The pea ( Pisum sativum L.) genes sym33 and sym40 control infection thread formation and root nodule function

Two novel non-allelic mutants that were unable to fix nitrogen (Fix⁻) were obtained after EMS (ethyl methyl sulfonate) mutagenesis of pea (Pisum sativum L.). Both mutants, SGEFix⁻–1 and SGEFix⁻–2, form two types of nodules: SGEFix⁻–1 forms numerous white and some pink nodules, while mutant SGEFix⁻–2 forms white nodules with a dark pit at the distal end and also some pinkish nodules. Both mutations are monogenic and recessive. In both lines the manifestation of the mutant phenotype is associated with the root genotype. White nodules of SGEFix⁻–1 are characterised by hypertrophied infection threads and infection droplets, mass endocytosis of bacteria, abnormal morphological differentiation of bacteroids, and premature degradation of nodule symbiotic structures. The structure of the pink nodules of SGEFix⁻–1 does not differ from that of the parental line, SGE. White nodules of SGEFix⁻–2 are characterised by “locked” infection threads surrounded with abnormally thick plant cell walls. In these nodules there is no endocytosis of bacteria into host-cell cytoplasm. The pinkish nodules of SGEFix⁻–2 are characterised by virtually undifferentiated bacteroids and premature degradation of nodule tissues. Thus, the novel pea symbiotic genes, sym40 and sym33, identified after complementation analysis in SGEFix⁻–1 and SGEFix⁻–2 lines, respectively, control early nodule developmental stages connected with infection thread formation and function. Received: 12 June 1998 / Accepted: 25 June 1998     

Effect of the products of the vital activity of yeast-like fungi on levorin synthesis

The effect on levorin synthesis of the cells and fermentation broth filtrates of Candida tropicalis after their cultivation in the fermentation medium was studied. It was found that the yeast-like fungi belonging to Candida excreted during their development some products capable of stimulating the synthesis of levorin by 40--60 per cent. When the actinomycete producing levorin was grown on the medium containing 80 per cent of the filtrate the level of levorin synthesis was the same as that observed with mixed cultivation of the actinomycete and C. tropicalis. The study on the conditions providing accumulation of the stimulating substances showed the following: production of the stimulating substances started during the first hours of the yeast growth and reached its maximum by the 48th hour, these substances being consumed by the actinomycete during the fermentation process. Aeration is required for production of the stimulating substances but its high levels are not necessary.     

Structure of a community of testate amoebae in a sphagnum dominated bog in upper sura flow (Middle Volga Territory)

Fifty nine species of testate amoebae were found in a sphagnum moss bog located in the upper Sura flow (Volga highland). The active diversity in communities of sphagnum moss biotopes was formed by 24 species. Minimal species diversity (3 species) and maximum density of organisms were noted in the driest habitat. In the habitats with the medium humidity levels, the level of species richness was similar (13–16 species) and the total density was determined by redox characteristics of the environment: under the conditions of oxygen deficit, it was two to three times lower than in an oxidized environment. The species composition specificity in sphagnum moss biotopes was determined by the degree of humidity: in the driest habitats, Arcella arenaria predominated; in the biotopes with medium humidity, Nebela tenella and Hyalosphenia elegans; and in the most humid biotopes, Hyalosphenia papilio and Heleopera sphagni. Communities of testate amoebae differed by species composition and integral characteristics at different sphagnum moss horizons: the abundance and species richness increased with depth. The proportion of living individuals in the total number of tests was 35 to 75%.     

Phasic coordination between locomotor and respiratory rhythms in Lymnaea. Real behavior and computer simulation

In the pond snail Lymnaea stagnalis, a firm phase-locked coupling of pneumostome movements to the locomotor cycle was observed during terrestrial locomotion, thus demonstrating that the coordination between locomotor and respiratory rhythms is a natural behavioral event in this animal. The results of computational modelling suggest a possible scheme of coordination between these motor rhythms which is based on inhibitory projection from the central pattern generator for locomotion to that for respiration. These findings allow the neuronal mechanisms underlying coordination of two rhythmic behaviors to be investigated.     

The treatment of isolated genera

Problems presented by genera, or small groups of genera, which have been given family rank are reviewed, and the genera are divided into a number of categories according to the closeness of their affinity to other genera or families. Satellite genera that stand in close relation to families should be united with them. Binary families, that have been divided into two (or more) related families, should be re–united. Families connected by linking genera, should, logically, be united but practical considerations usually prevent this. Clusters of diverse but more or less distantly related genera present unusual problems, being treated either as several, often monogeneric families or as a loosely structured family. Truly isolated genera must be given family and often ordinal rank.     

Locomotor rhythms in the pond snail Lymnaea stagnalis: site of origin and neurotransmitter requirements

1. We have found that, in preparations of isolated CNS of the pond snail Lymnaea stagnalis, both serotonin (5HT) and dopamine (DA), as well as their respective precursors, 5HTP and DOPA, are effective in producing fictive intense (muscular) locomotion. 2. Phase-coupled to each of the above pedal rhythms are numerous identifiable pedal neurons including the respiratory interneuron RPeD1, thus suggesting interaction between networks responsible for locomotion and air breathing. 3. The novel DA/DOPA-dependent motor rhythm resembles the 5HT/5HTP-dependent one in terms of activity of identifiable pedal neurons, being however considerably slower than the latter. 4. The results of transection experiments suggest that each of the rhythms is generated by a paired CPG lying entirely within the pedal ganglia.