Comparison of Palaeobotanical Observations with Experimental Data on the Leaf Anatomy of Durmast Oak [Quercus petraea(Fagaceae)] in Response to Environmental Change

To test whether stomatal density measurements on oak leaf remainsare reliable tools for assessing palaeoatmospheric carbon dioxideconcentration [CO₂], under changing Late Miocene palaeoenvironmentalconditions, young seedings of oak (Quercus petraea,Liebl.) weregrown at elevatedvs.ambient atmospheric [CO₂] and at high humiditycombined with an increased air temperature. The leaf anatomyof the young oaks was compared with that of fossil leaves ofthe same species. In the experiments, stomatal density and stomatalindex were significantly decreased at elevated [CO₂] in comparisonto ambient [CO₂]. Elevated [CO₂] induced leaf cell expansionand reduced the intercellular air space by 35%. Leaf cell sizeor length were also stimulated at high air humidity and temperature.Regardless of a temperate or subtropical palaeoclimate, leafcell size in fossil oak was not enhanced, since neither epidermalcell density nor length of the stomatal apparatus changed. Theabsence of these effects may be attributed to the phenologicalresponse of trees to climatic changes that balanced temporalchanges in environmental variables to maintain leaf growth underoptimal and stable conditions.Quercus petraea,which evolvedunder recurring depletions in the palaeoatmospheric [CO₂], maypossess sufficient phenotypic plasticity to alter stomatal frequencyin hypostomatous leaves allowing high maximum stomatal conductanceand high assimilation rates during these phases of low [CO₂].Copyright1998 Annals of Botany Company Atmospheric CO₂, high humidity, elevated temperature,Quercus petraea,durmast oak, Late Miocene, palaeoclimates, leaf anatomy, stomatal density, stomatal index     

Temperature effects on forest herbs assessed by warming and transplant experiments along a latitudinal gradient

Slow‐colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large‐scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short‐ and long‐term persistence. We combined transplant experiments along a latitudinal gradient with open‐top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow‐colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open‐top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.     

Comparison of Plantago Species from Nutrient-rich and Nutrient-poor Conditions: Growth Response, ATPases and Lipids of the Roots, as Affected by the Level of Mineral Nutrition

Two groups of Plantago species, one of relatively nutrient-rich habitats (Plantago major L., P. major L. ssp. pleiosperma Pilger and P. martrima L.) and the other of relatively nutrient poor habitats (P. lanceolata L., P. media L. and P. coronopus L.), were compared with respect to the response of the plants to alterations of the level of mineral nutrition. The comparison deals with growth response and root cell membrane functions (Ca²⁺ and Mg²⁺ stimulated ATPases and lipids). As far as these parameters are concerned species from relatively nutrientpoor habitats are not much affected by bringing the plants to high-salt conditions, while the reverse was true for species from relatively nutrient-rich habitats when transferred to low salt medium.     

Isometric partitioning of hydraulic conductance between leaves and stems: balancing safety and efficiency in different growth forms and habitats

Recent advances in modelling the architecture and function of the plant hydraulic network have led to improvements in predicting and interpreting the consequences of functional trait variation on CO₂ uptake and water loss. We build upon one such model to make novel predictions for scaling of the total specific hydraulic conductance of leaves and shoots (k_L and k_SH, respectively) and variation in the partitioning of hydraulic conductance. Consistent with theory, we observed isometric (slope = 1) scaling between k_L and k_SH across several independently collected datasets and a lower ratio of k_L and k_SH, termed the leaf‐to‐shoot conductance ratio (C_LSCR), in arid environments and in woody species. Isometric scaling of k_L and k_SH supports the concept that hydraulic design is coordinated across the plant. We propose that C_LSCR is an important adaptive trait that represents the trade‐off between efficiency and safety at the scale of the whole plant.     

The uptake of phosphate by Carex species from oligotrophic to eutrophic swamp habitats

Abstract Phosphate uptake by excised roots of Carex species from a range of oligotrophic to eutrophic swamps was investigated. The range of species from oligotrophic to eutrophic is: C.rostrata Stokes, C.limosa L., C.lasiocarpa Ehrh., C.diandra Schrank, C.hudsonii A.Benn. and C.acutiformis Ehrh. All species showed two phases for P_i uptake in the P_i concentration range of 0.01 – 50 μM. In phase 1, C.rostrata and C.lasiocarpa had relatively high Vmax:s and Km:s, whereas the species from richer areas had intermediate values. The lowest Vmax and Km values were found in C.limosa and C.hudsonii. In phase 2, apart from the high Vmax and Km values found for C.lasiocarpa, the kinetic constants showed little variation, indicating a similar P_i carrier mechanism for all the species. Results on phosphate uptake and leakage are discussed against the phosphate requirement of each species in its specific habitat, and against the literature data of agricultural crops, which generally show a much lower affinity for phosphate uptake.     

电损毁海马CA_3区及连合前穹窿对大鼠血浆胰岛素水平及胰岛细胞的影响

电损毁大鼠海马CA_3区(HCA_3-EL)或连合前穹窿纤维(ACHF-EL)后,其血浆胰岛素基础水平明显升高。HCA_3-EL两周后,大鼠空腹血糖浓度增高,且糖耐量降低。但胰岛B细胞对葡萄糖刺激之分泌反应却显著增强。HCA_3-EL或ACHF-EL大鼠经静脉糖耐量试验(IVGTT)后,其胰岛A细胞内胰高血糖素样及B细胞内胰岛素样免疫阳性物质的相对含量均明显低于对照组。HCA_3-EL组大鼠胰岛中生长抑素样免疫阳性物质的相对含量及阳性细胞数目均较对照组减少,而胰岛中胰多肽样免疫阳性物质却无明显变化。上述结果表明,海马CA_3区(HCA_3)及连台前穹窿(ACHF)对胰岛素的分泌有紧张性抑制作用。     

Exotic No More: Anthropology on the Front Lines

Exotic No More: Anthropology on the Front Lines. Jeremy MacClancy, ed. Chicago: University of Chicago Press, 2002. 456 pp.     

Lipid Composition of the Roots of Plantago Species: Response to Alteration of the Level of Mineral Nutrition and Ecological Significance

In a study of the adaptation of Plantago species to their specific environment the lipid composition of the roots of several species: Plantago major L. ssp. major, Plantago major L. ssp. pleiosperma Pilger, Plantago lanceolata L., Plantago media L., Plantago maritima L., Plantago coronopus L. was studied as well as the effect of the nutritional regime. Upon exposure to low-salt conditions Plantago major L. ssp. major L. and Plantago maritima L. maintained the level of free sterols in the roots, despite a depressed level of total sterols, and the root lipids were more saturated than under high-salt conditions. Both factors may reduce nutrient leakage from the roots to the low-salt condition. Upon exposure to low-salt conditions, all Plantago species showed a decreased level of galactolipid (exception: Plantago coronopus) and a decreased level of sitosterol (exception: Plantago maritima); the latter being compensated by an elevated level of cholesterol + tocopherol in Plantago major ssp. pleiosperma, Plantago lanceolata and Plantago media. Plantago coronopus was the only species which under low-salt conditions showed an increased level of free sterols, among which cholesterol was the most important; thus indicating a high degree of regulation of membrane permeability under alternating nutritional conditions. The level of sulfolipid was kept constant in all Plantago species, with the highest level observed in Plantago maritima. The role which various lipids may play in maintenance of membrane integrity under alternating nutritional conditions is discussed.     

Recognition of Phytophthora infestans Avr4 by potato R4 is triggered by C-terminal domains comprising W motifs

Oomycete RXLR-dEER effector proteins are rapidly evolving proteins with the selective pressure targeted predominantly at their C-terminal ends. The majority of RXLR-dEER proteins have recognizable motifs of 21–30 amino acids in the C-terminal domain that are named after conserved amino acid residues at fixed positions within the respective motifs. In this article, it is reported that the Phytophthora infestans RXLR-dEER protein Avr4 contains three W motifs and one Y motif in its C-terminal domain. Agroinfection assays using constructs encoding modified forms of PiAvr4 have shown that the region containing the W2 motif, in combination with either the W1 or W3 motif, triggers a necrotic response in potato plants carrying the resistance gene R4 . By mining the superfamily of avirulence homologues (Avh) deduced from three sequenced Phytophthora genomes, several Avh proteins were identified as homologues of PiAvr4: six in P. infestans , one in P. ramorum and seven in P. sojae . One very close homologue of PiAvr4 was cloned from the sibling species, P. mirabilis. This species is not pathogenic on potato but, similar to PiAvr4, PmirAvh4 triggered a necrotic response on potato clones carrying R4 , but not on clones lacking R4 . Genes encoding RXLR-dEER effectors are often located in regions showing genome rearrangements. Alignment of the genomic region harbouring PiAvr4 with syntenic regions in P. sojae and P. ramorum revealed that PiAvr4 is located on a 100-kb indel block and is surrounded by transposable elements.     

Morphology,Molecular Phylogeny,and Ecology of Binucleata daphniae n. g., n. sp. (Fungi: Microsporidia), a Parasite of Daphnia magna Straus, 1820 (Crustacea: Branchiopoda)

ABSTRACT. We describe a new microsporidian species Binucleata daphniae, n. g., n. sp., that infects the integument cells lining the hemocoele cavity of the carapace and the postabdomen of the cladoceran Daphnia magna Straus. Infected cells filled with spores accumulate as large clusters in the carapace cavity and heavily infected hosts are detected by their opaque appearance. Despite the parasite's presence, infected Daphnia grow and molt, but have a reduced fecundity. During the parasite's life cycle, chain‐like meronts with isolated nuclei are formed, giving rise to binucleate presporonts, the most frequently observed, characteristic developmental stage. In sporogony, the nuclei of the presporont separate, divide, and eight spores enclosed in a thin‐walled sporophorous vesicle are formed. Spores are 4.9 × 2.5 μm in size (fresh) and have an anisofilar polar filament with eight coils. DNA sequence analysis places B. daphniae in a clade of microsporidians that parasitize crustaceans and mosquitoes and have assumed complex life cycles. Binucleata daphniae, however, has a simple and direct life cycle and can be transferred to naïve hosts and maintained as persistent infections in populations of its host D. magna. We propose that B. daphniae has simplified its life cycle by losing its secondary host, rendering it unique in this clade.