Suppression of fungal β-glucan-induced plant defence in soybean (Glycine max L.) by cyclic 1,3-1,6-β-glucans from the symbiont Bradyrhizobium japonicum

The production of antimicrobial phytoalexins is one of the best-known inducible defence responses following microbial infection of plants or treatment with elicitors. In the legume soybean (Glycine max L.), 1,3-1,6--glucans derived from the fungal pathogen Phytophthora sojae have been identified as potent elicitors of the synthesis of the phytoalexin, glyceollin. Recently it has been reported that during symbiotic interaction between soybean and the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110 the bacteria synthesize cyclic 1,3-1,6--glucans. Here we demonstrate that both the fungal and the bacterial -glucans are ligands of -glucan-binding sites which are putative receptors for the elicitor signal compounds in soybean roots. Whereas the fungal -glucans stimulate phytoalexin synthesis at low concentrations, the bacterial cyclic 1,3-1,6--glucans appear to be inactive even at relatively high concentrations. Competition studies indicate that increasing concentrations of the bacterial 1,3-1,6--glucans progressively inhibit stimulation of phytoalexin synthesis in a bioassay induced by the fungal 1,3-1,6--glucans. Another type of cyclic -glucan, a 1,2--glucan from Rhizobium meliloti, that does not nodulate on soybean, seems to be inactive as elicitor and as ligand of the -glucan-binding sites. These results may indicate a novel mechanism for a successful plant-symbiont interaction by suppressing the plant's defence response.Abbreviations HG-APEA 1-[2-(4-aminophenyl)ethyl]amino-l-[hexaglucosyl]deoxyglucitol - HG-AzPEA l-[2-(4-azidophenyl)-ethyl]amino-l-[hexaglucosyl]deoxyglucitol - IC₅₀ concentration for half-maximal displacement We thank Ines Arlt for excellent technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 369), the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, Fonds der Chemischen Industrie (J.E.), and USDA CSRS NRI Competitive Research grant 93373059233 (A.A.B.).     

c-fos expression in the amygdala:In vivo antisense modulation and role in anxiety

Summary 1. The amygdaloid complex is a key structure in mechanisms of fear and anxiety. Expression of the immediate-early gene c-fos has been reported in the central nucleus of the amygdala following various stressors, but the functional role of this phenomenon has remained unknown.2. c-fos expression was observed in the central nucleus when rats were subjected to a pharmacologically validated animal model of anxiety, the Vogel conflict test, but not after mere exposure to the test apparatus. Bilateral amygdala injection of a 15-mer phosphorothioate c-fos antisense oligodeoxynucleotide prior to testing blocked conflict-induced c-fos expression and had behavioral effects similar to those of established antianxiety drugs.3. Separate experiments determined that antisense treatment did not affect conflict behavior by acting on shock thresholds or drinking motivation.4. These findings provide evidence that neuronal activation and c-fos induction in the amygdala may be of importance for mechanisms of fear and anxiety.     

Creatine metabolism and the consequences of creatine depletion in muscle

Currently, considerable research activities are focussing on biochemical, physiological and pathological aspects of the creatine kinase (CK) — phosphorylcreatine (PCr) — creatine (Cr) system (for reviews see [1, 2]), but only little effort is directed towards a thorough investigation of Cr metabolism as a whole. However, a detailed knowledge of Cr metabolism is essential for a deeper understanding of bioenergetics in general and, for example, of the effects of muscular dystrophies, atrophies, CK deficiencies (e.g. in transgenic animals) or Cr analogues on the energy metabolism of the tissues involved. Therefore, the present article provides a short overview on the reactions and enzymes involved in Cr biosynthesis and degradation, on the organization and regulation of Cr metabolism within the body, as well as on the metabolic consequences of 3-guanidinopropionate (GPA) feeding which is known to induce a Cr deficiency in muscle. In addition, the phenotype of muscles depleted of Cr and PCr by GPA feeding is put into context with recent investigations on the muscle phenotype of gene knockout mice deficient in the cytosolic muscle-type M-CK.Abbreviations Cr creatine - Crn creatinine - PCr phosphorylcreatine - CK creatine kinase - M-CK cytosolic muscle type CK isoenzyme - Mi-CK mitochondrial CK isoenzyme - AGAT L-arginine: glycine amidinotransferase - GAMT S-adenosylmethionine: guanidinoacetate methyltransferase - Arg arginine - Met methionine - GPA guanidinopropionate=-guanidinopropionate - PGPA phosphorylated GPA - GBA 3-guanidinobutyrate=-guanidinobutyrate - CPEO chronic progressive external ophthalmoplegia     

Structure of the stomatal complex of the monocot Flagellaria indica

The structure of the mature stomatal complex of Flagellaria indica L. was studied since the Flagellariaceae is reported to be one of a handful of nongrass families with a grass-type stoma, and since relatively little is known about stomatal ultrastructure in monocots other than grasses. Both the grass guard cell and its nucleus are dumbbell-shaped, and the walls that separate adjacent grass guard cells are perforated. Electron and fluorescence microscopy reveal that the Flagellaria guard cell lacks these features. Instead, the Flagellaria guard cell is neither dumbbellnor kidney-shaped, its nucleus is roughly kidney-shaped, and the end walls are thickened and imperforate. Additional structural features of the stomatal apparatus of Flagellaria include: 1) the subsidiary cells have a protuberance that underlies the middle of the guard cell and that forms an additional and innermost aperture of the pore; 2) guard and subsidiary cell walls are thickened differentially and are layered; and 3) organelles in both cell types appear to be confined to specific domains. Although Flagellaria is closely related to grasses, it does not have a grass or dumbbell-shaped type of stomate. This suggests that the grass type of stomate may be less widespread than reported.     

Site-directed mutagenesis of the yeast PRP20/1SRM1 gene reveals distinct activity domains in the protein product

Prp20/Srm1, a homolog of the mammalian protein RCC1 in Saccharomyces cerevisiae, binds to double-stranded DNA (dsDNA) through a multicomponent complex in vitro. This dsDNA-binding capability of the Prp20 complex has been shown to be cell-cycle dependent; affinity for dsDNA is lost during DNA replication. By analyzing a number of temperature sensitive (ts) prp20 alleles produced in vivo and in vitro, as well as site-directed mutations in highly conserved positions in the imperfect repeats that make up the protein, we have determined a relationship between the residues at these positions, cell viability, and the dsDNA-binding abilities of the Prp20 complex. These data reveal that the essential residues for Prp20 function are located mainly in the second and the third repeats at the amino-terminus and the last two repeats, the seventh and eighth, at the carboxyl-terminus of Prp20. Carboxyl-terminal mutations in Prp20 differ from amino-terminal mutations in showing loss of dsDNA binding: their conditional lethal phenotype and the loss of dsDNA binding affinity are both suppressible by overproduction of Gsp1, a GTP-binding constituent of the Prp20 complex, homologous to the mammalian protein TC4/Ran. Although wild-type Prp20 does not bind to dsDNA on its own, two mutations in conserved residues were found that caused the isolated protein to bind dsDNA. These data imply that, in situ, the other components of the Prp20 complex regulate the conformation of Prp20 and thus its affinity for dsDNA. Gsp1 not only influences the dsDNA-binding ability of Prp20 but it also regulates other essential function(s) of the Prp20 complex. Overproduction of Gsp1 also suppresses the lethality of two conditional mutations in the penultimate carboxyl-terminal repeat of Prp20, even though these mutations do not eliminate the dsDNA binding activity of the Prp20 complex. Other site-directed mutants reveal that internal and carboxyl-terminal regions of Prp20 that lack homology to RCC1 are dispensable for dsDNA binding and growth.     

Enantiomerization of 2,2′-diisopropylbiphenyl during chiral inclusion gas chromatography: Determination of the rotational energy barrier by computer simulation of dynamic chromatographic elution profiles

By computer simulation of experimental dynamic gas chromatographic elution profiles, the rotational energy barrier ΔG⁼ of racemic 2,2′-diisopropylbiphenyl has been determined as 114.6–115.0 kJ/mol (75–100°C). These data are in good agreement with a value that was determined previously by measuring the racemization kinetics of an enriched sample. This indicates that there is no measurable catalytic or inhibitory effect of the stationary phase. © 1994 Wiley-Liss, Inc.     

Opalinidae in African Anura. III. Genus Cepedea

During 1988 and 1989, 409 specimens of southern African Anura comprising 50 species in 9 families were checked for opalinids in the cloaca. Cepedea acuta n. sp. was found in six of 19 Tomopterna cryptotis and four of seven T. krugerensis (Ranidae); C. affinis (Nazaretskaja, 1992) in two of four Afrixalus aureus, two of four Hyperolius horstocki, 23 of 42 H. marmoratus, one of seven H. pusillus, two of six H. semidiscus, and eight of 12 H. tuberilinguis (Hyperoliidae); C. magna Metcalf, 1923 in one of 20 Bufo garmani, eight of 33 B. gutturalis and two of nine B. rangeri (all Bufonidae), one of two Heleophryne natalensis (juveniles) (Heleophrynidae), four of six Kassina maculata, three of seven K. senegalensis and two of six Semnodactylus wealii (all Hyperoliidae), three of five Phrynomerus bifasciatus (Microhylidae), three of 12 Phrynobatrachus natalensis, 11 of 19 Tomopterna cryptotis, 13 of 14 T. delalandii, one of seven T. krugerensis and one of six T. natalensis (all Ranidae), and four of five Chiromantis xerampelina (Rhacophoridae); Cepedea vanniekerkae n. sp. in one of 19 Tomopterna cryptotis. It is suggested that the Ranidae (in particular the genus Tomopterna) and the Hyperoliidae (in particular the genus Hyperolius) are among the major carriers of Cepedea in the Afrotropical Region.