Alternative risk-taking styles: The case of time-budgeting strategies of terrestrial gastropods

The terrestrial slugs Arion ater, Limax maximus and Ariolimax columbianus have similar morphological designs but differ remarkably in their life history tactics and behavioural time budgets. The adaptive value of particular risk-taking styles was investigated using a comprehensive computer simulation model. The model allowed each species' success (growth rates, food acquisition) and costs (distance travelled, hydration deficits, injury from aggressive encounters) to be evaluated in various types of weather (benign, harsh and surprise). This was interpreted in terms of the species' life history design. In addition, each species was simulated with the behavioural strategy of the other two species substituted for its natural programming. The simulation experiments demonstrated how variations in a few simple rules could lead to divergent cost-benefit consequences. The model also illustrated that coarsely-tuned sensitivity to the environment may be better than finely-tuned responses, depending on the animal's ability to respond quickly and the degree of risk. The simulations suggested that competition has shaped the time-budgeting tactics of A. ater and L. maximus. Each species actually performed better in harsh weather, using the behavioural program of the other. L. maximus is an aggressive species with a narrow, nocturnal activity period. The concentrated activity of L. maximus may allow it to displace competitors more effectively, whereas the broader time span of A. ater's activity may be necessary to avoid L. maximus.     

土地处理系统中悬浮固体的整体分析技术研究

1 前言 土地处理系统对悬浮固体具有很好的净化效果,其净化率要害99%以上,但实际过程中,一些干扰     

Preliminary results from the self-regulatory treatment of high-medication-consumption headache

Data are presented from a prospective clinical replication series of ten consecutive high-medication headache patients who presented for nondrug treatment of their headaches. For the first eight, an attempt was made to withdraw the patients from medication, with the assistance of relaxation training, prior to entering a comprehensive self-regulatory treatment program. For the last two, drug withdrawal accompanied the treatment. Six of the ten patients showed clinically significant reductions in headache activity, which held up over follow-ups of up to 12 months. Psychological tests provide some discrimination between success and failures.This research was supported in part by a grant from NINDS, No. NS-23340. Appreciation is expressed to Dr. Kenneth A. Appelbaum and Ms. Denise Michultka for their roles in this study.     

Exchange of colicin receptor capacity between strains of Escherichia coli sensitive or resistant to colicin K-K235

Phage and colicin-resistant mutants were derived from Escherichia coli K-12P678. Two classes of phage T6 and colicin K-resistant mutants (genotype tsx) were isolated. Tsx-2 mutants, which demonstrated mucoid growth and increased sensitivities to many antibiotics, became sensitive to colicin K when pretreated with ethylenediaminetetraacetate (EDTA), whereas Tsx-1 mutants did not. Reassociation of EDTA-released material partially restored resistance to colicin K for Tsx-2 mutants. When EDTA-released material from strain P678 was associated with either class of K-resistant mutant, an increase in colicin K sensitivity resulted. Observations suggest that colicin K can act on its target site once it penetrates the cell surface. In addition, results suggest that functional colicin K receptors can be transferred from sensitive to resistant strains, thus conferring colicin sensitivity.Non-standard Abbreviations SDS sodium dodecyl sulfate     

Effect of water stress on some oxidative enzymes and senescence in Vigna seedlings

Seedlings of Vigna catjang Endl. were subjected to water stress for 6, S and 10 days by withholding water to investigate the activities of some oxidative enzymes and the pattern of senescence in leaves of 17-day-old seedlings undergoing water stress. Increasing duration of stress produced a proportional increase in the activities of IAA-oxidase, AA-oxidase, peroxidase and glycolate oxidase but decreased catalase activity and the contents of both chlorophyll and protein, hastening senescence. Leaf water potential and relative water content were also lowered with incresing duration of stress. Permeability was increased in leaf tissue undergoing water stress for 8 days. Seed treatment with CaCl₂ (10⁻² and 10⁻¹⁴ M ) for 6 h improved the water status of leaves, decreased tissue permeability, activities of oxidative enzymes, decline of chlorophyll and protein contents and delayed senescence compared to untreated water stressed plants.     

Ultrastructural changes in the endoplasmic reticulum during dormancy release of apple embryos (Pyrus malus L.)

Apple embryos were treated by cold (0°C) within the fruits, to break their dormancy; the controls were treated at 12°C or at 20°C. Ultrastructural features of meristematic cells in the embryonic axis were compared for each treatment. The organization of the cells of dormant embryos was described: Endoplasmic reticulum consisted in some short rough cisternae; lipid droplets regularly arranged near the plasmalemma constituted a kind of shell; mitochondria had a few cristae; and dictyosomes were rarely observed. All these features are typical of dry seeds. After cold treatments, the only evolution observed was in the endoplasmic reticulum, where highly organized stacks appeared progressively as a function of time at 0°C. An intermediate temperature (12°C) induced similar formations in the reticulum but they were rarely observed and their degree of organization was lower than that obtained at 0°C. At 20°C, endoplasmic reticulum resembled that of the dormant embryo cells. The relation between the appearance of these structures in the reticulum and the disappearance of dormancy induced by cold is discussed.Abbreviations ER endoplasmic reticulum - RER rough endoplasmic reticulum     

Differentiation of embryogenic pollen in cold-treated buds ofNicotiana tabacum var. Badischer burley and nutritional requirements of the isolated pollen to form embryos

Summary Embryogenic pollen were selectively isolated from buds after cold treatment at 10 °C for 10 days; it was immaterial whether the buds were taken from short day and low temperature (SD and LT; 8 hours light, 18 °C) or long day and high temperature (LD and HT; 16 hours light, 24 °C) plants. However, in buds from SD and LT plants the differentiation of embryogenic pollen could be detected as early as 7 days after the cold treatment, and pollen from these plants formed embryos at higher frequency (up to 4% of cultured pollen) than those from LD and HT plants (up to 1% only).The embryogenic pollen, in isolated buds, differentiated by way of pollen dimorphism. During cold treatment a fraction of pollen remained small, retained clear cytoplasm and was capable of embryogenesis in comparison to gametophytic pollen which enlarged and acquired granular cytoplasm. In our experiments cold treatment was a key factor in the induction of pollen dimorphism. This aspect of cold treatment in pollen embryogenesis is reported for the first time and was possible on the basis of selection of embryogenic pollen by density gradient centrifugation. The ratio of embryogenic pollen was about one fifth of the total population.The nutritional requirements of isolated pollen for embryogenesis were rather simple. These pollen formed embryos which readily developed into plantlets on a mineral medium supplemented with sucrose provided the pH was 6.8.     

Magnesium (and trace substance) deficiencies in the pathogenesis of cancer

Except for a few experimental models of magnesium (Mg)-deficiency-induced neoplasms, less attention has been paid in the past quarter century in the Western world to this macromineral than to the trace elements; e.g., selenium (Se) and zinc (Zn), and to vitamins, deficiencies of which are each considered probable factors in oncogenesis. Although early epidemiologic studies showed an inverse correlation between the amount of Mg in soil and water and the incidence of (gastric) cancer, and several animal studies supported the premise that Mg has a prophylactic effect against induction of cancer, other studies showed that Mg supplementation increased the growth of established experimental tumors. Thus, enthusiasm for this approach subsided. The early epidemiologic findings have since been confirmed, and there have been studies demonstrating the importance of Mg in maintaining immunocompetence, and others indicating that immunodeficiencies increase susceptibility to the development of cancer. Evidence has now accrued that indicates that Mg deficiency increases susceptibility to chemical oncogens. The abnormal metabolism of tryptophan (yielding a carcinogenic metabolite) that indicates functional or absolute pyridoxine deficiency is an indirect clue to Mg deficiency. Vitamin B₆-activated enzymes require Mg as a cofactor. However, the early warnings against the use of Mg as part of an antineoplastic program against established cancer were justified, since rapidly metabolizing cells (such as cancers) are dependent on Mg. There are similarities between experiences with Mg and with Se and Zn. All three are required for normal metabolism; Se also protects against free radicals in the environment. Mg and Zn have increased established tumor growth, and their depletion has been applied to antineoplastic programs, with risks comparable to those of using antimetabolic agents.     

Membrane surface properties of sheep erythrocytes,an immunological reagent,after different treatments as reflected by partition in two-polymer aqueous phases

Sheep erythrocytes (E) which, with or without certain treatments, are currently used as “immunological reagents” to detect cells with specific receptors (by rosette-formation) have been partitioned in two-polymer aqueousphase systems selected so as to reflect charge-associatedor lipid-related membrane surface properties. We have found that the partitioning behavior of E is not affected in these phases by reacting the cells with anti-E antibody (either IgG or IgM), forming EA. The additional binding of complement to the cell-antibody complex, forming EAC, results, however, in a marked decrease in the partition coefficient,K. Apparently both the charge-associated and hydrophobic properties reflected by partitioning remain accessible to the phase polymers when the cells are coated with antibody, but are not with the addition of complement. It is interesting that EA can still rosette with T-lymphocytes (14), a property of E, while the additional coating with complement results in EAC which does not appreciably do so (26). Neuraminidase or trypsin treatments of E, which yield Es having quite different rosetting properties with T-lymphocytes (14), cause increasedKs and unchangedKs, respectively, in phases reflecting lipid-related surface properties. Either treatment causes reducedKs of E in charged-phase systems. Neuraminidase treatment also results in a reduced electrophoretic mobility of E, while trypsin treatment is not detectable by cell electrophoresis (25). We are currently studying the possible usefulness of employing cell electrophoresis and cell partitioning in charged-phase systems jointly to obtain information on events occurring at the shear plane versus those occurring deeper in the membrane.