青海高原主要C3植物的光合作用

青海高原主要 C_3植物叶片的净光合速率(Pn)日变化是随着自然条件下的日照和气温的变化而变化,呈典型的单峰曲线,无或有轻微的中午降低现象。表观量子需要量(AQR)在晴天的上午和下午基本不变,一天中不曾出现显著的光抑制现象。然而,在土壤严重缺水和气温超过30℃以上时,青海高原主要 C_3植物净光合速率的日变化仍呈双峰曲线。在一般情况下,青海高原主要 C_3植物的光补偿点和暗呼吸速率较低。光饱和点和表观量子需要量较高。因而,表观光合量子效率(_i=1/AQR)较低,这与青藏高原高海拔地区的低气压有关。     

Comparative Studies on Relation of Photosynthesis to Water Status of Two Species of Haloxylon Under Controlled Environments

The net photosynthetic rate,transpiration rate and water content of assimilating shoots of Haloscyion ammodendron and H. persicum were measured under different radiation intensities, temperatures changes and different water status. Their water potential under different water status was also measured. The experimental results showed. (1) The dependence of photosynthetic rate and transpiration rate on radiation intensit in the two species of Haloscylon. The increase of net photosynthetic rate and transpiration rate of H. arnrnodendron depending on radiation intensity was lower than that of H. persicurn. Two species of Haloxylon also maintained high transpiration rate under dark. (2) The average transpiration rate of H. persicurn was lower than H. arnrnodendron,showing that H. persicurn utilized water more efficiently than H. arnrnodendron. (3)The optimal temperature of photosynthesis of H. arnrnodendron was 24–32℃ and the optimal temperature of water utilization of H. arnrnodendron was 23. 5–25℃. (4) The water potential of H. amrnodendron was lower than –3.5 MPa whereas that of H. persicum was lower than –2.8MPa indicating that the two species of Haloscylon were under severe water stress ,and would lead to permanent wilting of their assimilating shoots.     

内蒙古中部中新世小哺乳动物群及其时代顺序

报道了内蒙古中部地区几个中新世小哺乳动物化石地点──嘎顺音阿得格、阿木乌苏、查干诺尔、沙拉等的新发现。探索了这些动物群体之间以及它们与经典的中中新世通古尔动物群和最晚中新世二登图动物群之间的关系。初步研究表明,嘎顺音阿得格动物群的时代更可能为早中新世,过去认为有属于晚渐新世的可能性不大。动物群的组成分析说明,中新世时内蒙古中部的生态环境具有浓厚的现代古北区的色彩。     

Net radiation balance for two forested slopes on opposite sides of a valley

Measurements of the net radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming radiation was adjusted according to the slopes angle to convert horizontally measured radiation data into surface-parallel radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal radiation fluxes were available, the calculation of surface-parallel radiation fluxes from the horizontally recorded net radiation components were compared with measured values. The net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the net radiation balance. In June, when the elevation of the sun is highest, incoming solar radiation K received on the NE-slope was 9% lower than K received on the SW-slope. During the winter months, the differences were much greater and incoming solar radiation to the NE-slope was 50% of that to the SW-slope. Due to the differing solar irradiance, net radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the net radiation balance between the slopes are important for the vegetation.     

The structure and function of oxidized albumin in hemodialysis patients: Its role in elevated oxidative stress via neutrophil burst

Oxidized albumin is a reliable marker of oxidative stress in hemodialysis (HD) patients. However, oxidized albumin in vivo and its possible clinical significance has been rarely investigated. In the present study, the qualitative modification of albumin in HD patients (n = 20) was examined and their results were compared with healthy age-matched controls (n = 10). The increase in plasma protein carbonyl levels in HD patients was largely due to an increase in oxidized albumin. Human serum albumin (HSA) of HD patients, HSA of HD patients (HD-HSA) and normal subjects (Normal-HSA) were purified on a blue Sepharose CL-6B column. Spectroscopic analysis confirmed that the HD-HSA samples contained higher levels of carbonyls than Normal-HSA. An HPLC analysis also suggested that the state of the purified HSA used throughout the experiments accurately reflects the redox state of albumin in blood. HD-HSA was found to have a decreased the antioxidant activity, and was able to trigger the oxidative burst of human neutrophils, compared to Normal-HSA. HD-HSA was conformationally altered, with its hydrophobic regions more exposed and to have a negative charge. In binding experiments, HD-HSA showed impaired Site II-ligand binding capabilities. Collectively, the oxidation of plasma proteins, especially HSA, might enhance oxidative stress in HD patients.     

Effects of photon flux density on the morphology,photosynthesis and growth of a CAM orchid, <Emphasis Type="Italic">Doritaenopsis</Emphasis> during post-micropropagation acclimatization

Micropropagated plantlets are fragile and often lack sufficient vigour to survive the acclimatization shock during transplantation to the soil. Effects of photosynthetic photon flux densities (PPFDs) on growth, photosynthesis and anatomy of micropropagated Doritaenopsis were studied after 4 months of acclimatization in a greenhouse at 25 °C. The plantlets were transferred to three different PPFDs for four months, i.e. low light (175), intermediate light (270) and high light (450 mol m^–2 s^–1). For most of the growth parameters measured i.e. leaf length, leaf area, leaf width, fresh weight, dry weight, chlorophyll (Chl) a/b ratio, were greater for the intermediate light levels after 4 months of acclimatization. The only exception was leaf thickness, which was increased more under high light levels. Results showed that the survival of Doritaenopsis plantlets was greatest (90%) in low light and intermediate light (89%) compared with only (73%) at high light. However, at low light levels, pigment concentrations (chlorophyll a, b and total chlorophyll) were higher. Net CO₂ assimilation (A), stomatal conductance (g) and transpiration (E) were higher in plantlets grown at high level PPFD than at low after 4 months of acclimatization. Photosynthetic efficiency (Fv/Fm) decreased insignificantly; only at mid day for the high light treatment whereas leaf temperature and stomatal closure increased compared to low light. Scanning electron microscopic (SEM) images of leaves from acclimatized plantlets showed an increase in wax formation for the high light grown plantlets compared to those at low light. Microscopic analysis of acclimatized root sections showed highly developed multiseriate-velamen layers and higher root cell activity; while shoots had larger leaf air spaces than those of in vitro grown plantlets. These results suggest that physiological acclimation occurs at the intermediate PPFD (270 mol m^–2 s^–1) in Doritaenopsis compared to treatment at the high light level.     

Influences of chronic and current season grazing by collared pikas on above-ground biomass and species richness in subarctic alpine meadows

We studied an alpine herbivory gradient established by collared pikas, a small central place foraging lagomorph, to examine the effects of multiple grazing levels on above-ground live biomass (AGB) and species richness (SR) in alpine tundra. The effects of within-season (four sampling periods), multi-season (across three summers) and longer-term dynamics (inferred from spatial location of vegetation with respect to pika haypiles) were examined. Along the grazing gradient, we found support for and against hypotheses that propose biphasic, increasing, or decreasing responses to herbivory, both in terms of AGB and SR. Our results suggest that plant–herbivore predictability is still weak. To further examine the impact of herbivory, we experimentally removed pikas using mesh exclosures placed at increasing distance from the edge of talus occupied by pikas. AGB after the second consecutive year of herbivore exclusion increased by 125% compared to control plots in highly grazed areas adjacent to talus (<1 m). In more lightly grazed sites at distances 1–6 m from talus, AGB increased by more than 40% after pikas were removed. No differences were observed in the ungrazed sites >6 m from talus. AGB was highest in meadow patches previously grazed by pikas compared to those with little grazing history, but this response was only observed after two seasons following release from herbivory. Grazed sites at distances of 1–6 m had the highest SR. These results indicate that multi-year measurements of growth are particularly relevant in ecosystems dominated by long-lived perennials in regions where productivity is low. Infrequent herbivore vacancies may provide local short-term release from pika grazing, thereby contributing to the persistence of productive, highly palatable vegetation.     

What determines interspecific variation in relative growth rate of <Emphasis Type="Italic">Eucalyptus</Emphasis> seedlings?

The present study examines relative growth rate (RGR) and its determinants in seedlings of nine Eucalyptus species. Species were selected from mesic (1,800 mm a⁻¹ rainfall) through to semi-arid habitats (300 mm a⁻¹), and thus, notionally vary in “stress” tolerance. Seedlings were grown in a glasshouse during early summer and received between 33 mol and 41 mol PAR m⁻² day⁻¹ . The mean RGR varied among species—from a minimum of 66 mg g⁻¹ day⁻¹ in E. hypochlamydea to a maximum of 106 mg g⁻¹ day⁻¹ in E. delegatensis. RGR was positively related to rainfall at the sites of seed collection. Neither specific leaf area (SLA) nor net assimilation rate was related to rainfall or RGR. While the absence of relationships with SLA and net assimilation rate contrasts with other studies and species, we cannot rule out the effects of sample size (n=9 species) and modest ranges in SLA and RGR. The ratio of leaf mass to total mass (LMR) varied from 0.49±0.07 g g⁻¹ in E. socialis to 0.74±0.04 g g⁻¹ in E. delegatensis and was strongly positively related with rainfall (r ²=0.77). Interspecific differences in RGR were strongly related to LMR (positive relationship, r ²=0.50) and the rate of dry matter production per mol of leaf nitrogen (positive relationship, r ²=0.64). Hence, the slow RGR of low-rainfall species was functionally related to a lower growth rate per mol of leaf nitrogen than high-rainfall species. Furthermore, slow RGR of low-rainfall species was related to greater allocation to roots at the expense of leaves. Increasing allocation to roots versus leaves is likely an adaptation to soil and atmospheric water deficits, but one that comes at the expense of a slow RGR.     

Budding yeast Cdc5 phosphorylates Net1 and assists Cdc14 release from the nucleolus

Lysophosphatidic acid (LPA) has been shown to be a potent mitogen for vascular smooth muscle cells. Src-dependent transactivation of receptor tyrosine kinases has been previously demonstrated to mediate LPA-induced activation of MAP kinase ERK1/2. Furthermore, generation of reactive oxygen species (ROS) by LPA is also known to contribute to MAP kinase activation. Rho family small G-proteins Rac and Cdc42, and their immediate downstream effector p21-activated kinase (PAK), have been demonstrated to mediate important effects on the cytoskeleton that are relevant for cell migration and proliferation. In the present report we evaluated stimulation of PAK by LPA in rat aortic vascular smooth muscle cells (VSMC) by PAK immunocomplex MBP in-gel kinase assay. LPA increased PAK activity 3-fold, peaking at 5 min and showing sustained activation up to 45 min. Inhibition of tyrosine kinases by pretreatment of VSMC with genistein or specific inhibition of Src by PP1 greatly diminished LPA-induced PAK activation, whereas specific inhibition of PDFG- and EGF receptor kinase by tyrphostin AG1296 and AG1478 had no effect. Furthermore, inhibition of Galpha(i) by pertussis toxin and inhibition of NADH/NADPH oxidase by diphenylene iodonium also diminished LPA-induced stimulation of PAK. This is the first study to demonstrate that LPA activates PAK. In VSMC, PAK activation by LPA is mediated by Galpha(i) and is dependent on Src, whereas EGF- or PDGF receptor transactivation are not involved. Furthermore, generation of ROS is required for LPA-induced activation of PAK.     

杉木中龄林针叶光合作用对光斑的响应

对18年生杉木(Cunninghamia lanceolata(Lamb．)Hook．)当年生针叶净光合速率(Pn)对不同时间和强度的猝发性辐射和模拟光斑响应的研究表明：经长时间低光或暗处理后针叶的Pn对猝发性连续强光的响应呈S形曲线,约需10～15min的光诱导才能达到相应光强下的最大值;猝发性辐射强度越大,所需光诱导时间越长;低光期越长,低光期辐射越小,所需光诱导期越长;但只要光斑间隔不是太长,针叶仍可保持原有的光诱导状态。针叶Pn对单个瞬时光斑的响应与光斑前的光诱导状态和光斑时间长短有关,充分诱导的针叶Pn对光斑的响应较未诱导或未充分诱导的针叶要灵敏得多,光斑时间延长可提高光诱导状态,从而提高Pn。光斑消失后Pn缓慢下降表明针叶对光斑的响应存在明显的光后CO2固定,在瞬时光斑较多的林内,光后CO2固定可占总同化量的相当大比例。