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Chickpea (Cicer arietinum L.), a cool season crop is severely affected by heat stress, predicted to increase due to warming climates. Research for identifying heat tolerance markers for potential chickpea genotype selection is imperative. The study assessed the response of four chickpea genotypes to a natural temperature gradient in the field using chlorophyll fluorescence, non-structural carbohydrate, chlorophyll concentrations, gas exchange and grain yield. Field experiments were carried out in two winter seasons at three locations with known differences in temperature in NE South Africa. Results showed two genotypes were tolerant to heat stress with an F v /F m of 0.83-0.85 at the warmer site, while the two sensitive genotypes showed lower F v /F m of 0.78-0.80. Both dark-adapted F v /F m and F q '/F m ' (where F q ' = F m ' -F) measured at comparable high light levels correlated positively with grain yield. The two tolerant genotypes also showed higher photosynthetic rates, starch, sucrose and grain yield than the sensitive genotypes at the warmer site. However, these parameters were consistently higher at the cooler sites than at the warmer. These results were further validated by a climate chamber experiment, where higher F v /F m decline in the sensitive compared to tolerant genotypes was observed when they were exposed to short-term heat treatments of 30/25 °C and 35/30 °C. Tolerant genotypes had higher F v /F m (0.78-0.81) and grain yield plant -1 (1.12-2.37g) compared to sensitive genotypes (0.74-0.75) and (0.32-0.89g plant -1 ) respectively in the 35/30 °C. It is concluded that chlorophyll fluorescence and leaf carbohydrates are suitable tools for selection of heat tolerant chickpea genotypes under field conditions, while the coolest site showed favourable conditions for chickpea production., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

Abstract The fluorescence emission spectrum of Synechocystis sp. PPC6803 cells, at room temperature, displays: i) significant bandshape variations when collected under open (F 0) and closed (F M) Photosystem II reaction centre conditions; ii) a marked dependence on the excitation wavelength both under F 0 and F M conditions, due to the enhancement of phycobilisomes (PBS) emission upon their direct excitation. As a consequence: iii) the ratio of the variable and maximal fluorescence (F V / F M), that is a commonly employed indicator of the maximal photochemical quantum efficiency of PSI I (Φ pc , PSII), displays a significant dependency on both the excitation and the emission (detection) wavelength; iv) the F V / F M excitation/emission wavelength dependency is due, primarily, to the overlap of PSI I emission with that of supercomplexes showing negligible changes in quantum yield upon trap closure, i. e. PSI and a PBS fraction which is incapable to transfer the excitation energy efficiently to core complexes. v) The contribution to the cellular emission and the relative absorption-cross section of PSI I, PSI and uncoupled PBS are extracted using a spectral decomposition strategy. It is concluded that vi) Φ pc , PSII is generally underestimated from the F V / F M measurements in this organism and, the degree of the estimation bias, which can exceed 50%, depends on the measurement conditions. Spectral modelling based on the decomposed emission/cross-section profiles were extended to other processes typically monitored from steady-state fluorescence measurements, in the presence of an actinic illumination, in particular non-photochemical quenching. It is suggested that vii) the quenching extent is generally underestimated in analogy to F V / F M but that viii) the location of quenching sites can be discriminated based on the combined excitation/emission spectral analysis. Highlights • The emission spectrum of Synechocystis changes significantly when PSII is in open or closed state. • The emission spectra exhibit significant dependence on the excitation, both at open and closed centres. • The variable fluorescence spectrum is instead close to excitation wavelength independent • The ratio of variable to maximal fluorescence is strongly dependent on both the excitation and emission wavelength. • The emission of PSI and of uncoupled PBS needs to be considered when interpreting fluorescence measurements in Synechocystis. [ABSTRACT FROM AUTHOR]

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A fotoinibição pode ser intensificada por fatores de estresse como alta temperatura. O objetivo deste trabalho foi determinar os efeitos da luminosidade e temperatura na fotossíntese e na recuperação da fotoinibição sob baixa irradiância em mogno (Swietenia macrophylla King) e acariquara (Minquartia guianensis Aubl.). As plantas cresceram sob baixa irradiância: 0,20 (acariquara) e 1,43 mol m-2 dia-1 (mogno). A fotossíntese líquida e as características da fluorescência foram avaliadas em duas irradiâncias, 1.000 e 1.700 mmol m-2 s-1 , e duas temperaturas foliares, 32 e 38ºC. A 32ºC, a fotossíntese máxima (Amáx) foi maior em mogno do que em acariquara. Em mogno, a exposição a 38ºC causou redução gradativa na fotossíntese, sendo a taxa fotossintética após 50 min similar à encontrada em acariquara. A 32ºC, o aumento na irradiância, de 1.000 para 1.700 mmol m-2 s-1 , intensificou a fotoinibição, mas Amáx não foi alterada. Em 1.700 mmol m-2 s-1, o aumento da temperatura, de 32 para 38ºC, não afetou a fotoinibição. Após 72 horas em baixa irradiância, a recuperação da fotoinibição foi de 80% em acariquara e 89% em mogno. Não houve efeito da temperatura da folha na fotoinibição.Photoinhibition may be exacerbated by stress factors such as high temperature. The aim of the work was to determine the effects of temperature and irradiance on photosynthesis and photoinhibition in mahogany (Swietenia macrophylla King) and acariquara (Minquartia guianensis Aubl.). Also to assess the effect of irradiance and temperature on the recovery from photoinhibition at low irradiance. Sapling were grown at low irradiance: 0.20 mol m-2 day-1 (mahogany) and 1.43 mol m-2 day-1 (acariquara). Photosynthesis and fluorescence characteristics were assessed in plants subjected to two irradiances 1,000 and 1,700 mmol m-2 s-1 , and two temperatures, 32 e 38ºC. At 32ºC, light saturated photosynthesis (Amax) was greater in mahogany than in acariquara. Mahogany plants exposed to 38ºC showed a consistent decline in carbon uptake, and after 50 min both species showed the same photosynthetic rates. In saplings exposed to 32ºC, increase in irradiance, from 1,000 to 1,700 mmol m-2 s-1 , exacerbated photoinhibition, but without reducing Amax values. At 1,700 mmol m-2 s-1 , the rise in temperature, from 32 to 38ºC, did not increase photoinhibition. After 72 hours at low irradiance, recovery from photoinhibition was 80% in acariquara and 89% in mahogany. There was no effect of leaf temperature on photoinhibition.

Abstract: The effects of exogenous spermine (Spm) on plant growth, chlorophyll fluorescence, ultrastructure and anti-oxidative metabolism of chloroplasts were investigated in Cucumis sativus L. under NaCl stress. Salt stress significantly reduced plant growth, chlorophylls content and F v/F m. These changes could be alleviated by foliar spraying with Spm. Salt stress caused an increase in malondialdehyde (MDA) content and superoxide anion generation rate in chloroplasts. Application of Spm significantly increased activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), and ascorbate peroxidase (APX, EC 1.11.1.11) which decreased the levels of and MDA in the salt-stressed chloroplasts. Salt stress decreased the activities of dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) in the chloroplasts and reduced the contents of dehydroascorbate (DAsA) and glutathione (GSH), but increased monodehydroascorbate reductase (MDAR, EC 1.6.5.4) activity. On the other hand, Spm significantly increased the activities of antioxidant enzymes and levels of antioxidants in the salt-stressed chloroplasts. Further analysis of the ultrastructure of chloroplasts indicated that salinity induced destruction of the chloroplast envelope and increased the number of plastoglobuli with aberrations in thylakoid membranes. However, Spm application to salt-stressed plant leaves counteracted the adverse effects of salinity on the structure of the photosynthetic apparatus. These results suggest that Spm alleviates salt-induced oxidative stress through regulating antioxidant systems in chloroplasts of cucumber seedlings, which is associated with an improvement of the photochemical efficiency of PSII. [Copyright &y& Elsevier]

Abstract: Phytoplankton and bacterioplankton dynamics were studied around South Shetland Islands (Antarctica) with special emphasis on the Drake Passage region, during austral summer, in order to expand our knowledge on the coupling between the autotrophic and heterotrophic microbial plankton compartments in polar ecosystems. In addition, we directly estimated bacterial growth efficiency in the Drake Passage with the aim of better constraining total bacterial carbon utilization in this important polar ecosystem. Integrated chlorophyll-a concentration (21–86mgm−2), primary production rates (0.7–19.3mgCm−3 d−1) and mean water-column photochemical efficiency (0.24–0.60) were significantly correlated with Si⁎ tracer (r 2=0.55, 0.46 and 0.64, respectively), which indirectly points to iron as the major limiting factor for phytoplankton growth in the area. Bacterial production was considerably low (0.002–0.3mgCm−3 d−1) and was best explained by chlorophyll-a concentration, protein-like fluorescence of dissolved organic matter and temperature (r 2=0.53, p<0.001). Water temperature appeared to influence bacterial activity when organic substrate availability is high. Bacterial production accounted on average for only 3.9% of co-occurring primary production, which has been frequently interpreted as an indicator of the marked uncoupling between bacteria and phytoplankton in cold waters. However, using the experimentally derived mean bacterial growth efficiency for the photic zone (6.1±1.3%) the bacterial carbon demand represented on average 63±18% of concomitant primary production, similar to what is found in warmer productive waters. Thus, our study suggests that bacterioplankton and phytoplankton appear to be connected in this polar area. [Copyright &y& Elsevier]

The use of black leaf-clips for dark adaptation under high solar radiation conditions is reported to underestimate the maximum quantum yield of PSII photochemistry (F/F) measured by the continuous-excitation fluorometer Pocket PEA. The decrease in F/F was due to a rise in minimum fluorescence emission (F), probably resulting from increased leaf temperature (T). In field-grown tomato and pepper, fluorescence parameters and T in the region covered by the black leaf clip were measured in clipped leaves exposed to solar radiation during dark adaptation (clipped-only leaves) and in clipped leaves protected from solar radiation by aluminium foil (shrouded clipped leaves). Results confirmed significant F/F underestimates in clipped-only leaves primarily due to increased F. In one tomato experiment, T increased from 30 to 44.5°C in clipped-only leaves, with a negligible rise in shrouded clipped leaves. In two respective pepper experiments, T in clipped-only leaves increased from 27 to 36.2°C and 33 to 40.9°C. Based on the results of this study, a clip-effect parameter (P) on fluorescence emission is proposed as the difference for F/F (or −F/F) between shrouded clipped leaves and clipped-only leaves, which resulted to be 0.706 for tomato, and 0.241 and 0.358 for the two pepper experiments. [ABSTRACT FROM AUTHOR]

In the pursuit of knowledge on the biological behavior of Brazilian Atlantic Forest tree species, this study evaluated the susceptibility of the light-demanding species, Schinus terebinthifolia Raddi., Pseudobombax grandiflorum (Cav.) A. Robyns and Joannesia princeps Vell., and of the shade-tolerant species, Hymenaea courbaril L. var. stilbocarpa and Lecythis pisonis Camb, to photoinhibition and acclimation capacity. These species were first cultivated under two irradiance conditions, I (20% direct sunlight radiation) and I (all-sky or direct sunlight) and then transferred from I to I. The effects of the sudden increase in light radiation intensity on photosynthetic activity were then evaluated through chlorophyll (Chl) fluorescence imaging, HPLC xanthophylls analysis, and cell membrane lipid peroxidation measurements. Light-demanding species were found to present a higher photochemical efficiency and higher acclimation capacity under high light irradiance than shade-tolerant species. The higher photoinhibition tolerance observed in light-demanding species was associated to their higher capacity for photochemical dissipation and dissipation of excess excitation energy via the xanthophyll cycle, leading to a lower ROS generation. The obtained results suggested that a knowledge of acclimation capacity, by means of Chl fluorescence imaging yields, is a useful indicator of species successional grouping. [ABSTRACT FROM AUTHOR]

Abstract: Changes in the ecophysiological performance of a plant species due to different environmental conditions generally reflect adaptations to the habitat where the plant grows and are often related to its survival capacity in a particular place. We examined this with the dioecious shrub Thymelaea velutina, in two contrasting populations representing the extremes of the altitudinal gradient where the species lives (coastal dunes and mountain habitats over 1000m). We measured net photosynthetic rates and stomatal conductance, estimated the level of plant stress by chlorophyll fluorescence, and assessed their correlations with growth rate, plant size, flower production and fruit set. We hypothesized that plants at high altitude were more photosynthetically stressed than at sea level and expected a gender×habitat interaction in performance as females need more resources than males. Plants in the mountain experienced chronic photoinhibition during winter and a reduced photosynthetic performance both in winter and spring compared to plants in coastal dunes. However, there was no association between any of the fluorescence variables and either plant growth or fecundity, suggesting that other factors are involved determining performance. Mountain plants showed also an apparent lower capacity of heat dissipation to excessive radiation than dune plants. In the dunes, the greater leaf area and mass can lead to a higher photosynthetic carbon gain by whole individuals compared to plants in the mountain. No effect of gender was detected on the ecophysiological performance of this species, which we partly attribute to the small size of fruits of the female plants. [Copyright &y& Elsevier]

The synergistic effect of ultraviolet radiation (UVR) and a polycyclic aromatic hydrocarbon (PAH) was tested on the coral Porites divaricata. Small branches were incubated in different concentrations of fluoranthene followed by exposure to ecologically relevant levels of natural solar radiation, with and without UVR. Exposure to the highest concentration of fluoranthene (60 μ g L-1) resulted in decreased photochemical efficiency of corals exposed concomitantly to UVR but not in corals exposed to 60 μ g L-1 fluoranthene without UVR. After 6 days, most coral samples that were exposed to fluoranthene and UVR bleached or died (78%) on the upper side of the branches. At 60 μ g L-1 fluoranthene with UVR, 11 out of 12 samples died and the remaining sample bleached, much greater than the number of samples that bleached in manipulation or solvent controls. On the under side of the same samples, where the coral polyps are naturally protected from UVR, 11 out of 12 samples remained healthy and intact. The high UVR doses that shallow water dwelling corals receive combined with the results of this study show that photoinduced toxicity of PAHs is a stress factor that needs to be studied in more detail in coral reef ecosystems. [ABSTRACT FROM AUTHOR]

Estuaries present a very dynamic environment for phytoplankton with large changes in salinity occurring over relatively short distances, usually with high turbidity. We investigated the photosynthetic characteristics of phytoplankton in the Scheldt estuary (Belgium and the Netherlands) along a salinity gradient using community and single-cell fluorescence measurements. Single-cell fluorescence measurements offer the opportunity to study differences between species that were formerly possible only using uni-algal cultures. The objective was to study differences in the photochemical efficiency of photosystem II (Fv/Fm) between different species or different genera (when identification to the species level was not possible) and to investigate the effect of salinity on individual species. The difference in Fv/Fm between species was small, but often significant (ANOVA, p < 0.05), and was found to be a true characteristic of species, as opposed to being caused by stochastic processes affecting cells of all species more or less equally. High algal mortality is implied by a large decline of biomass from freshwater towards higher salinity, as well as a complete change in the phytoplankton composition. Nevertheless, cells with low Fv/Fm, which would indicate decreased health, were rare. Fv/Fm of 93% of the measured cells was between 0.5 and 0.8. There was no obvious relation between Fv/Fm and species abundance. In laboratory studies, green algae are often reported to have a higher Fv/Fm than diatoms, but we found no indication of this in the Scheldt estuary. [ABSTRACT FROM AUTHOR]

We examined the spatio-temporal variations of chlorophyll fluorescence on a semi-arid Mediterranean shrubland in SE Spain during the 1998–1999 period. We performed the study on three species (Quercus coccifera, Pistacia lentiscus and Pinus halepensis) in two sites with contrasted slope aspect (north/south) located within a small distance from each other. Our main objectives were to assess the effect of slope aspect on the chlorophyll fluorescence features of these species, and to evaluate how this effect is influenced by temporal variations in climatic conditions. The results showed the presence of consistent higher values of maximum efficiency of photosystem II (Fv:Fm) in the north-facing slope at both predawn and midday throughout the study period, but with differences in patterns between the different species. For all species, midday values of Fv:Fm were considerably lower than predawn ones at the south-facing slope throughout 1999. For all species, and over the course of the day, the increase and subsequent decrease in radiation was closely followed by a pronounced decrease and subsequent increase of effective quantum yield of photosystem II, but it was less pronounced in the north-facing slope. Our results show how small-scale spatial differences in climate associated with slope aspect cause pronounced differences on the chlorophyll fluorescence features of shrubs. These differences could have important consequences for carbon assimilation and storage and for vegetation dynamics in Mediterranean semi-arid shrublands. [Copyright &y& Elsevier]

The photosynthetic performance of mungbean (Vigna radiata L.) leaves developed at (1) 30/25 °C+700 PFD (LT+HI), (2) 40/25 °C+700 PFD (HT+HI), and (3) 40/25 °C+200 PFD (HT+LI) was evaluated. Photosynthetic CO2 assimilation rate (Pn) and different Chl a fluorescence parameters of those leaves were measured at different temperatures and photon flux density (PFD). Pn of the LT+HI-developed leaves continued to increase till 2000 PFD while the Pn was lower in the leaves developed at high temperature. HT+HI-developed leaves showed higher Pn than that developed at the same temperature but with low light (HT+LI). Rapid light curves revealed that leaves developed at high light had better photosynthetic efficiency at fast changing light environment than those developed at low light irrespective of their growth temperatures. LT+HI-plants had the highest photochemical quenching (qP) as well as non-photochemical quenching (qN) compared to the plants developed at high temperature (HT+HL and HT+LI). Heat acclimation in the presence of high light appreciably protected the activity of photosynthetic apparatus from heat shock-damage. This was disclosed with the higher photosynthetic efficiency of HT+HI-grown plants after heat shock treatment up to 55 °C than the plants developed at the same temperature but with low light. Leaves developed at HT+LI showed severe photoinhibition of photosynthesis when exposed to strong light for 9 h and did not recover appreciably from the damage compared to those developed at high light (LT+HI and HT+HI). From the various Chl a fluorescence parameters that we determined it would appear that high light exposure protects efficiently the photochemical activity of leaf against its inactivation by heat compared to low light exposure. [Copyright &y& Elsevier]

Marine primary production (PP) is a key factor in the regulation of the global carbon cycle, with important potential feedback on climate. Seventy percent of marine PP is generated by phytoplankton photosynthesis. However, the phytoplankton productivity rate is dependent on the photo-physiological state of phytoplankton cells, as well as other environmental conditions. To consider these variables appropriately, refine the current estimates of PP, and reduce the laboursome and lengthy methodologies of radiocarbon estimates, we have created "Phyto-VFP" (Variable Fluorescence Phytoplankton Production), a new bio-optical model classified as a Wavelength and Depth-resolved (WDR) model. The model integrates the effect of the photo-acclimation processes on the "active" fraction of the phytoplankton population with the dynamic of the water column, parametrised through a series of laboratory experiments based on in vivo variable fluorescence measures on the marine diatom Skeletonema costatum (Greville) Cleve. The performance of Phyto-VFP was compared with concurrent estimates of radiocarbon (14C) uptakes, under different dynamic and optical conditions, during two oceanographic cruises (SAMCA3 and SAMCA4) in the Mediterranean Sea. The low Root Mean Square Differences (RMSDs) show that Phyto-VFP performs well when estimating phytoplankton PP. When compared to other bio-optical models, Phyto-VFP estimates of PP in coastal waters were closer to radiocarbon measurements than other models could predict [ e.g. , the Morel model (MM)]. The application of Phyto-VFP to the SAMCA dataset and its comparison to MM allowed the assessment of model performance under three different physical and biological conditions, in which it was possible to analyse how photo-physiological responses of phytoplankton influence PP. • Phyto-VFP estimates phytoplankton Primary Production using variable fluorescence. • Phyto-VFP combines phytoplankton physiological processes with water column dynamics. • The model attained a performance similar to the most widely Primary Production models. • Phyto-VFP shows a higher predictive skill than Morel model in coastal waters. [ABSTRACT FROM AUTHOR]