白纹伊蚊幼虫龄期的发育历期

在实验室内20±1℃, 23±1℃, 25±1℃, 28±1℃和30±1℃恒温条件下, 观察了白纹伊蚊(Aedes albopictus)幼虫(广州株)的发育历期.幼虫的总发育历期和各龄幼虫的发育历期随温度的上升而缩短, 各龄幼虫历期在总发育历期中占有恒定的百分比, 据此计算出其捕获机率.各龄幼虫的发育历期与温度呈直线回归关系.通过积温公式, 求出各龄幼虫的积温常数.此外还探索了营养对幼虫发育历期的影响, 从而影响各龄幼虫捕获机率的计算.     

Low temperature delays development of photosystem II activity in winter rye leaves

The ability of leaves to acclimate photosynthetically to low temperature was examined during leaf development in winter rye plants ( Secale cereale L. cv. Puma) grown at 20°C or at 6°C. All leaves grown at 6°C exhibit increased chlorophyll (Chl) levels per leaf area, higher rates of uncoupled, light-saturated photosystem I (PSI) electron transport, and slower increases in photosystem II (PSII) electron transport capacity, when compared with 20°C leaves. The stoiehiometry of PSI and PSII was estimated for each leaf age class by quantifying Chl in elcctrophorctic separations of Chl-protein complexes. The ratio of PSII/PSI electron transport in 20°C leaves is highly correlated with the ratio of core Chl a -proteins associated with PSII (CPa) to those associated with PSI (CP1). In contrast, PSII/PSI electron transport in 6°C leaves is not as well correlated with CPa/CP1 and is related, in part, to the amount and organization of light-harvesting Chl a/b -proteins associated with PSII. CPa/CP1 increases slowly in 6°C leaves, although the ratio of CPa/CP1 in mature 20°C and 6°C leaves is not different. The results suggest that increased PSI activity at low temperature is not related to an increase in the relative proportion of PSI and may reflect, instead, a regulatory change. Photosynthetic acclimation to low environmental temperature involves increased PSI activity in mature leaves shifted to 6°C. In leaves grown entirely at 6°C, however, acclimation includes both increased PSI activity and modifications in the rate of accumlation of PSII and in the organization of LHCII.     

Photoinhibition at chilling temperature

The effects of moderate light at chilling temperature on the photosynthesis of unhardened (acclimated to +18° C) and hardened (cold-acclimated) spinach (Spinacea oleracea L.) leaves were studied by means of fluorescence-induction measurements at 20° C and 77K and by determination of quantum yield of O₂ evolution. Exposure to 550 mol photons·m^-2·s^-1 at +4° C induced a strong photoinhibition in the unhardened leaves within a few hours. Photoinhibition manifested by a decline in quantum yield was characterized by an increase in initial fluorescence (F _o) and a decrease in variable fluorescence (F _v) and in the ratio of variable to maximum fluorescence (F _V/F _M), both at 77K and 20° C. The decline in quantum yield was more closely related to the decrease in the F _V/F _M ratio measured at 20° C, as compared with F _V/F _M at 77K. Quenching of the variable fluorescence of photosystem II was accompanied by a decline in photosystem-I fluorescence at 77K, indicating increased thermal de-excitation of pigments as the main consequence of the light treatment. All these changes detected in fluorescence parameters as well as in the quantum yield of O₂ evolution were fully reversible within 1–3 h at a higher temperature in low light. The fast recovery led us to the view that this photoinhibition represents a regulatory mechanism protecting the photosynthetic apparatus from the adverse effects of excess light by increasing thermal energy dissipation. Long-term cold acclimation probably enforces other protective mechanisms, as the hardened leaves were insensitive to the same light treatment that induced strong inhibition of photosynthesis in unhardened leaves.Abbreviations F ₀ initial fluorescence - F _M maximum fluorescence - F _V variable fluorescence (F _M-F ₀ - PFD photon flux density - PS photosystem     

Conformational change of bovine serum albumin by heat treatment

The thermal denaturation of bovine serum albumin (BSA) was studied at pH 2.8 and 7.0 in the range of 2–65°C. The relative proportions of -helix, -structure, and disordered structure in the protein conformation were determined as a function of temperature, by the curve-fitting method of circular dichroism spectra. With the rise of temperature at pH 7.0, the proportion of -helix decreased above 30°C and those of -structure and disordered structure increased in the same temperature range. The structural change was reversible in the temperature range below 45°C. However, the structural change was partially reversible upon cooling to room temperature subsequent to heating at 65°C. On the other hand, the structural change of BSA at pH 2.3 was completely reversible in the temperature range of 2–65°C, probably because the interactions between domains and between subdomains might disappear due to the acid expansion. The secondary structure of disulfide bridges-cleaved BSA remained unchanged during the heat treatment up to 65°C at pH 2.8 and 7.0.     

State transitions,photosystem stoichiometry adjustment and non-photochemical quenching in cyanobacterial cells acclimated to light absorbed by photosystem I or photosystem II

Cells of the cyanobacterium Synechococcus 6301 were grown in yellow light absorbed primarily by the phycobilisome (PBS) light-harvesting antenna of photosystem II (PS II), and in red light absorbed primarily by chlorophyll and, therefore, by photosystem I (PS I). Chromatic acclimation of the cells produced a higher phycocyanin/chlorophyll ratio and higher PBS-PS II/PS I ratio in cells grown under PS I-light. State 1-state 2 transitions were demonstrated as changes in the yield of chlorophyll fluorescence in both cell types. The amplitude of state transitions was substantially lower in the PS II-light grown cells, suggesting a specific attenuation of fluorescence yield by a superimposed non-photochemical quenching of excitation. 77 K fluorescence emission spectra of each cell type in state 1 and in state 2 suggested that state transitions regulate excitation energy transfer from the phycobilisome antenna to the reaction centre of PS II and are distinct from photosystem stoichiometry adjustments. The kinetics of photosystem stoichiometry adjustment and the kinetics of the appearance of the non-photochemical quenching process were measured upon switching PS I-light grown cells to PS II-light, and vice versa. Photosystem stoichiometry adjustment was complete within about 48 h, while the non-photochemical quenching occurred within about 25 h. It is proposed that there are at least three distinct phenomena exerting specific effects on the rate of light absorption and light utilization by the two photoreactions: state transitions; photosystem stoichiometry adjustment; and non-photochemical excitation quenching. The relationship between these three distinct processes is discussed.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F relative fluorescence intensity at emission wavelength nm - F _o fluorescence intensity when all PS II traps are open - light 1 light absorbed preferentially by PS I - light 2 light absorbed preferentially by PS II - PBS phycobilisome - PS photosystem     

Effects of cooling water discharge on the structure and dynamics of epilithic algal communities in the northern Baltic

The Forsmark Biotest Basin is a shallow coastal ecosystem that receives brackish cooling-water discharge from a nuclear power plant. The effects of the discharge on epilithic algal communities were investigated by analysing samples taken every third week throughout one year at 11 sites differentially affected by temperature and/or flow rate enhancement. Community variation was summarized in a canonical correspondence analysis (CCA) of species abundances as a function of site and date. The temperature increase favoured blue-green algae at the expense of red and brown algae. Blue-green algae were however abundant in summer in stagnant water, whether heated or not, and some red and brown algae became abundant in winter in heated sites with flowing water. Green algae and diatoms increased in biomass in the heated sites, but not in relative cover-abundance. The absence of ice and snow cover at sites with heated and/or flowing water caused autumn species to persist into winter, because of the higher light intensity (compared with natural conditions) and the absence of the mechanical abrasion by ice. The thermal discharge lowered species diversity (Shannon-Weaver index) both in summer and winter at sites with flowing water, but not at sites with quiescent or stagnant water. CCA showed alternate periods of stability and rapid change within the seasonal cycle. Individual species were placed according to their optimum; red and brown algae in winter/spring, green algae in spring/summer, blue-green algae in summer, and diatoms at various times. Exceptions to this pattern were species endo- or epiphytic on species of a different group. Analysis of the effects of temperature, flow rate and ice cover on the seasonal pattern of particular species showed that different species respond in individualistic ways to different combinations of these environmental variables.     

Substitution of a proline for alanine 183 in the hinge region of phosphoglycerate kinase: Effects on catalysis, activation by sulfate, and thermal stability

A hinge-bending domain movement has been postulated as an important part of the catalytic mechanism of phosphoglycerate kinase (PGK) (Bankset al., 1979). In order to test the role of the flexibility of a putative interdomain hinge in the substrate- and sulfate-induced conformational transitions, alanine-183 was replaced by proline using site-directed mutagenesis. The maximal velocity of the Ala 183Pro mutant, measured at saturating concentrations of ATP and phosphoglycerate (5 mM and 10 mM, respectively) and in the absence of sulfate ions, is increased approximately 21% in comparison to the wild type PGK. TheK _m values for both substrates are essentially unchanged. The effect of sulfate on the specific activity of the Ala 183Pro mutant and the wild type PGK was measured in the presence of 1 mM ATP and 2 mM 3-phosphoglycerate (3-PG). A maximum activation of 70% was observed at 20 mM sulfate for the mutant enzyme, as compared to 130% activation at 30 mM sulfate for the wild type PGK. These results demonstrate that the increased rigidity of the putative hinge, introduced by the AlaPro mutation, does not impair catalytic efficiency of phosphoglycerate kinase, while it appears to decrease the sulfate-dependent activation. The differential scanning calorimetry (DSC) studies demonstrate an increased susceptibility of the Ala 183 Pro mutant to thermal denaturation. In contrast to one asymmetric transition observed in the DSC scan for the wild type PGK, withT _m near 54°C, two transitions are evident for the mutant enzyme withT _m values of about 45 and 54°C. Using a thermodynamic model for two interacting domains, a decrease in the free energy of domain-domain interactions of about 2 kcal was estimated from the DSC data.     

Thermoregulatory adjustments during continuous heat exposure

Body temperature regulation was studied in 6 male subjects during an acclimation procedure involving uninterrupted heat exposure for 5 successive days and nights in a hot dry environment (ambient temperature = 35 degrees C, dew-point temperature = 7 degrees C; air velocity = 0.2 m.s-1). Data were obtained at rest and during exercise (relative mechanical workload = 35% VO2max). At rest, hourly measurements were made of oesophageal and 4 local skin temperatures, to allow the calculation of mean skin temperature, and of body motility and heart rate. During the working periods these measurements were made at 5 min intervals. Hourly whole-body weight loss was measured at rest on a sensitive platform scale while in the working condition just before starting and immediately after completing the bicycle exercise. The results show that, in both exercise and at rest, the successive heat exposures increased the sweat gland output during the first 3 days. Afterwards, sweat rate decreased without any corresponding change in body temperature. For the fixed workload, the sweat rate decline was associated with a decrease in circulatory strain. Adjustments in both sweating and circulatory mechanisms occur in the first 3 days of continuous heat exposure. The overall sweat rate decline could involve a redistribution of the regional sweating rates which enhances the sweat gland activities of skin areas with maximal evaporative efficiencies.     

Low temperature mortality of the peach-potato aphid Myzus persicae

ABSTRACT.

• 1 The mean supercooling points of first instar and adult Myzus persicae (Sulzer) maintained at 20°C and cooled at 1°C min^?1 were ?26.6 and ?25.0°C respectively.
• 2 The LT₅₀ (temperature) of the same age groups drawn from the same population and cooled at the same rate were ?8.1 and ?6.9°C, indicating extensive pre-freeze mortality in M.persicae under laboratory conditions.
• 3 Acclimation at 10 and 5°C did not affect supercooling but depressed the LT₅₀ of both first instars and adult aphids.
• 4 Freezing of leaves during feeding did not increase mortality above that expected from the direct effects of low temperature.
• 5 The level of cold in different winters can be expressed in terms of the total number of frost days, and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above.
• 6 The time of the first record of M.persicae in suction trap samples is correlated with January and February temperatures except in the west of England and Wales. Further north December and January temperatures are relatively more important.
• 7 Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration.