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PubMed1995

Thermal acclimation and dietary lipids alter the composition, but not fluidity, of trout sperm plasma membrane.

The effect of a long-term adaptation of rainbow trout to 8 and 18 degrees C combined with a corn oil- or a fish oil-supplemented diet on the characteristics of the spermatozoan plasma membrane was investigated. The experiment lasted up to 22 mon during which spermatozoa were collected from the mature males. Spermatozoan plasma membranes were isolated by nitrogen cavitation, and the cholesterol content, phospholipid composition and fatty acid pattern were investigated. Membrane viscosity was assessed on whole cells by electron spin resonance using spin-labeled phospholipids. Neither diet nor rearing temperature influenced the cholesterol content of the plasma membrane nor the phospholipid class distribution. The rearing temperature of the broodstock only slightly affected the phospholipid fatty acids. A minor decrease in 18:0 and increase in monounsaturated fatty acids was observed for the cold-adapted fish. These modifications were not sufficient to affect membrane fluidity, and we conclude that trout spermatozoa do not display any homeoviscous adaptations in these conditions. On the contrary, the dietary fatty acid intake greatly modified the fatty acid profile of plasma membrane phospholipids. The fish oil-fed trout displayed a much higher n-3/n-6 fatty acid ratio than did the corn oil-fed ones, but the 22:6n-3 levels remained unchanged. Modifications in plasma membrane composition by the diet were obtained although neither of the two diets was deficient in essential fatty acids. The enrichment in n-3 fatty acids, however, did not affect plasma membrane fluidity which was unchanged by the diets.

Acclimatization↗
PubMed1998

Acclimation of the photosynthetic response of Chromatium vinosum to light-limiting conditions.

The photosynthetic response of the purple sulfur bacterium Chromatium vinosum DSM 185 to different degrees of illumination was analyzed. The microorganism was grown in continuous culture, and samples were taken from the effluent of the culture and incubated at different irradiances to determine the specific rate of sulfur oxidation as a measure of the photosynthetic activity of the organism. The activities obtained were plotted as a function of the specific rate of light uptake, and for each set of data a photosynthesis equation was fitted, which allowed the estimation of Pmax (photosynthetic capacity), qk (the threshold irradiance for light limitation), and m (maintenance coefficient). The results indicated that cells grown under light limitation are able to achieve higher photosynthetic activities than cells grown under light saturation. The photosynthetic capacity (Pmax) remained constant under all the conditions of illumination tested, while the maintenance expenses (m) were higher under light limitation. The parameter qk, on the contrary, decreased considerably at limiting irradiances.

Acclimatization↗
PubMed2003

Comparison between NaCl tolerance response and acclimation to cold temperature in Shewanella putrefaciens.

Two strains of the spoiling bacterium S. putrefaciens showed an adaptation capacity to hyperosmotic shock when they were pretreated with a sublethal concentration of NaCl. The maximal tolerance factor for the CIP 69.29 strain was obtained when cells were incubated for 1 h in the presence of 1.5% NaCl, whereas for the J13.1 strain, an incubation of 15 min in the presence of 1% NaCl seemed to be the optimal conditions to harden the cells against a subsequent lethal salt treatment. During NaCl adaptation and growth at low temperatures (2 degrees C), 37 and 32 polypeptides were induced respectively. Interestingly, 11 proteins were common between the two different stress responses. These proteins and the corresponding genes seem to play a key role in the observed cross-protection towards the NaCl challenge induced by growth of the cultures at 2 degrees C. One of the overlapping proteins has been identified to correspond to the alkyl hydroperoxide reductase (AhpC) of S. putrefaciens. Northern blot analysis showed that induction of this enzyme was accompanied by accumulation of the corresponding transcript under both conditions.

Acclimatization↗
PubMed2004

Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems I and II.

Magnesium deficiency in plants is a widespread problem, affecting productivity and quality in agriculture, yet at a physiological level it has been poorly studied in crop plants. Here, a physiological characterization of Mg deficiency in Beta vulgaris L., an important crop model, is presented. The impact of Mg deficiency on plant growth, mineral profile and photosynthetic activity was studied. The aerial biomass of plants decreased after 24 days of hydroponic culture in Mg-free nutrient solution, whereas the root biomass was unaffected. Analysis of mineral profiles revealed that Mg decreased more rapidly in roots than in shoots and that shoot Mg content could fall to 3 mg g(-1) DW without chlorosis development and with no effect on photosynthetic parameters. Sucrose accumulated in most recently expanded leaves before any loss in photosynthetic activity. During the development of Mg deficiency, the two photosystems showed sharply contrasting responses. Data were consistent with a down-regulation of PSII through a loss of antenna, and of PSI primarily through a loss of reaction centres. In each case, the net result was a decrease in the overall rate of linear electron transport, preventing an excess of reductant being produced during conditions under which sucrose export away from mature leaf was restricted.

Adaptation, Physiological↗
PubMed1999

Acclimation of the summer annual species, lolium temulentum, to CO(2) enrichment

Lolium temulentum L. Ba 3081 was grown hydroponically in air (350 &mgr;mol mol(-1) CO(2)) and elevated CO(2) (700 &mgr;mol mol(-1) CO(2)) at two irradiances (150 and 500 &mgr;mol m(-2) s(-1)) for 35 days at which point the plants were harvested. Elevated CO(2) did not modify relative growth rate or biomass at either irradiance. Foliar carbon-to-nitrogen ratios were decreased at elevated CO(2) and plants had a greater number of shorter tillers, particularly at the lower growth irradiance. Both light-limited and light-saturated rates of photosynthesis were stimulated. The amount of ribulose-1, 5-bisphosphate carboxylase-oxygenase (Rubisco) protein was increased at elevated CO(2), but maximum extractable Rubisco activities were not significantly increased. A pronounced decrease in the Rubisco activation state was found with CO(2) enrichment, particularly at the higher growth irradiance. Elevated-CO(2)-induced changes in leaf carbohydrate composition were small in comparison to those caused by changes in irradiance. No CO(2)-dependent effects on fructan biosynthesis were observed. Leaf respiration rates were increased by 68% in plants grown with CO(2) enrichment and low light. We conclude that high CO(2) will only result in increased biomass if total light input favourably increases the photosynthesis-to-respiration ratio. At low irradiances, biomass is more limited by increased rates of respiration than by CO(2)-induced enhancement of photosynthesis.

Journal Article↗
PubMed2002

Differential gene expression in the brain of channel catfish ( Ictalurus punctatus) in response to cold acclimation.

Aquatic ectotherms can adapt to a wide range of temperature changes, but the molecular mechanisms that underlie this adaptability are not well understood. We identified genes that are differentially expressed in the catfish ( Ictalurus punctatus) brain using a cDNA microarray approach to gain an initial understanding of adaptation to low temperature. Among 660 genes analyzed, 61 were differentially expressed when compared at 12 degrees C and 24 degrees C. Gene induction was rapid, occurring within 2 h of the temperature shift. The major categories of differentially expressed genes included (1) genes for chaperones such as Hsp70 and Hsp70/Hsp90 organizing protein; (2) genes for transcription factors and gene products involved in signal transduction pathways such as zinc-finger proteins, calmodulin kinase inhibitor, the nuclear autoantigen SG2NA, interferon regulatory factor 3, and inorganic pyrophosphatase; (3) genes involved in lipid metabolism such as TB2 and acyl CoA binding protein; and (4) genes involved in the translational machinery such as ribosomal proteins. Some genes were induced transiently, whereas others were induced in an enduring fashion. Several genes, primarily ribosomal protein genes, were down regulated, indicating reduced metabolic activities after extended incubation at the low temperature. Thus channel catfish respond to low temperature by adjusting expression of a large number of genes. The rapid induction of proteins involved in signal transductions and chaperones suggests that both de novo synthesis of cold-induced proteins and modification of existing proteins are required for adaptation and tolerance of catfish to low environmental temperature.

Acclimatization↗
PubMed1996

The effects of soft-water acclimation on gill structure in the rainbow trout Oncorhynchus mykiss.

Rainbow trout (Oncorhynchus mykiss) were exposed to ion-poor (soft) water to test the hypothesis that naturally induced proliferation of branchial chloride cells causes a thickening of the blood-to-water diffusion barrier. This was achieved by using a combination of scanning and transmission electron-microscopic techniques. Fish were exposed to soft-water conditions ([Na+]= 0.055 mmol l-1, [Cl-] approximately 0.029 mmol 1(-1), [Ca2+] approximately 0.059 mmol 1(-1), and [K+] approximately 0.007 mmol 1(-1)) for 1, 2, and 4 weeks. Marked chloride cell proliferation was evident at all sampling times with an approximate doubling of the gill epithelial surface area covered by chloride cells exposed to the water ("chloride cell fractional area"). The increases in chloride cell fractional area resulted from both increased numbers of cells and expanded apical surfaces of exposed individual cells. As a result of chloride cell proliferation, soft-water exposure was associated with a doubling of the lamellar blood-to-water diffusion distance from 3.26+/-0.08 microM to 6.58+/-0.43 microM as determined from transmission electron micrographs. These data demonstrated a positive correlation between chloride cell fractional area and blood-to-water diffusion distance. We conclude that, in trout, chloride cell proliferation during soft-water exposure, while presumably benefiting ionic regulation, may impair gas transfer owing to the associated thickening of the blood-to-water diffusion barrier.

Acclimatization↗
PubMed2005

Nutritional differences and leaf acclimation of climbing plants and the associated vegetation in different types of an Andean montane rainforest.

Climbing plants are known to play an important role in tropical forest systems, but key features for their distribution are only partly understood. Investigation was carried out to find if climbers differ from self-supporting vegetation in their adjustment of leaf parameters over a wide variety of light regimes in different forest types along an altitudinal gradient. Relative photon flux density (PFDrel) was assessed above 75 pairs of strictly linked climbers and supporting vegetation on seven plots between 2,020 and 2,700 m a.s.l. along a mountain range in South-Ecuador up to the Páramo vegetation. Leaf samples from both growth forms were analyzed for leaf area (LA), specific leaf mass (LMA), mass and area-based carbon and nitrogen concentration (C, Carea, N, and Narea) and concentrations of P, K, Ca, Mg, Mn and Al. Leaf size of climbers was independent of general light condition, whereas the leaf size of the self-supporting vegetation increased in shade. LMA increased as expected with altitude and irradiance for both growth forms, but climbers generally built smaller leaves with lower LMA. N, P, and K concentrations were higher in the leaves of climbers than in their supporters. Relationships of LMA and Narea to the light conditions were more pronounced within the climbers than within their supporters. Slope for the regression between climber's Narea and LMA was twice as steep as for the supporter leaves. Al accumulators were only found within the self-supporting vegetation. The investigated traits indicate improved adjustment towards light supply within climbers compared to self-supporting vegetation. Thus climbing plants seem to have a higher potential trade off in resource-use efficiency regarding irradiance and nutrients.

Peru↗
PubMed2004

Expression of alpha-expansin genes during root acclimations to O2 deficiency in Rumex palustris.

Thirteen alpha-expansin genes were isolated from Rumex palustris , adding to the six already documented for this species. Five alpha-expansin genes were selected for expression studies in various organs/tissues of R. palustris , with a focus on roots exposed to aerated or O2)-deficient conditions, using real-time RT-PCR. Several cases of differential expression of alpha-expansin genes in the various root types of R. palustris were documented, and the identity of the dominant transcript differed between root types (i.e., tap root vs. lateral roots vs. adventitious roots). Several genes were expressed differentially in response to low O2. In situ hybridizations showed expansin mRNA expression in the oldest region of the tap root was localized to cells near the vascular cambium; this being the first report of expansin expression associated with secondary growth in roots. In situ hybridization also showed abundant expression of expansin mRNA in the most apical 1 mm of adventitious roots. Such early expression of expansin mRNA in cells soon after being produced by the root apex presumably enables cell wall loosening in the elongation zone of roots. In addition, expression of some expansin mRNAs increased in 'mature zones' of roots; these expansins might be involved in root hair formation or in formation of lateral root primordia. The present findings support the notion that large gene families of alpha-expansins enable flexibility in expression for various organs and tissues as a normal part of plant development, as well as in response to abiotic stress.

Acclimatization↗
PubMed1984

Changes in thermal phase transition of various membranes during temperature acclimation in Tetrahymena.

Changes in the thermal phase transition temperature of membrane lipids were studied by X-ray wide-angle diffraction during adaptation of Tetrahymena pyriformis to a lower growth temperature. After a shift in growth temperature from 39 to 15 degrees C, the phase transition temperature was lowered gradually in microsomal and pellicular phospholipids, whereas that in mitochondrial phospholipids was unchanged for 10 h after the temperature shift. Only a small decrease in the transition temperature of mitochondrial phospholipids was observed, even after 24 h following the shift. Transition temperatures of microsomal, pellicular and mitochondrial phospholipids reached the growth temperature (15 degrees C) about 6, 10 and 24 h after the temperature shift. The temperature dependence of the solid phase in membrane phospholipids was estimated from the 4.2 A peak of the X-ray diffraction pattern. In the case of the phospholipids extracted from cells grown at 39 degrees C, the solid phase was increased upon lowering temperature in a similar manner in all three membrane fractions: mitochondria, pellicles and microsomes. However, in the case of the phospholipids from cells exposed to a lower growth temperature (15 degrees C) for 10 h, the increase in the solid phase was significantly smaller in mitochondrial phospholipids than in two other membrane fractions. The difference in the thermal behaviour of mitochondrial lipid from pellicular and microsomal lipids is discussed in terms of phase transition and phase separation.

Adaptation, Physiological↗