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PubMed2002

The electrical impedance spectroscopy of Scots pine needles during cold acclimation.

The electrical impedance spectroscopy (EIS) was applied to current-year needles of Scots pine (Pinus sylvestris L.) in an 8-year provenance field trial in central Finland during frost hardening. The EIS analysis of the needles using a Model-A equivalent circuit indicated a sequence of events in the needles during their cold acclimation. Some of the EIS-parameters referred to maturation phenomena occurring during the pre-hardening phase at the end of the growing season, and some parameters displayed a clear coincidence with the frost hardening itself. Significant differences between provenances were found in several of the Model-A parameters. Extracellular resistance (re) and beta-coefficient decreased in all provenances in the pre-hardening phase in August and until mid-September. In the same phase, both the intracellular resistance (ri) and the cell membrane time constant (taum) first increased and then decreased. According to taum, re and beta there was a clear gradation between provenances in the pre-hardening phase. From the end of September significant differences were found in the intracellular resistance between provenances, corresponding with the differences in their hardening pattern. The dry weight (DW) content of needles increased during the study period but no clear differences were found between the provenances.

Journal Article↗
PubMed2005

Photosystem II core phosphorylation and photosynthetic acclimation require two different protein kinases.

Illumination changes elicit modifications of thylakoid proteins and reorganization of the photosynthetic machinery. This involves, in the short term, phosphorylation of photosystem II (PSII) and light-harvesting (LHCII) proteins. PSII phosphorylation is thought to be relevant for PSII turnover, whereas LHCII phosphorylation is associated with the relocation of LHCII and the redistribution of excitation energy (state transitions) between photosystems. In the long term, imbalances in energy distribution between photosystems are counteracted by adjusting photosystem stoichiometry. In the green alga Chlamydomonas and the plant Arabidopsis, state transitions require the orthologous protein kinases STT7 and STN7, respectively. Here we show that in Arabidopsis a second protein kinase, STN8, is required for the quantitative phosphorylation of PSII core proteins. However, PSII activity under high-intensity light is affected only slightly in stn8 mutants, and D1 turnover is indistinguishable from the wild type, implying that reversible protein phosphorylation is not essential for PSII repair. Acclimation to changes in light quality is defective in stn7 but not in stn8 mutants, indicating that short-term and long-term photosynthetic adaptations are coupled. Therefore the phosphorylation of LHCII, or of an unknown substrate of STN7, is also crucial for the control of photosynthetic gene expression.

Acclimatization↗
PubMed1988

Alpha 1- and beta-adrenergic receptors in brown adipose tissue of lean (Fa/?) and obese (fa/fa) Zucker rats. Effects of cold-acclimation, sucrose feeding and adrenalectomy.

1. The populations of alpha 1- and beta-adrenergic receptors in brown adipose tissue (BAT) of genetically obese Zucker rats (fa/fa) were studied with [3H]prazosin and [3H]CGP-12177 respectively. 2. The density of alpha 1-adrenergic receptors in BAT was significantly lower in obese than in lean Zucker rats, both at 2-4 months of age and at 6 weeks of age. The density of beta-adrenergic receptors was identical in BAT of lean and obese 6-week-old Zucker rats. 3. Cold-acclimation increased the alpha 1-receptor density significantly in BAT of both lean and obese Zucker rats, and the number of beta-receptors was also somewhat increased. 4. Sucrose feeding did not affect the density of alpha 1-receptors in BAT of lean or obese Zucker rats, but it increased beta-receptor density. 5. Adrenalectomy restored the density of alpha 1-adrenergic receptors in BAT of obese Zucker rats to the value observed in lean rats. 6. It is concluded that there is a direct correlation between alpha 1-receptor density and tissue recruitment, and that alpha 1-receptor density is thus positively correlated with sympathetic activity. beta-Receptor density is apparently better correlated with feeding conditions.

Adipose Tissue, Brown↗
PubMed1988

Changes in activities of some enzymes of glycerolipid synthesis in brown adipose tissue of cold-acclimated rats.

1. Measurements were made of the activities of the following enzymes of glycerolipid synthesis in homogenates of interscapsular brown adipose tissue obtained from rats subjected to a 4 degrees C environment for time periods of 6 h up to 12 days: fatty acyl-CoA synthetase (FAS), mitochondrial and microsomal forms of glycerolphosphate acyltransferase (GPAT), monoacylglycerolphosphate acyltransferase (MGPAT) and Mg2+-dependent phosphatidate phosphohydrolase (PPH). 2. Relative to tissue DNA content, the activities of mitochondrial GPAT, MGPAT and Mg2+-dependent PPH were significantly increased after 1 day of exposure to cold, and continued to increase thereafter. By contrast, FAS and microsomal GPAT activities were unchanged relative to tissue DNA. 3. The time profile of the increase in MGPAT activity correlated well with a concomitant increase in the microsomal marker NADP+-cytochrome c reductase. Changes in mitochondrial GPAT and in Mg2+-dependent PPH activities were larger in amplitude than that of MGPAT. 4. It is proposed that these selective changes in enzyme activity may be associated with the onset of brown-adipose-tissue hyperplasia or possibly with an increase in triacylglycerol synthesis during cold-acclimation.

1-Acylglycerol-3-Phosphate O-Acyltransferase↗
PubMed2002

Genotype-dependent transcriptional activation of novel repetitive elements during cold acclimation of alfalfa (Medicago sativa).

In a search for cold-regulated genes that are differentially expressed in alfalfa genotypes of contrasting freezing tolerance, we screened 1036 arrayed cDNA clones. The screening resulted in isolation of cDNA clones, which demonstrated dramatic differences in expression between hardy and un-hardy alfalfa varieties. Detailed analysis revealed that these cDNAs represent parts of novel non-coding repetitive elements carrying long-terminal repeats (LTR) and other retroelement-like features. Despite strong expression under low temperatures, DNA templates remained highly methylated, and a drug-induced decrease in methylation did not activate transcription under normal temperatures. We identified that these repetitive elements represent a large family and could insert into, or be adjacent to, the unrelated polyprotein sequences of putative retrotransposons. These retrotransposons also showed low temperature-induced transcriptional activation; however, this activation was not genotype-dependent. The retroelements described in this study are the first retroelement characterized in the Medicago genus. Furthermore, they represent the only known example of genotype-specific cold-induced transcriptional activation of multiple copies of a repetitive element whose expression is associated with a genotype difference in cold acclimation.

Acclimatization↗
PubMed2004

Photosynthetic acclimation to simultaneous and interacting environmental stresses along natural light gradients: optimality and constraints.

There is a strong natural light gradient from the top to the bottom in plant canopies and along gap-understorey continua. Leaf structure and photosynthetic capacities change close to proportionally along these gradients, leading to maximisation of whole canopy photosynthesis. However, other environmental factors also vary within the light gradients in a correlative manner. Specifically, the leaves exposed to higher irradiance suffer from more severe heat, water, and photoinhibition stresses. Research in tree canopies and across gap-understorey gradients demonstrates that plants have a large potential to acclimate to interacting environmental limitations. The optimum temperature for photosynthetic electron transport increases with increasing growth irradiance in the canopy, improving the resistance of photosynthetic apparatus to heat stress. Stomatal constraints on photosynthesis are also larger at higher irradiance because the leaves at greater evaporative demands regulate water use more efficiently. Furthermore, upper canopy leaves are more rigid and have lower leaf osmotic potentials to improve water extraction from drying soil. The current review highlights that such an array of complex interactions significantly modifies the potential and realized whole canopy photosynthetic productivity, but also that the interactive effects cannot be simply predicted as composites of additive partial environmental stresses. We hypothesize that plant photosynthetic capacities deviate from the theoretical optimum values because of the interacting stresses in plant canopies and evolutionary trade-offs between leaf- and canopy-level plastic adjustments in light capture and use.

Acclimatization↗
PubMed2004

Role of red carotenoids in photoprotection during winter acclimation in Buxus sempervirens leaves.

The red leaf coloration of several plant species during autumn and winter is due to the synthesis of phenolic compounds such as anthocyanins or red carotenoids. The latter occur very rarely and are non-ubiquitous and taxonomically restricted compounds. The present study shows that the leaves of common box ( Buxus sempervirens L.) accumulate red carotenoids (eschscholtzxanthin, monoanhydroeschscholtzxanthin, anhydroeschscholtzxanthin) as a response to photoinhibitory conditions during winter acclimation. These compounds are produced in a coordinated manner with the operation of other photoprotective systems: accumulation and sustained deepoxidation of VAZ pigments with a concomitant decrease in maximal photochemical efficiency, accumulation of alpha-tocopherol and a gradual decrease on chlorophyll content. All these processes were reversed when the photosynthetic tissues were transferred from photoinhibitory winter conditions to room temperature for 9 days. Buxus leaves showed a large degree of phenotype variation in the degree of reddening, ranging from green to orange. The differences in colour pattern were mainly due to differences in the accumulation of red carotenoids and xanthophyll esters. Red pigments were mainly anhydroeschscholtzxanthin and esters of eschscholtzxanthin. Conversely to fruit or petal chromoplasts, the plastids of red leaves in this species are not the terminal differentiated state but are able to redifferentiate again to chloroplasts. Their photoprotective role during winter as a light screen system or as antioxidants, in a similar way to other red pigments, and their implications on the wide ecological tolerance of this evergreen species are discussed.

Acclimatization↗
PubMed2006

High-light stress does not impair biomass accumulation of sun-acclimated tropical tree seedlings (Calophyllum longifolium Willd. and Tectona grandis L. f.).

Studies with seedlings of tropical rainforest trees ( Calophyllum longifolium Willd.; Tectona grandis L. f.) were designed to test whether high-light stress affects photosynthetic performance and growth. Seedlings were cultivated in pots at a field site in Central Panama (9 degrees N) and separated into two groups: (1) plants exposed to full solar radiation; (2) plants subjected to automatic neutral shading (48 %) whenever visible irradiance surpassed 1000, 1200, or 1600 micromol photons m-2 s-1. After 2-4 months, chlorophyll fluorescence (Fv/Fm ratio), photosynthetic net CO2 uptake, pigment composition, alpha-tocopherol content of leaves, and plant biomass accumulation were measured. Fully sun-exposed, compared to periodically shaded plants, experienced substantial high-light stress around midday, indicated by photoinhibition of photosystem II and depressed net CO2 uptake. Higher contents of xanthophyll cycle pigments, lutein, and alpha-tocopherol showed an enhancement of photoprotection in fully sun-exposed plants. However, in all experiments, the maximum capacity of net CO2 uptake and plant dry mass did not differ significantly between the two treatments. Thus, in these experiments, high-light stress did not impair productivity of the seedlings studied. Obviously, the continuously sun-exposed plants were capable of fully compensating for any potential costs associated with photoinhibition and repair of photosystem II, reduced CO2 assimilation, and processes of high-light acclimation.

Acclimatization↗
PubMed2005

Acclimation to ozone affects host/pathogen interaction and competitiveness for nitrogen in juvenile Fagus sylvatica and Picea abies trees infected with Phytophthora citricola.

In a two-year phytotron study, juvenile trees of European beech (Fagus sylvatica) and Norway spruce (Picea abies) were grown in mixture under ambient and twice ambient ozone (O3) and infected with the root pathogen Phytophthora citricola. We investigated the influence of O3 on the trees' susceptibility to the root pathogen and assessed, through a 15N-labelling experiment, the impact of both treatments (O3 exposure and infection) on belowground competitiveness. The hypotheses tested were that: (1) both P. citricola and O3 reduce the belowground competitiveness (in view of N acquisition), and (2) that susceptibility to P. citricola infection is reduced through acclimation to enhanced O3 exposure. Belowground competitiveness was quantified via cost/benefit relationships, i.e., the ratio of structural investment in roots relative to their uptake of 15N. Beech had a lower biomass acquisition and captured less 15N under enhanced O3 and P. citricola infection alone than spruce, whereas the latter species appeared to profit from the lower resource acquisition of beech in these treatments. Nevertheless, in the combined treatment, susceptibility to P. citricola of spruce was increased, while beech growth and 15N uptake were not further reduced below the levels found under the single treatments. Potential trade-offs between stress defence, growth performance, and associated nitrogen status are discussed for trees affected through O3 and/or pathogen infection. With respect to growth performance, it is concluded that O3 enhances susceptibility to the pathogen in spruce, but apparently raises the defence capacity in beech..

Acclimatization↗
PubMed1981

Circadian rhythm and hormonal sensitivity of lipoprotein lipase activity in cold acclimated rats.

To delineate the factors that may affect triglyceride capture in brown adipose tissue, we have determined the lipoprotein lipase activity (LPS) under conditions known to modulate this activity in other tissues. Acclimation temperature (28 degree C or 5 degree C) had no effect on circadian variations of white adipose tissue and heart LPL activity, LPL activity in brown adipose tissue of 28 degree C rats was similar to that in white adipose tissue (peak activity between 21:00 and 07:00 h), whereas LPL activity of the former was four times higher in 5 degree C rats and rhythmicity was altered (peak activity at 17:00 h as for heart). Brown adipose tissue LPL activity was increased in 28 degree C rats but not in 5 degree C rats after a single injection of insulin to fasting animals. A single injection of dexamethasone increased brown adipose tissue LPL activity only in 5 degree C rats, whereas enzyme activity was increased in both 28 degree C and 5 degree C rats by a single injection of norepinephrine to fed animals. These variations were discussed with relation to the role of brown adipose tissue at 5 degrees C and 28 degrees C.

Acclimatization↗
PubMed2005

AtFtsH6 is involved in the degradation of the light-harvesting complex II during high-light acclimation and senescence.

Degradation of the most abundant membrane protein on earth, the light-harvesting complex of Photosystem II (LHC II), is highly regulated under various environmental conditions, e.g., light stress, to prevent photochemical damage to the reaction center. We identified the LHC II degrading protease in Arabidopsis thaliana as a Zn(2+)-dependent metalloprotease, activated by the removal of unknown extrinsic factors, similar to the proteolytic activity directed against Lhcb3 in barley. By using a reversed genetic approach, the chloroplast-targeted protease FtsH6 was identified as being responsible for the degradation. T-DNA KO A. thaliana mutants, lacking ftsH6, were unable to degrade either Lhcb3 during dark-induced senescence or Lhcb1 and Lhcb3 during highlight acclimation. The A. thaliana ftsH6 gene has a clear orthologue in the genome of Populus trichocarpa. It is likely that FtsH6 is a general LHC II protease and that FtsH6-dependent LHC II proteolysis is a feature of all higher plants.

Acclimatization↗
PubMed2005

HOS10 encodes an R2R3-type MYB transcription factor essential for cold acclimation in plants.

We report the identification and characterization of an Arabidopsis mutant, hos10-1 (for high expression of osmotically responsive genes), in which the expression of RD29A and other stress-responsive genes is activated to higher levels or more rapidly activated than in wild-type by low temperature, exogenous abscisic acid (ABA), or salt stress (NaCl). The hos10-1 plants are extremely sensitive to freezing temperatures, completely unable to acclimate to the cold, and are hypersensitive to NaCl. Induction of NCED3 (the gene that encodes the rate-limiting enzyme in ABA biosynthesis) by polyethylene glycol-mediated dehydration and ABA accumulation are reduced by this mutation. Detached shoots from the mutant plants display an increased transpiration rate compared with wild-type plants. The hos10-1 plants exhibit several developmental alterations, such as reduced size, early flowering, and reduced fertility. The HOS10 gene encodes a putative R2R3-type MYB transcription factor that is localized to the nucleus. Together, these results indicate that HOS10 is an important coordinating factor for responses to abiotic stress and for growth and development.

Abscisic Acid↗
PubMed2006

The sulfur acclimation SAC3 kinase is required for chloroplast transcriptional repression under sulfur limitation in Chlamydomonas reinhardtii.

Sulfur (S) deprivation responses have been studied extensively in algae and land plants; however, little is known of the signals that link perception of S status to chloroplast gene expression. Here, we have compared the chloroplast S limitation response in WT vs. sac1 and sac3 sulfur acclimation mutants of the green alga Chlamydomonas reinhardtii. We provide evidence that in the WT, chloroplast transcriptional activity rapidly decreases after removal of S from the medium, leading to reduced transcript accumulation. This decrease correlates with reduced abundance of a sigma70-like factor, Sig1, which is most likely the unique chloroplast transcription specificity factor. We further show that reduced transcription activity and diminished Sig1 accumulation are mediated by the SAC3 gene product, a putative Snf1-type Ser/Thr kinase previously shown to have both positive and negative effects on nuclear gene expression. Inclusion of the protein kinase inhibitor 6-dimethylaminopurine during S limitation yielded a pattern of expression that was largely similar to that seen in the sac3 mutant, lending support to the hypothesis that Sac3 kinase activation leads to transcriptional repression and Sig1 proteolysis. The finding that Sac3 regulates chloroplast gene expression suggests that it has a previously unknown role in integrating the S limitation response in multiple subcellular compartments.

Animals↗
PubMed1996

A natural experiment on plant acclimation: lifetime stomatal frequency response of an individual tree to annual atmospheric CO2 increase.

Carbon dioxide (CO2) has been increasing in atmospheric concentration since the Industrial Revolution. A decreasing number of stomata on leaves of land plants still provides the only morphological evidence that this man-made increase has already affected the biosphere. The current rate of CO2 responsiveness in individual long-lived species cannot be accurately determined from field studies or by controlled-environment experiments. However, the required long-term data sets can be obtained from continuous records of buried leaves from living trees in wetland ecosystems. Fine-resolution analysis of the lifetime leaf record of an individual birch (Betula pendula) indicates a gradual reduction of stomatal frequency as a phenotypic acclimation to CO2 increase. During the past four decades, CO2 increments of 1 part per million by volume resulted in a stomatal density decline of approximately 0.6%. It may be hypothesized that this plastic stomatal frequency response of deciduous tree species has evolved in conjunction with the overall Cenozoic reduction of atmospheric CO2 concentrations.

Journal Article↗
PubMed2003

Anoxia tolerance in rice roots acclimated by several different periods of hypoxia.

Rice (Oryza sativa L.) seedlings were subjected to hypoxic pretreatment (H-PT; incubated in 5% O2 atmosphere) for various lengths of time followed by an anoxic stress. Anoxia tolerance of rice roots was improved with increasing duration of H-PT, but longer H-PT than 12 h gave no additional improvement. Concentrations of ATP and ethanol, and activities of pyruvate decarboxylase (EC 4.1.1.1) and alcohol dehydrogenase (EC 1.1.1.1) in the roots were increased by H-PT, and the times and patterns of increasing in these concentrations and activities were similar to those of increasing in the anoxia tolerance. These results suggest that the H-PT may increase anoxia tolerance due to maintenance of ATP levels with rapid induction of ethanolic fermentation, and hypoxic acclimation may occur within 12 h.

Adaptation, Physiological↗
PubMed2000

Acclimation of Chlamydomonas reinhardtii to its nutrient environment.

To cope with low nutrient availability in nature, organisms have evolved inducible systems that enable them to scavenge and efficiently utilize the limiting nutrient. Furthermore, organisms must have the capacity to adjust their rate of metabolism and make specific alterations in metabolic pathways that favor survival when the potential for cell growth and division is reduced. In this article I will focus on the acclimation of Chlamydomonas reinhardtii, a unicellular, eukaryotic green alga to conditions of nitrogen, sulfur and phosphorus deprivation. This organism has a distinguished history as a model for classical genetic analyses, but it has recently been developed for exploitation using an array of molecular and genomic tools. The application of these tools to the analyses of nutrient limitation responses (and other biological processes) is revealing mechanisms that enable Chlamydomonas to survive harsh environmental conditions and establishing relationships between the responses of this morphologically simple, photosynthetic eukaryote and those of both nonphotosynthetic organisms and vascular plants.

Adaptation, Physiological↗
PubMed2001

Biodegradation of isopropanol in a three phase fixed bed bioreactor: start up and acclimation using a previously-enriched microbial culture.

The aerobic biodegradation of high liquid phase concentrations of 2-propanol (IPA) by a previously enriched solvent-tolerant bacterial consortium within a 1.9 l fed-batch three phase fixed bed bioreactor was investigated. Solvent concentrations of up to 7.9 g l(-1) were investigated. Previously enriched solvent-tolerant bacterial cells were immobilised onto porous glass cylinders as a means obioprocess intensification. Bioreactor start-up and acclimation was studied anacetone concentration tracked as an indicator of IPA utilization, as the sole carbon source within a minimal salts medium (MSM). The initial batch treatment of IPA exhibited a biodegradation rate of 0.11 g l(-1) h(-1) prior to biofilm formation Biofilm growth during the second batch treatment was consistent with an increase in metabolic activity and an IPA biodegradation rate of 0.34 g l(-1), followed by a reduction of biodegradation rate to a constant value of 0.078 g l(-1) h(-1) after 650 h. A maximum acetone generation rate of 1.3 g l(-1) h(-1) was obtained during the fourth IPA addition although the maximum acetone biodegradation rate of 0.38 g l(-1) h(-1) was observed during the initial IPA addition. It is proposed that the metabolic lag resulting from switching from alcohol dehydrogenase to acetone carboxylase is a major rate-limiting step in the deep oxidation of IPA to acetone. The results demonstrate the potential of a previously enriched solvent-tolerant bacterial consortium in fixed bed bioreactor systems, for the aerobic treatment of concentrated solvent-containing wastestreams.

2-Propanol↗
PubMedDate not supplied

A comparative analysis of the upper thermal tolerance limits of eastern Pacific porcelain crabs, genus Petrolisthes: influences of latitude, vertical zonation, acclimation, and phylogeny.

Marine intertidal organisms are subjected to a variety of abiotic stresses, including aerial exposure and wide ranges of temperature. Intertidal species generally have higher thermal tolerance limits than do subtidal species, and tropical species have higher thermal tolerance limits than do temperate species. The adaptive significance of upper thermal tolerance limits of intertidal organisms, however, has not been examined within a comparative context. Here, we present a comparative analysis of the adaptive significance of upper thermal tolerance limits in 20 congeneric species of porcelain crabs, genus Petrolisthes, from intertidal and subtidal habitats throughout the eastern Pacific. Upper thermal tolerance limits are positively correlated with surface water temperatures and with maximal microhabitat temperatures. Analysis of phylogenetically independent contrasts (from a phylogenetic tree on the basis of the 16s rDNA gene sequence) suggests that upper thermal tolerance limits have evolved in response to maximal microhabitat temperatures. Upper thermal tolerance limits increased during thermal acclimation at elevated temperatures, the amount of increase being greater for subtidal than for intertidal species. This result suggests that the upper thermal tolerance limits of some intertidal species may be near current habitat temperature maxima, and global warming thus may affect the distribution limits of intertidal species to a greater extent than for subtidal species.

Acclimatization↗