1000 resultados para Cross acclimation
Resumo:
人类活动产生的氯氟烃化合物破坏了大气臭氧层,导致了到达地球表面的UV-B辐射大幅度增加。UV-B辐射增强可以影响到植物的生长、形态与发育等各个方面,因此有关增强UV-B辐射对植物的影响,及其与许多环境因子复合作用的研究都已经广泛开展。但是增强UV-B辐射与温度,特别是与低温的相互作用的研究报道很少。在北半球的晚秋至早春这段时期里,一些越冬生长的植物将面临着UV-B辐射增强和低温的双重胁迫,因此,迫切需要进行UV-B辐射和低温生长环境下植物的响应及其机制的研究。 以人工气候生长室中生长的冬小麦(Triticum aestivum)幼苗为试验材料,研究了低剂量(4.2 kJ m-2 d-1 UV-BBE,LUVB)和较高剂量(7.0 kJ m-2 d-1 UV-BBE,HUVB)UV-B辐射处理对20/16℃条件下幼苗抗寒力的交叉适应性及其抗氧化系统的反应;同时还研究了在两种生长温度(25/20℃和10/5℃)条件下,低剂量(4.2 kJ m-2 d-1 UV-BBE,LUVB)和超高剂量(10.3 kJ m-2 d-1 UV-BBE,SHUVB)UV-B辐射处理幼苗的生长速率、光合与荧光参数、叶黄素循环色素、抗氧化系统、以及抗寒性和酚类物质等生理反应,以期阐明不同温度条件下生长的冬小麦对UV-B辐射的生长、光合作用以及抗寒性响应与适应机制。主要结果如下: 1.在LUVB辐射处理下,在20/16℃和25/20℃条件下生长的冬小麦幼苗LT50值都显著降低,HUVB辐射处理对在20/16℃条件下生长的幼苗LT50值也可以显著降低,而SHUVB辐射对25/20℃条件下生长的幼苗LT50值没有显著影响。但是,LUVB和SHUVB辐射处理都导致了10/5℃条件下生长的幼苗LT50值的显著增加。表明适当的UV-B辐射能增强较高温度(20/16℃或25/20℃)条件下冬小麦幼苗的抗寒力,即表现出对冷冻低温的交叉适应性,但低温(10/5℃)生长条件却削弱了UV-B辐射下冬小麦的抗寒能力。 2.在20/16℃条件下接受UV-B辐射预处理的幼苗在-6℃条件下冷冻胁迫6 h再缓慢恢复6 h后,与未进行UV-B辐射处理的对照相比,其叶片过氧化氢酶(CAT)、愈创木酚过氧化物酶(GPX)、谷胱甘肽还原酶(GR)活性,谷胱甘肽氧化还原比例(GSH/GSSG)都显著提高,而由硫代巴比妥酸反应物质(TBARS)代表的膜质过氧化程度显著低于对照。此外,UV-B辐射期间处理幼苗的H2O2含量较对照显著增加,而冷冻恢复以后却明显低于对照。表明UV-B辐射诱导的抗寒力的提高应该与冷冻恢复后植株体内抗氧化系统的上调表达有关,H2O2可能参与了UV-B辐射对低温的交叉适应的信号传导。 3.除25/20℃生长条件下的LUVB处理的小麦幼苗外,UV-B辐射显著降低幼苗的相对生长速率(RGR)、净光合速率(Pn)、光系统II最大量子产量(Fv/Fm)、光系统II实际量子产量((F΄m−Fs)/F΄m)以及光化学淬灭(qP),但是UV-B辐射并不影响叶片胞间CO2浓度(Ci),而且冬小麦幼苗生长和光合作用的抑制被增加的UV-B辐射剂量和降低的温度加强。UV-B辐射引起的光抑制由非气孔限制所导致,而且主要与PS II光化学效率降低有关。 4.UV-B辐射显著增加了两个温度条件(20/16℃或25/20℃)下生长的冬小麦幼苗叶黄素循环过程中紫黄素(V)的合成,但抑制了V向玉米黄质(Z)的转化,从而造成了对照与LUVB辐射处理幼苗之间的叶片中脱环氧化比例(DEPS)和NPQ无显著性差异,但SHUVB辐射处理幼苗叶片中DEPS和NPQ显著降低。因此,在本试验条件下,增强UV-B辐射处理的冬小麦可能并不通过热耗散形式形成光保护机制,光抑制形成的过剩激发能的耗散可能更多地通过代谢途径来实现。 5.UV-B辐射处理提高了在25/20℃条件下幼苗的超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)和GR等活性,以及抗坏血酸氧化还原比例(AsA/DHA)和GSH/GSSG;但是在10/5℃下,UV-B辐射除了导致SOD和CAT活性升高之外,对APX活性和AsA/DHA并不产生明显影响,但GPX和GSH/GSSG则显著降低。说明UV-B辐射幼苗的抗氧化系统在较高生长温度下显著地增强,而在低温10/5℃下被严重地削弱或降低,即低温阻止了代谢途径的光保护机制的正常运转。 6.多酚物质在UV-B辐射或低温10/5℃条件下都能显著地累积,且在UV-B辐射和低温复合作用下增加尤其显著,表明多酚物质在两个温度生长条件下特别是低温条件下都参与了对UV-B辐射幼苗的保护。 7.在高温条件下仅仅SHUVB处理的幼苗TBARS含量显著增加,而低温10/5℃条件下两个UV-B辐射处理都非常显著地上升,说明与高温生长条件相比较,低温加重了UV-B辐射引起的氧化胁迫,低温10/5℃条件下幼苗多酚的增加以及抗氧化系统的部分增强都没有能阻止UV-B辐射对幼苗的伤害。
Resumo:
The present study examines how different pCO2 acclimations affect the CO2- and light-dependence of photophysiological processes and O2 fluxes in four Southern Ocean (SO) key phytoplankton species. We grew Chaetoceros debilis (Cleve), Pseudo-nitzschia subcurvata (Hasle), Fragilariopsis kerguelensis (O'Meara) and Phaeocystis antarctica (Karsten) under low (160 µatm) and high (1000 ?atm) pCO2. The CO2- and light-dependence of fluorescence parameters of photosystem II (PSII) were determined by means of a fluorescence induction relaxation system (FIRe). In all tested species, nonphotochemical quenching (NPQ) is the primary photoprotection strategy in response to short-term exposure to high light or low CO2 concentrations. In C. debilis and P. subcurvata, PSII connectivity (p) and functional absorption cross-sections of PSII in ambient light (sigma PSII') also contributed to photoprotection while changes in re-oxidation times of Qa acceptor (tQa) were more significant in F. kerguelensis. The latter was also the only species being responsive to high acclimation pCO2, as these cells had enhanced relative electron transport rates (rETRs) and sigma PSII' while tQa and p were reduced under short-term exposure to high irradiance. Low CO2-acclimated cells of F. kerguelensis and all pCO2 acclimations of C. debilis and P. subcurvata showed dynamic photoinhibition with increasing irradiance. To test for the role and presence of the Mehler reaction in C. debilis and P. subcurvata, the light-dependence of O2 fluxes was estimated using membrane inlet mass spectrometry (MIMS). Our results show that the Mehler reaction is absent in both species under the tested conditions. We also observed that dark respiration was strongly reduced under high pCO2 in C. debilis while it remained unaltered in P. subcurvata. Our study revealed species-specific differences in the photophysiological responses to pCO2, both on the acclimation as well as the short-term level.
Resumo:
Males of the eastern mosquito fish (Gambusia holbrooki) possess one of the widest reproductively active temperature ranges for any ectotherm, ranging across seasons from at least 18degreesC to 34degreesC. In this study, we tested the ability of male G. holbrooki to acclimate their sustained swimming performance following long-term exposure to 18degreesC or 30degreesC. We also investigated some of the possible physiological mechanisms associated with thermal acclimation responses in swimming performance, including changes in slow muscle fibre size and abundance and the expression of myosin heavy chains (MyHC). We found that U-crit, of 18degreesC-acclimated G. holbrooki was 20% greater at 18degreesC than 30degreesC-acclimated fish, and the Ucrit of the 30degreesC-acclimated group was more than 15% greater at 30degreesC. Slow, fast and intermediate muscle fibres were identified on the basis of their myosin ATPase staining reaction. Although the number of slow and intermediate muscle fibres was similar between groups, the total cross-sectional area of aerobic fibre types was 40% greater in 18degrees-than 30degreesC-acclimated fish, reflecting an increase in the average fibre diameter. An S58 antibody raised against chicken slow skeletal muscle myosin stained a sub-set of the slow fibres identified by myosin ATPase staining. The number of S58-positive muscle fibres was 50% greater in 30degreesC-than 18degreesC-acclimated fish, implying that different MyHCs are being expressed in cold and warm acclimated individuals. Given the sexually coercive mating system of this species, increases in the sustained swimming performance via thermal acclimation may benefit the ability of males to maintain a high rate of sneaky copulations. (C) 2004 Elsevier Ltd. All rights reserved.
Resumo:
The information on climate variations is essential for the research of many subjects, such as the performance of buildings and agricultural production. However, recorded meteorological data are often incomplete. There may be a limited number of locations recorded, while the number of recorded climatic variables and the time intervals can also be inadequate. Therefore, the hourly data of key weather parameters as required by many building simulation programmes are typically not readily available. To overcome this gap in measured information, several empirical methods and weather data generators have been developed. They generally employ statistical analysis techniques to model the variations of individual climatic variables, while the possible interactions between different weather parameters are largely ignored. Based on a statistical analysis of 10 years historical hourly climatic data over all capital cities in Australia, this paper reports on the finding of strong correlations between several specific weather variables. It is found that there are strong linear correlations between the hourly variations of global solar irradiation (GSI) and dry bulb temperature (DBT), and between the hourly variations of DBT and relative humidity (RH). With an increase in GSI, DBT would generally increase, while the RH tends to decrease. However, no such a clear correlation can be found between the DBT and atmospheric pressure (P), and between the DBT and wind speed. These findings will be useful for the research and practice in building performance simulation.
Resumo:
Purpose: In the present study, we consider mechanical properties of phosphate glasses under high temperatureinduced and under friction-induced cross-linking, which enhance the modulus of elasticity. Design/methodology/approach: Two nanomechanical properties are evaluated, the first parameter is the modulus of elasticity (E) (or Young's modulus) and the second parameter is the hardness (H). Zinc meta-, pyro - and orthophosphates were recognized as amorphous-colloidal nanoparticles were synthesized under laboratory conditions and showed antiwear properties in engine oil. Findings: Young's modulus of the phosphate glasses formed under high temperature was in the 60-89 GPa range. For phosphate tribofilm formed under friction hardness and the Young's modulus were in the range of 2-10 GPa and 40-215 GPa, respectively. The degree of cross-linking during friction is provided by internal pressure of about 600 MPa and temperature close to 1000°C enhancing mechanical properties by factor of 3 (see Fig 1). Research limitations/implications: The addition of iron or aluminum ions to phosphate glasses under high temperature - and friction-induced amorphization of zinc metaphosphate and pyrophosphate tends to provide more cross-linking and mechanically stronger structures. Iron and aluminum (FeO4 or AlO4 units), incorporated into phosphate structure as network formers, contribute to the anion network bonding by converting the P=O bonds into bridging oxygen. Future work should consider on development of new of materials prepared by solgel processes, eg., zinc (II)-silicic acid. Originality/value: This paper analyses the friction pressure-induced and temperature–induced the two factors lead phosphate tribofilm glasses to chemically advanced glass structures, which may enhance the wear inhibition. Adding the coordinating ions alters the pressure at which cross-linking occurs and increases the antiwear properties of the surface material significantly.