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Summary: Early stress detection of crops requires a thorough understanding of the signals showing the very first symptoms of the alterations in the photosynthetic light reactions. Detection of the activation of the regulated heat dissipation mechanism is crucial to complement passively induced fluorescence to resolve ambuiguities in energy partitioning.Using leaf spectroscopy, we evaluated the capability of pigment spectral unmixing to calculate the fluorescence quantum efficiency (FQE) and simultaneously retrieve fast absorption changes in a drought and nitrogen deficiency experiment with tomato. In addition, active fluorescence measurements and pigment analyses of xanthophylls, carotenes and chlorophylls were conducted.We observed notable responses in noninvasive proximal sensing‐retrieved FQE values under stress, but as expected, these alone were not enough to identify the constraints in photosynthetic efficiency. Reflectance‐based detection of the 535‐nm peak absorption change was able to complement FQE and indicate the activation of regulated heat dissipation for both stress treatments under growing light conditions. However, further complexity in the light harvesting energy regulation needs to be accounted for when considering additional light stress.Our results underscore the potential of complementary in vivo quantitative spectroscopy‐based products in the early and nondestructive stress diagnosis of plants, marking the path for further applications. [ABSTRACT FROM AUTHOR]

Drought‐related die‐off events have been observed throughout Europe in Scots pine (Pinus sylvestris L.). Such events are exacerbated by carbon starvation that is, an imbalance of photosynthetic productivity and resource usage. Recent evidence suggests that optically measurable photosynthetic pigments such as chlorophylls and carotenoids respond to water stress (WS). However, there is a lack of measurements using imaging spectroscopy, and the mechanisms linking xanthophyll‐related changes in reflectance captured by the photochemical reflectance index (PRI) and chlorophyll changes in red edge position (REP) to WS are not understood. To probe this, we conducted a greenhouse experiment where 3‐year‐old Pinus sylvestris saplings were subjected to water limitation and followed using hyperspectral imaging (HSI) spectroscopy, water status and photosynthetic measurements. Carotenoids (e.g., xanthophyll cycle) and chlorophylls responded to WS, which was observed using the HSI‐derived indices PRI and REP respectively. The spatial‐temporal response in these two pigment‐reflectance groupings differed. The spatial distribution of PRI represented the light intensity around the time of the measurement, whereas REP reflected the daily averaged light intensity over the experimental course. A further difference was noted upon rewatering, where the carotenoid‐related PRI partially recovered but the chlorophyll‐related REP did not. Summary statement: Hyperspectral imaging spectroscopy was used to detect water stress‐induced changes in Scots pine reflectance. Differential carotenoid and chlorophyll‐related responses were found, probably related to the experimental light environment. [ABSTRACT FROM AUTHOR]

SUMMARY: The determination of physiological tolerance ranges of photosynthetic species and of the biochemical mechanisms underneath are fundamental to identify target processes and metabolites that will inspire enhanced plant management and production for the future. In this context, the terrestrial green algae within the genus Prasiola represent ideal models due to their success in harsh environments (polar tundras) and their extraordinary ecological plasticity. Here we focus on the outstanding Prasiola antarctica and compare two natural populations living in very contrasting microenvironments in Antarctica: the dry sandy substrate of a beach and the rocky bed of an ephemeral freshwater stream. Specifically, we assessed their photosynthetic performance at different temperatures, reporting for the first time gnsd values in algae and changes in thylakoid metabolites in response to extreme desiccation. Stream population showed lower α‐tocopherol content and thicker cell walls and thus, lower gnsd and photosynthesis. Both populations had high temperatures for optimal photosynthesis (around +20°C) and strong constitutive tolerance to freezing and desiccation. This tolerance seems to be related to the high constitutive levels of xanthophylls and of the cylindrical lipids di‐ and tri‐galactosyldiacylglycerol in thylakoids, very likely related to the effective protection and stability of membranes. Overall, P. antarctica shows a complex battery of constitutive and plastic protective mechanisms that enable it to thrive under harsh conditions and to acclimate to very contrasting microenvironments, respectively. Some of these anatomical and biochemical adaptations may partially limit photosynthesis, but this has a great potential to rise in a context of increasing temperature. Significance Statement: By using Prasiola antarctica as a model system, this work highlights the relevance of constitutive protection mechanisms involved on chloroplast functioning in harsh environments, especially the high proportion of cylindrical galactolipids and xanthophylls, and also reports the first measured gnsd ('gm') values in algae. This species shows a remarkable plasticity to ensure its success in contrasting terrestrial and fresh‐water microenvironments due to anatomical and biochemical changes, such as engrossed cell walls and accumulation of tocopherol. [ABSTRACT FROM AUTHOR]

Bryophytes desiccate rapidly when relative humidity decreases. The capacity to withstand dehydration depends on several ecological and physiological factors. Volatile organic compounds (VOCs) may have a role in enhancing tolerance to desiccating bryophytes. However, the functions of VOCs in bryophytes have received little attention so far. We aimed to investigate the impact of a dehydration‐rehydration treatment on primary carbon metabolism and volatile terpenes (VTs) in three bryophytes with contrasting ecological traits: Vessicularia dubyana, Porella platyphylla and Pleurochaete squarrosa. First, we confirmed the desiccation sensitivity gradient of the species. Under fully hydrated conditions, the photosynthetic rate (A) was inversely associated with stress tolerance, with a lower rate in more tolerant species. The partial recovery of A in P. platyphylla and P. squarrosa after rehydration confirmed the desiccation tolerance of these two species. On the other hand, A did not recover after rehydration in V. dubyana. Regarding VT, each species exhibited a distinct VT profile under optimum hydration, with the highest VT pool found in the more desiccation‐sensitive species (V. dubyana). However, the observed species‐specific VT pattern could be associated with the ecological habitat of each species. P. squarrosa, a moss of dry habitats, may synthesize mainly non‐volatile secondary metabolites as stress‐defensive compounds. On the other hand, V. dubyana, commonly found submerged, may need to invest photosynthetically assimilated carbon to synthesize a higher amount of VTs to cope with transient water stress occurrence. Further research on the functions of VTs in bryophytes is needed to deepen our understanding of their ecological significance. [ABSTRACT FROM AUTHOR]

Terrestrialization by photosynthetic eukaryotes took place in the two branches of green microalgae: Chlorophyta and Charophyta. Within the latter, the paraphyletic streptophytic algae divide into two clades. These are named Klebsormidiophyceae‐Chlorokybophyceae‐Mesostigmatophyceae (KCM), which is the oldest, and Zygnematophyceae‐Coleochaetophyceae‐Charophyceae (ZCC), which contains the closest relatives of vascular plants. Terrestrialization required the emergence of adaptations in response to new challenges, such as irradiance, temperature oscillations and water deprivation. In this study, we evaluated lipid composition in species representative of distinct phylogenetic clusters within Charophyta and Chlorophyta. We aim to study whether the inherent thylakoid lipid composition, as well as its adaptability in response to desiccation, were fundamental factors for the evolutionary history of terrestrial plants. The results showed that the lipid composition was similar to that found in flowering land plants, differing only in betaine lipids. Likewise, the largest constitutive pool of oligogalactolipids (OGL) was found only in the fully desiccation‐tolerant species Klebsormidium nitens. After desiccation, the content of polar lipids decreased in all species. Conversely, the content of OGL increased, particularly trigalactosyldiacylglycerol and tetragalactosyldiacylglycerol in the ZCC clade. The analysis of the molecular species composition of the newly formed OGL may suggest a different biosynthetic route for the KCM and ZCC clades. We speculate that the appearance of a new OGL synthesis pathway, which eventually arose during the streptophyte evolutionary process, endowed algae with a much more dynamic regulation of thylakoid composition in response to stress, which ultimately contributed to the colonization of terrestrial habitats. [ABSTRACT FROM AUTHOR]

The understanding of the video encoding/decoding processes is a key skill for students of computer science, engineering, or telecommunications, especially those specialized in multimedia. The special characteristics of the video signals, and how such features are leveraged to compress the video frames using coding theory, are hard to understand for engineering students. In this paper, we describe MPEG‐2 analyzer, an educational tool designed to provide a comprehensive and interactive way to understand MPEG‐2 video compression and encoding techniques. We have used our tool to evaluate its usefulness in reinforcing the knowledge about the MPEG‐2 video (de)coding process to Telecommunication Engineering students. Results show that the evaluation of the tool is very positive, and it has helped them to understand many of the complex concepts covered in the course. [ABSTRACT FROM AUTHOR]

The SARS‐CoV‐2 pandemic and subsequent interruption of influenza circulation has lowered population immunity to influenza, especially among children with few prepandemic exposures. Using data from a prospective pediatric cohort study based in Managua, Nicaragua, we compared the incidence and severity of influenza A/H3N2 and influenza B/Victoria between 2022 and two prepandemic seasons. We found a higher incidence of A/H3N2 in older children in 2022 compared with pre‐2020 and a higher proportion of severe influenza in 2022, primarily among children aged 0–4, suggesting an influence of the SARS‐CoV‐2 pandemic on influenza incidence and severity in children. [ABSTRACT FROM AUTHOR]

Background: Much of the world's population has been infected with SARS‐CoV‐2. Thus, immunity from prior infection will play a critical role in future SARS‐CoV‐2 transmission. We investigated the impact of infection‐induced immunity on viral shedding duration and viral load. Methods: We conducted a household cohort study in Managua, Nicaragua, with an embedded transmission study that closely monitors participants regardless of symptoms. Real‐time reverse‐transcription polymerase chain reaction (RT‐PCR) and enzyme‐linked immunosorbent assays (ELISAs) were used to measure infections and seropositivity, respectively. Blood samples were collected twice annually and surrounding household intensive monitoring periods. We used accelerated failure time models to compare shedding times. Participants vaccinated ≥14 days prior to infection were excluded from primary analyses. Results: There were 600 RT‐PCR‐confirmed SARS‐CoV‐2 infections in unvaccinated participants between May 1, 2020, and March 10, 2022, with prior ELISA data. Prior infection was associated with 48% shorter shedding times (event time ratio [ETR] 0.52, 95% CI: 0.39–0.69, mean shedding: 13.7 vs. 26.4 days). A fourfold higher anti‐SARS‐CoV‐2 spike titer was associated with 17% shorter shedding (ETR 0.83, 95% CI: 0.78–0.90). Similarly, maximum viral loads (lowest cycle threshold [CT]) were lower for previously infected individuals (mean CT 29.8 vs. 28.0, p = 4.02 × 10−3), for adults and children ≥10 years, but not for children 0–9 years; there was little difference in CT levels for previously infected versus naïve adults aged above 60 years. Conclusions: Prior infection‐induced immunity was associated with shorter viral shedding and lower viral loads, which may be important in the transition from pandemic to endemicity. [ABSTRACT FROM AUTHOR]

The magnetic properties of MnxGa alloys critically depend on composition x, and the atomic‐scale origin of those dependences is still not fully disclosed. Molecular beam epitaxy has been used to produce a set of MnxGa samples (x = 0.7 ÷ 1.9) with strong perpendicular magnetic anisotropy, and controllable saturation magnetization and coercive field depending on x. By conducting 57Mn/Fe and 119In/Sn emission Mössbauer spectroscopy at ISOLDE/CERN, the Mn and Ga site‐specific chemical, structural, and magnetic properties of MnxGa are investigated as a function of x, and correlated with the magnetic properties as measured by superconducting quantum interference device magnetometry. Hyperfine magnetic fields of Mn/Fe (either at Mn or Ga sites) are found to be greatly influenced by the local strain induced by the implantation. However, In/Sn probes show clear angular dependence, demonstrating a huge transferred dipolar hyperfine field to the Ga sites. A clear increase of the occupancy of Ga lattice sites by Mn for x > 1 is observed, and identified as the origin for the increased antiferromagnetic coupling between Mn and Mn at Ga sites that lowers the samples' magnetization. The results shed further light on the atomic‐scale mechanisms driving the compositional dependence of magnetism in MnxGa. [ABSTRACT FROM AUTHOR]

Summary: Desiccation tolerant plants can survive extreme water loss in their vegetative tissues. The fern Anemia caffrorum produces desiccation tolerant (DT) fronds in the dry season and desiccation sensitive (DS) fronds in the wet season, providing a unique opportunity to explore the physiological mechanisms associated with desiccation tolerance.Anemia caffrorum plants with either DT or DS fronds were acclimated in growth chambers. Photosynthesis, frond structure and anatomy, water relations and minimum conductance to water vapour were measured under well‐watered conditions. Photosynthesis, hydraulics, frond pigments, antioxidants and abscisic acid contents were monitored under water deficit.A comparison between DT and DS fronds under well‐watered conditions showed that the former presented higher leaf mass per area, minimum conductance, tissue elasticity and lower CO2 assimilation. Water deficit resulted in a similar induction of abscisic acid in both frond types, but DT fronds maintained higher stomatal conductance and upregulated more prominently lipophilic antioxidants.The seasonal alternation in production of DT and DS fronds in A. caffrorum represents a mechanism by which carbon gain can be maximized during the rainy season, and a greater investment in protective mechanisms occurs during the hot dry season, enabling the exploitation of episodic water availability. [ABSTRACT FROM AUTHOR]

Snowmelt in alpine ecosystems brings ample water, and together with above‐freezing temperatures, initiates plant growth. In this scenario, rapid activation of photosynthesis is essential for a successful life‐history strategy. But, strong solar radiation in late spring enhances the risk of photodamage, particularly before photosynthesis is fully functional. We compared the photoprotective strategy of five alpine forbs: one geophyte not particularly specialised in subnival life (Crocus albiflorus) and four wintergreens differing in their degree of adaptation to subnival life, from least to most specialised: Gentiana acaulis, Geum montanum, Homogyne alpina and Soldanella alpina. We used distance to the edge of snow patches as a proxy to study time‐dependent changes after melting. We postulated that the photoprotective response of snowbed specialists would be stronger than of more‐generalist alpine meadow species. Fv/Fm was relatively low across wintergreens and even lower in the geophyte C. albiflorus. This species also had the largest xanthophyll‐cycle pool and lowest tocopherol and flavonoid glycoside contents. After snow melting, all the species progressively activated ETR, but particularly the intermediate snowbed species G. acaulis and G. montanum. The photoprotective responses after snowmelt were idiosyncratic: G. montanum rapidly accumulated xanthophyll‐cycle pigments, tocopherol and flavonoid glycosides; while S. alpina showed the largest increase in plastochromanol‐8 and chlorophyll contents and the greatest changes in optical properties. Climate warming scenarios might shift the snowmelt date and consequently alter the effectiveness of photoprotection mechanisms, potentially changing the fitness outcome of the different strategies adopted by alpine forbs. [ABSTRACT FROM AUTHOR]

Summary: Xanthophyll cycles are broadly important in photoprotection, and the reversible de‐epoxidation of xanthophylls typically occurs in excess light conditions. However, as presented in this review, compiling evidence in a wide range of photosynthetic eukaryotes shows that xanthophyll de‐epoxidation also occurs under diverse abiotic stress conditions in darkness. Light‐driven photochemistry usually leads to the pH changes that activate de‐epoxidases (e.g. violaxanthin de‐epoxidase), but in darkness alternative electron transport pathways and luminal domains enriched in monogalactosyl diacyl glycerol (which enhance de‐epoxidase activity) likely enable de‐epoxidation. Another 'dark side' to sustaining xanthophyll de‐epoxidation is inactivation and/or degradation of epoxidases (e.g. zeaxanthin epoxidase). There are obvious benefits of such activity regarding stress tolerance, and indeed this phenomenon has only been reported in stressful conditions. However, more research is required to unravel the mechanisms and understand the physiological roles of dark‐induced formation of zeaxanthin. Notably, the de‐epoxidation of violaxanthin to antheraxanthin and zeaxanthin in darkness is still a frequently ignored process, perhaps because it questions a previous paradigm. With that in mind, this review seeks to shed some light on the dark side of xanthophyll de‐epoxidation, and point out areas for future work. [ABSTRACT FROM AUTHOR]

Members of the cosmopolitan streptophycean genus Klebsormidium live in various habitats, including sand dunes and polar/alpine environments. To survive in these harsh conditions they must possess an array of adaptive physiological and structural mechanisms, for example, to deal with chilling and photochilling stresses. Since these mechanisms have not been studied in detail, the objectives of this study were (i) to determine the physiological and biochemical responses of Klebsormidium cf. flaccidum (K. cf. flaccidum) to chilling (low temperature [LT]) and photochilling (LT in combination with high light [HL]) stresses; and (ii) to understand the cross‐link between biochemical parameters and cellular ultrastructural changes. The results indicated that 5°C is a temperature threshold (i.e., at 5°C) but not at higher temperatures, physiological changes were observed (Fv/Fm and ETR decreased and energy‐partitioning distribution changed, with an increase in Y[NPQ] under LT and an increase in Y[NO] under HL‐LT). Also, pigment contents changed significantly, with increased concentrations of photoprotective pigments such as antheraxanthin, zeaxanthin, and total carotenes. All of these responses occurred under LT and, to a greater extent, under LT‐HL, indicating that the two stresses (temperature and light) are additive. The cold treatment applied here induced the formation of spores under both LL and HL. The degree of photoinhibition was higher in spores than in vegetative cells, indicating that spores are less susceptible to photodamage. This study demonstrated a broad acclimation potential in different developmental stages of K. cf. flaccidum, which helps to explain the ecological success of this genus. [ABSTRACT FROM AUTHOR]

Summary: Resurrection plants recover physiological functions after complete desiccation. Almost all of them are native to tropical warm environments. However, the Gesneriaceae include four genera, remnant of the past palaeotropical flora, which inhabit temperate mountains. One of these species is additionally freezing‐tolerant: Ramonda myconi. We hypothesise that this species has been able to persist in a colder climate thanks to some resurrection‐linked traits.To disentangle the physiological mechanisms underpinning multistress tolerance to desiccation and freezing, we conducted an exhaustive seasonal assessment of photosynthesis (gas exchange, limitations to partitioning, photochemistry and galactolipids) and primary metabolism (through metabolomics) in two natural populations at different elevations.R. myconi displayed low rates of photosynthesis, largely due to mesophyll limitation. However, plants were photosynthetically active throughout the year, excluding a reversible desiccation period. Common responses to desiccation and low temperature involved chloroplast protection: enhanced thermal energy dissipation, higher carotenoid to Chl ratio and de‐epoxidation of the xanthophyll cycle. As specific responses, antioxidants and secondary metabolic routes rose upon desiccation, while putrescine, proline and a variety of sugars rose in winter.The data suggest conserved mechanisms to cope with photo‐oxidation during desiccation and cold events, while additional metabolic mechanisms may have evolved as specific adaptations to cold during recent glaciations. [ABSTRACT FROM AUTHOR]

Summary: In this work, we review the physiological and molecular mechanisms that allow vascular plants to perform photosynthesis in extreme environments, such as deserts, polar and alpine ecosystems. Specifically, we discuss the morpho/anatomical, photochemical and metabolic adaptive processes that enable a positive carbon balance in photosynthetic tissues under extreme temperatures and/or severe water‐limiting conditions in C3 species. Nevertheless, only a few studies have described the in situ functioning of photoprotection in plants from extreme environments, given the intrinsic difficulties of fieldwork in remote places. However, they cover a substantial geographical and functional range, which allowed us to describe some general trends. In general, photoprotection relies on the same mechanisms as those operating in the remaining plant species, ranging from enhanced morphological photoprotection to increased scavenging of oxidative products such as reactive oxygen species. Much less information is available about the main physiological and biochemical drivers of photosynthesis: stomatal conductance (gs), mesophyll conductance (gm) and carbon fixation, mostly driven by RuBisCO carboxylation. Extreme environments shape adaptations in structures, such as cell wall and membrane composition, the concentration and activation state of Calvin–Benson cycle enzymes, and RuBisCO evolution, optimizing kinetic traits to ensure functionality. Altogether, these species display a combination of rearrangements, from the whole‐plant level to the molecular scale, to sustain a positive carbon balance in some of the most hostile environments on Earth. Significance Statement: The molecular and physiological mechanisms that drive photosynthesis in vascular species from extreme environments still remain largely unknown. Here we review the different adaptations (from the whole plant to the molecular level) that enable plants to succeed and sustain an annual positive carbon balance under the typical short and harsh growing seasons in these environments. [ABSTRACT FROM AUTHOR]

Desiccation tolerant (DT) plants withstand complete cellular dehydration, reaching relative water contents (RWC) below 30% in their photosynthetic tissues. Desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with differing degrees of DHT from truly DT plants. We developed a simple, feasible and portable protocol to differentiate between DT and different degrees of DHT in the photosynthetic tissues of seed plants and between fast desiccation (< 24 h) tolerant (FDT) and sensitive (FDS) bryophytes. The protocol is based on (1) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities that, consequently, induce three different speeds and extents of dehydration and (2) an evaluation of the average percentage of maximal photochemical efficiency of PSII (Fv/fm) recovery after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (1) imbibition of absorbent material with concentrated salt‐solutions inside the tubes provides stable relative humidity and avoids direct contact with samples; (2) for 50 ml capacity tubes, the optimal plant amount is 50–200 mg fresh weight; (3) the method is useful in remote locations due to minimal instrumental requirements; and (4) a threshold of 30% recovery of the initial Fv/fm upon reaching RWC ≤ 30% correctly categorises DT species, with three exceptions: two poikilochlorophyllous species and one gymnosperm. The protocol provides a semi‐quantitative expression of DHT that facilitates comparisons of species with different morpho‐physiological traits and/or ecological attributes. [ABSTRACT FROM AUTHOR]

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We expose some concepts concerning the channel impulse response (CIR) of linear time-varying (LTV) channels to give a proper characterization of the mobile-to-mobile underwater channel. We find different connections between the linear time-invariant (LTI) CIR of the static channel and 2 definitions of LTV CIRs of the dynamic mobile-to-mobile channel. These connections are useful to design a dynamic channel simulator from the static channel models available in the literature. Such feature is particularly interesting for overspread channels, which are hard to characterize by a measuring campaign. Specifically, the shallow water acoustic (SWA) channel is potentially overspread because of the signal low velocity of propagation, which prompts long delay spread responses and great Doppler effect. Furthermore, from these connections between the LTI static CIRs and the LTV dynamic CIRs, we find that the SWA mobile-to-mobile CIR does not only depend on the relative speed between transceivers, but also on the absolute speed of each of them referred to the velocity of propagation. Nevertheless, publications about this topic do not consider it and formulate their equations in terms of the relative speed between transceivers. We illustrate our find using 2 couples of examples where, even though the relative speed between the mobiles is the same, their CIRs are not. [ABSTRACT FROM AUTHOR]

There is increasing evidence that the circadian clock is a significant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, we maintained canopies of bean and cotton, after an entrainment phase, under constant (light or darkness) conditions for 30-48 h. Photosynthesis and quantum yield peaked at subjective noon, and non-photochemical quenching peaked at night. These oscillations were not associated with parallel changes in carbohydrate content or xanthophyll cycle activity. We observed robust oscillations of Chl a/ b during constant light in both species, and also under constant darkness in bean, peaking when it would have been night during the entrainment (subjective nights). These oscillations could be attributed to the synthesis and/or degradation of trimeric light-harvesting complex II (reflected by the rhythmic changes in Chl a/ b), with the antenna size minimal at night and maximal around subjective noon. Considering together the oscillations of pigments and photochemistry, the observed pattern of changes is counterintuitive if we assume that the plant strategy is to avoid photodamage, but consistent with a strategy where non-stressed plants maximize photosynthesis. [ABSTRACT FROM AUTHOR]

Winter evergreens living in mountainous areas have to withstand a harsh combination of high light levels and low temperatures in wintertime. In response, evergreens can activate a photoprotective process that consists of the downregulation of photosynthetic efficiency, referred to as winter photoinhibition (WPI). WPI has been studied mainly in woody evergreens and crops even when, in many instances, other functional groups such as lichens or bryophytes dominate in alpine and boreal habitats. Thus, we aimed to (1) assess the occurrence of WPI within overwintering evergreens comprising woody species, herbs, mosses and lichens, (2) compare the recovery kinetics among those groups and (3) clarify the role of thylakoid proteins and pigments in both processes: WPI and recovery. With this aim, WPI was analyzed in 50 species in the field and recovery kineticcs were studied in one model species from each functional group. Results showed that high levels of WPI are much more frequent among woody plants than in any other group, but are also present in some herbs, lichens and mosses. Winter conditions almost always led to the de-epoxidation of the xanthophyll cycle. Nevertheless, changes in the de-epoxidation level were not associated with the activation/deactivation of WPI in the field and did not match changes in photochemical efficiency during recovery treatments. Seasonal changes in thylakoid proteins [mainly D1 (photosystem II core complex protein) and PsbS (essential protein for thermal dissipation)] were dependent on the functional group. The results highlight the diversity of physiological solutions and suggest a physical-mechanical reason for the more conservative strategy of woody species compared with other groups. [ABSTRACT FROM AUTHOR]

Overwintering plants face a pronounced imbalance between light capture and use of that excitation for photosynthesis. In response, plants upregulate thermal dissipation, with concomitant reductions in photochemical efficiency, in a process characterized by a slow recovery upon warming. These sustained depressions of photochemical efficiency are termed winter photoinhibition (WPI) here. WPI has been extensively studied in conifers and in few overwintering crops, but other plant species have received less attention. Furthermore, the literature shows some controversies about the association of WPI with xanthophylls and the environmental conditions that control xanthophylls conversion. To overview current knowledge and identify knowledge gaps on WPI mechanisms, we performed a comprehensive meta-analysis of literature published over the period 1991-2011. All publications containing measurements of Fv/Fm for a cold period and a corresponding warm control were included in our final database of 190 studies on 162 species. WPI was estimated as the relative decrease in Fv/Fm. High WPI was always accompanied by a high (A+Z)/(V+A+Z). Activation of lasting WPI was directly related to air temperature, with a threshold of around 0°C. Tropical plants presented earlier (at a temperature of >0°C) and higher WPI than non-tropical plants. We conclude that (1) activation of a xanthophyll-dependent mechanism of WPI is a requisite for maintaining photosynthetic structures at sub-zero temperatures, while (2) absence (or low levels) of WPI is not necessarily related to low (A+Z)/(V+A+Z); and (3) the air temperature that triggers lasting WPI, and the maximum level of WPI, do not depend on plant growth habit or bioclimatic origin of species. [ABSTRACT FROM AUTHOR]

ABSTRACT The free volume holes of a shape memory polymer have been analyzed considering that the empty space between molecules is necessary for the molecular motion, and the shape memory response is based on polymer segments acting as molecular switches through variable flexibility with temperature or other stimuli. Therefore, thermomechanical analysis (TMA) and positron annihilation lifetime spectroscopy (PALS) have been applied to analyze shape recovery and free volume hole sizes in gamma-irradiated polycyclooctene (PCO) samples, as a noncytotoxic alternative to more conventional PCO crosslinked via peroxide for future applications in medicine. Thus, a first approach relating structure, free volume holes and shape memory properties in gamma-irradiated PCO is presented. The results suggest that free volume holes caused by gamma irradiation in PCO samples facilitate the recovery process by improving movement of polymer chains and open possibilities for the design and control of the macroscopic response. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1080-1088 [ABSTRACT FROM AUTHOR]

Photosynthetic pigment composition has been a major study target in plant ecophysiology during the last three decades. Although more than 2000 papers have been published, a comprehensive evaluation of the responses of photosynthetic pigment composition to environmental conditions is not yet available., After an extensive survey, we compiled data from 525 papers including 809 species (subkingdom Viridiplantae) in which pigment composition was described. A meta-analysis was then conducted to assess the ranges of photosynthetic pigment content., Calculated frequency distributions of pigments were compared with those expected from the theoretical pigment composition. Responses to environmental factors were also analysed. The results revealed that lutein and xanthophyll cycle pigments ( VAZ) were highly responsive to the environment, emphasizing the high phenotypic plasticity of VAZ, whereas neoxanthin was very stable., The present meta-analysis supports the existence of relatively narrow limits for pigment ratios and also supports the presence of a pool of free 'unbound' VAZ. Results from this study provide highly reliable ranges of photosynthetic pigment contents as a framework for future research on plant pigments. [ABSTRACT FROM AUTHOR]

The article discusses the protocol for the simultaneous quantification of chlorophyll (Chl) a and b described by D. I. Arnon in 1949. Topics covered include the citations received by Arnon's study, the imprecision of Arnon's equations, and an unusual bimodal pattern revealed in a chronological analysis of the citations of Arnon's paper.

The significant attenuation experienced by electromagnetic waves in sea water is the main reason why acoustic waves are generally preferred in underwater communication. Nevertheless, acoustic waves have various drawbacks. For example, they are negatively affected by factors such as mechanical noise, slow propagation speed, and, particularly, low bandwidth, which leads to digital links at a lower bit rate. However, in short-range links, these problems can be overcome by reconsidering the use of electric current communications. For instance, data collected by remote-control vehicles in offshore oil and gas and renewable energy plants can be transmitted at distances of even 1 m or less. This study uses previous frequency response measurements taken in deep water to explore the capacity of a short-range electromagnetic underwater channel. Because of water movement, the nonstatic position of the vehicle when the transmission occurs means that the channel is regarded as randomly time-variant. A statistical model is proposed and the ergodic capacity is calculated for a 7 MHz bandwidth channel at distances ranging from 0.5 m to 5 m as well as for different values of transmitter power. The results of this study reflect capacity values of tens of kbps at distances of approximately 5 m to several Mbps at distances of less than 1.5 m. [ABSTRACT FROM AUTHOR]

Photosynthetic, photoprotective and antioxidant responses during high temperature stress were determined in leaves of evergreen holm oak ( Quercus ilex L.), the main species in Mediterranean forests, during resprouting under elevated CO2 (750 μl·l−1). Leaf chemicals, chloroplast pigments and non-enzymatic antioxidants were quantified in a single measurement using NIRS (near-infrared spectroscopy), a rapid and suitable method for ecophysiological purposes. Resprouts from plants grown under elevated CO2 (RE) showed photosynthetic down-regulation, higher starch content and lower stomatal conductance, but similar stomatal density, than plants grown under current CO2 concentrations (350 μl·l−1) (RA). The photosynthetic sink reduction and need for more antioxidants and photoprotection in RE were reflected in an increased concentration of ascorbate (Asc) and phenolic compounds and in the contribution of the xanthophyll (Z/VAZ) and lutein epoxide cycles to excess energy dissipation as heat, and also reflected in chlorophyll fluorescence measurements. CO2 assimilation parameters were stable from 25 to 35 °C in RE and RA, declining thereafter in RA in spite of a 2.3 °C lower leaf temperature. RE showed a more marked decline in photorespiration above 35 °C and less sensitive stomatal responses to high temperature stress than RA. During heat stress, RE had higher Asc, Z/VAZ and phenolics content, together with delayed enhancement of chloroplast lipophilic antioxidant compounds (carotenes and tocopherols). The high contribution of photoprotective systems and high temperature tolerance in resprouts developed under elevated CO2 would mitigate the effect of photosynthesis acclimation during the regeneration of Q. ilex plants under climate change. [ABSTRACT FROM AUTHOR]

High irradiance and relatively low temperature, which characterize Mediterranean winters, cause chilling stress in plants. Downregulation of photosynthetic efficiency is a mechanism that allows plants to survive these conditions. This study aims to address whether this process shows a regular spatial pattern across leaf surface or not. Three species (Buxus sempervirens, Cistus albidus and Arctostaphylos uva-ursi) with contrasting responses to winter stress were studied. During 7 days, macro and micro Fv/Fm spatial patterns were monitored by the use of chlorophyll fluorescence imaging techniques. In the field, the strongest photoinhibition was found in B. sempervirens, while there was almost no chronic photoinhibition in C. albidus. In leaves of the first species, Fv/Fm decreased from base to tip while in C. albidus it was uniform over the leaf lamina. An intermediate behavior is shown by A. uva-ursi leaves. Spatial heterogeneity distribution of Fv/Fm was found inside the leaves, resulting in greater Fv/Fm values in the inner layers than in the outer ones. Neither xanthophyll-linked downregulation of Fv/Fm nor protein remobilization were the reasons for such spatial patterns since pigment composition and nitrogen content did not reveal tip-base differences. During recovery from winter, photoinhibition changes occurred in Fv/Fm, pigments and chloroplast ultrastructure. This work shows for the first time that irrespective of physiological mechanisms responsible for development of winter photoinhibition, there is an acclimation response with strong spatio-temporal variability at leaf level in some species. This observation should be taken into account when modeling or scaling up photosynthetic responses. [ABSTRACT FROM AUTHOR]

Leaves are the main photosynthetically active tissues in most plants. However, stems and fruits are also important for the overall carbon balance of the plant because of their contribution to fixation of the CO2 released by respiration. Photosynthesis could not be possible without a complete set of photoprotection mechanisms, which include the ubiquitous violaxanthin (V) cycle and the taxonomically restricted lutein epoxide (Lx) cycle. In this work, we characterise carotenoid stoichiometry in photosynthetic stems and fruits of avocado in comparison with that of leaves and specifically whether Lx is present in these tissues and also whether it is involved in a light-driven cycle. Avocado was selected as model species to study whether both cycles were functional in non-foliar photosynthetic structures (stems and fruits). An unusual pigment composition was observed in avocado fruit, with a high content of cis-V and cis-Lx, suggesting a different photosynthetic function. In stems, both xanthophylls de-epoxidated upon illumination, but only V recovered in the dark, indicating the existence of a possible ‘truncated’ Lx cycle. Lx in fruits was de-epoxidated only when its pool was higher than a threshold of 30 mmol mol−1 chlorophyll, indicating a high non-photoconvertible pool of Lx. We conclude that, at least in stems, the dynamic regulation of photosynthetic activity could also depend on the Lx cycle. [ABSTRACT FROM AUTHOR]

The earliest land photosynthesis would have increased the risk of photo-oxidations and the demand of anti-oxidative protection. In this work, we aimed to determine the evolutionary trends in photoprotection across a wide representation of the plant kingdom and to verify whether the non-ubiquitous lutein-epoxide (Lx) cycle is a polyphyletic or an ancient character. Carotenoids and α-tocopherol (α-toc) were analysed by HPLC in 266 species. Phylogenetic analyses of the presence of photoprotective compounds and zeaxanthin-epoxidase (ZE) sequences were performed. Violaxanthin-cycle pigments (VAZ) and α-toc were taxonomically ubiquitous. Ancient groups showed higher contents of VAZ than vascular plants, while α-toc showed the opposite pattern. Lutein-epoxide was present in 45% of the species. It showed a remarkable variation across groups but with a clear increasing trend from algae to basal angiosperms. Lutein-epoxide was also related to woody trait and leaf longevity. No correlation between the presence of Lx and recurrent mutations in ZE sequences, including the duplications, was found. Thus, there is an evolutionary trend to increase the content of α-toc and to decrease the total amount of VAZ pigments. Absence of Lx in algae discards an ancestral origin. Present results are also inconsistent with a polyphyletic origin of Lx in angiosperms. [ABSTRACT FROM AUTHOR]

Short- and long-term responses of the violaxanthin (V) and lutein epoxide (Lx) cycles were studied in two species of Lauraceae: sweet bay laurel ( Laurus nobilis L.) and avocado ( Persea americana L.). The Lx content exceeded the V content in shade leaves of both species. Both Lx and V were de-epoxidised on illumination, but only V was fully restored by epoxidation in low light. Violaxanthin was preferentially de-epoxidised in low light in L. nobilis. This suggests that Lx accumulates with leaf ageing, partly because its conversion to lutein is limited in shade. After exposure to strong light, shade leaves of avocado readjusted the total pools of α- and β-xanthophyll cycles by de novo synthesis of antheraxanthin, zeaxanthin and lutein. This occurred in parallel with a sustained depression of Fv/Fm. In Persea indica, a closely related but low Lx species, Fv/Fm recovered faster after a similar light treatment, suggesting the involvement of the Lx cycle in sustained energy dissipation. Furthermore, the seasonal correlation between non-reversible Lx and V photoconversions and pre-dawn Fv/Fm in sun leaves of sweet bay supported the conclusion that the Lx cycle is involved in a slowly reversible downregulation of photosynthesis analogous to the V cycle. [ABSTRACT FROM AUTHOR]

A new approach for analyzing the performance of coherent M-ary orthogonal signaling with maximal ratio combining over Ricean fading channels is presented here. A new series representation for the bit-error rate is derived, making it possible to compute error rates with guaranteed accuracy. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The pools of photoprotective molecules respond to changes in the environmental conditions and sometimes to leaf ageing. We asked to what extent both factors contribute to the contents of α-tocopherol and xanthophyll cycle [V + A + Z (VAZ)] pigments. To address this question, we used boxtree (Buxus sempervirens) as model species because its leaves are long-lived and evergreen and are subjected to a succession of different stress conditions during their lifespan. In three age classes of sun and shade leaves of this species, seasonal changes in photoprotective compounds were followed during 15 months and a leaf age interval of 40 months was covered. As could be expected, VAZ and α-tocopherol pools increased in parallel during stress periods (summer and winter), but only VAZ recovered to the initial pools once stress disappeared. As a result, the basal α-tocopherol level increased linearly in a time-dependent manner that was also higher in sun leaves of this species when compared with shade leaves, and in fact, the rate of tocopherol increase was directly proportional to irradiance in another evergreen (Laurus nobilis). To study whether light dependency of tocopherol accumulation is observed in other species, we performed a literature survey that revealed that this age-dependent tocopherol increase was significant in sun leaves from 65% of the species for which age-dependent tocopherol changes have been reported, and it was on average 2.2-fold higher in sun leaves as compared with shade leaves. We conclude that there are two components in the α-tocopherol pool, one dynamic that responds to environmental changes and one age-related which increases linearly with time in a light-dependent manner. The physiological meaning of the latter remains obscure. [ABSTRACT FROM AUTHOR]

Leaf growth irradiance determines the pools of photoprotective molecules. We asked whether the potential for acclimation of antioxidant pool size to changes in the leaf light environment is affected by the position of the leaf within the canopy profile. The study was conducted in a mixed canopy formed by Tilia cordata at the lower level and Populus tremula at the upper level. Leaves were either exposed to extra light or enclosed in shade bags. Ascorbate, glutathione and α -tocopherol pools increased with growth irradiance. Only α-tocopherol increased in leaves of both species in response to extra light. The slope of tocopherol changes was positively correlated with growth irradiance in both species. It also correlated with the slope of xanthophyll cycle (VAZ, sum of violaxanthin, antheraxanthin and zeaxanthin) pool changes with cumulative extra light in T. cordata. We conclude that α-tocopherol is the key antioxidant altering tolerance to high light, and that it may cooperate with zeaxanthin. The pools of hydrophilic anti-oxidants either acclimate more slowly, or their pools are large enough not to limit the overall acclimation to altered light environment. [ABSTRACT FROM AUTHOR]

ABSTRACT The present study investigated the interaction of growth irradiance (Q [sub int] ) with leaf capacity for and kinetics of adjustment of the pool size of xanthophyll cycle carotenoids (sum of violaxanthin, antheraxanthin and zeaxanthin; VAZ) and photosynthetic electron transport rate (J [sub max] ) after changes in leaf light environment. Individual leaves of lower-canopy/lower photosynthetic capacity species Tilia cordata Mill. and upper canopy/higher photosynthetic capacity species Populus tremula L. were either illuminated by additional light of 500–800 µ mol m[sup -2] s[sup -1] for 12 h photoperiod or enclosed in shade bags. The extra irradiance increased the total amount of light intercepted by two-fold for the upper and 10–15-fold for the lower canopy leaves, whereas the shade bags transmitted 45% of incident irradiance. In control leaves, VAZ/area, VAZ/Chl and J [sub max] were positively associated with leaf growth irradiance (Q [sub int] ). After 11 d extra illumination, VAZ/Chl increased in all cases due to a strong reduction in foliar chlorophyll, but VAZ/area increased in the upper canopy leaves of both species, and remained constant or decreased in the lower canopy leaves of T. cordata . The slope for VAZ/area changes with cumulative extra irradiance was positively associated with Q [sub int] only in T. cordata , but not in P. tremula . Nevertheless, all leaves of P. tremula increased VAZ/area more than the most responsive leaves of T. cordata . Shading reduced VAZ content only in P. tremula , but not in T. cordata , again demonstrating that P. tremula is a more responsive species. Compatible with the hypothesis of the role of VAZ in photoprotection, the rates of photosynthetic electron transport declined less in P. tremula than in T. cordata after the extra irradiance treatment. However, foliar chlorophyll contents of the exposed leaves declined significantly more in the upper canopy of P. tremula , which is not consistent with the suggestion that the leaves with the highest VAZ content are more resistant to photoinhibition. This study demonstrates that previous leaf light environment may significantly affect the adaptation capacity of foliage to altered light environment, and also that species differences in photosynthetic capacity and acclimation potentials importantly alter this interaction. [ABSTRACT FROM AUTHOR]

Duckweed (Lemna minor L.) plants grown under high light are characterized, when compared to low light acclimated plants, by a higher xanthophyll cycle (VAZ) pool content, but also by a higher proportion of photoconvertible violaxanthin and a superior ability to synthesize VAZ pigments. When duckweed plants were transferred to a high light environment a general response was the quick adjustment of the carotenoid composition, mainly xanthophyll cycle pigments. These changes resulted from a balance between a process of continuous light-independent carotenoid degradation and a light-induced accumulation. The use of norflurazon, an inhibitor of carotenogenesis, allowed us to demonstrate that the observed light induced increase of the VAZ pool was mainly caused by de novo synthesis through carotenogenesis. The extent of light-induced carotenogenesis was proportional to the light treatment and also to the operation of the VAZ cycle since it was partly abolished by treatments leading to a low activity of the VAZ cycle, such as low light, DTT or DCMU. These results suggest that not only the light itself, but also a mechanism triggered by a factor associated with the de-epoxidation state of the VAZ cycle controls carotenogenesis at some point before phytoene formation in the terpenoid biosynthesis pathway. [ABSTRACT FROM AUTHOR]

Plants of lucerne (Medicago sativa L. cv. Aragón) inoculated with several strains of Rhizobium meliloti were supplied with a low level of nitrate (5 mM).. After 1 week, normalised nodule mass, obtained by dividing nodule weight by shoot weight, was. decreased by one-fourth. This result closely paralleled the bacteroid protein content of nodules, whereas the cytosolic content remained constant. Nitrate reductase activity (NRA, BC I .799A) of bacteroids increased rapidly after nitrate supply, with actual rates being highly dependent on the Rhizobium strain. The expression of cytosolic NR (EC 1.6.6.1) also varied depending on the bacterial strain but was largely insensitive to nitrate feeding. Nitrite reductase activity (NiRA,EC 1.72.2) of either bacteroid or plant origin was independent of the R. meliloti strain. Activation occurred after 3 and 7 days, respectively, of nitrate feeding. Significant amounts of nitrite were obtained throughout the experimental period from buffered extracts of both bacteroids and cytosol of nodules. However, when these nodules were ground in the presence of inhibitors of enzyme activity, nitrite was only found, in nodules containing strain 102-F-51 after 1 week of treatment. These results agree with the recent hypothesis that nitrite plays a role in a secondary stage of nodule damage by nitrate. We propose that NiRA rather than NRA can be used as. an internal probe of nitrate access to the infected region of nodules. [ABSTRACT FROM AUTHOR]

Aging treatments in water and in air and controlled neutron irradiation were performed on commercial crosslinked low‐density polyethylene (XLPE) for promoting different mesostructural arrangements of crystallites and crosslinking degree. Infrared spectroscopy, differential scanning calorimetry, differential thermal analysis, thermogravimetry, and dynamic mechanical analysis were used as characterization techniques. The relaxation peak related to the mobility of the grain boundaries from crystalline zones in XLPE was identified at around 260 K (at 7 Hz), involving an activation energy of 90 ± 4 kJ mol−1. The usual equation for describing the grain boundary mobility in metals involving the movement of grain boundary dislocations was adapted for studying the mobility of the boundaries among the crystalline zones, successfully. In addition, a new mechanical relaxation peak that appears at around 300 K (at 7 Hz), which involves an activation energy of 94 ± 5 kJ mol−1, was found. The driving force controlling this peak was determined as the dragging of the polymer chains at the amorphous zones adjacent to the crystals controlled by the mobility of the crystallites boundaries. The chains movement was done with break away from the physical pinning points. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47605. [ABSTRACT FROM AUTHOR]

Members of the cosmopolitan streptophycean genus Klebsormidium live in various habitats, including sand dunes and polar/alpine environments. To survive in these harsh conditions they must possess an array of adaptive physiological and structural mechanisms, for example, to deal with chilling and photochilling stresses. Since these mechanisms have not been studied in detail, the objectives of this study were (i) to determine the physiological and biochemical responses of Klebsormidium cf. flaccidum (K. cf. flaccidum) to chilling (low temperature [LT]) and photochilling (LT in combination with high light [HL]) stresses; and (ii) to understand the cross‐link between biochemical parameters and cellular ultrastructural changes. The results indicated that 5°C is a temperature threshold (i.e., at 5°C) but not at higher temperatures, physiological changes were observed (Fv/Fm and ETR decreased and energy‐partitioning distribution changed, with an increase in Y[NPQ] under LT and an increase in Y[NO] under HL‐LT). Also, pigment contents changed significantly, with increased concentrations of photoprotective pigments such as antheraxanthin, zeaxanthin, and total carotenes. All of these responses occurred under LT and, to a greater extent, under LT‐HL, indicating that the two stresses (temperature and light) are additive. The cold treatment applied here induced the formation of spores under both LL and HL. The degree of photoinhibition was higher in spores than in vegetative cells, indicating that spores are less susceptible to photodamage. This study demonstrated a broad acclimation potential in different developmental stages of K. cf. flaccidum, which helps to explain the ecological success of this genus. [ABSTRACT FROM AUTHOR]