Changes In Light Regime Research Articles

Conspicuous chloroplast with light harvesting-photosystem I/II megacomplex in marine Prorocentrum cordatum.

Marine photosynthetic (micro)organisms drive multiple biogeochemical cycles and display a large diversity. Among them, the bloom-forming, free-living dinoflagellate Prorocentrum cordatum CCMP 1329 (formerly P. minimum) stands out with its distinct cell biological features. Here, we obtained insights into the structural properties of the chloroplast and the photosynthetic machinery of P. cordatum using microscopic and proteogenomic approaches. High-resolution FIB/SEM analysis revealed a single large chloroplast (∼40% of total cell volume) with a continuous barrel-like structure, completely lining the inner face of the cell envelope and enclosing a single reticular mitochondrium, the Golgi apparatus, as well as diverse storage inclusions. Enriched thylakoid membrane fractions of P. cordatum were comparatively analyzed with those of the well-studied model-species Arabidopsis (Arabidopsis thaliana) using 2D BN DIGE. Strikingly, P. cordatum possessed a large photosystem-light harvesting megacomplex (>1.5 MDa), which is dominated by photosystems I and II (PSI, PSII), chloroplast complex I, and chlorophyll a-b binding light harvesting complex proteins. This finding parallels the absence of grana in its chloroplast and distinguishes from the predominant separation of PSI and PSII complexes in A. thaliana, indicating a different mode of flux balancing. Except for the core elements of the ATP synthase and the cytb6f-complex, the composition of the other complexes (PSI, PSII, and pigment-binding proteins, PBPs) of P. cordatum differed markedly from those of A. thaliana. Furthermore, a high number of PBPs was detected, accounting for a large share of the total proteomic data (∼65%) and potentially providing P. cordatum with flexible adaptation to changing light regimes.

Environmentally adaptive reshaping of plant photomorphogenesis by karrikin and strigolactone signaling.

Coordinated morphogenic adaptation of growing plants is critical for their survival and propagation under fluctuating environments. Plant morphogenic responses to light and warm temperatures, termed photomorphogenesis and thermomorphogenesis, respectively, have been extensively studied in recent decades. During photomorphogenesis, plants actively reshape their growth and developmental patterns to cope with changes in light regimes. Accordingly, photomorphogenesis is closely associated with diverse growth hormonal cues. Notably, accumulating evidence indicates that light-directed morphogenesis is profoundly affected by two recently identified phytochemicals, karrikins (KARs) and strigolactones (SLs). KARs and SLs are structurally related butenolides acting as signaling molecules during a variety of developmental steps, including seed germination. Their receptors and signaling mediators have been identified, and associated working mechanisms have been explored using gene-deficient mutants in various plant species. Of particular interest is that the KAR and SL signaling pathways play important roles in environmental responses, among which their linkages with photomorphogenesis are most comprehensively studied during seedling establishment. In this review, we focus on how the phytochemical and light signals converge on the optimization of morphogenic fitness. We also discuss molecular mechanisms underlying the signaling crosstalks with an aim of developing potential ways to improve crop productivity under climate changes.

IGT/LAZY genes are differentially influenced by light and required for light-induced change to organ angle

BackgroundPlants adjust their growth orientations primarily in response to light and gravity signals. Considering that the gravity vector is fixed and the angle of light incidence is constantly changing, plants must somehow integrate these signals to establish organ orientation, commonly referred to as gravitropic set-point angle (GSA). The IGT gene family contains known regulators of GSA, including the gene clades LAZY, DEEPER ROOTING (DRO), and TILLER ANGLE CONTROL (TAC).ResultsHere, we investigated the influence of light on different aspects of GSA phenotypes in LAZY and DRO mutants, as well as the influence of known light signaling pathways on IGT gene expression. Phenotypic analysis revealed that LAZY and DRO genes are collectively required for changes in the angle of shoot branch tip and root growth in response to light. Single lazy1 mutant branch tips turn upward in the absence of light and in low light, similar to wild-type, and mimic triple and quadruple IGT mutants in constant light and high-light conditions, while triple and quadruple IGT/LAZY mutants show little to no response to changing light regimes. Further, the expression of IGT/LAZY genes is differentially influenced by daylength, circadian clock, and light signaling.ConclusionsCollectively, the data show that differential expression of LAZY and DRO genes are required to enable plants to alter organ angles in response to light-mediated signals.

Microphytobenthic impact on benthic pelagic nutrient exchange in temperate shallow estuaries

Microphytobenthos (MPB) form a light-sensitive “nutrient filter” between sediment and bottom water in shallow coastal systems and the MPB activity is believed to have important implications for nutrient availability in such systems. We quantified this light-driven control on nutrient fluxes by analyzing benthic flux measurements from >3000 sediment cores sampled in five Danish estuaries. Light responses and the seasonality of benthic primary production (BPP), benthic nutrient fluxes and the MPB impact on these fluxes showed that MPB significantly intercepted fluxes of ammonium (NH4+), nitrate (NO3−) and dissolved silica (DSi) both under light and dark conditions. Phosphate (PO43−) fluxes were only significantly intercepted in light. The microphytobenthos had a large relative impact on nutrient fluxes during spring and a weaker impact in the autumn, despite significant photosynthetic activity of the MPB at this time of the year. The proportion of the annual sediment-water flux impacted by MPB reached maximum values of 65%, 73%, 89% and 96% for NH4+, NO3−, PO43− and DSi, respectively. The relative impact depended on the magnitude of the base fluxes and the relative impact increased with light availability at the stations above a threshold of 5% light at the seafloor. This documents that changing light regimes alter the MPB control on nutrient dynamics in shallow systems.

Applicability and limitations of high-throughput algal growth rate measurements using invivo fluorescence in microtiter plates

Micro-algae play important roles in primary production, nutrient cycling, and applied biotechnology. Mico-algae are phylogenetically, morphologically and physiologically diverse and often easy to grow in cultures. Growth is the key parameter of viability and crucial for survival insitu and efficiency invitro. Therefore, growth is often used in eco-physiological experiments to describe the fundamental niche and optimum conditions. Invivo chlorophyll-a fluorescence (IVCF) is a well-established proxy for the growth of micro-algae and is based on constant cell properties during exponential growth. High-throughput IVCF measurements have been applied for about 20 years for few, mostly green algal strains. Here, we tested the IVCF using microtiter plates on strains of four different algal phyla (Chlorophyceae, Cyanobacteria, Bacillariophyceae, Rhodophyceae) and compared the data with cell counts and chlorophyll contents. The microtiter plate reader based IVCF (MPR-IVCF) approach worked best for the diatom Cylindrothecaclosterium and the cyanobacterium Synechococcuselongatus. Differences between IVCF and cell count-based growth rates were found for Chlorellavulgaris and Rhodella sp. The IVCF growth rates were lower than the growth rates based on cell counts in both cases, thus underestimating absolute growth rates. The MPR-IVCF method is robust in terms of light scattering and non-photosynthetic contamination but prone to changes in light regimes and also to aggregating algal cells. Thus, we recommend using the MPR-IVCF approach (1) for diatoms and cyanobacteria as an absolute growth rate measure, (2) for relative measures of growth rates, intra and interspecific during the same experiment, also for all algal phyla except Rhodophyta.

Earlier or delayed seasonal broodstock spawning changes nutritional status and metabolic programming of growth for next-generation Atlantic salmon

Atlantic salmon (Salmo salar) breeding companies depend on changing light, temperature and feeding regimes to achieve new generations outside the natural spawning season. However, there have been few conducted trials reported that have studied whether this shift affects important traits. We test whether an induced shift of two months earlier or two months later than normal spawning season affects the nutritional status (folate, methionine, vitamin B12, vitamin B6, free amino acids, N-metabolites and lipids) in broodstock liver and muscle and whether this affects the levels of the same nutrients in the offspring. The results showed significant seasonal differences in the Cahill cycle (glucose-alanine cycle), 1C metabolism and for free amino acids catabolized in the citric acid cycle all which are important for embryonic growth The broodstock nutritional status was reflected in the eggs. Nutritional status of broodstock liver and muscle and newly fertilized eggs showed two general scenarios: Advanced spawning period did not obtain optimal deposition of nutrients in the eggs. Delayed spawning broodstock displayed a metabolic profile which indicated that it had enhanced catabolization of muscle protein which led to accumulation of aminogroups from muscle breakdown to such a degree that these amino groups were increased in the eggs. The total body weight at start-feeding stage revealed best growth for both the normal and late spawning compared to early spawning. We show here that environmental alterations in broodstock husbandry influence the nutrient status of the next generation via nutritional and metabolic programming. This is an important concept which needs more careful awareness as the metabolism compensate and regulate the energy between catabolism and anabolism through the early stages of cell divisions which give rise to changes in permanent traits for the next generation.

Morphological characteristics of meristem potato plants (Solanum tuberosum) under various LED light sources

When growing potato regenerants in vitro fluorescent or sodium lamps are most often used as light sources. This is due to significant energy consumption and limited spectral capabilities of these light sources. Therefore, research was aimed to study the growth anddevelopment of meristem potato plants in vitro using LEDs of different technical design as light sources and to find out lights that can contribute to the most efficient plant growth and development. The research was conducted during April and May 2021, at the Laboratory of Biotechnology of Agricultural Plants of the Samara Scientific Research Agriculture Institute named after N.M. Tulajkov, Branch of the SamSC RAS, Bezenchuk vill., Russia, using meristem potato var. Rosara, Arosa and Riviera. The explants were cultivated on a Murashige-Skoog growing medium for 30 days using various LED artificial illumination sources with a 16-hour light period, an air temperature of 22- 24 °C, and a relative air humidity of 70-75%. After 10, 20 and 30 days of cultivation, the plant length and the number of internodes were measured. A positive effect on plants of LED lights was revealedduring in vitro propagation. The most developed regenerants with a high number of internodes were obtained using LED lamps UnielA60 10W, UnielA60 16W, T8-phyto, and Era FITO. On averagefor three studied varieties after 30 days of cultivation, regenerants with the maximum length were those, which were grown under illumination with T8-phyto and Era FITO lamps that mean variants with the highest level of photosynthetic photon flux of 21.8 μmol/sand 32.4 μmol/s and a wavelength of 450-650 nm. It was shown that the lighting conditionshad the greatest impact on potato growth in the period from 10th to 30th days of cultivation.Different variety reactions to changes in light regime were detected.

Dynamics of growth parameters of Gentiana lutea L. in vitro plants under different lighting conditions

Aim. Study of the dynamics Gentiana lutea L. plant growth processes in vitro depending on the light regime changes of their cultivation in order to develop a scheme to increase their adaptive potential. Methods. Methods of plant cultivation in vitro, biometric method, as well as ANOVA variance analysis and middle group analysis in pairs using the Tukey test (Tukey test) were used. Results. It is shown that the cultivation of G. lutea plants in vitro using 25 W/m2 light flux intensity in the region of photosynthetically active radiation and the ratio of blue (Eb): green (Eg): red (Er) ranges = 41.8%: 42.7 %: 15.5% triggers non-specific photomorphogenesis reactions for intact plants, which lead to poor root system development, stem elongation, formation of small leaves with a thin leaf blade, overall low productivity and low adaptation potential of G. lutea plants to ex vitro and in situ conditions. Increasing the light flux intensity to 44 W/m2 and increasing the red wave proportion up to 20.3% allows not only to improve the bioproductivity of G. lutea plants which are cultivated in vitro, but also to increase the coefficient of microclonal reproduction without the additional use of exogenous growth regulators. The greatest growth of the aboveground and underground parts, increase in effective leaf surface are observed in vitro plants during cultivation at 135 W/m2 light flux intensity and spectral composition Eb: Eg: Er = 29.5%: 32.5%: 38.0%. Conclusions. It is possible to improve plant bioproductivity by changing the light conditions of plant cultivation in vitro, and, accordingly, to increase the adaptive potential to ex vitro and in situ conditions.
 Keywords: Gentiana lutea L., in vitro plants, light flux intensity, spectral composition, growth parameters.

Phytoindication assessment of the effect of reconstruction on the light regime of an urban park

The ecological restoration of urban parks is used to increase their recreational attractiveness, improve air quality, mitigate urban heat island effects, improve stormwater infiltration, and provide other social and environmental benefits. The dynamics of plant communities after urban forest restoration requires investigation. The study assessed the impact of urban park reconstruction on the state of grass cover, phytoindication of changes in light regime caused by park reconstruction and found out the dependence of reliability of phytoindication assessment on the number of species in the relevant area. The study was conducted in the recreational area of the Botanical Garden of the Oles Honchar Dnipro National University (Ukraine). A tree plantation was created after the Second World War in the location of a natural oak forest. In 2019, a 2.8 ha area of the park was reconstructed. The samples were taken within polygons, two of which were placed in the reconstruction area and two of which were placed in a similar section of the park where no reconstruction was performed. During the reconstruction process, walkways were rebuilt, shrubs were removed, old, damaged trees were removed, and tree crowns were trimmed. Juvenile trees were planted in place of the removed old trees. Old outbuildings, which greatly impaired the aesthetic perception of the park, were also removed. Transport and construction machinery was involved in the reconstruction. A total of 65 plant species were found within the studied polygons. The number of herbaceous species in the park area after reconstruction was higher than without reconstruction. The crown closure in the reconstructed area was significantly lower than that in the untreated conditions. The phytoindication assessment showed that the light regime varies from the conditions suitable for the scyophytes (plants of typical foliage forests) to the conditions suitable for the sub-heliophytes (plants of light forests and shrubberies, or high herbaceous communities; lower layers are in the shade). The light regime in the park area after reconstruction was statistically significantly different from the regime in the untreated park area. The lighting regime after the reconstruction was favourable to sub-heliophytes, and without reconstruction the regime favoured hemi-scyophytes. Tree canopy crown closure negatively correlated with grass height and herbaceous layer projective cover. The tree canopy crown closure, grass height, and herbaceous layer projective cover were able to explain 86% of the phytoindication assessment of the lighting regime variation. These parameters negatively affected the light regime. The prospect of further research is to investigate the dependence of indicative reliability of the assessment of other environmental factors with the help of phytoindication depending on the number of species. In addition to the indication of traditional ecological factors it is of particular interest to clarify the aspect of the dynamics of hemeroby indicators as a result of park reconstruction.

A Novel Miniaturized Biosensor for Monitoring Atlantic Salmon Swimming Activity and Respiratory Frequency.

Simple SummaryGood fish welfare is one of the prerequisites for sustainable aquaculture. Knowing how fish respond to the production conditions would allow us to better understand their biology and to further optimize production. The new miniaturized biosensor AEFishBIT was successfully used to monitor individual physical activity and respiratory frequency of two Mediterranean farmed fish species (gilthead sea bream and European sea bass). In this study, we aimed to test the use of AEFishBIT to monitor the performance of Atlantic salmon under experimental conditions. An adapted tagging procedure for salmon was developed and used to record salmon responses to handling and changing light conditions. AEFishBIT data showed a stabilization of swimming activity 8 h after handling and tagging with changes in activity or activity and respiratory quotient after changes in light intensity regimes. The results of this study supported the use of AEFishBIT to generate new behavior insights in Atlantic salmon culture.The advanced development of sensor technologies has led to the emergence of fish biosensors that are currently used for research and commercial purposes. AEFishBIT is a miniaturized biosensor attached to fish operculum that measures physical activity and respiration frequencies. In this study, we determined the effect of the tagging method and evaluated the use of this biosensor to monitor post-smolt Atlantic salmon in a tank-based system. The use of piercing fish tag had a negative impact on the gills and operculum, unlike the identical protocols used in gilthead sea bream and European sea bass. In contrast, a surgical thread did not show any apparent tissue damage. Two data recording schedules were considered to monitor immediate early reaction to fish handling and light regime changes (records every 15 min over 2 days) or adaptation to new light conditions (records every 30 min over 4 days). Data showed stabilization of physical activity 8 h post-tagging, with different steady states for the activity/respiratory ratio after changes in light intensity that reflected a different time course adaptation to new light conditions. High correlations were observed between AEFishBIT and video recording data. These findings supported the use of AEFishBIT as a promising tool for smart sensing of Atlantic salmon.

The Cell Division Cycle of Euglena gracilis Indicates That the Level of Circadian Plasticity to the External Light Regime Changes in Prolonged-Stationary Cultures.

In unicellular photosynthetic organisms, circadian rhythm is tightly linked to gating of cell cycle progression, and is entrained by light signal. As several organisms obtain a fitness advantage when the external light/dark cycle matches their endogenous period, and aging alters circadian rhythms, senescence phenotypes of the microalga Euglena gracilis of different culture ages were characterized with respect to the cell division cycle. We report here the effects of prolonged-stationary-phase conditions on the cell division cycles of E. gracilis under non-24-h light/dark cycles (T-cycles). Under T-cycles, cells established from 1-month-old and 2-month-old cultures produced lower cell concentrations after cultivation in the fresh medium than cells from 1-week-old culture. This decrease was not due to higher concentrations of dead cells in the populations, suggesting that cells of different culture ages differ in their capacity for cell division. Cells from 1-week-old cultures had a shorter circadian period of their cell division cycle under shortened T-cycles than aged cells. When algae were transferred to free-running conditions after entrainment to shortened T-cycles, the young cells showed the peak growth rate at a time corresponding to the first subjective night, but the aged cells did not. This suggests that circadian rhythms are more plastic in younger E. gracilis cells.

Comparative characterization of two cyanobacteria strains of the order Spirulinales isolated from the Baltic Sea - polyphasic approach in practice

With the improved understanding of the cyanobacterial diversity, the polyphasic approach has become a widely accepted way to classify the organisms. The aim of the study was to describe and compare phenotypic and molecular traits of two strains of filamentous, helically coiled cyanobacteria CCNP1310 and 06S082, originating from different habitats of the Baltic Sea. Genotypic and phylogenetic analyses were focused on 16S rDNA, cpcBA-IGS and mcyE target sequences, while the phenotypic characterization included morphology, ultrastructures visualized with transmission electron microscopy, pigment and other metabolite profiles, determined with high-performance liquid chromatography and liquid chromatography-mass spectrometry, respectively. Results indicated that both tested strains belong to the Spirulinales order. 16S rDNA phylogeny confirmed that in the case of the analyzed microorganisms, cryptic diversity may occur. The final reclassification of this order requires analysis of a larger group of strains. Despite the high morphological similarity, the strains showed significant differences in the produced metabolites. The analysis of photosynthetic pigments indicated that in the cyanobacteria of the order Spirulinales the model of response to changing light regime might be preserved even after a long time of growth in culture. Cyanometabolite profiles determined spectrometrically showed that the characterized organisms differ in terms of the produced metabolites. The presented, comprehensive characterization of the strains can also be useful in further studies on the diversity, taxonomy, and metabolic potential of cyanobacteria of the order Spirulinales.

Вплив довготривалої зміни режиму освітлення на рівень статевих гормонів у крові щурів

The modern lifestyle of many people takes place in conditions of "light pollution". Prolongation of the photoperiod not only inhibits the synthesis and secretion of melatonin (universal endogenous adaptogen), but also causes induction of anovulation and promotes premature puberty and premature aging, which may occur against the background of impaired secretion of sex hormones. The purpose of the study was to examine the long-term change in the light regime to the level of sex hormones, testosterone and estradiol in the blood plasma of rats. The experiment was performed on 120 Wistar rats. According to the nature of the action and intensity of lighting, we formed 3 groups (20 rats in each): K – control (intact), the animals of which were in natural light; group 12/12 – under the influence of artificial lighting for 12 hours a day: from 6 am to 6 pm and group 24/00 – under the influence of noctidial artificial lighting. Artificial lighting was carried out with an incandescent lamp with a power of 100 watts. The light intensity in the cages, which was measured using a Yu-117 luxmeter, was 40-50 lux. The content of free testosterone and estradiol was determined in the blood plasma of rats by enzyme-linked immunosorbent assay. Statistical processing of the obtained data was performed by methods of mathematical statistics. A statistically significant difference in averages was established using Student's test (t). The changes were considered significant at p≤0.05. While processing the obtained data, the ratio of testosterone/estradiol was calculated, the median estimate was given, and the oscillation ranges were 25-75% of the intervals. The study proved that in males, the change in light regime caused a statistically significant decrease in free testosterone levels and an increase in estradiol in plasma, while in females the opposite changes were observed. Hypertestosteronemia in females and hypotestosteronemia in males with changes in estradiol levels were also shown to be adaptive responses to the changes in the photoperiod. We found out that a statistically significant decrease in the ratio of testosterone/ estradiol in males (in the 12/12 group by 42.6%; in the 24/00 group – by 65%) and its increase in females (in the 12/12 group by 60.6%, in the 24/00 group – by 79%), were probably compensatory reactions to the stress factor, which was a long-term change in lighting. In general, a higher range of testosterone/estradiol index deviations in 24-hour rats (24/00) indicated that they had a more acute stress response to changes in lighting and reduced adaptability. This "adaptation fee" is generally aimed at survival, but leads to sexual dysfunction in rats

The effect of the salinity, light regime and food source on carbon and nitrogen uptake in a benthic foraminifer

Abstract. Foraminifera are unicellular organisms that play an important role in marine organic matter cycles. Some species are able to isolate chloroplasts from their algal food source and incorporate them as kleptoplasts into their own metabolic pathways, a phenomenon known as kleptoplastidy. One species showing this ability is Elphidium excavatum, a common foraminifer in the Kiel Fjord, Germany. The Kiel Fjord is fed by several rivers and thus forms a habitat with strongly fluctuating salinity. Here, we tested the effects of the food source, salinity and light regime on the food uptake (via 15N and 13C algal uptake) in this kleptoplast-bearing foraminifer. In our study E. excavatum was cultured in the lab at three salinity levels (15, 20 and 25) and uptake of C and N from the food source Dunaliella tertiolecta (Chlorophyceae) and Leyanella arenaria (Bacillariophyceae) were measured over time (after 3, 5 and 7 d). The species was very well adapted to the current salinity of the sampling region, as both algal N and C uptake was highest at a salinity of 20. It seems that E. excavatum coped better with lower than with higher salinities. The amount of absorbed C from the green algae D. tertiolecta showed a tendency effect of salinity, peaking at a salinity of 20. Nitrogen uptake was also highest at a salinity of 20 and steadily increased with time. In contrast, C uptake from the diatom L. arenaria was highest at a salinity of 15 and decreased at higher salinities. We found no overall significant differences in C and N uptake from green algae vs. diatoms. Furthermore, the food uptake at a light–dark rhythm of 16:8 h was compared to continuous darkness. Darkness had a negative influence on algal C and N uptake, and this effect increased with incubation time. Starving experiments showed a stimulation of food uptake after 7 d. In summary, it can be concluded that E. excavatum copes well with changes of salinity to a lower level. For changes in light regime, we showed that light reduction caused a decrease of C and N uptake by E. excavatum.

Diurnal dynamics of the Arabidopsis rosette proteome and phosphoproteome.

Plant growth depends on the diurnal regulation of cellular processes, but it is not well understood if and how transcriptional regulation controls diurnal fluctuations at the protein level. Here, we report a high‐resolution Arabidopsis thaliana (Arabidopsis) leaf rosette proteome acquired over a 12 hr light:12 hr dark diurnal cycle and the phosphoproteome immediately before and after the light‐to‐dark and dark‐to‐light transitions. We quantified nearly 5,000 proteins and 800 phosphoproteins, of which 288 fluctuated in their abundance and 226 fluctuated in their phosphorylation status. Of the phosphoproteins, 60% were quantified for changes in protein abundance. This revealed six proteins involved in nitrogen and hormone metabolism that had concurrent changes in both protein abundance and phosphorylation status. The diurnal proteome and phosphoproteome changes involve proteins in key cellular processes, including protein translation, light perception, photosynthesis, metabolism and transport. The phosphoproteome at the light–dark transitions revealed the dynamics at phosphorylation sites in either anticipation of or response to a change in light regime. Phosphorylation site motif analyses implicate casein kinase II and calcium/calmodulin‐dependent kinases among the primary light–dark transition kinases. The comparative analysis of the diurnal proteome and diurnal and circadian transcriptome established how mRNA and protein accumulation intersect in leaves during the diurnal cycle of the plant.

Impaired chloroplast positioning affects photosynthetic capacity and regulation of the central carbohydrate metabolism during cold acclimation

Photosynthesis and carbohydrate metabolism of higher plants need to be tightly regulated to prevent tissue damage during environmental changes. The intracellular position of chloroplasts changes due to a changing light regime. Chloroplast avoidance and accumulation response under high and low light, respectively, are well known phenomena, and deficiency of chloroplast movement has been shown to result in photodamage and reduced biomass accumulation. Yet, effects of chloroplast positioning on underlying metabolic regulation are less well understood. Here, we analysed photosynthesis together with metabolites and enzyme activities of the central carbohydrate metabolism during cold acclimation of the chloroplast unusual positioning 1 (chup1) mutant of Arabidopsis thaliana. We compared cold acclimation under ambient and low light and found that maximum quantum yield of PSII was significantly lower in chup1 than in Col-0 under both conditions. Our findings indicated that net CO2 assimilation in chup1 is rather limited by biochemistry than by photochemistry. Further, cold-induced dynamics of sucrose phosphate synthase differed significantly between both genotypes. Together with a reduced rate of sucrose cycling derived from kinetic model simulations our study provides evidence for a central role of chloroplast positioning for photosynthetic and metabolic acclimation to low temperature.

Стан окиснювального метаболiзму в тканинах серцевого та скелетних м’язів щурів за умов світлової депривації

The article considers the features of oxidative metabolism of cardiac and skeletal muscle tissue in the changed photoperiod, under the influence of round-the-clock light deprivation in combination with the introduction of exogenous melatonin. Material and methods. The experimental study was performed on male Wistar rats. Two groups were formed for research: intact and experimental. The animals of the intact group were in standard housing and feeding conditions, without changes in light regime. The animals of the experimental group for 30 days were in conditions of round-the-clock light deprivation on the background of the introduction of melatonin at a dose of 1.0 mg/kg body weight. Results and discussion. The level of production of reactive oxygen species was evaluated by the formation of a superoxide anion radical. To assess the prooxidant-antioxidant system in the homogenate of the studied tissues was determined by the concentration of thiobarbituric acid reactive substances. The efficiency of the enzyme link was evaluated by catalase and superoxide dismutase activity. We revealed an increase in the production of superoxide anion radical due to the activity of phagocytes compared to the intact group in the heart muscle under conditions of light deprivation on the background of the introduction of melatonin. In skeletal muscle tissue homogenate the production of superoxide anion radical by the mitochondrial electron transport chain production is likely was reduced compared to the intact group. Light deprivation on the background of exogenous administration of melatonin reduces the intensity of production of reactive oxygen species, which is confirmed by a decrease in the level of superoxide anion radical in the homogenate of the quadriceps femoris muscle tissues of experimental animals. Melatonin as an antioxidant reduces the production of superoxide anion radical by mitochondrial oxidation in the quadriceps femoris muscle. In this case, the excess melatonin stabilizes the fluidity of the membrane, reducing its permeability, which may indicate the protective properties of this substance. Conclusion. Thus, modeling the conditions of excess melatonin modifies the generation of superoxide anion radical from various sources. The above experimental conditions contribute to multidirectional changes in the quantitative generation of the superoxide anion radical in the heart and skeletal muscles. Changes in the indicators of prooxidant-antioxidant status in the homogenate of the studied tissues under the selected experimental conditions were not detected

Longer photoperiods through range shifts and artificial light lead to a destabilizing increase in host-parasitoid interaction strength.

Many organisms are experiencing changing daily light regimes due to latitudinal range shifts driven by climate change and increased artificial light at night (ALAN). Activity patterns are often driven by light cycles, which will have important consequences for species interactions. We tested whether longer photoperiods lead to higher parasitism rates by a day-active parasitoid on its host using a laboratory experiment in which we independently varied daylength and the presence of ALAN. We then tested whether reduced nighttime temperature tempers the effect of ALAN. We found that parasitism rate increased with daylength, with ALAN intensifying this effect only when the temperature was not reduced at night. The impact of ALAN was more pronounced under short daylength. Increased parasitoid activity was not compensated for by reduced life span, indicating that increased daylength leads to an increase in total parasitism effects on fitness. To test the significance of increased parasitism rate for population dynamics, we developed a host-parasitoid model. The results of the model predicted an increase in time-to-equilibrium with increased daylength and, crucially, a threshold daylength above which interactions are unstable, leading to local extinctions. Here we demonstrate that ALAN impact interacts with daylength and temperature by changing the interaction strength between a common day-active consumer species and its host in a predictable way. Our results further suggest that range expansion or ALAN-induced changes in light regimes experienced by insects and their natural enemies will result in unstable dynamics beyond key tipping points in daylength.

Indications for a Central Role of Hexokinase Activity in Natural Variation of Heat Acclimation in Arabidopsis thaliana.

Diurnal and seasonal changes of abiotic environmental factors shape plant performance and distribution. Changes of growth temperature and light intensity may vary significantly on a diurnal, but also on a weekly or seasonal scale. Hence, acclimation to a changing temperature and light regime is essential for plant survival and propagation. In the present study, we analyzed photosynthetic CO2 assimilation and metabolic regulation of the central carbohydrate metabolism in two natural accessions of Arabidopsis thaliana that originate from north western Russia and south Italy during exposure to heat and a combination of heat and high light. Our findings indicate that it is hardly possible to predict photosynthetic capacities under combined stress from single stress experiments. Further, capacities of hexose phosphorylation were found to be significantly lower in the Italian than in the Russian accession, which could explain an inverted sucrose-to-hexose ratio. Together with the finding of significantly stronger accumulation of anthocyanins under heat/high light, these observations indicate a central role of hexokinase activity in the stabilization of photosynthesis and carbohydrate metabolism during environmental changes.

Photoacclimation and Photoprotection of Juvenile Sporophytes of Macrocystis pyrifera (Laminariales, Phaeophyceae) Under High-light Conditions During Short-term Shallow-water Cultivation1.

This study was designed to understand better if and how juvenile sporophytes of Macrocystis pyrifera can photoacclimate to high-light conditions when transplanted from 10 to 3 meters over 7d. Acclimation of adult sporophytes to light regimes in the bathymetric gradient has been extensively documented. It primarily depends on photoacclimation and translocation of resources among blades. Among other physiological differences, juvenile sporophytes of M. pyrifera lack the structural complexity shown by adults. As such, juveniles may primarily depend on their photoacclimation capacities to maintain productivity and even avoid mortality under changing light regimes. However, little is known about how these mechanisms operate in young individuals. The capacity of sporophytes to photoacclimate was assessed by examining changes in their photosynthetic performance, pigment content, and bio-optical properties of the blade. Sporophytes nutritional status and oxidative damage were also determined. Results showed that juvenile sporophytes transplanted to shallow water were able to regulate light harvesting by reducing pigment concentration, and thus, absorptance and photosynthetic efficiency. Also, shallow-water sporophytes notably enhanced the dissipation of light energy as heat (NPQ) as a photoprotective mechanism. Generally, these adjustments allowed sporophytes to manage the absorption and utilization of light energy, hence reducing the potential for photo-oxidative damage. Furthermore, no substantial changes were found in the internal reserves (i.e., soluble carbohydrates and nitrogen) of these sporophytes. To our knowledge, these results are the first to provide robust evidence of photoprotective and photoacclimation strategies in juveniles of M. pyrifera, allowing them to restrict or avoid photodamage during shallow-water cultivation.