Chlorophyll Fluorescence Techniques Research Articles

Dieback of royal poinciana (Delonix regia) trees induced by Alternaria tenuissima and its impact on photochemical efficiency of photosystem II

In Saudi Arabia, poinciana (Delonix regia) trees are afflicted by dieback disease, manifesting symptoms that can lead to complete defoliation and, ultimately, the demise of trees in advanced stages. To investigate the dieback symptoms, samples were collected from branches at the transition zone. Identification of fungal isolates involved the assessment of colony and spore morphology, as well as PCR amplification and sequencing of the internal transcribed spacer (ITS) gene regions. The predominant fungus isolated was Alternaria tenuissima. Chlorophyll a fluorescence quenching and polyphasic fluorescence induction kinetics were conducted to assess the photochemical and nonphotochemical processes of Photosystem II (PSII) in stem barks affected by dieback. The dieback disease significantly reduced chlorophyll content, potentially hindering PSII performance in terms of maximum photochemical efficiency, quantum yield, electron flux, and photoprotection. These findings suggest that compromised photochemistry and photoprotection render poinciana trees inoculated by dieback less efficient in utilizing light energy and more susceptible to photoinhibition. Additionally, this study implies the use of non-invasive chlorophyll fluorescence techniques as a phenotyping tool for assessing photoprotective and photoinhibitory responses of stems to dieback stress.

Gas exchange and chlorophyll fluorescence responses of Camellia sinensis grown under various cultivations in different seasons

Sod culture (SC) and conventional agriculture (CA) represent two distinct field management approaches utilized in the cultivation of tea plants in Taiwan. In this study, we employed gas exchange and chlorophyll fluorescence techniques to assess the impact of SC and CA methods on the photosynthetic machinery of Camellia sinensis cv. TTES No.12 (Jhinhsuan) in response to variable light intensities across different seasons. In spring, at photosynthetic photon flux densities (PPFD) ranging from 800 to 2,000 μmol photon m-2 s-1, the net photosynthesis rate (Pn, 10.43 μmol CO2 m-2 s-1), stomatal conductance (Gs, 126.11 mmol H2O m-2 s-1), electron transport rate (ETR, 137.94), and ΔF/Fm’ and Fv/Fm (50.37) values for plants grown using SC were comparatively higher than those cultivated under CA. Conversely, the non-photochemical quenching (NPQ) values for SC-grown plants were relatively lower (3.11) compared to those grown under CA at 800 to 2,000 PPFD in spring. Additionally, when tea plants were exposed to PPFD levels below 1,500 μmol photon m− 2 s− 1, there was a concurrent increase in Pn, Gs, ETR, and NPQ. These photosynthetic parameters are crucial for devising models that optimize cultivation practices across varying seasons and specific tillage requirements, and for predicting photosynthetic and respiratory responses of tea plants to seasonally or artificially altered light irradiances. The observed positive impacts of SC on maximum photosynthetic rate (Amax), Fv/Fm, Gs, water-use efficiency (WUE), and ETR suggest that SC is advantageous for enhancing the productivity of tea plants, thereby offering a more adaptable management model for tea gardens.

Application of Chlorophyll Fluorescence Analysis Technique in Studying the Response of Lettuce (Lactuca sativa L.) to Cadmium Stress.

To reveal the impact of cadmium stress on the physiological mechanism of lettuce, simultaneous determination and correlation analyses of chlorophyll content and photosynthetic function were conducted using lettuce seedlings as the research subject. The changes in relative chlorophyll content, rapid chlorophyll fluorescence induction kinetics curve, and related chlorophyll fluorescence parameters of lettuce seedling leaves under cadmium stress were detected and analyzed. Furthermore, a model for estimating relative chlorophyll content was established. The results showed that cadmium stress at 1 mg/kg and 5 mg/kg had a promoting effect on the relative chlorophyll content, while cadmium stress at 10 mg/kg and 20 mg/kg had an inhibitory effect on the relative chlorophyll content. Moreover, with the extension of time, the inhibitory effect became more pronounced. Cadmium stress affects both the donor and acceptor sides of photosystem II in lettuce seedling leaves, damaging the electron transfer chain and reducing energy transfer in the photosynthetic system. It also inhibits water photolysis and decreases electron transfer efficiency, leading to a decline in photosynthesis. However, lettuce seedling leaves can mitigate photosystem II damage caused by cadmium stress through increased thermal dissipation. The model established based on the energy captured by a reaction center for electron transfer can effectively estimate the relative chlorophyll content of leaves. This study demonstrates that chlorophyll fluorescence techniques have great potential in elucidating the physiological mechanism of cadmium stress in lettuce, as well as in achieving synchronized determination and correlation analyses of chlorophyll content and photosynthetic function.

Alcobiosis, an algal-fungal association on the threshold of lichenisation

Alcobiosis, the symbiosis of algae and corticioid fungi, frequently occurs on bark and wood. Algae form a layer in or below fungal basidiomata reminiscent of the photobiont layer in lichens. Identities of algal and fungal partners were confirmed by DNA barcoding. Algal activity was examined using gas exchange and chlorophyll fluorescence techniques. Carbon transfer from algae to fungi was detected as 13C, assimilated by algae, transferred to the fungal polyol. Nine fungal partners scattered across Agaricomycetes are associated with three algae from Trebouxiophycae: Coccomyxa sp. with seven fungal species on damp wood, Desmococcus olivaceus and Tritostichococcus coniocybes, both with a single species on bark and rain-sheltered wood, respectively. The fungal partner does not cause any obvious harm to the algae. Algae enclosed in fungal tissue exhibited a substantial CO2 uptake, but carbon transfer to fungal tissues was only detected in the Lyomyces-Desmococcus alcobiosis where some algal cells are tightly enclosed by hyphae in goniocyst-like structures. Unlike lichen mycobionts, fungi in alcobioses are not nutritionally dependent on the algal partner as all of them can live without algae. We consider alcobioses to be symbioses in various stages of co-evolution, but still quite different from true lichens.

Stimulative Effects of Lupinus sp. and Melilotus albus Underseed on the Photosynthetic Performance of Maize (Zea mays) in Two Intercropping Systems

In order to evaluate influential mechanisms for photosynthetic processes on the yields of an intercropping system composed of maize (Zea mays), Lupinus sp. and Melilotus albus, three treatments were designed and conducted in southern Moravia (Czech Republic) in the form of agronomy trials. The treatments included sole maize (SM), maize with Lupinus sp. (ML) and maize with field melilot (MM). The photosynthetic processes of Zea mays were monitored using several chlorophyll fluorescence techniques on the three treatments for 20 days in the late summer season. An analysis of fast chlorophyll fluorescence transients (OJIP) showed that the capacity of photochemical photosynthetic reactions in photosystem II (FV/FM), as well as the photosynthetic electron transport rate (ET0/RC), declined in response to a four-day episode of extremely warm days with full sunshine. Similarly, the performance index (PI), an indicator of general plant vitality, declined. The episode activated protective mechanisms in photosystem II (PSII), which resulted in an increase of thermal dissipation. For the majority of Z. mays photosynthetic parameters, their values decreased for particular treatments in the following order: MM, ML, SM. The MM and ML intercropping systems had a positive effect on the primary photosynthetic parameters in Z. mays.

Improved photosynthetic performance induced by Fe3O4 nanoparticles.

Interaction between 11nm-sized magnetite nanoparticles and Cichorium intybus plants was studied in this work. In particular, the effect of these nanoparticles on the photosynthesis electron chain was carefully analysed. Magnetite nanoparticles were synthesised and physically characterised by Transmission electron microscopy (TEM), Scanning electron microscopy (SEM)), Energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Magnetic hysteresis cycles and UV-visible spectroscopy. Suspensions of the obtained magnetite nanoparticles with different concentrations (10-1000ppm) were sprayed over chicory leaves and their photosynthetic activity was evaluated using chlorophyll fluorescence techniques. The study was complemented with the determination of pigment concentration and spectral reflectance indices. The whole set of results was compared to those obtained for control (non-treated) plants. Magnetite nanoparticles caused an increment in the content of Chlorophyll a (up to 36%) and Chlorophyll b (up to 41%). The ratio Chlorophyll/ Carotenoids significantly increased (up to 29%) and the quotient Chlorophyll a/b remained relatively constant, except for a sharp increase (19%) at 100ppm. The reflectance index that best manifested the improvement in chlorophyll content was the modified Normalised Difference Vegetation Index (mNDI), with a maximum increase of about 35%. Electronic transport fluxes were favoured and the photosynthetic parameters derived from Kautsky's kinetics were improved. An optimal concentration of nanoparticles (100ppm) for the most beneficial effects on photosynthesis was identified. For this dose, the probability by which a trapped electron in PSII was transferred up to PSI acceptors (ΦRE0) was doubled and the parameter that quantifies the energy conservation of photons absorbed by PSII up to the reduction of PSI acceptors ([Formula: see text]), augmented five times. The fraction of absorbed energy used for photosynthesis increased to 86% and the energy lost as heat by the non-photochemical quenching mechanism was reduced to 31%. Beyond 100ppm, photosynthetic parameters declined but remained above the values of the control.

Determination of some phenolic substances in six different populations of turkish hazel (Corylus colurna L.) leaves and comparison of phenolic fluctuation with water deficiency

Turkish hazel (Corylus colurna L.) is one of the naturally grown hazelnut species in Turkey. It can be easily separated from other hazel species with its thick single stem and tall appearance. It can be used in afforestation and erosion control studies due to low demand for habitat and strong root system. It contains substances with high medicinal value in its fruits and leaves. Hazel leaves have strong antioxidant activity due to their high phenolic content. Objective of the study was primarily to determine the individual phenolic constituents of six different population of Turkish Hazelnut and then to evaluate the effect of water deficiency stress generated by irrigation regime on phenolic constituents and photosystem II activity on these genotypes. Grafted plants were produced by taking scions from six different populations of Turkish Hazelnut (Oğuzlar, Erenler, Merkeşler, Seben, Güney Felakettin and Pelitcik). The study was started when the grafted seedlings were 7 years old in greenhouse. During the experiment (June and July), two different levels of irrigation were applied (W1: the soil was fully irrigated to reach field capacity in each irrigation; W2: 50% reduction of W1 irrigation water). After the application of two different irrigation regimes, leaves were collected for each month, dried, extracted with methanol and then quantitatively analyzed and compared for individual phenolic constituents (gallic acid monohydrate, caffeic acid, rutin hydrate, luteolin-7-O-β-D glucoside, kaempferol, rosmarinic acid, myricetin, quercetin, coumarin and apigenin) by using high performance liquid chromatography (HPLC) coupled with a diode array detector (DAD). Generally, rutin, kaempferol and luteolin were dominant individual phenols in methanol extracts of Turkish hazelnut leaves. Pelitcik population was noticeable source of rutin and kaempferol in June, and the halved irrigation regime significantly increased the levels of both phenols in July. Similarly, the highest total phenolic content was observed in the Pelitcik population in June and the halved irrigation regime significantly increased the total phenolic content in both months in this population. It was also determined to what extent water deficiency physiologically affects the quantum efficiency (Fv/Fm) of photosystem II activity through chlorophyll fluorescence technique in hazelnut leaves. Generally, Fv/Fm value decreased with water deficiency. This study showed that water deficiency stress generally caused an increase in phenolic constituents in Turkish Hazel leaves and they may be proper natural sources of phenolic constituents with abiotic stress applications in pharmaceutical and food industry.

Assessing and modeling nitrite inhibition in microalgae-bacteria consortia for wastewater treatment by means of photo-respirometric and chlorophyll fluorescence techniques

Total nitrite (TNO2 = HNO2 + NO−2) accumulation due to the activity of ammonia-oxidizing bacteria (AOB) was monitored in microalgae-bacteria consortia, and the inhibitory effect of nitrite/free nitrous acid (NO2-N/FNA) on microalgae photosynthesis and inhibition mechanism was studied. A culture of Scenedesmus was used to run two sets of batch reactors at different pH and TNO2 concentrations to evaluate the toxic potential of NO2-N and FNA. Photo-respirometric tests showed that NO2-N accumulation has a negative impact on net oxygen production rate (OPRNET). Chlorophyll a fluorescence analysis was used to examine the biochemical effects of NO2-N stress and the mechanism of NO2-N inhibition. The electron transport rate (ETR), non-photochemical quenching (NPQ), and JIP-test revealed that the electron transport chain between Photosystems II and I (PS II and PS I) was hindered at NO2-N concentrations above 25 g N m−3. Electron acceptor QA was not able to reoxidize and could not transfer electrons to the next electron acceptor, QB, accumulating P680+ (excited PS II reaction center) and limiting oxygen production.A semi-continuous reactor containing a Scenedesmus culture was monitored by photo-respirometry tests and Chlorophyll a fluorescence to calibrate NO2-N inhibition (5–35 g N m−3). Non-competitive inhibition and Hill-type models were compared to select the best-fitting inhibition equations. Inhibition was correctly modeled by the Hill-type model and a half inhibition constant (KI) for OPRNET, NPQ, maximum photosynthetic rate (ETRMAX) and the performance index PIABS was 23.7 ± 1.2, 26.36 ± 1.10, 39 ± 2 and 26.5 ± 0.4, respectively.

Increased CO2 Relevant to Future Ocean Acidification Alleviates the Sensitivity of a Red Macroalgae to Solar Ultraviolet Irradiance by Modulating the Synergy Between Photosystems II and I.

While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO2 levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO2 concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O2-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (Fk) of Kautsky curves relative to the amplitude of FJ−Fo (Wk) and a decrease of the maximum quantum yield of PSII (Fv/Fm). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO2 assimilation. When the algal thalli were grown under increased CO2 and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO2 levels and OA.

Combined chlorophyll fluorescence techniques to study environmental impact on the mountain moss Polytrichum commune

Two chlorophyll fluorescence (ChlF) methods were used to study the effects of high light (photoinhibition) and dehydration, common stressors of the alpine environment, on primary photosynthetic processes in the moss Polytrichum commune from the Czech Republic, the Jeseníky Mountains. Photoinhibition (PI) was studied in fully hydrated thalli of P. commune and during the period of spontaneous desiccation. Time courses of Kautsky kinetics (KK) of ChlF and derived parameters: maximum quantum yield (FV/FM), effective quantum yeld (ΦPSII), and non-photochemical quenching parameters, were measured before and after the samples were treated with high light (1500 µmol m-2 s-1 PAR) for 60 min. Dehydration effects were tested in two sets of experiments with a Pulse-Amplitude-Modulation fluorometry (PAM) and Fast Chlorophyll Fluorescence induction curve (OJIP) techniques. In PAM tests, the desiccating samples were exposed to saturating light pulses every 10 min. in order to obtain ΦPSII and non-photochemical quenching (NPQ). In the second dehydration experiment, OJIP transients of ChlF were repeatedly recorded, OJIP-derived ChlF parameters were plotted against relative water content (RWC) monitored during desiccation. Combined ChF techniques provided insights into the mechanisms activated during P. commune desiccation, such as dissipation of excess absorbed energy through heat dissipation, and conformational changes or destructions of the light harvesting complexes. Combination of stressors resulted in amplified interference with the photosynthetic machinery, even when the added stressor (dehydration) was applied in low dose.

Resistance of Antarctic moss Sanionia uncinata to photoinhibition: chlorophyll fluorescence analysis of samples from the western and eastern coasts of the Antarctic Peninsula.

Interspecific differences in sensitivity of the Antarctic moss Sanionia uncinata from King George Island (KGI) and James Ross Island (JRI) to photoinhibitory treatment were studied in laboratory conditions using chlorophyll fluorescence techniques. Slow (Kautsky) and fast (OJIP) kinetics were used for the measurements. Samples were exposed to a short-term (60min) photoinhibitory treatment (PIT, 2000μmol·m-2 ·s-1 PAR). The photoinhibitory treatment (PIT) led to photoinhibition which was indicated by the decrease in FV /FM and ΦPSII in KGI but not in JRI samples. However, this decrease was small and full recovery was reached 90min after PIT termination. Non-photochemical quenching (NPQ) was activated during the PIT, and rapidly relaxed during recovery. Early stages of photoinhibition showed a drop in FV /FM and ΦPSII to minimum values within the first 10s of the PIT, with their subsequent increase apparent within fast (0-5min PIT) and slow (5-50min PIT) phases of adjustment. The PIT caused a decrease in the performance index (Pi_Abs), photosynthetic electron transport per reaction centre (RC) (ET0 /RC). The PIT induced an increase in thermal dissipation per RC (DI0 /RC), effectivity of thermal dissipation (Phi_D0 ), absorption per RC (ABS/RC) and trapping rate per RC (TR0 /RC). In conclusion, PIT led to only slight photoinhibition followed by fast recovery in S. uncinata from KGI and JRI, since FV /FM and ΦPSII returned to pre-photoinhibitory conditions. Therefore, S. uncinata might be considered resistant to photoinhibition even in the wet state. The KGI samples showed higher resistance to photoinhibition than the JRI samples.

Phycoremediation and photosynthetic toxicity assessment of lead by two freshwater microalgae Scenedesmus acutus and Chlorella pyrenoidosa.

Heavy metal (HM) pollution is a serious agro-economic concern and algae can be used as one of the bioremediating agents as it can grow in different water bodies. In this study, the Scenedesmus acutus and Chlorella pyrenoidosa were exposed to various concentrations of Pb2+ for 96 h and a multidimensional toxicity assessment has been performed by pulse amplitude modulation technique and Fourier transform infrared spectroscopy (FTIR). High-angle annular dark-field scanning transmission electron microscopy coupled energy dispersive spectroscopy (HAADF-S/TEM-EDS) detected intracellular localization of Pb2+ , thus confirming algal bio-accumulation abilities. Sensitivity assay demonstrated that 500 and 400 ppm of Pb2+ as minimum inhibitory concentrations (MIC50) for S. acutus and C. pyrenoidosa, respectively, which inhibited growth (OD) by >50% in 96 h. During bioremoval studies, S. acutus and C. pyrenoidosa were found to remove ∼52 and ∼32% of total Pb2+ , respectively. The particulate analysis of Pb2+ by ICP-OES showed >99.5% biosorption capacity by both the species. The biomass characterization by FTIR showed the involvement of various cell wall functional groups such as hydroxyl, alkane, and C=C groups in the biosorption of Pb2+ by both the species. The noninvasive chlorophyll fluorescence techniques provide a quick insight on heavy metal stress and can be adapted as a rapid detection tool to study the Pb2+ stress. S. acutus strain showed higher tolerance and higher bioremoval capacity than C. pyrenoidosa. However, both the species can be exploited for biosorption of Pb2+ from aquatic streams as an alternative way for low cost Pb2+ recovery systems.

Physiological introspection of leaf photochemical activity and antioxidant metabolism in selected indigenous finger millet genotypes in relation to drought stress

Drought stress often impairs growth and yield of finger millets worldwide. The present study investigated the drought stress responses in four indigenous finger millets (Gangabali, Dengsameli, Kada and Badu) of Koraput compared to one improved variety (Bhairabi) under simulated drought condition at the early growth stage. The physiological and biochemical responses of indigenous finger millets were assessed through chlorophyll fluorescence technique, photosynthetic pigments, antioxidants, proline, protein and lipid peroxidation. The results showed that drought treatment significantly declined the photosystem (PS) II activity by declining the maximal fluorescence, maximum photochemical efficiency of PSII, yield of PSII photochemistry, electron transport rate and photochemical quenching with concomitant increase in minimum fluorescence and non-photosynthetic quenching compared to the respective control plants. Further, the present finding indicates that finger millet leaves responded to PEG-induced drought stress by significantly enhancing antioxidant enzyme activity. The proline accumulation was increased with increasing concentration of drought, which suggests that plants’ ability to resist the effect of drought. Based on the phenotypic response under drought stress, indigenous finger millet genotypes such as Gangabali and Badu showed superior drought tolerance capacity than the improved genotype (Bhairabi) during seedling stages. Overall, the results suggest that these indigenous finger millet genotypes may be beneficial for rainfed areas affected by drought stresses and can be used for future breeding programs.

Uptake of microalgae as sublethal biomarker reveals phototoxicity of oxytetracycline to the crustacean Daphnia magna

Antibiotics are considered emerging pollutants as their presence in the environment is increasingly common. Although their environmental concentrations are generally low, they can pose risk to organisms through bioaccumulation, causing sublethal effects. Furthermore, solar radiation can trigger reactions in certain compounds after their accumulation within organisms or in the environment. Toxicity and photoinduced toxicity of oxytetracycline (OTC, widely used antibiotic in salmon aquaculture) on Daphnia magna (Crustacea, Cladocera) and microalgae Raphidocelis subcapitata (Chlorophyceae) as its food source was assessed via aqueous exposure. Also, the impact via diet (microalga) to the crustacean was examined. In addition to lethal (immobility) effect, in vivo chlorophyll fluorescence techniques were used to determine food ingestion (gut content as a biomarker of physiological health) in D. magna and physiological status of microalgae. OTC (≤10 mg L − 1) was not acutely (24 h) toxic to R. subcapitata when measured as maximum quantum yield (Fv/Fm) in darkness. However, under short (1 h) UV exposure OTC caused irreversible decrease of Fv/Fm (50%) at ≥0.5 mg L − 1. OTC was not acutely lethal to D. magna (≤10 mg L − 1), however, sublethal effects (43% decrease in food ingestion) at 10 mg L − 1 were demonstrated. UV exposure (4.5 h) strongly exacerbated toxicity of OTC, leading to lethal (87% immobility) and sublethal (81% decrease of feeding in survived individuals) effects. Uptake of OTC (aqueous exposure) and its photosensitization in tissues of D. magna under UV exposure was confirmed. On the other hand, rapid bioadsorption of OTC on cell surface was evident in R. subcapitata. Uptake of OTC in D. magna through diet could not be confirmed at short-term. Photomodification of OTC under UV exposure was observed through changes in its absorption spectrum. The results show that short exposure to summer UV levels of southern Chile can rapidly induce phototoxicity of OTC, suggesting a potential risk to aquatic organisms.

Photosystems I and II in Ulva lactuca are well protected from high incident sunlight

We investigated the individual as well as combined performance of photosystem II and photosystem I in the ubiquitous green macroalga Ulva lactuca under diurnally changing light conditions using a dual pulse-amplitude modulated chlorophyll fluorescence technique. Along with rising levels of sunlight, the effective and maximal quantum yields of photosystem II decreased with increasing non-photochemical quenching. With declining irradiances in the afternoon, these photosystem II characteristics recovered gradually, such that they reached the same levels in the evening as in the morning without any signs of photodamage during the day. The values of non-photochemical quenching were higher in the afternoon than during pre-noon at equivalent irradiances, indicating the existence of energy-dissipating cycles that lessened energy transfer from photosystem II to photosystem I. The effective quantum yield of photosystem I decreased only slightly during the daytime and recovered fully in the afternoon, showing that photosystem I was also well protected from photodamage. These results were complemented by analyses of short-term fluorescence induction OKJIP-transients of Kautsky curves, showing 1) that the photosystem II electron donor side was kept fully active throughout the day, 2) that there was no change in the activity of the photosystem II acceptor side, 3) highly efficient electron transport through photosystem I, and 4) an enhanced cyclic electron flow around photosystem I with increasing irradiances. Such non-destructive photoprotective capabilities may in part explain the successful adaptation of the genus Ulva to a wide range of irradiance conditions locally as well as globally.

Productivity and heat-stress tolerance in Canadian poplar (Populus × canadensis Moench) clones with different ecological optimum

Cultivation of fast growing poplar (Populus sp.) clones represents an effective means for reaching the 2020 target of the EU-28 renewable energy production. However, considering the continuous climate change, their growth can be markedly affected by summer heat stress episodes in Slovakia. Therefore, in this work two Canadian poplar (Populus × canadensis Moench) clones of different ecological optimum, ‘Gigant' and ‘Pannonia', were investigated in respect of productivity and heat stress tolerance. After three-year cultivation, tree height in the clone ‘Gigant' was 8.9 m, breast trunk diameter 9.3 cm and trunk volume 0.021 m3 compared to 7.9 m, 7.0 cm and 0.012 m3 in clone ‘Pannonia' (despite of relatively more stable trunk growth rate in summer). Trunks of the latter clone contained 12% bark (vs. 10% in ‘Gigant'), 1.5% ash in the wood (vs. 3%) and showed significantly larger wood density (440 vs. 380 kg m−3) but lower wood free energy content (14.5 vs. 16 MJ kg−1). Both of clones were proved to be diploids (2x). Clone ‘Pannonia' exhibited larger heat stress tolerance, as tested in leaves of different developmental stage exposed to 40 °C using chlorophyll fluorescence technique (decreasing from mature to juvenile leaves), lower specific leaf area and higher leaf carotenoid and cytokinin (particularly BAP derivatives) concentration. In spite of lower heat stress tolerance and higher ash content, clone ‘Gigant' showed larger productivity than clone ‘Pannonia', suggesting potential of the latter for cultivation in much more stressful conditions.

Elevated NO2 damages the photosynthetic apparatus by inducing the accumulation of superoxide anions and peroxynitrite in tobacco seedling leaves.

This study aimed to further understand the toxicity of high concentrations of nitrogen dioxide (NO2) to plants, especially to plant photosynthesis. Tobacco plants in the six-leaf stage were exposed to 16.0μLL-1 NO2 to determine the activities of photosystem II (PSII) and photosystem I (PSI) reaction centers, the blocking site of PSII electron transport, the degree of membrane peroxidation and the relative expression of PsbA, PsbO and PsaA genes in the third fully expanded leaves by using gas exchange and chlorophyll fluorescence techniques, biochemical and RT-PCR analysis. The results showed that 16.0μLL-1 NO2 caused necrotic lesions to form on leaves and significantly increased the generation rate of superoxide anions (O2-) and the content of peroxynitrite (ONOO-) in leaves of tobacco seedling, leading to damage to cell membrane, chlorophyll content and net photosynthetic rate reduction, and photosynthetic apparatus destruction. Fumigation with 16.0μLL-1 NO2 decreased the activity of PSII reaction center and oxygen evolution complex, and the relative expression of PabA in leaves of tobacco seedlings to inhibit the electron transport from the donor side to the receptor side of PSII, especially blocking the electron transport from QA to QB on the receptor side. The activity of the PSI reaction center and the relative expression of PsaA decreased, weakening the ability to accept electrons and inhibiting the electron transfer from PSII to PSI, which further increased the damage of PSII of tobacco seedling leaves caused by 16.0μLL-1 NO2. Therefore, 16.0μLL-1 NO2 leaded to the accumulation of O2- and ONOO-, which damaged the cell membrane and thylakoid membrane, inhibit the electron transport, and destroyed the photosynthetic apparatus in leaves of tobacco seedlings. The results from this study emphasized the importance of reducing the NO2 concentration in the atmosphere.

The highly efficient NDH-dependent photosystem I cyclic electron flow pathway in the marine angiosperm Zostera marina.

Zostera marina, a fully submerged marine angiosperm with a unique evolutionary history associated with its terrestrial origin, has distinct photochemical characteristics caused by its oxygen-evolving complex (OEC) being prone to deactivation in visible light. Based on the present phylogenetic analysis, the chloroplast NADPH dehydrogenase-like (NDH) complex was found to be completed in of Z. marina, unlike other marine plants, suggesting its crucial role. Thus, the responses of electron transport to irradiation were investigated through multiple chlorophyll fluorescence techniques and Western blot analysis. Moreover, the respective contribution of the two photosystem I cyclic electron flow (PSI-CEF) pathways to the generation of trans-thylakoid proton gradient (∆pH) was also examined using inhibitors. The contributions of the two PSI-CEF pathways to ∆pH were similar; furthermore, there was a trade-off between the two pathways under excess irradiation: the PGR5/L1-dependent PSI-CEF decreased gradually following its activation during the initial illumination, while NDH-dependent PSI-CEF was activated gradually with exposure duration. OEC inactivation was continuously under excess irradiation, which exhibits a positive linear correlation with the activation of NDH-dependent PSI-CEF. We suggest that PGR5/L1-dependent PSI-CEF was preferentially activated to handle the excess electron caused by the operation of OEC during the initial illumination. Subsequently, the increasing OEC inactivation with exposure duration resulted in a deficit of electrons. Limited electrons from PSI might preferentially synthesize NADPH, which could support the function of NDH-dependent PSI-CEF to generate ∆pH and ATP via reducing ferredoxin, thereby maintaining OEC stability.

Advancing Bromegrass Breeding Through Imaging Phenotyping and Genomic Selection: A Review.

Breeding forage crops for high yields of digestible biomass along with improved resource-use efficiency and wide adaptation is essential to meet future challenges in forage production imposed by growing demand, declining resources, and changing climate. Bromegrasses (Bromus spp.) are economically important forage species in the temperate regions of world, but genetic gain in forage yield of bromegrass is relatively low. In particular, limited breeding efforts have been made in improving abiotic stress tolerance and resource-use efficiency. We conducted a literature review on bromegrass breeding achievements and challenges, global climate change impacts on bromegrass species, and explored the feasibility of applying high-throughput imaging phenotyping techniques and genomic selection for further advances in forage yield and quality selection. Overall genetic gain in forage yield of bromegrass has been low, but genetic improvement in forage yield of smooth bromegrass (Bromus inermis Leyss) is somewhat higher than that of meadow bromegrass (Bromus riparius Rehm). This low genetic gain in bromegrass yield is due to a few factors such as its genetic complexity, lack of long-term breeding effort, and inadequate plant adaptation to changing climate. Studies examining the impacts of global climate change on bromegrass species show that global warming, heat stress, and drought have negative effects on forage yield. A number of useful physiological traits have been identified for genetic improvement to minimize yield loss. Available reports suggest that high-throughput imaging phenotyping techniques, including visual and infrared thermal imaging, imaging hyperspectral spectroscopy, and imaging chlorophyll fluorescence, are capable of capturing images of morphological, physiological, and biochemical traits related to plant growth, yield, and adaptation to abiotic stresses at different scales of organization. The more complex traits such as photosynthetic radiation-use efficiency, water-use efficiency, and nitrogen-use efficiency can be effectively assessed by utilizing combinations of imaging hyperspectral spectroscopy, infrared thermal imaging, and imaging chlorophyll fluorescence techniques in a breeding program. Genomic selection has been applied in the breeding of forage species and the applications show its potential in high ploidy, outcrossing species like bromegrass to improve the accuracy of parental selection and improve genetic gain. Together, these new technologies hold promise for improved genetic gain and wide adaptation in future bromegrass breeding.

Differential responses to salt concentrations of lichen photobiont strains isolated from lichens occurring in different littoral zones

AbstractAn interesting biota of lichen-forming fungi occurs along rocky seashores of cold and warm-temperate regions in both hemispheres. Most of the species belong to the family Verrucariaceae and form symbioses with an extraordinarily diverse group of photobionts. We isolated the photobionts of three species: Hydropunctaria maura and H. amphibia from the supralittoral zone, and Wahlenbergiella striatula from the upper intertidal zone. We characterized the isolated strains structurally by means of transmission electron microscopy, and molecularly using the nrSSU and nrITS and chloroplast RPL10A regions. Additionally, we studied the response of the strains to different salt concentrations, analyzed the concentration of osmoregulatory solutes, and measured photosynthesis performance by chlorophyll fluorescence and CO2 assimilation techniques. All strains belong to the recently described species Halofilum ramosum, although we found differences in the ITS and RPL10A regions among the strains shared by H. maura and H. amphibia and the strain isolated from W. striatula. Differences were also found in the main osmoregulatory response of the strains growing under high salt concentrations: W. striatula accumulated glycerol, while H. maura and H. amphibia synthetized sucrose. Analyses of photosynthesis performance also indicated differences in physiological behavior between supralittoral-dwelling and intertidal-dwelling species, W. striatula showing lower photosynthetic activity under high irradiance. Our results highlight the role of photobionts in determining lichen zonation on rocky seashores.