Entropy effects on the ion-diffusion rate in transmembrane protein channels

We treat the transport of univalent cations through pore-like protein channels in biological membranes analytically, using two models (A + B) for the channel and the ion-channel interaction. A Lennard-Jones-type repulsion between the ions and the pore wall is introduced. We also include Van der Waals- and coulomb-type interactions between polar ligands of the pore-forming protein (e.g., carbonyl groups directed towards the axis of the channel) and the migrating particles. In model A, the polar groups are assumed to occur in pairs of dipoles pointing in opposite directions (as in the gramicidin A channel), while in model B the channel is treated as a pore with a radially isotropic charge distribution. In both models the ion-channel interaction leads to the occurrence of periodic potentials, corresponding to quasi-equilibrium and transition state sites of the ion in the pore. The diffusion rate can be calculated employing rate-theoretical concepts on the basis of microscopic parameters. It is demonstrated that the anomaly (inversion of the normal mass effect) for the transport rates of different ions can be related to differences in the activation entropy. The latter quantity is estimated analytically for both models. As a test, we performed numerical calculations with parameters based on the gramicidin A model. The results are in good agreement with experimental data and data from computer simulations. This shows that simple analytic expressions are well suited for predicting trends in the ionic conductivity of protein channels on the basis of microscopic interactions.     

Biological control of thrips [Thysanoptera: Thripidae] on greenhouse cucumber byAmblyseius cucumeris

The predatory miteAmblyseius cucumeris (Oudemans) [Acarina: Phytoseiidae] was evaluated as a biological control forThrips tabaci Lindeman andFrankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] on greenhouse grown seedless cucumber.A. cucumeris spread throughout the greenhouses and provided control of both species of thrips.A. cucumeris adults persisted on plants for 7 weeks in the virtual absence of prey, and increased numerically in response to increases in prey population. On the basis of these resultsA. cucumeris is recommended as a useful biological control forT. tabaci andF. occidentalis on greenhouse cucumber. Publication No. 361, Agassiz Research Station, Agriculture Canada, Agassiz, B.C. Canada VOM 1AO.     

我国特有植物银杉的资源、分布及其环境

我国银杉自1955年发现以来,陆续发现了它的新分布,至今已知在四省、区7个分布区的30多个分布点上,自然生长着银杉3200余株。它们是:广西花坪林区(越城岭南部)6个点有银杉1040抹,其中高5米以上的68株,1～5米的49株,1米以下的923株,最高21.1米,最大胸径83厘米;广西大瑶山4个点有银杉143株,其中高10米以上的94株,1～3米的3株,1米以下的46株,最高30米,最大胸径79.2厘米;湖南罗汉洞(越城岭北部)2个点有银杉58株,5米以上的有45株,最高18米,最大胸径43厘米;湖南罗霄山脉八面山有银杉707株,高1米以上的334株,最高24米,最大胸径46厘米;四川南川金佛山(大娄山东段北部)6个点有银杉527株,其中成年树400余株,最高17米,最大胸径50厘米;百枝山有银杉52株,最高8米,最大胸径27厘米;贵州道真沙河林区(大娄山东段南部)3处12个点有银杉729株,其中高5米以上的105株,2～5米的209株,1～2米的111株,1米以下的304株,最高18.8米,最大胸径48厘米;贵州桐梓白菁有银杉10株,高4～5米的2株,1～3米的6株,1米以下的2株。 银杉分布区范围自北纬24°5′～29°13′14″,东经107°10′～113°40′。其垂直分布自海拔940～1840米,金佛山银杉分布最高,为1600～1840米;罗汉洞银杉分布最低,为940～1060米。分布区内,年均温8.2°～17℃,绝对最低温     

Population structure and responses to disturbance of the basidiomycete Resinicium bicolor

Summary Resinicium bicolor (Alb. & Schw. ex Fr.) Parm. [=Odontia bicolor (Alb. & Schw. ex Fr.) Bres.] is an outcrossing resupinate basidiomycete associated with root and butt rots of trees, but is itself only very weakly pathogenic. The distribution of genets among every spruce stump in a 70-year-old 1250 m² spruce stand was analysed using somatic incompatibility testing. R. bicolor was present on 40% of 8-to 10-year-old stumps. Nineteen genets were found occupying 32 stumps; yielding probabilities of colonisation following establishment by basidiospores of 0.20–0.24 and by mycelial extension or dispersal of 0.16–0.20. The probability of colonisation decreased with increasing distance from a point of establishment. R. bicolor responded to both enrichment and destructive disturbances by the formation of an extensive cord system which enabled it to colonise discontinuously distributed resources and to overgrow fungi adjacent to it in a single resource unit, including Heterobasidion annosum.     

Inheritance of antagonistic properties and lytic enzyme activities in sexual crosses of Talaromyces flavus

Two wild-type strains and three benomyl-resistant mutants of the antagonistic ascomycete Talaromyces flavus were crossed in six combinations, two of which yielded hybrid cleistothecia. Parental strains and their ascospore progenies varied in several traits considered to play an important role in the capacity to control soilborne fungal pathogens: extracellular activities of glucose oxidase and cell-wall degrading enzymes, antibiosis towards Verticillium dahliae, and parasitism and biocontrol of Sclerotium rolfsii. A non-Mendelian quantitative mode of inheritance was found for β-1, 3-glucanase and chitinase activities but only the latter exhibited a normal frequency distribution. Some of the progenies exhibited higher glucanase and chitinase activities than those found in the parental strains. Progeny analysis for chitinase, glucanase, cellulase, and glucose oxidase activities revealed no genetic association between any two of these enzymes. Antibiosis was correlated with glucose-oxidase activity in one cross, but not in the other. The ability to reduce bean root rot caused by S. rolfsii was correlated with mycoparasitic activity against S. rolfsii sclerotia in one cross, but not in the other. One out of the 20 progenies tested was able to reduce bean root rot more effectively than its parent strains, thus demonstrating the feasibility of improving a biocontrol agent by conventional breeding.     

Parasitization of the cottony-cushion scale in relation to host size

Measurements of body length of cottony-cushion scales,Icerya purchasi Maskell, are presented. Although length increased markedly with developmental stage, the length distributions of successive stages were found to overlap, making length an imperfect indicator of stage andvice versa. The likelihood of parasitism by the fly,Cryptochaetum iceryae (Williston), was found to increase with increasing scale size when scales of different sizes were concurrently made available to the parasites under field conditions. Also, parasite loads (no. of parasites per parasitized host) were found to increase with host size. The size ofC. iceryae pupae was found to depend on the developmental stage of the scale host in which pupation took place — the more developed (larger) the host, the larger the pupa. This result suggests that parasite growth is food limited in the smaller hosts, and that therefore its apparent preference for larger hosts is to the parasite's advantage.      

A native nitrogen-fixing shrub facilitates weed invasion

Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.     

Biological diversity and cultural heritage

In this paper some examples of the development of communities of microorganisms and plants on historic buildings and montiments are shown. When the building stones differ from the surrounding natural substrata, an increase in the biological diversity of the area is produced. In some cases, monuments can come to constitute a true refuge for a few species when the natural habitat is threatened. It is suggested that biological diversity, when it does not represent a threat for the cultural heritage, should be considered worthy of preservation.     

Differential impact of egg predation by Zetzellia mali (Acari: Stigmaeidae) on Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

The differential impact of Zetzellia mali on the phytoseiids Metaseiulus occidentalis and Typhlodromus pyri was studied in the laboratory and by analysis of population from orchard plots that contained either phytoseiid, similar numbers of prey mites and high or low densities of Z. mali. Five hypotheses were evaluated to explain why Z. mali had more impact on M. occidentalis in the field than on T. pyri. Given equal opportunity, Z. mali adult females did not consume more M. occidentalis eggs than T. pyri eggs nor did adult females of either phytoseiid inflict greater mortality on Z. mali eggs or larvae through attack or consumption. There was no difference in the within-tree association of Z. mali adult females with eggs of either phytoseiid species nor were there differences in the way prey mites (all life stages) were spatially partitioned between adult female Z. mali as compared with adults and deutonymphs (combined) of either phytoseiid. The foraging area of adult female Z. mali and the oviposition locations of the two phytoseiids from both field and laboratory data were compared using spatial statistics. Metaseiulus occidentalis laid significantly more eggs in the primary foraging area of adult female Z. mali than T. pyri. This was the only factor identified which may explain the greater impact of Z. mali on M. occidentalis. The impact of these interspecific effects on the persistence of predatory mite guilds and biological control are discussed.