Moderate heat stress reduces the pH component of the transthylakoid proton motive force in light-adapted, intact tobacco leaves

We measured the Δ Ψ and ΔpH components of the transthylakoid proton motive force ( pmf ) in light-adapted, intact tobacco leaves in response to moderate heat. The Δ Ψ causes an electrochromic shift (ECS) in carotenoid absorbance spectra. The light–dark difference spectrum has a peak at 518 nm and the two components of the pmf were separated by following the ECS for 25 s after turning the light off. The ECS signal was deconvoluted by subtracting the effects of zeaxanthin formation (peak at 505 nm) and the qE-related absorbance changes (peak at 535 nm) from a signal measured at 520 nm. Heat reduced ΔpH while Δ Ψ slightly increased. Elevated temperature accelerated ECS decay kinetics likely reflecting heat-induced increases in proton conductance and ion movement. Energy-dependent quenching (qE) was reduced by heat. However, the reduction of qE was less than expected given the loss of ΔpH. Zeaxanthin did not increase with heat in light-adapted leaves but it was higher than would be predicted given the reduced ΔpH found at high temperature. The results indicate that moderate heat stress can have very large effects on thylakoid reactions.     

Photosynthetic electron transport and proton flux under moderate heat stress

Moderate heat stress has been reported to increase PSI cyclic electron flow (CEF). We subjected leaves of Arabidopsis (Arabidopsis thaliana) mutants disrupted in the regulation of one or the other pathway of CEF flow—crr2 (chlororespiratory reduction, deficient in regulation of chloroplast NAD(P)H dehydrogenase-dependent CEF) and pgr5 (proton gradient regulation, proposed to have reduced efficiency of antimycin-A-sensitive-CEF regulation) to moderate heat stress. Light-adapted leaves were switched from 23 to 40°C in 2 min. Gas exchange, chlorophyll fluorescence, the electrochromic shift (ECS), and P700 were measured. Photosynthesis of crr2 and pgr5 was more sensitive to heat and had less ability to recover than the genetic background gl. The proton conductance in light was increased by heat and it was twice as much in pgr5, which had much smaller light-induced proton motive force. We confirmed that P700 becomes more reduced at high temperature and show that, in contrast, the proportion of PSII open centers (with Q _A oxidized) increases. The two mutants had much slower P700⁺ reduction rate during and after heat than gl. The proportion of light absorbed by PSI versus PSII was increased in gl and crr2 during and after heat treatment, but not in pgr5. We propose that heat alters the redox balance away from PSII and toward PSI and that the regulation of CEF helps photosynthesis tolerate heat stress.     

Characterization of a sHsp of Schizosaccharomyces pombe, SpHsp15.8, and the implication of its functional mechanism by comparison with another sHsp, SpHsp16.0

There exist two small heat shock proteins (sHsps) in the fission yeast, Schizosaccharomyces pombe (S. pombe), whose expressions are highly induced by heat stress. We have previously expressed, purified, and characterized one of the sHsps, SpHsp16.0. In this study, we examined the other sHsp, SpHsp15.8. It suppressed the thermal aggregation of citrate synthase (CS) from porcine heart and dithiothreitol-induced aggregation of insulin from bovine pancreas with very high efficiency. Almost one SpHsp15.8 subunit was sufficient to protect one protein molecule from aggregation. Like SpHsp16.0, SpHsp15.8 dissociated into small oligomers and then interacted with denatured substrate proteins. SpHsp16.0 exhibited a clear enthalpy change for denaturation occurring over 60 degrees C in differential scanning calorimetry (DSC). However, we could not observe any significant enthalpy change in the DSC of SpHsp15.8. The difference is likely to be caused by the adhesive characteristics of SpHsp15.8. The oligomer dissociation of SpHsp15.8 and SpHsp16.0 and their interactions with denatured substrate proteins were studied by fluorescence polarization analysis (FPA). Both sHsps exhibited a temperature-dependent decrease of fluorescence polarization, which correlates with the dissociation of large oligomers to small oligomers. The dissociation of the SpHsp15.8 oligomer began at about 35 degrees C and proceeded gradually. On the contrary, the SpHsp16.0 oligomer was stable up to approximately 45 degrees C, but then dissociated into small oligomers abruptly at this temperature. Interestingly, SpHsp16.0 is likely to interact with denatured CS in the dissociated state, while SpHsp15.8 is likely to interact with CS in a large complex. These results suggest that S. pombe utilizes two sHsps that function in different manners, probably to cope with a wide range of temperatures and various denatured proteins.     

Comparison of life-history characteristics of island and mainland populations of the swamp antechinus

The reproductive ecology of the swamp antechinus Antechinus minimus , a small dasyurid (Dasyuridae) marsupial with obligate male semelparity, was investigated in populations inhabiting the mainland coast and on a nearby offshore island in south-eastern Australia. The size and sex ratios of litters, individual body mass and size, timing of births and female longevity were determined from live-trapped animals. The island population had significantly smaller litter sizes and greater adult body mass in comparison with the mainland population. This is consistent with features of the 'island syndrome', which predicts directional selection for these traits in high-density populations with reduced extrinsic mortality. However, inter-annual variability in litter sizes in the island population suggests that litter size is more responsive to fluctuating local conditions, such as population density, which is likely to affect food availability, rather than directional genetic changes. In contrast with other antechinus species, biased sex ratios were not evident. In addition, large variations of the timing of births were estimated at both sites and these appear to be related to seasonal conditions such as autumn rainfall and female body mass before mating.     

1956—1998年间中纬度近海与内陆城市年气温与热岛效应的变化趋势

选取纬度相近、发展规模类似的近海（济南）与内陆（西安）城市为研究对象,对比分析了1956—1998年间济南和西安气温与热岛效应的变化趋势.结果表明：1956—1978年间,除济南年均最低气温以0.37 ℃·10 a^-1的速率上升外,2个城市的气温指标均无明显变化趋势;1979—1998年间,2个城市则表现出显著的增温趋势,其中西安年均最高气温和年均气温的增加速率大于济南,济南年均最低气温的增加速率大于西安.1956—1978年间,2个城市均存在城市热岛效应但无显著增加趋势,1979—1998年间的热岛效应明显强化,以西安在年均气温（0.22 ℃·10 a^-1）和年均最低气温（0.32 ℃·10 a^-1）上表现的热岛效应的增加趋势更为明显.济南热岛效应强度和年际波动均大于西安,但其增加速率却小于西安.济南年均最高气温、年均气温和年均最低气温的增温速率和热岛效应强度明显不同,西安则较接近.3个气温指标中以年均最低气温的增加趋势最明显,同时对热岛效应的响应最显著,年均最高气温的波动性最大.地理位置不但影响城市增温的幅度,而且也深刻影响着城市增温的形式与热岛效应强度.     

Comparison of cold tolerance in eggs of two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata, in relation to climate warming

The population of the cicada Cryptotympana facialis began to increase in Osaka, Japan, during the late 20th century. Climate warming is considered a major cause, although the relationship between temperature and the cicada population increase remains unclear. By examining cold tolerance in overwintering eggs of C. facialis in relation to another cicada, Graptopsaltria nigrofuscata , whose population has recently decreased in Osaka, we tested the hypothesis that warming has caused the population increase of C. facialis by decreasing egg mortality due to winter temperatures. A short-term (24 h) cold exposure experiment demonstrated that the half-lethal temperatures (LT50) of C. facialis and G. nigrofuscata were −23.3°C and −28.9°C, respectively, although these extreme low temperatures never occurred in Osaka during the 20th century. Prolonged exposure to −5°C for up to 30 days had no harmful effects on the hatching rate in either species. Overwintering mortality was also assessed under naturally fluctuating conditions by transferring eggs to cooler elevated sites that mimicked the environment prior to the current warming. Eggs of C. facialis that overwintered at the cooler site exhibited similar hatching rates to those maintained at the original site. The results of these experiments consistently indicated that overwintering eggs of C. facialis possess adequate tolerance to the low temperatures of the 20th century. Therefore, we rejected our initial hypothesis that recent increases in the C. facialis population have been caused by warming-related reductions in overwintering egg mortality.     

The prehistory and biogeography of terrestrial vertebrates on Guam, Mariana Islands

Aim By establishing a prehistoric fossil record for the vertebrate fauna of Guam, we can document the composition of the island’s fauna prior to Western contact. It will also complement the extensive prehistoric fossil data already known from the nearby islands of Rota, Tinian and Aguiguan, and improve our understanding of natural distributional patterns through a chronologically deeper view of the biogeography of the Mariana Islands. Location Northern Guam, Mariana Islands, Micronesia. Methods Fossil‐bearing sediment was removed from karst features with vertically and horizontally controlled excavation methods. Age determinations of the fossils were estimated by radiocarbon dating associated wood charcoal samples. Results The 3314 bones (fossils) of terrestrial vertebrates date to the past two millennia and represent 34 species. Among 12 species of squamate reptiles, one is extinct (a gekkonid lizard) and another, the monitor lizard, Varanus indicus, was introduced to Guam no later than about 1600 years ago. The 17 species of birds feature five that are extinct. Two others not recorded previously on Guam are extirpated. Eight others were lost on Guam in historic times. We also recovered bones of two species of indigenous bats, (Pteropus sp., extirpated; Emballonura semicaudata, probably extirpated), and non‐native rodents, (Rattus spp.). Main conclusions Guam’s contemporary faunal losses have been well documented since invasion of the Brown Treesnake (Boiga irregularis) during or shortly after WWII. Other exotics, as well as habitat deterioration, have abetted this snake’s deleterious presence. Our data further show that human impact led to declines or losses of vertebrate populations by late prehistoric times. Numerous anthropogenic extirpations would not be evident without studying fossils. Our chrono‐stratigraphic evidence argues for the arrival of non‐native rats (Rattus sp.) only about 1000 years ago, which helps to explain why a flightless rail survived on Guam into modern times, unlike on most other islands in Oceania.     

Population genetic structure of rock ptarmigan in the 'sky islands' of French Pyrenees: implications for conservation

Expected consequences of global warming include habitat reduction in many cool climate species. Rock ptarmigan is a Holarctic grouse that inhabits arctic and alpine tundra. In Europe, the Pyrenean ptarmigan inhabits the southern edge of the species' range and since the last glacial maximum its habitat has been severely fragmented and is restricted to high-alpine zones or 'sky islands'. A recent study of rock ptarmigan population genetic in Europe found that the Pyrenean ptarmigan had very low genetic diversity compared with that found in the Alps and Scandinavia. Habitat fragmentation and reduced genetic diversity raises concerns about the viability of ptarmigan populations in the Pyrenees. However, information on population structuring and gene flow across the Pyrenees, which is essential for designing a sound management plan, is absent. In this study, we use seven microsatellites and mitochondrial control region sequences to investigate genetic variation and differentiation among five localities across the Pyrenees. Our analyses reveal the presence of genetic differentiation among all five localities and a significant isolation-by-distance effect that is likely the result of short dispersal distances and high natal and breeding philopatry of Pyrenean ptarmigan coupled with severe habitat fragmentation. Furthermore, analysis of molecular variance, principal component analysis and Bayesian analysis of genetic structuring identified the greatest amount of differentiation between the eastern and main parts of the Pyrenean chain separated by the Sègre Valley. Our data also show that the Canigou massif may host an isolated population and requires special conservation attention. We propose a management plan which includes the translocation of birds. If a sky island structure affects genetic divergence in rock ptarmigan, it may also affect the genetic structure of other sky island species having low dispersal abilities.