Maximum Quantum Yield Of Photosystem Research Articles

Strigolactone and salicylic acid regulate the expression of multiple stress-related genes and enhance the drought resistance of cherry rootstocks

Drought is one of the most significant abiotic stress factors, which disrupts plant growth and development and restricts cherry (Cerasus spp.) production. Exploring effective methods to enhance the tolerance of cherry rootstocks to drought stress is a top urgency for scions to thrive. Strigolactones (SLs) and salicylic acid (SA) have been demonstrated to participate in various biotic and abiotic stresses. In current study, the effects of SLs and SA on cherry rootstocks under drought stress were investigated. The net photosynthetic rate, the maximum quantum yield of photosystem II, and the relative water content of the rac-GR24 and SA pretreatment groups were all higher under drought stress compared with well-watered group, but the antioxidant enzyme activities were lower, indicating that they greatly increased drought resistance. RNA-Seq analysis of leaf samples treated with drought stress (T1), drought stress along with 1 mM SA (T2), 1 μM rac-GR24 (T3), and 5 μM rac-GR24 (T4) pretreatments revealed that 837, 755, 586 and 489 differentially expressed genes (DEGs), respectively. Transcriptome analysis suggested that many of DEGs were ABA-related genes (PavNCED, and PavPP2C51), stress-related transcription factors (PavWRKY, and PavMYB), antioxidant enzyme genes (PavGST and PavPOD), and osmotic adjustment genes (PavUGTs, PavSUSs, and PavSPS1). In our study, PavDBP2D, PavABCG15-like, PavPUP9, PavLOG1-like, and PavENT8 were significantly activated by drought treatment, and rac-GR24 or SA pretreatment decreased these genes expression levels under the drought stress condition. Overall, our findings will provide a basic understanding of drought tolerance in cherry rootstocks modulated by SA and SLs, as well as new insights into regulatory mechanisms of drought tolerance in woody plants.

Symbiodiniaceae in and ex hospite have differential physiological responses under different heat stress scenarios

ABSTRACT Extreme seawater temperatures are linked to increasingly frequent cnidarian bleaching, a breakdown of the symbiosis between host and endosymbiotic dinoflagellates. This can be driven by several anthropogenic stressors, of which seawater warming is a major and frequent one. It remains unclear whether this is caused by intrinsic properties of the host or exclusively by the symbiont. This study investigates the response to elevated temperatures of dinoflagellate symbionts in and ex hospite, particularly to find out whether thermal tolerance differs between endosymbionts and free-living micro-algae. Maximum quantum yield of photosystem II (Fv/Fm ) and symbiont cell density were measured in seven different cnidarian species and five cultures of isolated endosymbionts subjected to temperatures of 26°C (control), 30°C and 34°C for 21 days. Isolated dinoflagellate cells showed a susceptibility to elevated temperatures of 30°C, evidenced by a decrease in photochemical efficiency and cell density of the cultures, as well as a progressive disintegration of cellular structures and loss of pigmentation of all but two cultures during the first week of exposure. Bleaching of coral holobionts at 30°C could be explained by reduced density of algae cells in host tissue. This effect was particularly evident in soft corals. Exposure to 34°C resulted in drastic bleaching of stony coral species, anemones and jellyfish, and even the death of soft corals. Data from this study show different responses to elevated thermal conditions across several species and different genera of symbionts and emphasize the important role of dinoflagellate symbionts in the holobiont response to elevated seawater temperatures.

Ecophysiological responses of seedlings of six dipterocarp species to short-term drought in Borneo

To predict the dynamics of tropical rainforest ecosystems in response to climate change, it is necessary to understand the drought tolerance and related mechanisms of trees in tropical rainforests. In this study, we assessed the ecophysiological responses of seedlings of six dipterocarp species (Dipterocarpus pachyphyllus, Dryobalanops aromatica, Shorea beccariana, S. curtisii, S. parvifolia, and S. smithiana) to experimental short-term drought conditions. The seedlings were initially grown in plastic pots with sufficient irrigation; irrigation was then stopped to induce drought. Throughout the soil-drying period, we measured various ecophysiological parameters, such as maximum photosynthetic and transpiration rates, stomatal conductance, water-use efficiency, predawn water potential, the maximum quantum yield of photosystem II (Fv/Fm), leaf water characteristics (using pressure-volume curves), leaf water content, and total sugar and starch contents. In all six dipterocarp species studied, the Fv/Fm values dropped sharply when the soil water content fell below 8%. However, there were interspecific differences in physiological responses to such a decrease in soil water content: S. parvifolia and S. beccariana actively controlled their stomata during drought to reduce water consumption via an isohydric response, but showed an increase (S. parvifolia) or no change (S. beccariana) in leaf drought tolerance; Di. pachyphyllus and Dry. aromatica maintained photosynthesis and transpiration close to the wilting point during drought without reducing water consumption via an anisohydric response, and also increased their leaf drought tolerance over the drying period; and S. curtisii and S. smithiana maintained their photosynthetic capacity without stomatal closure, but showed no change or a slight decrease in leaf drought tolerance. Our results indicate that extreme drought can cause the death of dipterocarp seedlings via various drought response, which could substantially impact the future distribution, population dynamics, and structure of tropical rainforests.

Underwater light attenuation inhibits native submerged plants and facilitates the invasive co‐occurring plant Cabomba caroliniana

AbstractAimDecreasing in the diversity and distribution of native submerged plants have been widely observed in recent decades. Global underwater darkening, which is mainly caused by radiation dimming and a decrease in transparency due to, e.g. eutrophication, has emerged as a general trend that strongly hampers the growth of submerged plants in lakes by decreasing the light available for photosynthesis. However, few studies have attempted to compare the responses of native and invasive submerged plants to underwater darkening. In this study, we aimed to compare the effects of light attenuation on the growth and photosynthesis traits of native and invasive submerged plants.LocationEast China.MethodThrough field investigations and a mesocosm experiment, the responses of functional traits of two representative native [water thyme (Hydrilla verticillata), Eurasian watermilfoil (Myriophyllum spicatum)] and one invasive [Carolina fanwort (Cabomba caroliniana)] plant species to various environmental factors, notably to underwater light attenuation, were studied.ResultsUnderwater photosynthetically active radiation (PAR) exerted a substantial effect on the relative coverage and abundance of the three studied submerged plants in their natural freshwater habitats. Invasive C. caroliniana showed relatively superior growth (total biomass and relative growth rate) and photosynthesis traits (maximum quantum yield of photosystem II Fv/Fm, chlorophyll a content, chlorophyll b content and the ratio of Chl a and b contents) compared to the two native plants under low underwater PAR conditions. In contrast, under high underwater PAR conditions, C. caroliniana showed the opposite response.Main ConclusionsLight attenuation inhibits the growth of native submerged plants but facilitates the growth of invasive plant species. Restoration of freshwater lakes by reducing deterioration from underwater darkening (for instance, by reducing of external nutrients loading) may therefore constrain the growth and spread of the invasive C. caroliniana.

Responses of photosystem to long-term light stress in a typically shade-tolerant species Panax notoginseng.

Photosynthetic adaptive strategies vary with the growth irradiance. The potential photosynthetic adaptive strategies of shade-tolerant species Panax notoginseng (Burkill) F. H. Chen to long-term high light and low light remains unclear. Photosynthetic performance, photosynthesis-related pigments, leaves anatomical characteristics and antioxidant enzyme activities were comparatively determined in P. notoginseng grown under different light regimes. The thickness of the upper epidermis, palisade tissue, and lower epidermis were declined with increasing growth irradiance. Low-light-grown leaves were declined in transpiration rate (Tr) and stomatal conductance (Cond), but intercellular CO2 concentration (C i) and net photosynthesis rate (P n) had opposite trends. The maximum photo-oxidation (P m) was greatly reduced in 29.8% full sunlight (FL) plants; The maximum quantum yield of photosystem II (F v/F m) in 0.2% FL plants was significantly lowest. Electron transport, thermal dissipation, and the effective quantum yield of PSI [Y(I)] and PSII [Y(II)] were declined in low-light-grown plants compared with high-light-grown P. notoginseng. The minimum value of non-regulated energy dissipation of PSII [Y(NO)] was recorded in 0.2% FL P. notoginseng. OJIP kinetic curve showed that relative variable fluorescence at J-phase (V J) and the ratio of variable fluorescent F K occupying the F J-F O amplitude (W k) were significantly increased in 0.2% FL plants. However, the increase in W k was lower than the increase in V J. In conclusion, PSI photoinhibition is the underlying sensitivity of the typically shade-tolerant species P. notoginseng to high light, and the photodamage to PSII acceptor side might cause the typically shade-tolerant plants to be unsuitable for long-term low light stress.

Day-night cycle as a key environmental factor affecting coral-Symbiodiniaceae symbiosis

Interpreting the coral-Symbiodiniaceae symbiosis in light of the day-night cycle may provide missing links in understanding the function of endosymbiosis. In this study, we found the photo-physiology, Symbiodinaiceae cell density and gene transcription of two coral holobionts (Acropora pruinosa-Cladocopium sp. and Pocillopora damicornis-Durusdinium sp.) have clear day-night oscillations. These two coral holobionts showed lower maximum quantum yield of photosystem II but higher Symbiodiniaceae cell density at day-time, as compared to at night-time. At day-time, the genes related to circadian rhythm and symbiosis in both hosts were up-regulated, while those related to immunity were down-regulated. Simultaneously, both symbionts had lower abundances of genes involved in the light reaction, Calvin cycle and glycolysis, but higher abundances of genes involved in the NH4+ assimilation. These results indicated the high density of Symbiodiniaceae at day-time might be attributed to up-regulating of genes involved in symbiosis and nitrogen metabolism but down-regulating of genes involved in immunity. Moreover, the A. pruinosa-Cladocopium sp. holobiont had larger day-night oscillations than P. damicornis-Durusdinium sp. holobiont, in terms of photo-physiology, Symbiodinaiceae cell density and gene transcription, revealing species-specific day-night oscillation. This study provides valuable insights into the cooperation strategies of coral holobionts to adapt to the day-night environmental changes.

Leaf thermal tolerance and sensitivity of temperate tree species are correlated with leaf physiological and functional drought resistance traits

Climate change is causing more frequent and severe climatic events, such as extreme heat and co-occurring drought, potentially accelerating tree mortality. Which tree species will cope better with those extreme events is still being researched. This study focuses on heat as a physiological stress factor and interspecific variation of thermal tolerance and sensitivity traits in 15 temperate coniferous and broad-leaved tree species. We investigate (1) whether thermal tolerance and sensitivity traits correlate with a drought-related physiological trait, particularly the leaf turgor loss point (πtlp, wilting point), and (2) how thermal tolerance and sensitivity traits co-vary within different tree-functional types classified by morphological and physiological traits of the leaf, i.e., leaf mass per area (LMA) and percentage loss of area (PLA). The study was carried out in the Traunstein Forest Dynamics Plot of the ForestGEO network in Germany. The temperature response of the maximum quantum yield of photosystem II (Fv/Fm) on leaf discs was determined, from which various physiological leaf traits were estimated, one of which is the breaking point temperature (T5), the temperature at which Fv/Fm declines by 5%. Additionally, the temperature of 50% (T50) and 95% (T95) decline in Fv/Fm was evaluated. The decline width between T50 and T5 (DWT50−T5) was taken as an indicator of the species’ thermal sensitivity. The breaking point temperature ranged from 35.4 ± 3.0 to 47.9 ± 3.9 °C among the investigated tree species and T50 ranged between 46.1 ± 0.4 and 53.6 ± 0.7 °C. A large interspecific variation of thermal tolerance and sensitivity was found. European ash (Fraxinus excelsior L.) was the most heat-sensitive species, while Wild cherry (Prunus avium L.) was the least heat-sensitive species. Species with a more negative πtlp tended to have a higher breaking point temperature than species with a less negative πtlp. A lower thermal sensitivity characterized species with a higher LMA, and high PLA was found in species with low thermal sensitivity. Accordingly, species with thicker and tougher leaves have lower thermal sensitivity which coincides with a lower wilting point. We conclude that species that develop drought-adapted foliage can cope better with heat stress. Further, they might be able to maintain transpirational cooling during combined heat and drought stress, which could lessen their mortality risk during climatic extremes.

Characterization of Neochloris oleoabundans under Different Cultivation Modes and First Results on Bioactivity of Its Extracts against HCoV-229E Virus

Microalgae are proposed in several biotechnological fields because of their ability to produce biomass enriched in high-value compounds according to cultivation conditions. Regarding the health sector, an emerging area focuses on natural products exploitable against viruses. This work deals with the characterization of the green microalga Neochloris oleoabundans cultivated under autotrophic and mixotrophic conditions as a source of whole aqueous extracts, tested as antivirals against HCoV-229E (Coronaviridae family). Glucose was employed for mixotrophic cultures. Growth and maximum quantum yield of photosystem II were monitored for both cultivations. Algae extracts for antiviral tests were prepared using cultures harvested at the early stationary phase of growth. Biochemical and morphological analyses of algae indicated a different content of the most important classes of bioactive compounds with antiviral properties (lipids, exo-polysaccharides, and total phenolics, proteins and pigments). To clarify which phase of HCoV-229E infection on MRC-5 fibroblast cells was affected by N. oleoabundans extracts, four conditions were tested. Extracts gave excellent results, mainly against the first steps of virus infection. Notwithstanding the biochemical profile of algae/extracts deserves further investigation, the antiviral effect may have been mainly promoted by the combination of proteins/pigments/phenolics for the extract derived from autotrophic cultures and of proteins/acidic exo-polysaccharides/lipids in the case of mixotrophic ones.

Combined effect of marine heatwaves and light intensity on the cellular stress response and photophysiology of the leather coral Sarcophyton cf. glaucum

Marine heatwaves (MHW) are threatening tropical coral reef ecosystems, leading to mass bleaching events worldwide. The combination of heat stress with high irradiance is known to shape the health and redox status of corals, but research is biased toward scleractinian corals, while much less is known on tropical symbiotic soft corals. Here, we evaluated the cellular stress response and the photophysiological performance of the soft coral Sarcophyton cf. glaucum, popularly termed as leather coral, under different global change scenarios. Corals were exposed to different light intensities (high light, low light, ∼662 and 253 μmol photons m−2 s−1) for 30 days (time-point 1) and a subsequent MHW simulation was carried out for 10 days (control 26 vs 32 °C) (time-point 2). Subsequently, corals were returned to control temperature and allowed to recover for 30 days (time-point 3). Photophysiological performance (maximum quantum yield of photosystem II (Fv/Fm), a measure of photosynthetic activity; dark-level fluorescence (F0), as a proxy of chlorophyll a content (Chl a); and zooxanthellae density) and stress biomarkers (total protein, antioxidants, lipid peroxidation, ubiquitin, and heat shock protein 70) were assessed in corals at these three time-points. Corals were especially sensitive to the combination of heat and high light stress, experiencing a decrease in their photosynthetic efficiency under these conditions. Heat stress resulted in bleaching via zooxanthellae loss while high light stress led to pigment (Chl a) loss. This species' antioxidant defenses, and protein degradation were particularly enhanced under heat stress. A recovery was clear for molecular parameters after 30 days of recovery, whereby photophysiological performance required more time to return to basal levels. We conclude that soft corals distributed along intertidal areas, where the light intensity is high, could be especially vulnerable to marine heatwave events, highlighting the need to direct conservation efforts toward these organisms.

Key stress indicators from chlorophyll fluorescence in five desert plant species

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

A story of resilience: Arctic diatom Chaetoceros gelidus exhibited high physiological plasticity to changing CO2 and light levels.

Arctic phytoplankton are experiencing multifaceted stresses due to climate warming, ocean acidification, retreating sea ice, and associated changes in light availability, and that may have large ecological consequences. Multiple stressor studies on Arctic phytoplankton, particularly on the bloom-forming species, may help understand their fitness in response to future climate change, however, such studies are scarce. In the present study, a laboratory experiment was conducted on the bloom-forming Arctic diatom Chaetoceros gelidus (earlier C. socialis) under variable CO2 (240 and 900 µatm) and light (50 and 100 µmol photons m-2 s-1) levels. The growth response was documented using the pre-acclimatized culture at 2°C in a closed batch system over 12 days until the dissolved inorganic nitrogen was depleted. Particulate organic carbon and nitrogen (POC and PON), pigments, cell density, and the maximum quantum yield of photosystem II (Fv/Fm) were measured on day 4 (D4), 6 (D6), 10 (D10), and 12 (D12). The overall growth response suggested that C. gelidus maintained a steady-state carboxylation rate with subsequent conversion to macromolecules as reflected in the per-cell POC contents under variable CO2 and light levels. A substantial amount of POC buildup at the low CO2 level (comparable to the high CO2 treatment) indicated the possibility of existing carbon dioxide concentration mechanisms (CCMs) that needs further investigation. Pigment signatures revealed a high level of adaptability to variable irradiance in this species without any major CO2 effect. PON contents per cell increased initially but decreased irrespective of CO2 levels when nitrogen was limited (D6 onward) possibly to recycle intracellular nitrogen resources resulting in enhanced C: N ratios. On D12 the decreased dissolved organic nitrogen levels could be attributed to consumption under nitrogen starvation. Such physiological plasticity could make C. gelidus "ecologically resilient" in the future Arctic.

Root hypoxia causes oxidative damage on photosynthetic apparatus and interacts with light stress to trigger abscission of lower position leaves in Capsicum

Oxidants produced by roots in hypoxic soil and stress caused by intense light are two causes of reduced photosynthetic capacity and efficiency. Moreover, they promote the formation of leaf abscission zones, which has detrimental effects on crop growth. It remains unclear how leaf position, an endogenous factor in nonstress-induced senescence, affects leaf senescence caused by oxidative stress. Thus, we used Capsicum plants to examine how leaf senescence and abscission changed photosynthetic capacity and efficiency at five leaf positions. We analyzed the association between photosynthetic changes and leaf abscission. Our results demonstrated that hypoxia resulted in lower root biomass, lower water uptake in leaves, and lower leaf carotenoid content. Moreover, the interaction between hypoxia and intense light stress causes lower carotenoid and chlorophyll content, suggesting that leaf oxidative stress levels affect the degree of photoprotection conferred by the presence of carotenoids. We also found a significant reduction in the maximum quantum yield of photosystem II under hypoxia conditions, especially in leaves at lower positions on the plant. Finally, we observed that the combined stress of hypoxia and intense light induced abscission at these lower leaf positions. Our results suggested that the level of oxidative damage in respective leaf caused by hypoxia and high light stress is significantly affected by leaf position, and stress interactions cause abscission in the lower leaves near the roots.

Foliar application of moringa leaf extract (MLE) enhanced antioxidant system, growth, and biomass related attributes in safflower plants

The use of synthetic fertilizers is a potential source of environmental hazards. Natural plant-based growth regulators are eco-friendly, inexpensive and their use is highly recommended. Moringa (Moringa oleifera L.) is also known as a miracle plant with high nutritional content, medicinal and plant growth-promoting properties due to the presence of appreciable levels of hormones, vitamins, micro, and macronutrients. However, no literature has been found regarding the effect of moringa leaf extract (MLE) application on safflower plants (Carthamus tinctorius L.). Therefore, the present experiment investigated the effect of two different concentrations of MLE (3 and 20%) on various biochemical, mineral content, growth, and biomass-related attributes of safflower plants. Results revealed that application of MLE significantly improved chlorophyll content, maximum quantum yield of photosystem II (Fv/Fm), shoot and root length, fresh and dry biomass. Moreover, MLE application also significantly enhanced activities of leaf superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) while decreasing H2O2 and MDA content. Foliar application of MLE also resulted in a notable increase in proline, glycine betaine, and mineral content. The application of MLE (20%) manifested maximum improvement in all attributes when compared to MLE (3%). Pearson's correlation analysis revealed positive correlation among growth, biomass, biochemical and mineral content, whereas a strong negative correlation was found between these traits and oxidative stress markers (H2O2 and MDA) under MLE application. The present experimental findings indicate that MLE application can be employed as a natural plant growth regulator. Furthermore, the MLE enhanced the antioxidant system and reduced oxidative stress, therefore, it can be used to ameliorate the detrimental effects of environmental adversities on plants.

Analysis of the Physiological and Yield Performance of Six Quinoa Cultivars in Colombia Under Controlled Conditions

The great diversity of quinoa allows variations in physiological, production, and compositional performance. This study aimed to evaluate six quinoa cultivars through the physiological and nutritional responses of their seeds. Different dynamics were identified in the plant height, and the number of leaves was adjusted to sigmoidal models with R2 greater than 0.97 and 0.77, respectively. The chlorophyll concentration varied through the phenological phases, as did the maximum quantum yield of photosystem II. Differences in the quinoa grains were found between CIEL*a*b* colorimetric coordinates and protein, carbohydrate, and fat contents. In this sense, quinoa cultivars manifest different biological behaviors associated with their genetic nature. Besides, a relationship between cultivars and seed composition was recognized. These results will allow researchers to study other significant differences between the precocity expressed by the Puno, Nariño, and Titicaca cultivars and those with a longer phenological cycle such as the Soracá cultivar.

Downregulation of PSI regulates photosynthesis in early successional tree species. Evidence from a field survey across European forests

Photosynthesis rates and electron transport are key physiological traits that distinguish the successional status of plants (early successional – ES, and late successional – LS) in a community. ES plants can respond quickly to sudden changes in sunlight radiation exposure and display a greater photosynthetic plasticity, with respect to the LS ones, thanks to their ability to regulate the photosynthesis. Photosynthesis regulation is connected to the efficiency of the two photosystems (PSI and PSII). PSI plays an important role in the photosynthetic machinery functioning to respond against sudden changes of metabolism in response to heterogeneous environmental conditions. It can be downregulated under high pressure of reductants, to maintain the balance between the reductant pressure and the metabolic demand. The efficiency of PSII and of PSI can be estimated, respectively, by the maximum quantum yield of photosystem II (FV/FM) and the contribution of the thermal phase in the chlorophyll fluorescence emission (expressed by the parameter ΔVIP, that quantify the I-P phase in the fluorescence emission transient). Both parameters are evaluated in dark-adapted samples and can be measured by prompt fluorescence technique. Here, we analyzed a large dataset from a European-wide survey on mature forests, considering four representative forest tree species growing at six sampling sites distributed along a latitudinal gradient. Two early successional (Pinus sylvestris and Betula pendula) and two late successional (Picea abies and Fagus sylvatica) species were considered. The correlations between FV/FM and I-P phase were mostly positive for different plant species at each sampling site for FV/FM values < 0.82 (assumed as optimal threshold for this parameter), but not for FV/FM values > 0.82. In this last case, the correlations were mostly negative for early successional species, and not significant for late successional species. Foliar nitrogen concentration plays a relevant role for the PSI regulation in early successional species: trees with high nitrogen content have higher I-P phase values and negative correlations between FV/FM and I-P phase for FV/FM > 0.82. An opposite pattern was found in tree species with low foliar nitrogen level. We conclude that the late successional tree species show a substantial regulation and stability of the photosynthetic machinery and photosystem stoichiometry, whereas early successional species have more dynamic behavior of PSI. Early successional species can modulate the photosynthetic efficiency and are able both to up-regulate and down-regulate the PSI concentration and activity in relation to quantum yield capacity and leaf nitrogen content.

5-Aminolevulinic acid promotes low-light tolerance by regulating chloroplast ultrastructure, photosynthesis, and antioxidant capacity in tall fescue

The vital signaling molecule 5-Aminolevulinic acid (ALA) plays critical roles in signal transduction and biological modulation under abiotic stresses. In this study, we explored the effects of exogenous ALA on low-light (LL) stress-induced photosynthesis and antioxidant system damage in tall fescue (Festuca arundinacea Schreb.) seedlings. LL stress decreased morphological index values and chlorophyll contents, while also reduced net photosynthetic rate (Pn) and the maximum quantum yield of photosystem II photochemistry (Fv/Fm). Notably, these restrictions were substantially alleviated by exogenous ALA. Moreover, the contents of chlorophyll and its synthetic precursors were significantly increased after ALA treatment. Meanwhile, ALA observably enhanced expression level of FaCHLG, FaHEMA, FaPOR, and FaCAO, which encode the chlorophyll precursors biosynthesis enzymes. Exogenous ALA repaired the damage to the chloroplast ultrastructure caused by LL stress and promoted the formation of ordered thylakoids and grana lamella. ALA also improved Rubisco activity and expression level of the photosynthetic enzyme genes FaRuBP, FaPRK, and FaGADPH. Additionally, application of exogenous ALA decreased relative electrolytic leakage and the accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide radicals (O2∙-), and increased the gene expression levels and activity of antioxidant enzymes. The ratios of ascorbic acid (AsA) to dehydroascorbic acid (DHA) and reduced glutathione (GSH) to oxidized glutathione (GSSG) were also increased significantly by application of ALA. Furthermore, all responses could be reversed by treatment with levulinic acid (LA). Thus, these results indicated that ALA protects tall fescue from LL stress through scavenging ROS, improving photosynthetic enzyme activity levels, increasing photosynthetic pigments contents, repairing chloroplast damage, and enhancing the photosynthesis rate.

Seasonal and inter‐annual variability in the heatwave tolerance of the kelp Saccharina latissima (Laminariales, Phaeophyceae)

SummaryThe geographical distribution of organisms, such as the foundation kelp species Saccharina latissima, is mainly driven by temperature. Globally increasing sea surface temperature and further intensification of marine heatwaves have already resulted in local extinction of kelp populations worldwide. In the present study, we investigated temporal variation in the thermal susceptibility of S. latissima by assessing stress responses of field sporophytes sampled from Helgoland (German Bight) in June 2018, August 2018 and August 2019 in heatwave scenarios. We analyzed survival, growth, maximum quantum yield of photosystem II (Fv/Fm) and pigment composition. Survival decreased with increasing environmental and experimental temperatures. Growth revealed seasonal patterns, being higher in June than in August, whereas Fv/Fm decreased with increasing temperature, independent of the sampling time. We found an increase in the concentration of light harvesting pigments and in the de‐epoxidation state of the xanthophyll cycle with higher treatment temperature. This pattern was even more pronounced at higher environmental temperature prior to the experiment (June 2018 &lt; August 2019 &lt; August 2018). Our results show that the thermal tolerance of S. latissima towards heatwaves in summer is significantly affected by the environmental history it previously experienced.

Phytoplankton photophysiology across tropical eddies: Deconvolving nutrient, light, and community signals

Fast repetition rate fluorometry (FRRf) based on active chlorophyll fluorescence is a powerful, noninvasive tool for studying phytoplankton physiological status at high spatial and temporal resolution. The South China Sea (SCS) is one of the largest tropical–subtropical marginal seas in the world, which plays an important role in modulating regional carbon budget and climate. In this study, underway in situ FRRf measurements were carried out throughout the outer continental shelf of the northern SCS, the basin of the northern SCS, the cyclonic eddy influenced domain in the western SCS, and the basin of the southeastern SCS. Pronounced diurnal variability of FRRf-derived parameters were observed, characterized by a large midday depression and slight nocturnal depression of the maximum quantum yield of photosystem II (Fv/Fm) and a slight increase in the functional absorption cross-section of photosystem II photochemistry (σPSII) at noon. Fv/Fm at the surface was typically as low as 0.1–0.3 and exhibited higher values (~0.4) where internal waves occurred. The cyclonic eddy increased Fv/Fm slightly, implying that it had a limited impact on surface phytoplankton photophysiology. With proper interpretation, FRRf has been a powerful tool to assess the physiological status of phytoplankton in the sea and to correlate that to ocean dynamics in an unprecedented fine scale.

Adaptive Responses of the Sea Anemone Heteractis crispa to the Interaction of Acidification and Global Warming.

Simple SummaryThis study investigated the effects of the interaction of acidification and warming on the photosynthetic apparatus and sterol metabolism of sea anemone Heteractis crispa. Thermal stress is the dominant driver of the deteriorating health of H. crispa, which might be relatively insensitive to the impact of ocean acidification; upregulation of chlorophyll content is suggested as an important strategy for symbionts to adapt to high pCO2. However, warming and acidification (alone or combined) significantly affected the cholesterol or sterol levels. Indeed, environmental changes like warming and acidification will affect the sterol metabolism and health of H. crispa in the coming decades.Ocean acidification and warming are two of the most important threats to the existence of marine organisms and are predicted to co-occur in oceans. The present work evaluated the effects of acidification (AC: 24 ± 0.1 °C and 900 μatm CO2), warming (WC: 30 ± 0.1 °C and 450 μatm CO2), and their combination (CC: 30 ± 0.1 °C and 900 μatm CO2) on the sea anemone, Heteractis crispa, from the aspects of photosynthetic apparatus (maximum quantum yield of photosystem II (PS II), chlorophyll level, and Symbiodiniaceae density) and sterol metabolism (cholesterol content and total sterol content). In a 15-day experiment, acidification alone had no apparent effect on the photosynthetic apparatus, but did affect sterol levels. Upregulation of their chlorophyll level is an important strategy for symbionts to adapt to high partial pressure of CO2 (pCO2). However, after warming stress, the benefits of high pCO2 had little effect on stress tolerance in H. crispa. Indeed, thermal stress was the dominant driver of the deteriorating health of H. crispa. Cholesterol and total sterol contents were significantly affected by all three stress conditions, although there was no significant change in the AC group on day 3. Thus, cholesterol or sterol levels could be used as important indicators to evaluate the impact of climate change on cnidarians. Our findings suggest that H. crispa might be relatively insensitive to the impact of ocean acidification, whereas increased temperature in the future ocean might impair viability of H. crispa.

English

Stay green is the plant&rsquo;s ability to sustain photosynthetically functional green leaf area for longer periods, even with excessive water stress. This study was done to understand the gene action that controlled inheritance of the stay green trait with the general objective of contributing to breeding more drought tolerant maize varieties. 10 F1 hybrids from crosses between highly performing and the least performing drought tolerant inbred lines as regards selected stay green physiological determinants were planted under a rain out shelter with a well-watered control and excessive water-stress treatments applied from six weeks after planting and eight weeks after planting. With progress in days after flowering, data were collected on relative chlorophyll per unit leaf area (RC: LAUG), maximum quantum yield of photosystem II photochemistry (&Phi;II), non-photochemical quenching (NPQ) and linear electron flow (LEF). RC: LAUG and NPQ were mainly inherited by additive gene action. &Phi;II was controlled more by the environment than interallelic interactions while LEF inheritance was controlled mainly by interallelic interactions. Key words: Additive, inheritance, non-additive, photosynthesis, stay green.