Light perception in higher plants

Photosynthetic plants depend on sunlight as their energy source. Thus, they need to detect the intensity, quality and direction of this critical environmental factor and to respond properly by optimizing their growth and development. Perception of light is accomplished by several photoreceptors including phytochromes, blue/ultraviolet (UV)-A and UV-B light photoreceptors. In recent years, genetic, molecular genetic and cell biological approaches have significantly increased our knowledge about the structure and function of the photoreceptors, and allowed the identification of several light signal transduction components. Furthermore, this research led to fruitful interaction between different disciplines, such as molecular biology and ecology. It is safe to assume that we can expect more milestones in this research field in the upcoming years.     

The association of phytoecdysteroids with flowering in fat hen,Chenopodium album,and other members of the Chenopodiaceae

Very high concentrations of ecdysteroid are associated with flowering inChenopodium album. Highest concentrations are found in anthers, but significant levels are also found in the stamens, carpels and sepals. In contrast, pollen contains only low levels. The ecdysteroid profile is the same in anthers as in whole-plant extracts, with 20-hydroxyecdysone and polypodine B predominating. The results for flowers ofC. album are compared with the patterns determined for other chenopods (C. capitatum, C. polyspermum, C. anthelminticum, C. giganteum, C. quinoa andC. foliosum). The significance of these findings for plant-insect interactions and the relationship to the mode of plant pollination are discussed.     

Ecdysteroids: possible candidates for the hormone which triggers salivary gland degeneration in the ixodid tickAmblyomma hebraeum

Summary Following engorgement, female ixodid ticks secrete a tick salivary gland degeneration factor (TSGDF) into the hemolymph. Here we show that the arthropod ecdysteroid hormones, ecdysome and 20-hydroxyecdysone, induce degeneration of tick salivary glands maintained in organ culture. The effective dose range in vitro is 30–300 ng/ml, a range reported to be physiological for this species following repletion. In addition, infusion of 20-hydroxyecdysome in vivo induces salivary gland degeneration. We therefore propose that TSGDF may be an ecdysteroid.Acknowledgments. Some of the data reported here were presented to the annual meeting of the Canadian Society of Zoologists, 15–18 May 1983; Program of abstracts, page 53. Financial support of the Canadian National Sportsmen's Fund and NSERC Canada to W.R.K. is gratefully acknowledged.     

Effects of ingested phytoecdysteroids in the female soft tickOrnithodoros moubata

The effects of the ingestion of some phytoecdysteroids were studied in the soft tickOrnithodoros moubata. Supernumerary moulting and malformations of first leg pairs were obtained with 22-oxo-20-hydroxyecdysone, 20-hydroxyecdysone-22-acetate, and 20-hydroxyecdysone-22-benzoate. Egg-yield was reduced with 20-hydroxyecdysone-22-acetate and carthamosterone. Finally, drying-out of eggs was observed with carthamosterone and 22-deoxy-20,26-dihydroxyecdysone. In addition, we demonstrated that there is a correlation between the number of completed gonotrophic cycles and the impossibility of inducing supernumerary moulting.     

Resveratrol-type oligostilbenes from Iris clarkei antagonize 20-hydroxyecdysone action in the Drosophila melanogaster B(II) cell line

Bioassay-guided high-performance liquid chromatography analysis of a MeOH extract of Iris clarkei seeds yielded the resveratrol-type oligomeric stilbenes, ampelopsin B and α-viniferin, which antagonize the action of 20-hydroxyecdysone; with a 20-hydroxyecdysone concentration of 50 nM, the ED₅₀ values were 33 μM and 10 μM, respectively. The structures of these compounds were determined by spectroscopic analysis, notably ultraviolet, liquid secondary ion mass spectrometry and modern one- and two-dimensional nuclear magnetic resonance techniques. Received 4 November 1999; accepted 13 December 1999     

Ecdysteroid conjugates in the ovaries of the silkworm,Bombyx mori: 3-phosphates of 2,22-dideoxy-20-hydroxyecdysone and of bombycosterol

Summary Two novel ecdysteroid conjugates, 2,22-dideoxy-20-hydroxyecdysone 3-phosphate (1) and bombycosterol 3-phosphate (2), as well as four known ecdysteroid 22-phosphate esters, have been isolated and characterized from the ovaries of the silkworm,Bombyx mori.     

Mechanisms of self-incompatibility in flowering plants

Self-incompatibility is a widespread mechanism in flowering plants that prevents inbreeding and promotes outcrossing. The self-incompatibility response is genetically controlled by one or more multi-allelic loci, and relies on a series of complex cellular interactions between the self-incompatible pollen and pistil. Although self-incompatibility functions ultimately to prevent self-fertilization, flowering plants have evolved several unique mechanisms for rejecting the self-incompatible pollen. The self-incompatibility system in the Solanaceae makes use of a multi-allelic RNase in the pistil to block incompatible pollen tube growth. In contrast, the Papaveraceae system appears to have complex cellular responses such as calcium fluxes, actin rearrangements, and programmed cell death occurring in the incompatible pollen tube. Finally, the Brassicaceae system has a receptor kinase signalling pathway activated in the pistil leading to pollen rejection. This review highlights the recent advances made towards understanding the cellular mechanisms involved in these self-incompatibility systems and discusses the striking differences between these systems. Received 10 May 2001; received after revision 20 June 2001; accepted 20 June 2001     

On the existence of cytokines in invertebrates

Based on the assumption that invertebrates, like vertebrates, possess factors regulating responses to infection or wounding, studies dealing with the evolution of immunity have focussed on the isolation and characterisation of putative cytokine-related molecules from invertebrates. Until recently, most of our knowledge of cytokine- and cytokine receptor-like molecules in invertebrates relies on functional assays and similarities at the physicochemical level. As such, a phylogenetic relationship between invertebrate cytokine-like molecules and vertebrate counterparts could not be convincingly demonstrated. Recent genomic sequence analyses of interleukin-1-receptor-related molecules, that is Toll-like receptors, and members of the transforming growth factor-β superfamily suggest that the innate immune system of invertebrates and vertebrates evolved independently. In addition, data from protochordates and annelids suggest that invertebrate cytokine-like molecules and vertebrate factors do not have the same evolutionary origin. We propose instead that the convergence of function of invertebrate cytokine-like molecules and vertebrate counterparts involved in innate immune defences may be based on similar lectin-like activities. Received 27 November 2000; received after revision 11 December 2000; accepted 13 December 2000     

Short-range linkage relationships, genomic organisation and sequence comparisons of a cluster of five HSP70 genes in Fugu rubripes

Twelve cosmids containing sequences resembling genes encoding members of the 70-kDa heat-shock protein family, HSP70, have been isolated from Fugu rubripes. They can be broadly divided into three groups of overlapping cosmids. Restriction analysis and sequencing of one set of five cosmids have revealed five intronless Fugu HSP70 genes spanning 42 kb, arranged in a combined head-to-head, tail-to-tail and head-to-tail orientation. The levels of DNA and amino acid identity are very high with respect to one another, and are most similar to HSP70 sequences linked to the major histocompatibility complex (MHC) region in other species. Putative heat-shock consensus elements are identified. Non-HSP70 sequences with homology to known genes have been found physically linked to this Fugu HSP70 cluster: the Drosophila melanogaster SOL gene, the Drosophila melanogaster nemo gene, the Caenorhabditis elegans T17E9.1 gene and the sequence encoding the serine protease domain. The linkage relationships described here so far bear no resemblance to those of HSP70 in other organisms. Convergence of mammalian HSP70 and MHC class I and II loci probably occurred after fish had diverged. Received 17 November 1998; received after revision 25 February 1999; accepted 26 February 1999     

The functions of mucosal T cells in containing the indigenous commensal flora of the intestine

There is an immense load of non-pathogenic commensal bacteria in the distal small intestine and the colon of mammals. The physical barrier that prevents penetration (translocation) of these organisms into the body is a simple epithelium comprised of the single enterocyte/colonocyte cell layer with its overlying mucus. In this review, we discuss the roles of intestinal T cells in initiating and regulating innate and adaptive mucosal immune responses of the mucosal immune system that avoid or limit penetration of the commensal intestinal bacteria. Received 9 August 2002; accepted 9 September 2002 RID="*" ID="*"Corresponding author.     

Structure and assembly of the 20S proteasome

The barrel-shaped 20S proteasome is one of the two components of a larger 26S particle, the multicatalytic 2000-kDa protease complex. The proteolytic sites are located in the inner chamber of the 20S particle and are only accessible via narrow entrances. This paper reviews the current knowledge concerning proteasome formation, proteolytic activities, structural aspects and assembly. Eukaryotic proteasomes are made up by four rings each of which contains seven different subunits occurring at fixed positions. While the outer rings contain α-type subunits, the inner ones comprise β-type subunits. The current assembly model for eukaryotic 20S proteasomes is based upon the detection of 13S and 16S intermediates, respectively, in addition to previous findings with archaebacterial and eubacterial proteasome assembly. The available data suggest a cooperative assembly of the α-type and β-type subunits into half proteasome-like complexes followed by dimerization into proteasomes. During or after dimerization of half proteasomes, the β-type subunits are processed. The prosequence of the β-type subunits is essential for the assembly process and prevents protease activity of immature proteasomes.     

Role of low ecdysteroid levels in the early last larval instar ofBombyx mori

The relationship between juvenile hormone and ecdysteroid titers during the early stage of the last larval instar of the silkworm,Bombyx mori, was examined in this study. When larvae were fed 20-hydroxyecdysone-supplemented mulberry leaves throughout the last larval instar, 100% underwent supernumerary larval molting instead of metamorphosis. The application of juvenile hormone mimic during the early last instar did not induce supernumerary larval molting, but did delay metamorphosis. Temporal and quantitative ecdysteroid titer measurements revealed that in normal larvae the titers maintained very low levels (3–12 ng/ml) during the early stage of the last instar; however, in 20-hydroxyecdysone-treated larvae, levels ranging from 24 to 45 ng/ml were detected, and a major peak (246 ng/ml) was observed on day 6. These results show that very low ecdysteroid titer levels during the early stage of the last larval instar may play an important role in initiating decreases in juvenile hormone titers as well as in directing metamorphosis.     

Insect hormones in vertebrates: Anabolic effects of 20-hydroxyecdysone in Japanese quail

Ecdysteroids are hormones controlling cell proliferation, growth and the developmental cycles of insects and other invertebrates¹. They are occasionally present in various unrelated plants for no apparent reason; no phytohormonal function has yet been identified. In certain cases, ecdysteroids are accumulated to high levels in leaves, roots or seeds. Some ecdysteroid-containing plants have been known as medicinal plants for centuries. One of them,Leuzea carthamoides Iljin (Asteraceae), growing in Central Asia, contains 0.4% ecdysteroid in dry roots and 2% in seeds. A pharmacological preparation from this plant, Ecdisten, is already available as a commercial preparation for its anabolic, tonic and other effects, for medical use (review²). It remained problematic, however, whether ecdysteroids were truly responsible for these effects, becauseLeuzea contains a number of other biologically active compounds in addition to ecdysteroids. We extracted and purified ecdysteroids from the seeds ofLeuzea. With 6 g of 96% 20-hydroxyecdysone (20E), we made a large-scale feeding assay with Japanese quail to find out whether ecdysteroid alone could duplicate the anabolic effects of the seeds. We found that the 96% ecdysteroid increased the mass of the developing quails in a dose-dependent manner, with the rate of increase proportional to the ecdysteroid content in the seeds; there was a 115% increase in living mass with 100 mg kg^–1 of pure 20E compared with 109.5% increase with 100–180 mg kg^–1 20E equivalents in the seeds. We conclude that the plethora of growth-promoting, vitamin-like effects induced in vertebrates byLeuzea is mediated by ecdysteroids.     

Occurrence of 3-epi-22-deoxy-20-hydroxyecdysone and its phosphoric ester in diapause eggs of the silkworm,Bombyx mori

Ecdysteroids in diapause eggs of the silkworm,Bombyx mori, were analyzed using high-performance liquid chromatography (HPLC) combined with radioimmunoassay (RIA). A relatively large amount of an unidentified free ecdysteroid and its phosphoric ester (conjugated form) were detected. These two compounds were isolated by a combination of column chromatography on silicic acid, thin-layer chromatography (TLC), and HPLC using a reverse-phase (RP) column. The purified compounds were identified as 3-epi-22-deoxy-20-hydroxyecdysone (22d20E) and 3-epi-22-deoxy-20-hydroxyecdysone 2-phosphate (22d20E2P) by means of mass spectrometry and nuclear magnetic resonance spectroscopy. to our knowledge, this is the first report of 22d20E and 22d20E2P.     

On the distribution in brain of monoamines and of enzymes responsible for their formation

Zusammenfassung Im menschlichen Gehirn kommen grosse Mengen von 3-Hydroxytyramin im Nucleus Caudatus und dem Putamen vor.Injektion von 3,4-Dihydroxyphenylalanin in Kaninchen bringt eine schnelle Akkumulation von 3-Hydroxytyramin in den Gehirnteilen, die reich an Katecholaminen sind, zustande. Die Fähigkeit das akkumulierte 3-Hydroxytyramin abzubauen scheint im ganzen Gehirn dieselbe zu sein.Hemmungsversuche und Aktivitätsuntersuchungen der Fermente in verschiedenen Gehirnteilenin vitro sprechen dafür, dass 5-Hydroxytryptophan und 3,4-Dihydroxyphenylalanin von einem und demselben Ferment decarboxyliert werden.     

On the normative dimension of the St. Petersburg paradox

In this paper I offer an account of the normative dimension implicit in D. Bernoulli’s expected utility functions by means of an analysis of the juridical metaphors upon which the concept of mathematical expectation was moulded. Following a suggestion by the late E. Coumet, I show how this concept incorporated a certain standard of justice which was put in question by the St. Petersburg paradox. I contend that Bernoulli would have solved it by introducing an alternative normative criterion rather than a positive model of decision making processes.