In several systems, from plant's canopy to algal bioreactors, the decrease of the antenna size has been proposed as a strategy to increase the photosynthetic efficiency. However, still little is ...known about possible secondary effects of such modifications. This is particularly relevant because the modulation of the antenna size is one of the most important light acclimation responses in photosynthetic organisms. In our study, we used an Arabidopsis thaliana mutant (dLhcb2), which has a 60% decrease of Lhcb1 and Lhcb2, the two main components of the major Photosystem II antenna complex. We show that the mutant maintains the photosynthetic and photoprotective capacity of the Wild Type (WT) and adapts to different light conditions by remodelling its photosynthetic apparatus, but the regulatory mechanism differs from that of the WT. Surprisingly, it does not compensate for the decreased light‐harvesting capacity by increasing other pigment‐protein complexes. Instead, it lowers the ratio of the cytochrome b6f and ATP synthase to the photosystems, regulating linear electron flow and maintaining the photosynthetic control at the level of these complexes as in the WT. We show that targeting the reduction of two specific antenna proteins, Lhcb1 and Lhcb2, represents a viable solution to obtain plants with a truncated antenna size, which still maintain the capacity to acclimate to different light conditions.
Plants with reduced light‐harvesting complexes II (LHCII) content adapt to different light conditions using strategies different from WT plants, without modulating the pigment content. The reduction of LHCII can thus be a viable strategy to increase light‐use efficiency in the canopy.
Summary
Evergreen conifers are champions of winter survival, based on their remarkable ability to acclimate to cold and develop cold hardiness. Counterintuitively, autumn cold acclimation is ...triggered not only by exposure to low temperature, but also by a combination of decreasing temperature, decreasing photoperiod and changes in light quality. These environmental cues control a network of signaling pathways that coordinate cold acclimation and cold hardiness in overwintering conifers, leading to cessation of growth, bud dormancy, freezing tolerance and changes in energy metabolism. Advances in genomic, transcriptomic and metabolomic tools for conifers have improved our understanding of how trees sense and respond to changes in temperature and light during cold acclimation and the development of cold hardiness, but there remain considerable gaps deserving further research in conifers. In the first section of this review, we focus on the physiological mechanisms used by evergreen conifers to adjust metabolism seasonally and to protect overwintering tissues against winter stresses. In the second section, we review how perception of low temperature and photoperiod regulate the induction of cold acclimation. Finally, we explore the evolutionary context of cold acclimation in conifers and evaluate challenges imposed on them by changing climate and discuss emerging areas of research in the field.
A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how ...the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat, by examining the benefits of heat acclimation, cooling strategies and hyperhydration. Finally, contemporary controversies are summarized and future research directions provided.
Extreme environmental conditions, such as heat, salinity, and decreased water availability, can have a devastating impact on plant growth and productivity, potentially resulting in the collapse of ...entire ecosystems. Stress-induced systemic signaling and systemic acquired acclimation play canonical roles in plant survival during episodes of environmental stress. Recent studies revealed that in response to a single abiotic stress, applied to a single leaf, plants mount a comprehensive stress-specific systemic response that includes the accumulation of many different stress-specific transcripts and metabolites, as well as a coordinated stress-specific whole-plant stomatal response. However, in nature plants are routinely subjected to a combination of two or more different abiotic stresses, each potentially triggering its own stress-specific systemic response, highlighting a new fundamental question in plant biology: are plants capable of integrating two different systemic signals simultaneously generated during conditions of stress combination? Here we show that plants can integrate two different systemic signals simultaneously generated during stress combination, and that the manner in which plants sense the different stresses that trigger these signals (i.e., at the same or different parts of the plant) makes a significant difference in how fast and efficient they induce systemic reactive oxygen species (ROS) signals; transcriptomic, hormonal, and stomatal responses; as well as plant acclimation. Our results shed light on how plants acclimate to their environment and survive a combination of different abiotic stresses. In addition, they highlight a key role for systemic ROS signals in coordinating the response of different leaves to stress.
Absorbed light energy is converted into excitation energy. The excitation energy is distributed to photosystems depending on the wavelength and drives photochemical reactions. A non‐destructive, ...mechanistic and quantitative method for estimating the fraction of the excitation energy distributed to photosystem II (f) was developed. For the f values for two simultaneously provided actinic lights (ALs) with different spectral distributions to be estimated, photochemical yields of the photosystems were measured under the ALs and were then fitted to an electron transport model assuming the balance between the electron transport rates through the photosystems. For the method to be tested using leaves with different properties in terms of the long‐term and short‐term acclimation (adjustment of photosystem stoichiometry and state transition, respectively), the f values for red and far‐red light (R and FR) were estimated in leaves grown (~1 week) under white light without and with supplemental FR and adapted (~10 min) to R without and with supplemental FR. The f values for R were clearly greater than those for FR and those of leaves grown with and adapted to supplemental FR tended to be higher than the controls. These results are consistent with previous studies and therefore support the validity of the proposed method.
Excitation energy distribution between PSII and PSI determines photosynthetic light use efficiency of a leaf and is adjusted in response to the light environment.
We propose a quantitative, non‐destructive and mechanistic method for estimating the fraction of the excitation energy distributed to PSII (f) based on optical measurements.
The in vivo contributions of short‐term and long‐term photosynthetic acclimation responses to supplemental far‐red light irradiation on the f values are evaluated by applying the proposed method on cucumber leaves.
It is generally accepted as a fact in the biogas technology that protein-rich biomass substrates should be avoided due to inevitable process inhibition. Substrate compositions with a low C/N ratio ...are considered difficult to handle and may lead to process failure, though protein-rich industrial waste products have outstanding biogas generation potential. This common belief has been challenged by using protein-rich substrates, i.e. casein and precipitated pig blood protein in laboratory scale continuously stirred mesophilic fed-batch biogas fermenters. Both substrates proved suitable for sustained biogas production (0.447 L CH4/g protein oDM, i.e. organic total solids) in high yield without any additives, following a period of adaptation of the microbial community. The apparent key limiting factors in the anaerobic degradation of these proteinaceous materials were the accumulation of ammonia and hydrogen sulfide. Changes in time in the composition of the microbiological community were determined by next-generation sequencing-based metagenomic analyses. Characteristic rearrangements of the biogas-producing community upon protein feeding and specific differences due to the individual protein substrates were recognized. The results clearly demonstrate that sustained biogas production is readily achievable, provided the system is well-characterized, understood and controlled. Biogas yields (0.45 L CH4/g oDM) significantly exceeding those of the commonly used agricultural substrates (0.25-0.28 L CH4/g oDM) were routinely obtained. The results amply reveal that these high-energy-content waste products can be converted to biogas, a renewable energy carrier with flexible uses that can replace fossil natural gas in its applications. Process control, with appropriate acclimation of the microbial community to the unusual substrate, is necessary. Metagenomic analysis of the microbial community by next-generation sequencing allows a precise determination of the alterations in the community composition in the course of the process.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Summary
Thermal limits of ectotherms have been studied extensively and are believed to be evolutionarily constrained, leaving ectotherms at risk under future climate change. Phenotypic plasticity may ...extend the thermal limits, but we lack detailed characterizations of thermal limit reaction norms as well as an understanding of the interspecific variation in these reaction norms.
Here, we investigated the interspecific variation in phenotypic plasticity of thermal limits in 13 Drosophila species. We obtained high‐resolution reaction norms for upper and lower thermal limits across the permissive developmental thermal range (12·5–30 °C). The estimated phenotypes were then associated (while accounting for phylogeny) with climatic parameters from the species’ distributional range.
All species showed linear reaction norms for cold tolerance (CTmin) and heat tolerance (CTmax) across developmental acclimation temperatures. We observed strong beneficial cold acclimation to lower temperatures in all species. Conversely, the heat acclimation response was non‐existent in some species, and decreasing or increasing with increasing developmental acclimation temperatures in other species. The degree of phenotypic plasticity of CTmin and CTmax was related neither to the basal thermal limits (trade‐off hypothesis) nor to climatic parameters connected to latitudinal distributions (latitudinal hypothesis).
A substantial and linear developmental plasticity of lower thermal limits is a general characteristic of Drosophila species, which allows for straightforward application in species distribution models. In general, upper thermal limits also show linear norms of reaction, but their adaptive significance is limited and highly variable among species, making general predictions across species rather impossible.
High‐resolution estimates of norms of reaction of thermal limits can considerably increase our understanding of the capacity of ectotherms to acclimate to different thermal environments. However, our understanding of the environmental drivers of the evolution of phenotypic plasticity and thus of the interspecific differences remains ambiguous, potentially constrained by limited microclimate information.
A lay summary is available for this article.
Lay Summary
Insects in tropical wet or dry seasons are likely to cope with starvation stress through plastic changes (developmental as well as adult acclimation) in energy metabolites. Control and experimental ...groups of
flies were reared under wet or dry conditions, but adults were acclimated at different thermal or humidity conditions. Adult flies of the control group were acclimated at 27°C and low (50%) or high (60%) relative humidity (RH). For experimental groups, adult flies were acclimated at 32°C for 1 to 6 days and under low (40%) or high (70%) RH. For humidity acclimation, adult flies were acclimated at 27°C but under low (40%) or high (70%) RH for 1 to 6 days. Plastic changes in experimental groups as compared with the control group (developmental as well as adult acclimation) revealed significant accumulation of body lipids owing to thermal or humidity acclimation of wet season flies, but low humidity acclimation did not change the level of body lipids in dry season flies. Starvation resistance and body lipids were higher in the males of dry season flies but in the females of wet season flies. Adults acclimated under different thermal or humidity conditions exhibited changes in the rate of utilization of body lipids, carbohydrates and proteins. Adult acclimation of wet or dry season flies revealed plastic changes in mean daily fecundity; and a reduction in fecundity under starvation. Thus, thermal or humidity acclimation of adults revealed plastic changes in energy metabolites to support starvation resistance of wet or dry season flies.
Thermal macrophysiology is an established research field that has led to well-described patterns in the global structuring of climate adaptation and risk. However, since it was developed primarily in ...animals, we lack information on how general these patterns are across organisms. This is alarming if we are to understand how thermal tolerances are distributed globally, improve predictions of climate change, and mitigate effects. We approached this knowledge gap by compiling a geographically and taxonomically extensive database on plant heat and cold tolerances and used this dataset to test for thermal macrophysiological patterns and processes in plants. We found support for several expected patterns: Cold tolerances are more variable and exhibit steeper latitudinal clines and stronger relationships with local environmental temperatures than heat tolerances overall. Next, we disentangled the importance of local environments and evolutionary and biogeographic histories in generating these patterns. We found that all three processes have significantly contributed to variation in both heat and cold tolerances but that their relative importance differs. We also show that failure to simultaneously account for all three effects overestimates the importance of the included variable, challenging previous conclusions drawn from less comprehensive models. Our results are consistent with rare evolutionary innovations in cold acclimation ability structuring plant distributions across biomes. In contrast, plant heat tolerances vary mainly as a result of biogeographical processes and drift. Our results further highlight that all plants, particularly at mid-to-high latitudes and in their nonhardened state, will become increasingly vulnerable to ongoing climate change.
Rising atmospheric carbon dioxide (CO2) concentrations may warm northern latitudes up to 8°C by the end of the century. Boreal forests play a large role in the global carbon cycle, and the responses ...of northern trees to climate change will thus impact the trajectory of future CO2 increases. We grew two North American boreal tree species at a range of future climate conditions to assess how growth and carbon fluxes were altered by high CO2 and warming. Black spruce (Picea mariana, an evergreen conifer) and tamarack (Larix laricina, a deciduous conifer) were grown under ambient (407 ppm) or elevated CO2 (750 ppm) and either ambient temperatures, a 4°C warming, or an 8°C warming. In both species, the thermal optimum of net photosynthesis (ToptA) increased and maximum photosynthetic rates declined in warm‐grown seedlings, but the strength of these changes varied between species. Photosynthetic capacity (maximum rates of Rubisco carboxylation, Vcmax, and of electron transport, Jmax) was reduced in warm‐grown seedlings, correlating with reductions in leaf N and chlorophyll concentrations. Warming increased the activation energy for Vcmax and Jmax (EaV and EaJ, respectively) and the thermal optimum for Jmax. In both species, the ToptA was positively correlated with both EaV and EaJ, but negatively correlated with the ratio of Jmax/Vcmax. Respiration acclimated to elevated temperatures, but there were no treatment effects on the Q10 of respiration (the increase in respiration for a 10°C increase in leaf temperature). A warming of 4°C increased biomass in tamarack, while warming reduced biomass in spruce. We show that climate change is likely to negatively affect photosynthesis and growth in black spruce more than in tamarack, and that parameters used to model photosynthesis in dynamic global vegetation models (EaV and EaJ) show no response to elevated CO2.
We grew two North American boreal tree species, tamarack and black spruce, at a range of future climate conditions to assess how high carbon dioxide (CO2) and warming alter growth and physiology. Climate change negatively affected photosynthesis and growth in black spruce more than in tamarack. Photosynthetic capacity (maximum rates of Rubisco carboxylation, Vcmax, and of electron transport, Jmax) and respiration were reduced in warm‐grown seedlings, correlating with reductions in leaf N and chlorophyll concentrations. We also show that parameters used to model photosynthesis in dynamic global vegetation models (the activation energies of Vcmax and Jmax) showed no response to elevated CO2.
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