Rapid reorganization of microtubular cytoskeleton accompanies early changes in nuclear ploidy and chromatin structure in postmitotic cells of barley leaves infected with powdery mildew

Summary Post-mitotic epidermal cells of barley leaves were found to contain, in addition to cortical microtubules (CMTs), distinct arrays of endoplasmic microtubules (EMTs). These encircle nuclei and continuously merge into the CMT arrays that underly the plasmalemma. Detailed three-dimensional reconstruction of both types of MTs during fungal infection showed that profound and very rapid MT rearrangements occurred especially in the case of incompatible (resistant) barley-powdery mildew genotype combination. The most early MT responses, followed by their subsequent complete disintegration, were recorded around nuclei. These events might be relevant for the induction of such nuclear processes as onset of DNA synthesis and nuclear chromatin condensation. Observed pattern of early infection events, as well as less prominent responses in the case of compatible (susceptible) barley-powdery mildew genotype combination, both findings suggest that rapid reorganization of the MT cytoskeleton could be involved in recognition of the fungus by host cells and in the initiation of resistance responses in barley leaves. We hypothesize that the integrity and dynamics of the MT cytoskeleton, especially of its perinuclear part, might participate in control mechanisms involved in activation of resistance genes.Abbreviations CMTs cortical microtubules - EMTs endoplasmic microtubules - MT microtubules - PI propidium iodide - SC sensitive combination - RC resistant combination     

Thoughts on the origin and nature of life and intelligence on earth

Believing, for good reasons, that our Universe engenders the occurrence of Life, it is probable that Life appeared more than once on young planet Earth. The universality of our genetic code indicates though, that only one line produced a population that was cellular, autopoietic, responsive intelligently (i.e., to its advantage) to its environment, and capable of reproduction. Its evolution took time during which other intermediate or incipient forms of life disappeared. Trying to retrace ab initio the preceding chemical evolution on our young planet, we may not repeat the chemistry which led to our line. One can argue that it may be profitable to attempt to construct artificial life forms using the kind of building blocks that we learned to know through studying the chemistry of our life. Independently, computers are being built, or are planned, which possess memory that can be used appropriately (intelligently), and which to some extent can repair and reproduce themselves. Such Life does not depend on our biochemistry. However, these machines do perform as yet only partly along the lines of our human intelligence which is guided by self-awareness and a sense of individual integrity, and are thereby not equipped to search for Understanding and Self-expression.     

Trophic links,nutrient fluxes,and natural history in the Allium ursinum food web,with particular reference to life history traits of two hoverfly herbivores (Diptera: Syrphidae)

The food web centering on Allium ursinum (Liliaceae) in a beech forest (Germany) is described, and temporal variation of active trophic links is related to species' life cycles. The most important insect herbivores are Cheilosia fasciata (a larval leaf miner) and Portevinia maculata (a larva bulb miner) (Diptera: Syrphidae). Energy, carbon and nitrogen flow in the food chain (Allium-Cheilosia-Phygadeuon ursini) are investigated and analysed with respect to differences in resource allocation by the leaf miner and its hymenoptereous parasitoid. In C. fasciata nitrogen is likely to be the limiting resource, while growth in Phygadeuon ursini appears energy-limited. Larval feeding habits of C. fasciata and Portevinia maculata determined the timing of the species' life cycles and, as a consequence, appeared to preclude the existence of a pupal parasitoid in Portevinia maculata. Further details of life history traits are demonstrated and discussed.     

Natural Control of Helicoverpa armigera in Sunflower: Assessment of the Role of Predation

In three field experiments in Kenya , the seasonal population trend of Helicoverpa armigera (Hubner) (= Heliothis armigera) in sunflower was followed in plots from which predators were excluded and in plots from which predators were not excluded . In experiment 1 , complete exclusion of crawling predators (predominantly Pheidole spp . of ants occurring at densities of 25 per plant) resulted in H. armigera densities 3 - 5 times higher than in plots where ants were not excluded . Pheidole sp . had more impact on young H. armigera larvae (instars 2 - 3) than on older larvae (instars 4 - 6) . The results of experiment 2 were less striking , because H. armigera infestation was low , and ant densities were moderate . Here , Myrmicaria spp . and Camponotus spp . were the predominant ants . Exclusion of ants resulted in a 1 . 8 - fold increase in densities of large H. armigera instars . In experiment 3 , the impact of predators on H. armigera was studied under three conditions: exclusion of crawling predators , exclusion of both crawling and flying predators , and the control where no predators were excluded . To evaluate the role of predation in total mortality , the recruitment of H. armigera larvae was determined with Southwood and Jepson ' s graphical method , and recruitment of newly laid eggs was directly measured on trap plants . Because it was difficult to detect older eggs due to colour change , the direct measurement of egg recruitment was superior to the graphical method . Ants and Anthocoridae were the dominant predators . M ortality from egg to older larvae (instars 4 - 6) was 73 - 78% . Exclusion of ants and anthocorids did not affect the densities of H. armigera larvae . Anthocorid predators increased only after the main oviposi tion peak of H. armigera and , therefore , their exclusion had little impact on the pest . Ant density was considerably lower than in experiment 1 , and did not significantly suppress H. armigera.     

Laboratory culture and taxonomy of two species ofPedobesia (Bryopsidales,Chlorophyceae) in Japan

The morphology ofPedobesia lamourouxii andDerbesia ryukyuensis, both collected in Shimoda and the adjacent areas in central Japan, was studied from field specimens and laboratory cultures. Specimens which had the same morphology as EuropeanP. lamourouxii produced stephanokont zoospores which developed into either prostrate filaments or expanded discoidal thalli similar to those described by Feldmann and Codomier (1974) and Feldmannet al. (1975). Erect filament identical with the thallus found in nature developed directly from prostrate filaments. The specimens which had morphology similar to that ofDerbesia ryukyuensis described by Yamada and Tanaka (1938) also produced stephanokont zoospores which developed similarly to those ofP. lamourouxii. This species is, therefore, a member ofPedobesia, and it is made a new combinationP. ryukyuensis (Yamada et Tanaka) Kobara et Chihara, comb. nov.     

Laboratory culture and taxonomy of two species ofDerbesia (Class Chlorophyceae) in Japan

Two species ofDerbesia (Class Chlorophyceae),D. marina andD. tenuissima, have been studied for the purpose of obtaining a better understanding of their morphological details and life histories, using preserved and living specimens as well as laboratory cultures. The life histories of both species were completed in the laboratory, starting from both zoospores and zygotes. Specimens were collected at Asamushi, Aomori-ken, and Shimoda, Shizuoka-ken. Their life history types are fundamentally identical, zoospores giving rise upon germination toa Halicystis-phase, while zygotes grow into aDerbesia-phase. The thallus of theHalicystis-phase which alternates withD. marina is the same as that ofH. ovalis which grows in the northern regions of Japan. On the other hand, the thallus of theHalicystis-phase alternating withD. tenuissima is the same as that ofH. parvula known to occur in the temperate to subtropical regions of Japan. These results coincide with those obtained withD. marina andD. tenuissima in Europe, where the type localities of both species are located. Specimens assignable to these two species were collected at several localities in Japan and, as a result of detailed examination of the morphology, they are believed to be identical with eitherD. marina orD. tenuissima.     

Population dynamics of the swallowtail butterfly,Papilio xuthus L., in a deforested area

The long-term population dynamics of the swallowtail butterfly, Papilio xuthus, were studied by means of life table analysis in a deforested area, where the host tree, Zanthoxylum ailanthoides, was growing. The number of eggs laid on host trees in the deforested area decreases as secondary succession progresses. When the trees were classified into three groups, i. e. tall, medium and short, according to their height relative to the surrounding vegetation, less eggs were laid on tall than on short host trees. Life tables for the natural populations in each generation were developed on the basis of mean values for 6 years. Eggs and larvae in early stages were attacked chiefly by small- and middle-sized predators, such as ants, spiders, bugs and orthopterids, while later stage larvae were attacked chiefly by birds or Polistes wasps. An inchneumonid wasp was the most important mortality factor in the pupal stage. Key-factor analysis was tested on the life table data of each immature stage. The late larval stage was a key stage, and most mortality factors were considered to operate independently. The test for density dependency did not show any tendencies. The analysis of variance in two-way classifications was carried out for the difference of survival rate among the tree groups. It was suggested that tall host trees were unsuitable for P. xuthus. The construction of life tables for artificially inoculated populations on large host trees showed that high physiological death rate were characteristic of such trees in comparison with natural populations on smaller trees. The characteristics of the population dynamics of P. xuthus in the deforested area are compared among some kinds of the habitat, and the interrelationship between P. xuthus and its host plant are discussed.     

Phenotypic variation in the breeding phenology of the woodlouse Armadillidium vulgare

Summary The breeding phenology of temperate wood-lice is strongly seasonal, the result of physiological constraints and precise environmental cues for reproduction. The adaptive value of such mechanisms is that the release of offspring coincides with favourable conditions for growth and survival (Willows 1984). We recorded the breeding phenology of Armadillidium vulgare (Latreille) on two grassland sites in Great Britain and found between-site and between-year variation in the onset of reproduction, the duration of reproductive activity, the release of offspring, the size of reproductive females and the number of broods per female. Between 82.7 and 97.7% of gravid females sampled were semelparous at 23 months, with the remainder iteroparous, producing a second brood after 35 months. On one site (Weeting Health) improved growth conditions during 1984 allowed some females (19.3% of gravid females sampled in that year) to produce a brood after 11 months. There was also an increase in the number of 3-year-old females found to be gravid. An experimental manipulation of the same habitat confirmed that such changes in life history tactics could be phenotypic responses. The observed phenotypic variation was sufficient to produce a range of life history tactics within a population. Mixtures of life history tactics within a population may be typical of invasive species and populations at the edge of the species range. Our results support the idea that phenotypic plasticity can be an appropriate tactic to maximise fitness in a fluctuating environment (Caswell 1983, 1989).