EFFECTS OF RED AND FAR-RED RADIATION ON CELL DIVISION AND ELONGATION IN THE STEM OF PINTO BEAN SEEDLINGS

Nine-day-old Pinto bean seedlings, Phaseolus vulgaris L., were treated daily for 12 days with supplementary red or far-red radiation following daily exposure to 8 hr of daylight. Stem elongation was nearly exponential from the 4th to the 12th day of treatment and was about 2.9 times greater under far-red radiation. Cell division and cell elongation were promoted essentially equally by far-red radiation. There was virtually no difference in either the rate of leaf initiation or the duration of growth of internodes under the supplementary radiation.     

HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (CHYTRIDIOMYCOTA)1

Some chytrids are host‐specific parasiticfungithat may have a considerable impact on phytoplankton dynamics. The phylum Chytridiomycota contains one class, the Chytridiomycetes, and is composed of five different orders. Molecular studies now firmly place the Chytridiomycota within the fungal kingdom. Chytrids are characterized by having zoospores, a motile stage in their life cycle. Zoospores are attracted to the host cell by specific signals. No single physical–chemical factor has been found that fully explains the dynamics of chytrid epidemics in the field. Fungal periodicity was primarily related to host cell density. The absence of aggregated distributions of chytrids on their hosts suggested that their hosts did not vary in their susceptibility to infection. A parasite can only become epidemic when it grows faster than the host. Therefore, it has been suggested that epidemics in phytoplankton populations arise when growth conditions for the host are unfavorable. No support for such a generalization was found, however. Growth of the parasitic fungus Rhizophydium planktonicum Canter emend, parasitic on the diatom Asterionella formosa Hassal, was reduced under stringent nutrient limitation,because production and infectivity of zoospores were affected negatively. A moderate phosphorous or light limitation favored epidemic development, however. Chytrid infections have been shown to affect competition between their algal hosts and in this way altered phytoplankton succession. There is potential for coevolution between Asterionella and the chytrid Zygorhizidium planktonicum Canter based on clear reciprocal fitness costs, absence of overall infective parasite strains, and possibly a genetic basis for host susceptibility and parasite infectivity.     

Sindbis病毒的蛋白质合成与细胞骨架的关系

我们以Sindbis病毒感染BHK-21细胞为模式,研究了病毒的感染与细胞骨架的关系。结果显示:在病毒感染早期,细胞的蛋白质合成迅速被抑制,细胞的多聚核糖体(polysome)和mRNA从骨架上脱落,而病毒的RNA结合到骨架上。我们的结果还进一步表明,病毒的RNA是通过其3′-尾端与骨架结合的。另一方面在对Sindbis病毒非结构蛋白在体内与体外合成与加工的比较中,我们发现病毒蛋白在体外翻译加工的速度远低于体内,并且出现很多未成熟蛋白(premature protein),这种区别可能在某种程度上反应细胞骨架在蛋白质合成与加工中的作用。此外,在用秋水仙素和细胞松驰素B破坏微管和微丝后,病毒非结构蛋白的合成与加工没有明显变化,而结构蛋白的合成则受到明显的抑制。这表明病毒的两类蛋白的合成所依赖的细胞骨架成分可能有所不同,在结构蛋白合成过程中,微丝和微管起了重要作用,在非结构蛋白合成过程中,中间丝很可能起了重要作用。     

AEROBIOLOGY OF SYMPLOCARPUS FOETIDUS: INTERACTIONS BETWEEN THE SPATHE AND SPADIX

The aerobiology of the skunk cabbage, Symplocarpus foetidus (l .) Nutt., is examined as a factor contributing to efficient pollination and temperature regulation around the spadix. Field measurements show that the compass orientation of the asymmetrical opening of the spathe is random, while wind tunnel studies reveal that similar patterns of airflow are generated around the spadix regardless of the orientation of the spathe opening to the direction of airflow. Temperature measurements within a model of the inflorescence reveal that airflow around the spathe effectively maintains heat generated by the spadix, even at airflow speeds of 1.5 m/s. These results are discussed as exaptations of the spathe for pollination and for temperature regulation in sub-freezing weather.     

INTERACTIONS BETWEEN CETACEANS AND THE TUNA FISHERY IN THE AZORES

We studied the operational and ecological interactions between cetaceans and the tuna-fishery in the Azores, based on reports of observers placed on board tuna fishing vessels from 1998 to 2000. Data were collected during 617 fishing trips (representing 43% of total fishing trips) and 6,554 fishing events. Cetaceans were present during <10% of the observed fishing events, with common dolphins ( Delphinus delphis ) accounting for 78% of the occurrences. The presence of cetaceans during fishing varied both spatially and temporally, depending on the distribution of fishing effort and on the pattern of occurrence of each cetacean species in the region. Overall, cetaceans interfered in 5% of the fishing events. This interference resulted in a higher proportion of events with no catches. In the three years, 49 dolphins were caught in the fishing lines but were released alive, although it is impossible to determine if they survived the interaction. Annual estimates of incidental capture of cetaceans by all the tuna fleet were calculated based on total tuna landings. An estimated 55 dolphins were captured in 1999, 38 in 1998, and 16 in 2000. Overall, our results suggest a low level of interaction between cetaceans and this fishery.     

STUDIES IN THE INTERACTIONS BETWEEN SPECIES OF VERTICILLIUM

It is shown that five parasitic species of Verticillium , viz. V. alboatrum, V. Dahliae, V. ticorpus, V. nigrescens and V. nubilum , developed together on agar media or wheat grains as saprophytes without causing mutual antagonism but, when these were injected together, as a mixed spore suspension, into antirrhinum and tomato, suppression of V. tricorypus, V. nigescens and V. nubilum by either one or other of the remaining two invariably resulted. The two most virulent pathogens, V. alboatrum and V. Dahliae , were not recoverable from soil after the elapse of 6 months from the time of inoculation; while the other three less virulent pathogens could be isolated after about 12 months in the soil. It is concluded that V. alboatrurn and V. Dahliae may be described as 'root inhabiting' and V. nigrescens and V. nubilurn as 'soil inhabiting', while V. tricorpus may be considered as an intermediate type.     

不同株的熊蜂短膜虫与宿主生存的关系

ＴＨＥＲＥＬＡＴＩＯＮＳＨＩＰＢＥＴＷＥＥＮＤＩＦＦＥＲＥＮＴＳＴＲＡＩＮＳＯＦＣＲＩＴＨＩＤＩＡＢＯＭＢＩＡＮＤＴＨＥＳＵＲＶＩＶＡＬＯＦＴＨＥＩＲＨＯＳＴＢＵＭＢＬＥＢＥＥＳ不同株的熊蜂短膜虫与宿主生存的关系ＫｅｙｗｏｒｄｓＣｒｉｔｈｉｄｉａｂｏ...     

基因组时代生态-遗传学科交叉的现状与前景

生态学与遗传学的学科交叉首先建立在种群概念基础上,文献统计表明,目前这方面的研究以揭示种群遗传结构的形成和维持机制为主要方向,同时开始注重关键生化途径与环境适应之间的关系。基因组学的快速发展,为系统研究生理代谢在生态适应过程中的作用提供了可能性。分离具有重要生态学意义的基因,并对比近缘类群中基因表达模式的差异成为生态 遗传学科交叉的新生长点。在对研究实例进行分析后提出了此类研究的特点,同时从研究思路、分析方法和研究侧重点方面讨论了生态学在新学科交叉领域中所具有的重要价值。     

INTERACTIONS BETWEEN SOIL BACTERIA AND THE MOLLUSCAN ALIMENTARY TRACT

The alimentary tract is a major site of interaction betweenan animal's ecosystem and its physiology. It may be intermittentlyor permanently populated by microorganisms from its environmentthat could be beneficial or pathogenic in their influence. Thebacterial populations of the snail (H. aspersa) and the woodlouse(O. asellus) have therefore been estimated in terms of colonyforming units. gm body weight^–1. The bacteria in the snailappear to be similar to those found in soil and show wide resistanceto antibiotics. The main types are gram negative rods tentativelyidentified as belonging to Pseudomonas, Xanthomonas, Acinobacter,Vibrio and Enterobacteriaceae. Some gram positive and endosporeforming bacteria of Bacillus, Staphylococcus and Micrococcusspp were also present. The numbers of bacteria increase towardsthe posterior of the alimentary tract although the numbers inthe digestive gland are more constant. An artificial diet is described that can be used to feed snailsand study the effects of known amounts of additives. When starvedor kept under clean conditions the bacterial population of thesnail gut falls and the thickness of the alimentary tract decreases.All the indications are that the bacteria in the alimentarytract of the snail are indiscriminately accumulated from thenatural environment and are transient populations. (Received 7 June 1989; accepted 24 July 1989)     

ON THE RELATION BETWEEN MEASUREMENTS OF INTENSITY DISCRIMINATION AND OF VISUAL ACUITY IN THE HONEY BEE

1. Bees respond by a characteristic reflex to a movement of their visual field. By confining the field to a series of parallel stripes of two alternating different brightnesses it is possible to determine for any width of stripe, at any brightness of one of the two sets of stripes, the brightness of the second at which the bee will first respond to a displacement of the field. Thus the relations between visual acuity and intensity discrimination can be studied. 2. For each width of stripe and visual angle subtended by the stripe the discrimination power of the bee''s eye for different brightnesses was studied. For each visual acuity the intensity discrimination varies with illumination in a characteristic, consistent manner. The discrimination is poor at low illuminations; as the intensity of illumination increases the discrimination increases, and reaches a constant level at high illuminations. 3. From the intensity discrimination curves obtained at different visual acuities, visual acuity curves can be reconstructed for different values of ΔI/I. The curves thus obtained are identical in form with the curve found previously by direct test for the relation between visual acuity and illumination.     

CELL KINETICS OF IRRADIATED EXPERIMENTAL TUMORS: RELATIONSHIP BETWEEN THE PROLIFERATING AND THE NONPROLIFERATING POOL

The role of nonproliferating cells in tumor regeneration has been studied after subcurative doses of low L.E.T. irradiation. Radiation was applied in a single dose at three different levels, 0–47, 0–94 and 1–88 krad. Studies included estimation of the absolute number of cells per tumor, differential cell counts, and autoradiographic determination of kinetic variables, employing transplantable mouse mammary adenocarcinoma DBAH. Quantitative changes of morphologically denned proliferating and non-proliferating cell pools were followed at different time intervals after irradiation. Irradiation resulted in reduction of the number of cells in both pools, with apparent sparing of nonproliferating cells. The regenerative period started with a gradual increase in the number of cells in the proliferating pool, whereas the number of cells in the nonproliferating pool continued to fall in tumors irradiated with 0–94 and 1 -88 krad. In the late phase of tumor regrowth, the increasing number of cells in the non proliferating pool corresponded to its replenishment by cell transition from the proliferating pool. In an effort to clarify whether cell transition from the nonproliferating to the proliferating pool may take place during the regrowth of radiation perturbed tumors, cell loss rates from both pools were estimated using experimental data. In addition to cell losses from the tumor as a whole, the ‘net loss rate’ of the non-proliferating pool reflects the rate of cell transition from the nonproliferating to the proliferating pool, minus the rate of transition in the opposite direction. A similar definition applies to cell loss rates from the proliferating pool. The results showed: (1) high losses in both pools, with excess losses in the proliferating during the early phase after irradiation; (2) in the early stage of regrowth after irradiation, the cell net loss rate for the nonproliferating pool increased, in contrast to the behavior of cell loss rate for the proliferating pool and the average cell loss rate for the tumor as a whole; (3) in the late stage of regrowth a decrease in net loss rate for the nonproliferating pool reflects the excess production of nonproliferating cells over control tumors. These results suggest that cell transition from the nonproliferating to the proliferating pool takes place at the beginning of tumor regrowth after subcurative single-dose irradiation.     

电导法研究表面活性剂与蛋白质的相互作用

较系统地研究了溶液中离子型表面活性剂与蛋白质相互作用时电导率的变化,并根据实验现象得出表面活性剂与蛋白质作用的两种模式－ 疏水作用模式和电荷作用模式。表面活性剂采用疏水作用模式与蛋白质结合时,蛋白质的二硫键逐一断裂,三级结构逐渐打开,电导率曲线出现一些小“平台”;采用电荷作用模式吸附蛋白质时,首先形成疏水复合体,产生白色浑浊,随离子型表面活性剂浓度的增加,疏水复合体转变成亲水复合体,白色浑浊完全溶解。在有的体系中,两种作用并不是界限分明,它们可以同时表现出来。并将实验结果做为研究蛋白质所引起的乳化及破乳机理的依据