Utilization of carbon and nitrogen sources and acid/alkali production by cowpea rhizobia

Summary Sixteen slow-growing strains of rhizobia (15 cowpea rhizobia and oneR. japonicum) were examined to determine the effects of carbon and nitrogen sources on acid/alkali production in culture media. We found that the pH changes of the medium were more influenced by nitrogen sources than carbon sources (with the exception of ribose). When ammonium sulphate was used as a nitrogen source, all the cowpea rhizobia strains produced acid. When yeast-extract was used as a nitrogen source, however, a heterogenous pattern for acid/alkali production was found. The majority of the strains produced alkali from nitrate, glutamate and urea irrespective of carbon sources and acid from ribose irrespective of nitrogen sources.     

Amino-acid-transport mutant of Nicotiana tabacum L.

The structure of spinach ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) has been investigated by tilted-view electron microscopy of negatively stained monolayer crystals and image processing. The structure determined consists of a cylinder of octagonal cross-section with a large central hole. Based on this and other available evidence a model for the arrangement of the large and small subunits is suggested with the eight small subunits arranged equatorially around the core of eight large subunits.Abbreviations LS large subunit - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - SS small subunit     

Aspects of the numerical and functional respones of the aphid parasite, Aphidius sonchi, in the laboratory

The fecundity, reproductive rates, and adult survival of Aphidius sonchi Marshall (Hymenoptera: Aphidiidae) parasitizing second and third instar nymphs of the sowthistle aphid, Hyperomyzus lactucae (L.) (Homoptera: Aphididae) were measured at six different host densities under constant laboratory conditions. At host densities of less than 50 aphids per flowering shoot per female per day, oviposition constraints resulting from the lack of hosts reduced the number of eggs laid, enhanced the extent of superparasitization and, as a result, effectively lowered the fecundity and reproductive rates of the parasites. Above this host density the parasites laid on average 220–230 eggs, but the effective fecundity and reproductive rates continued to increase with the host density. By contrast, the survivorship of the parasites seemed unaffected by host density, with an average adult life span of 4–5 days at all densities. Analysis of the data showed that the intrinsic rate of increase (r_m) of the parasite varied with the host density and could reach values higher than that of the host under identical conditions. The response of r_m to changes in host density and parasite sex ratio is illustrated.Overall, A. sonchi showed a typical convex functional response, to host density. However, the response showed obvious changes through the parasite's adult life and, furthermore, the rates of changes were not consistent at all host densities. The frequency distributions of parasite eggs were generally indistinguishable from random, and the number of hosts parasitized were predicted satisfactorily by the random oviposition equation.

---

Résumé L'étude a porté sure l'influence de 6 densités différentes d'Hyperomyzus lactucae (L.) (Homoptera: Aphididae), en conditions constantes de laboratoire, sur la fécondité, le taux de reproduction et la survie des adultes d'Aphidius sonchi Marshall (Hym. Aphidiidae, parasite des larves de 2e et 3e stades. A des densités inférieures à 50 pucerons par tige fleurie de Sonchus oleraceus L, par femelle et par jour, la limitation de la ponte due à l'absence d'hôtes a réduit le nombre d'oeufs émis, élevé le taux de superparasitisme et, en conséquence, diminué la fécondité et le taux de reproduction des parasites. Aux densités d'hôtes supérieures, les parasites ont pondu, en moyenne, 220 à 230 oeufs, mais la fécondité réelle et les taux de reproduction ont continué à augmenter avec la densité des pucerons. Par contre, la longévité des parasites n'a pas été affectée par la densité des hôtes, avec une durée moyenne de vie de 4 à 6 jours. L'analyse des données a montré que le taux d'accroissement intrinsèque (r_m) du parasite a changé avec la densité des hôtes, et pourrait atteindre des valeurs supérieures à celles de l'ôte sous des conditions identiques. Les réponses de r_m aux changements de densité des hôtes et au taux sexuel du parasite sont expliquées.Globalement, A. sonchi a présenté une réponse fonctionnelle convexe typique à la densité des hôtes. Cependant, cette réponse a changé au cours de la vie des images et, de plus, les taux de changement ne sont pas logiques à toutes les densités d'hôtes La fréquence de distribution des oeufs n'est généralement pas séparable d'une distribution au hasard, et le nombre d'hôtes parasites peut être prédit d'une façon satisfaisante en utilisant une équation de ponte au hasard.

     

Calcium- and Calmodulin-Dependent Phosphorylation of Diphosphoinositide in Acetylcholine Receptor-Rich Membranes from Electroplax of Narke japonica

The phosphorylation of phosphoinositides in the acetylcholine receptor (AChR)-rich membranes from the electroplax of the electric fish Narke japonica has been examined. When the AChR-rich membranes were incubated with [gamma-32P]ATP, 32P was incorporated into only two inositol phospholipids, i.e., tri- and diphosphoinositide (TPI and DPI). Even after the alkali treatment of the membrane, AChR-rich membranes still showed a considerable DPI kinase activity upon addition of exogenous DPI. It is likely that the 32P-incorporation into these lipids was realized by the membrane-bound DPI kinase and phosphatidyl inositol (PI) kinase. Such a membrane-bound DPI kinase was activated by Ca2+ (greater than 10(-6) M), whereas the PI kinase appeared to be inhibited by Ca2+. The effect of Ca2+ on the DPI phosphorylation was further enhanced by the addition of ubiquitous Ca2+-dependent regulator protein calmodulin. Calmodulin antagonists such as chlorpromazine (CPZ), trifluoperazine (TFP), and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the phosphorylation of DPI in the AChR-rich membranes. It is suggested that the small pool of TPI in the plasma membrane is replenished by such Ca2+- and calmodulin-dependent DPI kinase responding to the change in the intracellular Ca2+ level.     

Modulation of [3H]Diazepam Binding in Rat Cortical Membranes by GABAA Agonists

GABAA receptor agonists modulate [3H]diazepam binding in rat cortical membranes with different efficacies. At 23 degrees C, the relative potencies for enhancement of [3H]diazepam binding by agonists parallel their potencies in inhibiting [3H]gamma-aminobutyric acid [( 3H]GABA) binding. The agonist concentrations needed for enhancement of [3H]diazepam binding are up to 35 times higher than for [3H]GABA binding and correspond closely to the concentrations required for displacement of [3H]bicuculline methochloride (BMC) binding. The maximum enhancement of [3H]diazepam varied among agonists: muscimol = GABA greater than isoguvacine greater than 3-aminopropane sulphonic acid (3APS) = imidazoleacetic acid (IAA) greater than 4,5,6,7-tetrahydroisoxazolo (4,5,6)-pyridin-3-ol (THIP) = taurine greater than piperidine 4-sulphonic acid (P4S). At 37 degrees C, the potencies of agonists remained unchanged, but isoguvacine, 3 APS, and THIP acquired efficacies similar to GABA, whereas IAA, taurine, and P4S maintained their partial agonist profiles. At both temperatures the agonist-induced enhancement of [3H]diazepam binding was reversible by bicuculline methobromide and by the steroid GABA antagonist RU 5135. These results stress the importance of studying receptor-receptor interaction under near-physiological conditions and offer an in vitro assay that may predict the agonist status of putative GABA receptor ligands.     

Variation in cellular ribulose-1,5-bisphosphate-carboxylase content in leaves of Triticum genotypes at three levels of ploidy

Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 1.1.39) (RuBPCase) was quantified using polyacrylamide-gel electrophoresis in whole 9-d-old first leaves of 14 genotypes of Triticum, and cellular RuBPCase levels calculated. Diploids, tetraploids and hexaploids were analysed and it was confirmed that the RuBPCase level per cell is closely related to ploidy in wheat. Inter-genotypic variation in RuBPCase levels per cell and per leaf were surveyed. It was found that the interactions between leaf size, cell size and RuBPCase levels result in small variations in RuBPCase levels per unit leaf area between genotypes.Abbreviation RuBPCase ribulose-1,5-bisphosphate carboxylase/oxygenase     

Structural organization of ultrarapidly frozen barley aleurone cells actively involved in protein secretion

The ultrastructural organization of actively secreting barley (Hordeum vulgare L. cv. Himalaya) aleurone cells was examined using ultrarapid-freezing (<-10 000°C s^-1) followed by freeze-fracture and freeze-substitution. Our analysis indicates that much of the evidence supporting a direct pathway from the endoplasmic reticulum (ER) to the plasma membrane (i.e. bypassing the Golgi apparatus) for the secretion of -amylase (EC 3.2.1.1) may not be valid. Cryofixed ER cisternae show no sign of vesiculation during active -amylase secretion in gibberellic acid (GA₃)-treated cells. At the same time, Golgi complexes are abundant and numerous small vesicles are associated with the edges of the cisternae. Vesicles appear to be involved in the delivery of secretory products to the plasma membrane since depressions containing excess membrane material appear there. Treatment with GA₃ also induces changes in the composition of Golgi membranes; most notably, the density of intramembrane particles increases from 2700 m^-2 to 3800 m^-2 because of an increase of particles in the 3–8.5-nm size range. A slight decrease in 9–11-nm particles also occurs. These changes in membrane structure appear to occur as the Golgi complex becomes committed to the processing and packaging of secretory proteins. We suggest that secretory proteins in this tissue are synthesized in the abundant rough ER, packaged in the Golgi apparatus, and transported to the plasma membrane via Golgi-derived secretory vesicles. Mobilization of reserves is also accompanied by dynamic membrane events. Our micrographs show that the surface monolayer of the lipid bodies fuses with the outer leaflet of the bilayer of protein-body membranes during the mobilization of lipid reserves. Following the breakdown of the protein reserves, the protein bodies assume a variety of configurations.Abbreviations ER endoplasmic reticulum - GA₃ gibberellic acid - P protoplasmic - E exoplasmic     

Studies on graft unions

Summary The occurrence of plasmodesmata in the graft interfaces of two heteroplastic grafts (Impatiens walleriana onImpatiens olivieri andHelianthus annum onVicia faba) has been studied. For both systems two types of intercellular strand are described: 1. Continuous plasmodesmata interconnecting the cells of stock and scion and 2. half plasmodesmata traversing the wall part of one partner cell without connection to the abutting cell. Single strands or branched forms occur in both types of plasmodesma. In the case of half plasmodesmata, branchings with extended median nodules predominate. The distribution of half and continuous plasmodesmata varies with the different areas of a graft interface: in the region of bridging vascular tissues most cell connections are continuous. In areas where cortex or pith-derived callus cells and those of misaligned tissues (cortex/vascular tissue; cortex/pith; pith/vascular tissue) match, discontinuous strands predominate.Branched half plasmodesmata also occur in presumably fused walls between related callus cells; they are typical structures secondarily formed in non-division walls.The results are discussed with regard to compatibility/incompatibility phenomena in heterografts and the development and function of interspecific cell bridges.     

Multiline varieties and disease control

Summary A general model for the evolution of pathogen populations on mixtures or multilines is developed. This model is used to extend previous analyses of the effects of the widespread cultivation of multilines on the evolution of virulence in obligate parasites to mixtures of lines carrying different numbers of resistance genes. It is concluded that the composition of an equilibrium pathogen population growing on a multiline may vary within wide limits and the prinicipal determinant of its composition is the number of components in the multiline and the resistance genes they carry. Other factors of importance are (i) the relative contribution made by each host class (with different numbers of resistance genes) to the pathogen spore pool each generation; (ii) the levels of stabilizing selection against unnecessary virulence genes; and (iii) the way in which unnecessary genes for virulence combine to reduce pathogen fitness. Conditions for the fixation of avirulent biotypes in the pathogen population and the evolution of a pathogen superrace are given for multilines of various compositions.Paper No. 9246 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina. This investigation was supported in part by NIH Research Grant No. GM 11546 from the National Institute of General Medical Sciences     

Genetical investigations into β-glucan content in barley

Summary Random inbred lines produced by doubled haploidy (DH) and single seed descent (SSD) have been used to investigate the genetics of -glucan (gum) content in barley (Hordeum vulgare). Genetical analyses indicated that gum content is controlled by a simple additive genetic system. Significant negative genetic correlations were observed between -glucan content, thousand grain weight and height in the DH samples. These correlations were much reduced in the SSD samples and would suggest linkage of the genes controlling these characters. The presence of repulsion linkages could be exploited in a barley breeding programme by producing F1 derived DH to generate recombinants with high thousand grain weight and low -glucan content. Genetical parameters estimated from DH and F3 samples have successfully been used to predict the number of inbred lines transgressing the parental range for -glucan content and bivariate combinations involving -glucan.