Race non-specific resistance to Bremia lactucae

Three ways of measuring race non-specific resistance to Bremia lactucae in lettuce were studied to determine the most important components of this form of resistance. Tests were conducted on leaf discs from 4–6 wk-old plants that were quantitatively inoculated and incubated under controlled conditions. Observations were made of disease intensity, latent period and production of conidia. Inoculum concentration markedly influenced disease intensity and latent period. Cv. Iceberg exhibited race non-specific resistance and this was characterised by a longer latent period, a lower disease intensity and reduced production of conidia compared to the susceptible control cv. Cobham Green. On older, intact plants, the differences in latent period and disease intensity between cultivars were even greater. Production of conidia was a particularly good criterion for discriminating levels of resistance.     

Blue, red and blue plus red light control of chlorophyll content and CO2 gas exchange in barley leaves: Quantitative description of the effects of light quality and fluence rate

The dependence of the Chl content and the rate of CO₂ gas exchange (RGE) on both blue and red quanta fluence rates have been studied in primary leaves of barley ( Hordeum vulgare L. cv. Viner). Empirical equations connecting the two photosynthetic indices with fluence rates of blue or red light were developed. These equations consist of 3 (Chl content) or 2 (RGE) terms, each reflecting the involvement of a specific reaction in the long-term light control of the development of the photosynthetic apparatus. On the basis of the equations the effects of mixed blue plus red light on both the Chl content and RGE were calculated. An additive mode of the co-action of blue and red light in the range of high PFDs (10–170 μmol m⁻² s⁻¹) becomes evident from the comparison of the experimental results and calculated data. The results indicate the involvement of phytochrome, cryptochrome and chlorophyll in the long-term regulation of the Chl content and RGE.     

关于低强度激光疗法的机理及其临床应用研究

刘承宜等人提出了低强度激光疗法的生物信息模型。根据ＢＩＭＬ,绿,兰和紫等冷色兴奋Ｇａ蛋白介导的生理过程,红,产黄等暖色兴奋Ｇｑ或Ｇｉ蛋白或受体关联蛋白酶介导的生理过程。本文将激光的生物效应分为直接效应和间接效应两类,根据ＢＩＭＬ成功地解释了已知第二信使生理功能的系统的低强度激光照射的作用机理和临床应用,可望用于开发低强度激光疗法的临床新应用。     

Grazing Behavior of Heterotrophic NanoFlagellates Observed with a High Speed VTR System

The grazing patterns of heterotrophic nanoflagellates ( Cafeteria roenbergensis and Actinomonas mirabilis ) were recorded by high speed video micrography. Experiments were carried out at 10, 15 and 25° C at a salinity of 36 psu and at 20° C when the salinity was either 20 or 36 psu. Bacteria entrained in a stream of water generated by flagellar beating were propelled toward the cell body (phase 1). Each bacterium destined for ingestion made contact with the anterior end of the flagellum of Cafeteria or was captured with an actinopod of Actinomonas (phase 2). The captured bacterium was drawn close to the cell body (phase 3) and ingested (phase 4). Cafeteria was observed during 38 grazing events and appeared to have two different patterns of ingestion, "enclosing" and "pocket phagocytosis." The mean time for food capture was 0.10 s and the subsequent ingestion was complete on average in 1.59 s. No further bacteria were captured until ingestion was complete. Actinomonas was observed during 27 grazing events in which capture of panicles on an actinopod was followed by transport to the cell body and subsequent "enclosing phagocytosis." The mean time to complete grazing was 39.16 s, which is about 25 times longer than for Cafeteria ; the phase of transport to the cell body occupied most of this time. During the grazing cycle, Actinomonas captured other bacteria on the actinopodia, but sometimes released them. Grazing time in Cafeteria was positively correlated with temperature but not correlated with salinity. Grazing behavior in Actinomonas was correlated with neither temperature nor salinity.     

Methods for quantifying fire severity in shrubland-fires

Methods are presented to relate temperature-residence-time at the soil surface, i.e., time above 150 ºC as an estimation of the severity of a fire, with measurements made during an experimental fire or on two post hoc measurements. The experiment was carried out in a shrubland dominated by the woody-legume Cytisus striatus subsp. eriocarpus, in Central Spain. Temperature-sensitive paints, and steam-releasing open-calorimeters were used as fire-meters during the burn. Post hoc measurements used were estimations of heat output per unit area, and measurements of the minimum diameter of branches of Cytisus remaining after the fire. Time above 150 ºC was obtained from measurements made with thermocouples placed at the soil surface in 20 contiguous 1×1 m squares of the burn plot. All other measurements were made at each 1×1 m in the 22×3 m rectangle surrounding, and including, the thermocouple squares. Various simple and multiple regression models were constructed to predict time above 150 ºC from each of the four measurements made during or after the fire. Maximum coefficients of determination obtained for regressions were 0.61 and 0.62 for water mass loss from open-calorimeters and branch diameter, respectively. Using all the variables in a multiple regression model, time above 150 ºC was related to water mass loss from open-calorimeters and heat output per unit area with a coefficient of determination of 0.77. It is concluded that estimations of time above 150 ºC at the soil surface during the passage of fire may be possible based on simple devices, such as open-calorimeters, or on biological indicators, such as minimum branch diameters. Additionally, combining two methods (open-calorimeters, estimations of heat output per unit area) may allow the reconstruction of the time above 150 ºC during the fire at a scale of 1 ², an important characteristic of a burn to understand ecosystem response to fire.     

STABILIZING SELECTION AND VARIANCE IN FIG WASP SEX RATIOS

Theory predicts that the phenotypic variance observed in a trait subject to stabilizing selection should be negatively correlated with the trait's impact on fitness. However, this relationship has rarely been tested directly. The offspring sex ratios produced by pollinating fig wasp foundresses upon entrance to a fruit and oviposition alone (single foundress sex ratios) are subject to stabilizing selection because too many males reduce the total number of dispersing females and too few males will result in unmated females or complete loss of the brood. Furthermore, we argue that the impact on fitness of, and therefore the intensity of stabilizing intensity on, single foundress sex ratios are correlated to how frequently a species produces single foundress broods in nature. Specifically, the intensity of stabilizing selection will be greater in species that encounter single foundress broods more frequently, both because the trait is expressed more often and because fitness shows a greater sensitivity to variation (narrower fitness profile) when that trait is expressed. Across 16 species of Panamanian pollinating fig wasps, the phenotypic variance in single foundress sex ratios was negatively correlated with the frequency with which that species encounters single foundress broods in nature. In addition, a formal comparative analysis based upon a molecular phylogeny of the wasps gave results that were the same as when species were used as independent data points.     

羊草无性系构件在不同环境下的可塑性变化

对温室内栽培羊草,人为控制温度及光照强度的条件,观测无性系构件的生长与分化的结果表明,羊草的无性系构件生长存在明显的可塑性变化,长时间的低温显著抑制羊草根茎和无性小株的分化（Ｐ＜０．０５）,而对分蘖无明显抑制作用．遮荫显著抑制根茎和无性小株的分化（Ｐ＜０．０５）,但对分蘖的影响并不显著．羊草的这种生态适应特征有利于对环境变化的适应．     

光照强度对中华鳖稚鳖摄食和生长的影响

在３０００，１０００，３００和１０１ｘ的光照强度下，测定了中华鳖稚鳖的最大日摄食量和特定生长率。结果表明，光照强度对中华鳖稚瞥珠最大日摄食量影响显著，随着光照强度的减弱，中华鳖稚鳖的最大日摄食量逐渐增加，二者之间呈线性负相关。     

The phytoplankton community of the River Meuse,Belgium: seasonal dynamics (year 1992) and the possible incidence of zooplankton grazing

Qualitative and quantitative aspects of the phytoplankton of the River Meuse were studied during 1992, at a point 537 km from the source. The phytoplankton was dominated by diatoms and green algae. The Stephanodiscus hantzschii-group was especially prominent. Other important taxa were Cyclotella meneghiniana, small Cyclotella and Thalassiosira, Aulacoseira ambigua and Nitzschia acicularis. Cell abundances varied from less than 1000 units ml^–1 to about 25 000 – 30 000 units ml^–1 during the blooms. The Stephanodiscus hantzchii-group constituted almost entirely the first spring bloom. During the summer period, small Thalassiosiraceae developed markedly and large Thalassiosira weissflogii appeared. During this period, green algae dominated diatoms as expressed in cell abundances. The main Chlorococcales were Scenedesmus quadricauda, Scenedesmus div. sp., Dictyosphaerium ehrenbergianum and Pediastrum duplex. Dinophyceae contributed a significant biomass during the summer period. Total biomass varied between 100 and 3 650 µg Cl^–1. As previously observed (Descy, 1987), the factors regulating the phytoplankton growth were clearly physical variables: discharge, temperature and irradiance. However, in the summer period, low abundances might indicate a regulation by biotic factors. The impact of grazing by zooplankton is discussed, on the basis of observations of zooplankton development in the River Meuse and on the basis of simulation by a mathematical model. A comparison is carried out with recent data of phytoplankton in large European rivers.