Long-term Acclimation Research Articles

Efficient high light acclimation involves rapid processes at multiple mechanistic levels.

Like no other chemical or physical parameter, the natural light environment of plants changes with high speed and jumps of enormous intensity. To cope with this variability, photosynthetic organisms have evolved sensing and response mechanisms that allow efficient acclimation. Most signals originate from the chloroplast itself. In addition to very fast photochemical regulation, intensive molecular communication is realized within the photosynthesizing cell, optimizing the acclimation process. Current research has opened up new perspectives on plausible but mostly unexpected complexity in signalling events, crosstalk, and process adjustments. Within seconds and minutes, redox states, levels of reactive oxygen species, metabolites, and hormones change and transmit information to the cytosol, modifying metabolic activity, gene expression, translation activity, and alternative splicing events. Signalling pathways on an intermediate time scale of several minutes to a few hours pave the way for long-term acclimation. Thereby, a new steady state of the transcriptome, proteome, and metabolism is realized within rather short time periods irrespective of the previous acclimation history to shade or sun conditions. This review provides a time line of events during six hours in the 'stressful' life of a plant.

Forced adaptation: plant proteins to fight climate change.

Increasing distress about climate change consequences is noticeable in daily press releases and science news articles. In the last 5 years more than 3 hundred thousand scientific articles included the terms “climate change,” “drought stress” and/or “climate adaptation” as a main topic. This build-up of energy devoted to understand climate change significance parallels the fact that any living organism must be able to cope with environmental changes to survive. Plant's sessile condition reinforces even more the need of an efficient adaptive response to counteract a suboptimal environment. Such adaptive strategies synchronize growth and development adjustments, as well as cellular and molecular activities, aimed at an efficient use of scarce resources, e.g., water. Plant hormones are often involved as systemic mediators of the perception and integration of environmental cues. For instance, abscisic acid (ABA) accumulation upon drought perception serves as an initial signal for long-term acclimation reactions, which eventually involve the differential expression of genes leading to changes in transcript and protein patterns (Valdes et al., 2013). Plant-specific homeodomain leucine-zipper (HD-Zip) class I genes have been for long time suggested as players in the signal transduction to adjust growth and development under stress circumstances (Soderman et al., 1996; Olsson et al., 2004), but it was not until recently that their specific regulatory mechanism within the drought-induced ABA signaling pathway was discovered (Valdes et al., 2012). The authors reported two Arabidopsis HD-Zip I transcription factors, named ATHB7 and ATHB12, down-regulating a number of genes encoding ABA-receptor proteins, in addition to up-regulating protein phosphatases type 2C. Both ABA receptors and protein phosphatases 2C are well established components of the ABA signaling pathway (Santiago et al., 2009). This fine modulation of the stress perception confers the plant with the capacity to adapt to exposure to constant levels of ABA, thus causing the ABA response to be transient in character and providing the plant with the possibility to turn on and off the adaptive response at will. Stress adaptation is essential to evolutionary fitness and, as such, it has been discovered that a similar biological function is retained by orthologous HD-Zip I proteins in many plant species (Song et al., 2012; Zhao et al., 2014). As previously mentioned, developmental changes and morphological alterations are part of the plant adaptation and, besides controlling stress responses, HD-Zip I genes have additional roles in controlling development (Ariel et al., 2010). An interesting point raised by Valdes et al. (2012) is that other HD-Zip genes sharing targets, but differing in expression patterns or dependence on specific external conditions may have similar functions in modulating the ABA signal perception. HD-Zip superfamily of transcription factors includes also class III, which are major polarity and patterning determinants (Prigge et al., 2005). A potential HD-Zip I/HD-Zip III antagonism in the control of ABA-receptor genes has been recently proposed (Brandt et al., 2014), manifesting that complex relationships between classes appear to lead the integration of environmental and developmental cues. Though class I and class III members do not seem to regulate the same ABA receptors (Liu et al., 2012; Valdes et al., 2012) it may be possible that both families oppositely regulate the expression of related genes in a cell-type specific manner (Brandt et al., 2014). Similar genetic interactions between proteins belonging to different class families have been described in the integration of shade escape control and leaf patterning (Brandt et al., 2012). Besides water availability, the plant environmental context is defined by additional, simultaneous external factors, e.g., light and temperature, and should these factors influence the transcript levels of HD-Zip proteins the dynamic behavior of the ABA-driven stress response becomes automatically dependent on such factors. This implies that cross-communication between different signaling systems should be mediated by the same HD-Zip proteins. In this sense, available genomic and proteomic data have predicted in silico interactions between genes early regulated in the shade-avoidance response and, ATHB7 and ATHB12 that highlight their potential participation also in light signaling pathways (Ciolfi et al., 2013). The intricate network established within this superfamily of transcription factors suggest that the plant-specific and evolutionary highly conserved HD-Zip proteins are crucial players modulating stress responses and may be linking patterning and adaptation by acting to adjust developmental programs to specific environmental situations.

Cold-hardening during long-term acclimation in a freeze-tolerant woolly bear caterpillar, Pyrrharctia isabella.

The banded woolly bear caterpillar, Pyrrharctia isabella (Lepidoptera: Erebidae), overwinters in leaf litter and survives freezing under natural conditions. Following 18 weeks of cold acclimation at 5°C, all caterpillars could survive 1 week of continuous freezing at -20°C or seven cycles of freezing-thawing at -20°C, but none survived freezing at -80°C. Field-collected caterpillars had a temperature of crystallization of -7.7±0.5°C that decreased significantly to -9.5±0.6°C after 12 weeks of acclimation at 5°C. Hemolymph levels of free proline, total amino acids and proteins reached a peak during the first 4 weeks of acclimation; concomitantly, hemolymph osmolality increased markedly during this interval (from 364 to 1282 mosmol kg(-1)). In contrast, hemolymph pH decreased during the first 4 weeks of acclimation before this trend reversed and pH values gradually returned to initial values. However, pH reached its peak value following 1 week at -20°C, but decreased after longer periods of freezing. During cold acclimation, cholesterol levels decreased in the hemolymph and the membrane fraction of fat body but not in other tissues. Lethal freezing at -80°C reduced cell survival in foregut tissue and caused leakage of free proline, total amino acids and proteins from tissues into the hemolymph. The addition of glycerol to the bathing medium reduced freezing injury in fat body cells, as evidenced by reduced leakage of amino acids and proteins.

Distinct Testicular Steroidogenic Response Mechanisms Between Neonatal and Adult Heat-Acclimated Male Rats

Background: In comparison to short-term gonad heat exposure, little is known about the molecular mechanisms that regulate testicular steroidogenesis during long-term whole body heat acclimation. Material and Methods: Testicular slices from neonatal (NHA) and adult (AHA) heat-acclimated Wistar rats were analysed in vitro to assess the mRNA expression and enzymatic activity of steroidogenic enzymes under basal and luteinising hormone (LH) or prolactin (PRL) stimulated conditions compared with control rats (CR). Furthermore, a de-acclimated group (DA) was created by transferring adult NHA rats to control conditions. Results: Heat acclimation significantly increased plasma LH levels in the AHA group and LH and PRL in the NHA group compared with the CR group; however, after heat acclimation, the T and E2 levels did not differ from the control levels. All heat-acclimated groups showed high basal intra-testicular steroid production in vitro. Moreover, basal Cyp11a1 and Hsd3b1 levels were upregulated in vitro in the NHA and DA groups versus the CR group. LH in vitro stimulation upregulated Cyp11a1 expression in the NHA and AHA groups and PRL stimulation upregulated Cyp17a1 levels in the NHA and DA groups compared with the basal expression levels. In the AHA group, decreased basal Star and CYP11A activities but increased HSD3B1 and CYP17A1 activities were found. Conclusion: Our data revealed that despite the similar steroid levels in plasma and secreted in vitro by neonatal and adult heat-acclimated rat testicular slices, the molecular mechanisms underlying the steroidogenic response to heat acclimation during these different developmental stages were distinct.

Elevated Atmospheric CO2 Enhances Daily Carbon Export from Photosynthetic Source Organs and Thus Controls the Increased Growth of Vascular Plants, Tracheophytes

IntroductionLeaves of the higher vascular plants, tracheophytes, have two primary functions(1). First they serve as organs of C-fixation. Second they are major sources of assimilates for development of ‘sink’ tissues that also regulate plant growth potential especially at elevated- CO2 (EC). MethodsA leaf is a heterogeneous structure exporting both in day and night. Organ and organism gas-exchanges and 14C-analyses were integrated showing that quantitatively numerous C3, C3/C4-intermediate and C4 plants export mostly while light energy is trapped and more at EC. ResultsC4's fix and export more than C3’at ambient-CO2(AC). Interestingly, some C3's exporting assimilates, other than sucrose, have translocation rates that proportional to fixation are comparable to C4's. At EC, C3's achieve higher C-fixation rates, and C-export is comparable with C4's. Transition experiments between AC and EC, show that temporary acidification of the apoplast occurs but a brief perturbation of intercellular [H]+ ion levels correlates with only a temporary reduction in assimilate loading and 14C-export. Export is reestablished and source-leaf-strength at EC is greater than AC supporting faster growth. DiscussionDepending on the stage of canopy development, long-term acclimation to EC can result in a depression in single-leaf-photosynthesis, an observation that merely correlates to a more rapid turnover of key proteins, such as RUBISCO, that are signs of enhanced canopy maturation. Improving crop production necessitates a strategy that maximizes source to sink balance throughout the life-cycle. Recent studies, with transgenic lines of Arabidopsis thaliana, in which dark respiratory processes associated with pyruvate-flux were targeted (2,3) suggest that daily patterns of canopy photosynthesis, respiration and growth are enhanced at EC. EC not only enhances the metabolism of the (laminar) rosette leaves, but also that of the non-laminar photosynthetic organs (e.g., stems and branches of the inflorescence) that by the time of seed filling can supply over 90% of daily-C-fixed.

Elevated temperature causes metabolic trade-offs at the whole-organism level in the Antarctic fish Trematomus bernacchii.

As a response to ocean warming, shifts in fish species distribution and changes in production have been reported that have been partly attributed to temperature effects on the physiology of animals. The Southern Ocean hosts some of the most rapidly warming regions on earth and Antarctic organisms are reported to be especially temperature sensitive. While cellular and molecular organismic levels appear, at least partially, to compensate for elevated temperatures, the consequences of acclimation to elevated temperature for the whole organism are often less clear. Growth and reproduction are the driving factors for population structure and abundance. The aim of this study was to assess the effect of long-term acclimation to elevated temperature on energy budget parameters in the high-Antarctic fish Trematomus bernacchii. Our results show a complete temperature compensation for routine metabolic costs after 9 weeks of acclimation to 4°C. However, an up to 84% reduction in mass growth was measured at 2 and 4°C compared with the control group at 0°C, which is best explained by reduced food assimilation rates at warmer temperatures. With regard to a predicted temperature increase of up to 1.4°C in the Ross Sea by 2200, such a significant reduction in growth is likely to affect population structures in nature, for example by delaying sexual maturity and reducing production, with severe impacts on Antarctic fish communities and ecosystems.

Sediment preference, salinity tolerance and COX-1 genetic differences in two purportive species ofLuidia(Echinodermata: Asteroidea)

Specimens collected in or near Pensacola Bay, Florida matching the descriptions ofLuidia lawrenceiandLuidia clathrata(the congener from whichL. lawrenceiwas recently split) were compared to determine whether their recent taxonomic separation is supported by differences in sediment preference, salinity tolerance andCOX-1mtDNA sequences.Luidia clathratahas a preference for smaller grain sizes, while no statistically significant preference was found forLuidia lawrencei, and no significant difference was found between the species.Luidia clathratais more tolerant of lower salinity based on the righting response thanLuidia lawrencei, especially at salinities lower than 25 g kg−1. TheCOX-1comparison returned over 99% homology among individuals of the two species. While sediment preference and salinity tolerance results indicate differences in response to habitat dissimilarities, theCOX-1genetic result is strong evidence against the recently proposed separation of the species. In light of theCOX-1result, we interpret the sediment and salinity results as long-term acclimation responses.

Xenobiotic metabolism modulation after long-term temperature acclimation in juveniles of Solea senegalensis

The Senegalese sole, Solea senegalensis, originates from subtropical waters and displays great adaptability to environmental factors such as temperature. A comprehensive study on the effect of long-term temperature acclimation on xenobiotic metabolism, along with the assessment of other parameters related to physiological status, was designed to characterize the response of this species to temperature fluctuations within a realistic range. S. senegalensis juveniles were acclimated for a period of 60 days to two different ambient temperatures, 15 and 20 °C. Several hepatic, gill, muscular and plasmatic parameters were measured over time at the two temperatures. The lower temperature triggered, over time, the synthesis of hepatic microsomal cytochrome P450-related enzymes (e.g. 7-ethoxyresorufin O-deethylase (EROD), carboxylesterases, and the conjugating enzyme uridine diphosphate glucuronosyltransferase and, more significantly, EROD activity in gills. The antioxidant enzyme activities: catalase and glutathione reductase in liver were positively correlated to temperature. Plasmatic parameters (glucose, lactate, triglycerides and osmolality) were consistent with a good physiological status of the experimental fish. The expression of heat shock proteins in muscle did not significantly change in the two temperature groups. The results evidenced that the subtropical species S. senegalensis also uses the temperature compensation strategy to different degrees for most biotransformation enzymes; this response was more intense and faster in gills than in liver. This compensatory strategy did not apply to antioxidant enzymes and GST. The present findings highlight the need to consider the thermal history of the fish when using S. senegalensis as a sentinel in a biomarker-based pollution monitoring study. The fish plasticity on its strategy of physiological adaptation to temperature changes could contribute to explain the success in the geographical expansion of this species.

Photosynthesis in extreme environments: responses to different light regimes in the Antarctic alga Koliella antarctica.

Antarctic algae play a fundamental role in polar ecosystem thanks to their ability to grow in an extreme environment characterized by low temperatures and variable illumination. Here, for prolonged periods, irradiation is extremely low and algae must be able to harvest light as efficiently as possible. On the other side, at low temperatures even dim irradiances can saturate photosynthesis and drive to the formation of reactive oxygen species. Colonization of this extreme environment necessarily required the optimization of photosynthesis regulation mechanisms by algal organisms. In order to investigate these adaptations we analyzed the time course of physiological and morphological responses to different irradiances in Koliella antarctica, a green microalga isolated from Ross Sea (Antarctica). Koliella antarctica not only modulates cell morphology and composition of its photosynthetic apparatus on a long-term acclimation, but also shows the ability of a very fast response to light fluctuations. Koliella antarctica controls the activity of two xanthophyll cycles. The first, involving lutein epoxide and lutein, may be important for the growth under very low irradiances. The second, involving conversion of violaxanthin to antheraxanthin and zeaxanthin, is relevant to induce a fast and particularly strong non-photochemical quenching, when the alga is exposed to higher light intensities. Globally K. antarctica thus shows the ability to activate a palette of responses of the photosynthetic apparatus optimized for survival in its natural extreme environment.

Cellular changes associated with the acclimation of the intertidal sea anemone Actinia tenebrosa to ultraviolet radiation.

To assess the relative importance of long- and short-term cellular defense mechanisms in seasonally UV-R-acclimated Actinia tenebrosa (Anthozoa, Actiniidae), individuals were exposed to summer doses of PAR, UV-A, UV-B and enhanced UV-B (20%) for a period of 4days. Mycosporine-like amino acids (MAAs) and cyclobutane pyrimidine dimer (CPD) concentrations were quantified, while oxidative damage to lipids and proteins, and the activities or levels of the antioxidant enzymes SOD, CAT, GR, GPOX and total glutathione were determined. Our results show that summer UV-R-acclimated individuals had a higher UV-R tolerance, with no significant increases in CPDs levels, than winter-acclimated sea anemones possibly due to higher MAA concentrations. Summer-acclimated individuals showed increased lipid and protein oxidation and GPOX activity only when they were exposed to UV-B at 20% above ambient UV-R levels. In contrast, winter-acclimated sea anemones showed elevated levels of oxidative damage, GPOX and SOD activities after exposure to UV-A or UV-B at ambient and elevated levels. Thus, this study indicates that long-term UV-R acclimation mechanisms such as the accumulation of MAAs could be more important than short-term increases in antioxidant defenses with respect to reducing indirect UV-R damage in intertidal sea anemones.

Type 2 iodothyronine deiodinase is upregulated in rat slow- and fast-twitch skeletal muscle during cold exposure.

During cold acclimation, shivering is progressively replaced by nonshivering thermogenesis. Brown adipose tissue (BAT) and skeletal muscle are relevant for nonshivering thermogenesis, which depends largely on thyroid hormone. Since the skeletal muscle fibers progressively adapt to cold exposure through poorly defined mechanisms, our intent was to determine whether skeletal muscle type 2 deiodinase (D2) induction could be implicated in the long-term skeletal muscle cold acclimation. We demonstrate that in the red oxidative soleus muscle, D2 activity increased 2.3-fold after 3 days at 4°C together with the brown adipose tissue D2 activity, which increased 10-fold. Soleus muscle and BAT D2 activities returned to the control levels after 10 days of cold exposure, when an increase of 2.8-fold in D2 activity was detected in white glycolytic gastrocnemius but not in red oxidative gastrocnemius fibers. Propranolol did not prevent muscle D2 induction, but it impaired the decrease of D2 in BAT and soleus after 10 days at 4°C. Cold exposure is accompanied by increased oxygen consumption, UCP3, and PGC-1α genes expression in skeletal muscles, which were partialy prevented by propranolol in soleus and gastrocnemius. Serum total and free T3 is increased during cold exposure in rats, even after 10 days, when BAT D2 is already normalized, suggesting that skeletal muscle D2 activity contributes significantly to circulating T3 under this adaptive condition. In conclusion, cold exposure is accompanied by concerted changes in the metabolism of BAT and oxidative and glycolytic skeletal muscles that are paralleled by type 2 deiodinase activation.

Habitat pollution and thermal regime modify molecular stress responses to elevated temperature in freshwater mussels (Anodonta anatina: Unionidae)

Elevated temperature and pollution are common stressors in freshwater ecosystems. We study cellular stress response to acute warming in Anodonta anatina (Unionidae) from sites with different thermal regimes and pollution levels: a pristine area and an agriculturally polluted site with normal temperature regimes (F and A, respectively) and a polluted site with elevated temperature (N) from the cooling pond of an electrical power plant. Animals were exposed to different temperatures for 14days and stress response markers were measured in gills, digestive gland and hemocytes. Mussels from site N and A had elevated background levels of lactate dehydrogenase activity indicating higher reliance on anaerobic metabolism for ATP production and/or redox maintenance. Exposure to 25°C and 30°C induced oxidative stress (indicated by elevated levels of lipid peroxidation products) in digestive gland and gills of mussels from A and F sites, while in mussels from N sites elevated oxidative stress was only apparent at 30°C. Temperature-induced changes in levels of antioxidants (superoxide dismutase, metallothioneins and glutathione) were tissue- and population-specific. Acute warming led to destabilization of lysosomal membranes and increased frequencies of nuclear lesions in mussels from F and A sites but not in their counterparts from N site. Elevated temperature led to an increase in the frequency of micronuclei in hemocytes in mussels from F and A sites at 25°C and 30°C and in mussels from N site at 30°C. The mussels from N site also demonstrated better survival at elevated temperature (30°C) than their counterparts from the F and A sites. Taken together, these data indicate that long-term acclimation and/or adaptation of A. anatina to elevated temperatures result in increased thermotolerance and alleviate stress response to moderate temperature rise. In contrast, extreme warming (30°C) is harmful to mussels from all populations indicating limit to this induced thermotolerance.

Nitrite survival and nitrous oxide production of denitrifying phosphorus removal sludges in long-term nitrite/nitrate-fed sequencing batch reactors

Nitrite-based phosphorus (P) removal could be useful for innovative biological P removal systems where energy and carbon savings are a priority. However, using nitrite for denitrification may cause nitrous oxide (N2O) accumulation and emissions. A denitrifying nitrite-fed P removal system (SBRNO2−) was successfully set up in a sequencing batch reactor (SBR) and was run for 210 days. The maximum pulse addition of nitrite to SBRNO2− was 11 mg NO2−-N/L in the bulk, and a total of 34 mg NO2−-N/L of nitrite was added over three additions. Fluorescent in situ hybridization results indicated that the P-accumulating organisms (PAOs) abundance was 75 ± 1.1% in SBRNO2−, approximately 13.6% higher than that in a parallel P removal SBR using nitrate (SBRNO3−). Type II Accumulibacter (PAOII) (unable to use nitrate as an electron acceptor) was the main PAOs species in SBRNO2−, contributing 72% to total PAOs. Compared with SBRNO3−, SBRNO2− biomass had enhanced nitrite/free nitrous acid (FNA) endurance, as demonstrated by its higher nitrite denitrification and P uptake rates. N2O accumulated temporarily in SBRNO2− after each pulse of nitrite. Peak N2O concentrations in the bulk for SBRNO2− were generally 6–11 times higher than that in SBRNO3−; these accumulations were rapidly denitrified to nitrogen gases. N2O concentration increased rapidly in nitrate-cultivated biomass when 5 or 10 mg NO2−-N/L per pulse was added. Whereas, N2O accumulation did not occur in nitrite-cultivated biomass until up to 30 mg NO2−-N/L per pulse was added. Long-term acclimation to nitrite and pulse addition of nitrite in SBRNO2− reduced the risk of nitrite accumulation, and mitigated N2O accumulation and emissions from denitrifying P removal by nitrite.

Enhancing biomass production and yield by maintaining enhanced capacity for CO2 uptake in response to elevated CO2

Dahal, K., Weraduwage, S. M., Kane, K., Rauf, S. A., Leonardos, E. D., Gadapati, W., Savitch, L., Singh, J., Marillia, E.-F., Taylor, D. C., Micallef, M. C., Knowles, V., Plaxton, W., Barron, J., Sarhan, F., Hüner, N., Grodzinski, B. and Micallef, B. J. 2014. Enhancing biomass production and yield by maintaining enhanced capacity for CO2 uptake in response to elevated CO2. Can. J. Plant Sci. 94: 1075–1083. Using four model plants, two members of the Gramineae, rye and wheat, and two Brassicaceae, Brassica napus and Arabidopsis thaliana, two fundamental approaches were exploited to determine how regulating source-sink development would alter photosynthesis, productivity and yield during long-term acclimation to elevated CO2. In one approach we exploited the cold acclimation response of winter wheat, rye and B. napus. In the other approach we modified the dark respiration in A. thaliana to alter availability of respiratory substrates required for anabolic processes, such as fatty acid metabolism, thus reducing sink limitations on canopy photosynthesis at elevated CO2. Taken together, the data show the importance of maintaining strong demand from active sinks when the above-ground canopy is being exposed to elevated levels of the primary substrate of photosynthesis, CO2.

The protective effect of heat acclimation from hypoxic damage in the brain involves changes in the expression of glutamate receptors

Long-term heat acclimation (34 °C, 30d) alters the physiological responses and the metabolic state of organisms. It also improves ability to cope with hypoxic stress via a cross-tolerance mechanism. Within the brain, the hippocampal and frontal cortex neurons are the most sensitive to hypoxia and cell death is mainly caused by calcium influx via glutamate-gated ion channels, specifically NMDA and AMPA receptors. GluN1 subunit levels of NMDA-R correspond to NMDA-R levels. GluN2B/GluN2A subunit ratio is a qualitative index of channel activity; a higher ratio implies lower calcium permeability. The GluA2 subunit of AMPA-R controls channel permeability by inhibiting calcium penetration. Here, in rats model we (i)used behavioral-assessment tests to evaluate heat acclimation mediated hypoxic (15’ 4.5 ± 0.5% O2) neuroprotection, (ii) measured protein and transcript levels of NMDA-R and AMPA-R subunits before and after hypoxia in the hippocampus and the frontal cortex, to evaluate the role of Ca2+ in neuro-protection/cross-tolerance. Behavioral tests confirmed hypoxic tolerance in long-term (30d) but not in short-term (2d) heat acclimated rats. Hypoxic tolerance in the long-term acclimated phenotype was accompanied by a significant decrease in basal NMDA receptor GluN1 protein and an increase in its mRNA. The long-term acclimated rats also showed post ischemic increases in the GluN2B/GluN2A subunit ratio and GluA2 subunit of the AMPA receptor, supporting the hypothesis that reduced calcium permeability contributes to heat acclimation mediated hypoxia cross-tolerance. Abrupt post ischemic change in GluN2B/GluN2A subunit ratio with no change in NMDA-R subunits transcript levels implies that post-translational processes are inseparable acclimatory cross-tolerance mechanism.

Long-term acclimation of anaerobic sludges for high-rate methanogenesis from LCFA

Inhibition of methanogens by long chain fatty acids (LCFA) and the low numbers of LCFA-degrading bacteria are limitations to exploit biogas production from fat-rich wastewaters. Generally reactors fail due to excessive LCFA accumulation onto the sludge. Here, long-term acclimation and bioaugmentation with a LCFA-degrading coculture were hypothesized as strategies to enhance methanogenic conversion of these compounds. Anaerobic sludges previously exposed to LCFA for more than 100 days converted a specific biomass-associated substrate of (3.2 ± 0.1) kg·kg−1 with very short lag phases (<1 day), whereas non-acclimated sludges showed lag phases of 11–15 days for metabolizing (1.6–1.8) kg·kg−1. Addition of a coculture of Syntrophomonas zehnderi and Methanobacterium formicicum to sludges previously loaded with LCFA and containing different amounts of biomass-associated substrate (from (0.5–3.2) kg·kg−1) did not improve methane production neither lag phases were shortened, indicating that the endogenous microbiota are not a limiting factor. Clearly, we show that long-term sludge acclimation to LCFA is essential for high rate methanogenesis from LCFA.

Modulation of metallothionein and metal partitioning in liver and kidney of Solea senegalensis after long-term acclimation to two environmental temperatures

Juveniles of Solea senegalensis were fed with commercial pellets under controlled conditions at two environmental Mediterranean temperatures (15 and 20°C) for two months. After this period, the accumulation of essential and non-essential metals and metallothionein (MT) levels was measured in liver and kidney by inductively coupled plasma mass spectrometry (ICP-MS) and pulse polarography, respectively. The bioaccumulation factor (BAF) for selected metals in both tissues was calculated in relation to levels present in the feed. Tissue partitioning (liver/kidney) and molar ratios, considering the metal protective mechanisms: MT and Selenium (Se), were included for evaluating the detoxification capacity of each tissue. Ag, Cd, Cu and Mn were preferentially accumulated in the liver whereas Co, Fe, Hg, Se and Zn were found in larger concentrations in the kidney, and higher temperature enhanced the accumulation of some of them, but not all. MT content in liver, but not in kidney, was also influenced by temperature changes and by length of exposure. The BAF revealed that Cu was taken up mainly by the liver whereas Se was efficiently taken up by both tissues. The high molar ratios of MT and most metals denoted the kidney׳s remarkable spare capacity for metal detoxification through MT binding. Moreover, the potential protective role of Se was also more evident in kidney as a higher Se:Cd and Se:Ag molar ratios were reached in this organ. In contrast to other fish, the storage of Cd in kidney was particularly low.

Implications of the mesophyll conductance to CO2 for photosynthesis and water‐use efficiency during long‐term water stress and recovery in two contrasting Eucalyptus species

Water stress (WS) slows growth and photosynthesis (A(n)), but most knowledge comes from short-time studies that do not account for longer term acclimation processes that are especially relevant in tree species. Using two Eucalyptus species that contrast in drought tolerance, we induced moderate and severe water deficits by withholding water until stomatal conductance (g(sw)) decreased to two pre-defined values for 24 d, WS was maintained at the target g(sw) for 29 d and then plants were re-watered. Additionally, we developed new equations to simulate the effect on mesophyll conductance (g(m)) of accounting for the resistance to refixation of CO(2). The diffusive limitations to CO(2), dominated by the stomata, were the most important constraints to A(n). Full recovery of A(n) was reached after re-watering, characterized by quick recovery of gm and even higher biochemical capacity, in contrast to the slower recovery of g(sw). The acclimation to long-term WS led to decreased mesophyll and biochemical limitations, in contrast to studies in which stress was imposed more rapidly. Finally, we provide evidence that higher gm under WS contributes to higher intrinsic water-use efficiency (iWUE) and reduces the leaf oxidative stress, highlighting the importance of gm as a target for breeding/genetic engineering.

Predicting ecosystem carbon balance in a warming Arctic: the importance of long-term thermal acclimation potential and inhibitory effects of light on respiration

The carbon balance of Arctic ecosystems is particularly sensitive to global environmental change. Leaf respiration (R), a temperature-dependent key process in determining the carbon balance, is not well-understood in Arctic plants. The potential for plants to acclimate to warmer conditions could strongly impact future global carbon balance. Two key unanswered questions are (1) whether short-term temperature responses can predict long-term respiratory responses to growth in elevated temperatures and (2) to what extent the constant daylight conditions of the Arctic growing season inhibit leaf respiration. In two dominant Arctic species Eriophorum vaginatum (tussock grass) and Betula nana (woody shrub), we assessed the extent of respiratory inhibition in the light (RL/RD), respiratory response to short-term temperature change, and respiratory acclimation to long-term warming treatments. We found that R of both species is strongly inhibited by light (averaging 35% across all measurement temperatures). In E. vaginatum both RL and RD acclimated to the long-term warming treatment, reducing the magnitude of respiratory response relative to the short-term response to temperature increase. In B. nana, both RL and RD responded to short-term temperature increase but showed no acclimation to the long-term warming. The ability to predict plant respiratory response to global warming with short-term temperature responses will depend on species-specific acclimation potential and the differential response of RL and RD to temperature. With projected woody shrub encroachment in Arctic tundra and continued warming, changing species dominance between these two functional groups, may impact ecosystem respiratory response and carbon balance.

Enhancing biomass production and yield by maintaining enhanced capacity for CO2 uptake in response to elevated CO2

Dahal, K., Weraduwage, S. M., Kane, K., Rauf, S. A., Leonardos, E. D., Gadapati, W., Savitch, L., Singh, J., Marillia, E.-F., Taylor, D. C., Micallef, M. C., Knowles, V., Plaxton, W., Barron, J., Sarhan, F., Huner, N., Grodzinski, B. and Micallef, B. J. 2014. Enhancing biomass production and yield by maintaining enhanced capacity for CO2 uptake in response to elevated CO2. Can. J. Plant Sci. 94: 1075-1083. Using four model plants, two members of the Gramineae, rye and wheat, and two Brassicaceae, Brassica napus and Arabidopsis thaliana, two fundamental approaches were exploited to determine how regulating source-sink development would alter photosynthesis, productivity and yield during long-term acclimation to elevated CO2. In one approach we exploited the cold acclimation response of winter wheat, rye and B. napus. In the other approach we modified the dark respiration in A. thaliana to alter availability of respiratory substrates required for anabolic processes, such as fatty acid metabolism, thus reduc...