UV-C Radiation on the Photosynthetic Apparatus of Euglena

Although the kinetic chlorophyll fluorescence signals are rich in information, most of the chlorophyll fluorescence related studies deal only with the quantum yield of primary photochemistry (Fv/Fm). JIP-test based OJIP fluorescence transient analysis is relatively a new technique to investigate the environmental stress responses of photosynthetic organisms. In the present study, the deleterious effects of ultraviolet (UV) radiation on the photosynthetic machinery were probed by the JIP-test in Euglena, one of the most potent organisms for the future space stations. The cells were exposed to a series of UV-C doses and immediately after exposure, survival percentage was determined with Neutral Red staining, and the chlorophyll fluorescence was measured using AquaPen AP-C 100 fluorometer. Resultant OJIP transients were analyzed according to JIP-test, and several functional and structural parameters were derived to explain the PSII behavior. Results indicated that the UV-C induced inhibition of electron transport is severely affected due to higher sensitivity of dark reactions after QA -, represented as ψo, the electron transfer probability, than of the light dependent reactions, represented as φPo, the trapping probability. The performance index (PIABS) of PSII, which is a combination of the indices of three independent parameters, decreased markedly in exponential manner in response to UVC. Results illustrate the advantage of using a number of fluorescent parameters over the use of one parameter, often the Fv/Fm. DOI: http://dx.doi.org/10.3126/ijasbt.v2i4.10510 Int J Appl Sci Biotechnol, Vol. 2(4): 553-558

Pathways of hydrogen photoproduction by immobilized Chlamydomonas reinhardtii cells deprived of sulfur

The green algae Сhlamydomonas reinhardtii entrapped in a thin alginate film have been shown to sustain elevated rates of hydrogen photoproduction under anaerobic incubation in sulfur/phosphorus depleted tris-acetate medium. In the present work we studied mechanisms, underlying hydrogen photoproduction by the immobilized culture, particularly, the roles of PSII and starch accumulation/breakdown. DCMU, a specific inhibitor of electron transport in PSII, is known to suppress hydrogen evolution by circa 80% in suspension cultures of S-deprived C. reinhardtii. In immobilized cells DCMU caused successive stimulatory and inhibitory effects on hydrogen photoproduction, both depending on the deprivation status of the algal cell. The inhibitory effect of DCMU was 25% at 70 h of S deficiency when maximal rates of hydrogen photoproduction were observed. Measurements of the light-induced prompt and delayed chlorophyll fluorescence transients and reflectance at 820 nm (P700 redox transitions) revealed very rapid decline of PSII activity in the entrapped S-deprived cells as compared with the suspension culture, whereas PSI suffered less. The immobilized culture showed a high capacity to accumulate starch during early stages of S deprivation and relatively high rates of anaerobic starch degradation during the following hydrogen evolution period. DCMU partly inhibited starch breakdown. Results of the present work brought us to the conclusion that PSII-independent pathway of hydrogen evolution is elevated in the immobilized S-deprived cells rather due to the rapid inactivation of PSII, efficient starch catabolism and non-photochemical PQ reduction.

In vivo assessment of effect of phytotoxin tenuazonic acid on PSII reaction centers

Tenuazonic acid (TeA), a phytotoxin produced by the fungus Alternaria alternata isolated from diseased croftonweed (Ageratina adenophora), exhibits a strong inhibition in photosystem II (PSII) activity. In vivo chlorophyll fluorescence transients of the host plant croftonweed, show that the dominant effect of TeA is not on the primary photochemical reaction but on the biochemical reaction after QA. The most important action site of TeA is the QB site on the PSII electron-acceptor side, blocking electron transport beyond QA− by occupying the QB site in the D1 protein. However, TeA does not affect the antenna pigments, the energy transfer from antenna pigment molecules to reaction centers (RCs), and the oxygen-evolving complex (OEC) at the donor side of PSII. TeA severely inactivated PSII RCs. The fraction of non-QA reducing centers and non-QB reducing centers show a time- and concentration-dependent linear increase. Conversely, the amount of active QA or QB reducing centers declined sharply in a linear way. The fraction of non-QB reducing centers calculated from data of fluorescence transients is close to the number of PSII RCs with their QB site filled by TeA. An increase of the step-J level (VJ) in the OJIP fluorescence transients attributed to QA− accumulation due to TeA bound to the QB site is a typical characteristic response of the plants leaf with respect to TeA penetration.

Photosynthetic response of the macroalga,Gracilaria lemaneiformis(Rhodophyta), to various N and P levels at different temperatures

Gracilaria lemaneiformis, a commercial red macroalga with multiple uses, was cultivated under different combinations of temperatures (10, 20, and 30°C) and nutrients (seawater and four different levels of enrichment) to determine its photo-physiological response pattern. O2 evolution-based photosynthesis–irradiance (P–I) curves and chlorophyll fluorescence-based polyphasic chlorophyll fluorescence transients (OJIP) curves increased with increasing temperature up to 20–30°C, but were nutrition insensitive. The same responsive patterns were followed by their corresponding derived specific photosynthetic parameters. The high photosynthetic tolerance of G. lemaneiformis to nutrient-loaded stress at a wide range of temperatures, makes it a potential candidate for bioremediating eutrophic mariculture zones.

Alteration of photochemistry and protein degradation of photosystem II from Chlamydomonas reinhardtii under high salt grown cells

In this study, we evaluated the inhibitory effect of NaCl on cell growth, photochemistry and protein profile of photosystem (PS) II in Chlamydomonas reinhardtii. To study the effect of NaCl on the photosynthetic apparatus, the C. reinhardtii cells were grown at different concentrations (0, 50, 100 and 150mM). NaCl induced flagellar resorption due to which the cells lost their motility, formation of palmelloids, reduced cell size and slower cell division. Chlorophyll fluorescence transients at different NaCl concentrations had decreased intensities of all peaks (OJIP) indicating the apparent inactivation energies of both donor and acceptor side of PSII. Consequently, inhibition of electron transport occurred particularly at PSII. Further, low temperature emission spectra showed that the rate of damage to the PSII was more when compared to PSI. Also, we have carried out the visible circular dichroism spectra from thylakoids where the major peaks contributed to chlorophyll a and b are equally reduced in different salt grown cells, which may explain the changes at the level of inter pigment–pigment interactions. Furthermore protein profile analysis of PSII revealed that the major subunit of light harvesting complex (LHC)II is more prone to salt stress than core proteins of PSII indicating the light harvesting funnel from LHCII to PSII core is impaired.

Probing the effects of high-light stress on pigment and lipid metabolism in nitrogen-starving microalgae by measuring chlorophyll fluorescence transients: Studies with a Δ5 desaturase mutant of Parietochloris incisa (Chlorophyta, Trebouxiophyceae)

We investigated effects of irradiance on the relationships between chlorophyll fluorescence transients (OJIP), carotenoid-to-chlorophyll ratio, and fatty acids in a nitrogen-deprived Parietochloris incisa (Chlorophyta, Trebouxiophyceae) Δ5 desaturase mutant accumulating valuable LC-PUFA dihomo-γ-linolenic acid (DGLA). High light (270μE·m−2·s−1 PAR) and nitrogen starvation brought about a decrease in maximum quantum yield of photosystem II (ΦP0) and electron transport (ΦE0) but enhanced the quantum yield of thermal dissipation (ΦD0) and induced non-photochemical quenching (NPQ) in an irradiance-dependent manner. Under high irradiance a decline in the rate of total fatty acid accumulation and DGLA percentage in comparison with the cultures grown under 130μE·m−2·s−1 PAR was recorded. Increasing irradiance from 130 to 270μE·m−2·s−1 enhanced total fatty acid accumulation only within the first week of nitrogen starvation and negatively affected DGLA production. Regardless of irradiance, ΦP0, ΦE0, and ΦD0 exhibited tight (r2=0.8–0.9) relationships with the stress-induced changes of total fatty acid and DGLA content and the carotenoid-to-chlorophyll ratio. The applicability and limitations of OJIP and its derived parameters for on-line monitoring of physiological condition and accumulation of value-added products in microalgal cultures grown in photobioreactors are discussed.

Interplay between non-photochemical plastoquinone reduction and re-oxidation in pre-illuminated Chlamydomonas reinhardtii: a chlorophyll fluorescence study

In photosynthetic eukaryotes, the redox state of the plastoquinone (PQ) pool is an important sensor for mechanisms that regulate the photosynthetic electron transport. In higher plants, a multimeric nicotinamide adenine dinucleotide (phosphate) (NAD(P))H dehydrogenase (NDH) complex and a plastid terminal oxidase (PTOX) are involved in PQ redox homeostasis in the dark. We recently demonstrated that in the microalgae Chlamydomonas reinhardtii, which lacks the multimeric NDH complex of higher plants, non-photochemical PQ reduction is mediated by a monomeric type-II NDH (Nda2). In this study, we further explore the nature and the importance of non-photochemical PQ reduction and oxidation in relation to redox homeostasis in this alga by recording the 'dark' chlorophyll fluorescence transients of pre-illuminated algal samples. From the observation that this fluorescence transient is modified by addition of propyl gallate, a known inhibitor of PTOX, and in a Nda2-deficient strain we conclude that it reflects post-illumination changes in the redox state of PQ resulting from simultaneous PTOX and Nda2 activity. We show that the post-illumination fluorescence transient can be used to monitor changes in the relative rates of the non-photochemical PQ reduction and reoxidation in response to different physiological situations. We study this fluorescence transient in algae acclimated to high light and in a mutant deficient in mitochondrial respiration. Some of our observations indicate that the chlororespiratory pathway participates in redox homeostasis in C. reinhardtii.

Control of Hydrogen Photoproduction by the Proton Gradient Generated by Cyclic Electron Flow in Chlamydomonas reinhardtii

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H₂ production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein. Under aerobiosis, nonphotochemical quenching of fluorescence (NPQ) is strongly decreased in pgrl1. Under anaerobiosis, H₂ photoproduction is strongly enhanced in the pgrl1 mutant, both during short-term and long-term measurements (in conditions of sulfur deprivation). Based on the light dependence of NPQ and hydrogen production, as well as on the enhanced hydrogen production observed in the wild-type strain in the presence of the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, we conclude that the proton gradient generated by CEF provokes a strong inhibition of electron supply to the hydrogenase in the wild-type strain, which is released in the pgrl1 mutant. Regulation of the trans-thylakoidal proton gradient by monitoring pgrl1 expression opens new perspectives toward reprogramming the cellular metabolism of microalgae for enhanced H₂ production.

Manganese-depleted/reconstituted photosystem II core complexes in solution and liposomes

Chlorophyll fluorescence transients measurements were employed to study the functioning of spinach photosystem II (PS II) core complexes in solution or reconstituted into liposomes. Lipid vesicles were prepared from soybean phospholipids (asolectine) or a mixture of spinach thylakoid lipids. In comparison with intact PS II core complexes comprising two distinct fluorescence phases, designated as O–J and J–P, complete suppression of the latter phase in Mn-depleted samples was observed. An increase of magnitude of the J–P phase in the presence of exogenous MnCl 2 (4 Mn/RC) indicate in favor of partial restoring of oxygen-evolution activity of PS II. The J–P phase observed in PS II in solution was characterized by a lifetime of ∼320 ms, while in liposome-reconstituted samples this phase was accelerated up to ∼20 ms in case of asolectine and up to ∼9 ms in case of a mixture of thylakoid lipids. These data clearly suggest that lipid environment stimulates the steady-state rate of oxygen evolution. The effect of lipids is likely based on keeping the embedded proteins in optimal structure for efficient functioning.

Shrub species affect distinctively the functioning of scattered Quercus ilex trees in Mediterranean open woodlands

A low tree stand density has been showed as necessary to thrive with summer drought in semiarid Mediterranean open woodlands. Shrub encroachment of these open woodlands is currently recommended to guarantee the persistence of the system, due to the nursery effect of shrubs on tree seedling. However, the increase in abundance and cover of a shrub understory in these water limited woodlands could bring consequences to tree overstory functioning. The present study analyzes the physiological status of scattered Quercus ilex L. trees in paired adjacent plots with and without the presence of a shrubby understory in CW Spain. Two contrasting shrub strategies were addressed in order to take into account possible species-specific effects: a dense-shallow rooting shrub ( Cistus landanifer L.) and a sparse-deep rooting shrub ( Retama sphaerocarpa (L.) Boiss). Leaf water potential (at predawn and midday), leaf gas exchange parameters (net photosynthetic rate and stomatal conductance), leaf nitrogen content and chlorophyll fluorescence transients (maximum photochemical efficiency and performance index, sensu Strasser et al., 2004) were measured during three consecutive summers. Trees growing with Cistus as understory showed significant lower leaf water potential, leaf gas exchange parameters, leaf nitrogen content and chlorophyll photochemical efficiency than trees growing without shrub competence. However, the presence of the legume Retama did not affect significantly the physiological state of Q. ilex. Thus, we conclude that the presence of a shrubby understory has the potential to modify the functioning of scattered trees, but these effects are species-specific.

EFFECTS OF PESTICIDE ON THE CHLOROPHYLL FLUORESCENCE PARAMETERS IN NO-HEADING CHINESE CABBAGE

To probe pollution ecology effects of pesticide in vegetables, the chlorophyll fluorescence transients were measured by a Plant Efficiency Analyzer (PEA; Hansatech Ltd., King's Lynn, Norfolk, England) in no-heading Chinese cabbage, and the activity of photosystem II (PS II) was analyzed by the fluorescence transient (the JIP-test). Three pestcides, including phorate, phoxin and cypermetrin, were sprayed on the leaves of no-heading Chinese cabbage. The results showed that on the third day after treatments, these pesticides could promote reducing from primary quinone acceptor Q A to Q A - in PS II, e.g., increasing parameters in relation to J phase, i.e., relative variable fluorescence at the J-step (V J ) and approximated initial slope of the fluorescence transient (M o ). Meanwhile they prohibited electron transmission from Q A - to Q B in PS II, e.g., sharply decreasing parameters of electron transport flux per PS II reaction center (ETo/RC), probability that a trapped exciton moved an electron into the electron transport chain beyond Q A - (ψ o ) and quantum yield of electron transport (ϕ Eo ), and further resulted in sharping decrease of driving force on absorption and cross section basis of PS II (DF ABS and DF CS ), respectively. Effects of phorate on the above parameters showed that dynamic change of residuals was significant and strongly related to the dosage, which would be loss of effect gradually from the fifth day after treatment.

Change of chlorophyll fluorescence transients in Arabidopsis plants irradiated with low-dose radiation using a gamma phytotron

The present study characterised chlorophyll fluorescence transients significantly altered in Arabidopsis leaves upon exposure to gamma radiation for 7.5 days at a low-dose rate of 0.8 Gy day−1 in a gamma phytotron. The JIP transients of Kautsky fluorescence induction were substantially affected by the consecutive exposure to the low-dose-rate gamma radiation. The performance index of photosynthesis (PI), which is based on the JIP transients, was decreased by up to about 40% in irradiated leaves. However, the maximum photochemical efficiency (Fv/Fm) and phenotypic traits were almost the same between the control and irradiated leaves. Based on these results, the PI is suggested to be a sensitive and reliable parameter for physiological evaluation of irradiated plants after exposure to low-dose gamma radiation.