Occurrence of bacterivory in Cryptomonas,a common freshwater phytoplankter

Summary Bacterivory was detected by incorporation of 0.57 m diameter, fluorescent polystyrene beads and fluorescently labeled bacteria (FLB) in two cultured species of Cryptomonas (C. ovata and C. erosa), and a population of Cryptomonas sp in a humic, mesotrophic lake. Rates of ingestion and clearance were very low, and similar for the cultures and the in situ population. The in situ population incorporated 0.7–1.7 bacteria cell^-1 h^-1, thereby ingesting 0.3%–2.0% of the total bacterial numbers present in the water per day, and receiving less than 2% of its carbon content per day through bacterivory. Thus, bacterivory by Cryptomonas was quantitatively important neither as a sink for bacterial biomass, nor as a carbon source for the algal cells. Possibly, it served in the uptake of essential nutrients.     

Response of grasshoppers (Orthoptera: Acrididae) to livestock grazing in southeastern Arizona: differences between seasons and subfamilies

Summary Grasshopper densities were compared between grazed and ungrazed semidesert grassland sites in southeastern Arizona. Bouteloua-dominated perennial grass cover was about 1.5 times greater on the livestock exclosure. Grasshoppers were 3.7 times more abundant on the protected area in the summers of 1983 and 1984, when dominant species were grass-feeding members of the subfamily Gomphocerinae. In fall 1984, grasshoppers were 3.8 times more common on the grazed site, when dominants were mainly herb-feeders in the subfamily Melanoplinae. These results indicate important seasonal and taxonomic differences in the responses of grasshoppers to the activities of vertebrate grazers.     

Local and systemic changes in gene expression induced in tomato plants by wounding and by elicitor treatment

Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants have been wounded to induce the accumulation of proteinase-inhibitor proteins (PI proteins) at the local site of injury and systemically in unwounded tissues. To determine the range of genes affected in the wound-response, polysomal mRNA has been isolated from the damaged leaves and from systemically responding leaves over a time-course of 2, 4, 10 and 24 h after wounding. Changes in the pattern of ³⁵S-translation products indicate that the events that occur at the local wound-site are different from those that occur systemically, both with respect to the number of genes that are regulated and the timing of their regulation. In order to compare the effects of wounding and an endogenous systemic signal generated at the wound-site with those of elicitor (proteinase-inhibitor-inducing factor, PIIF) treatment of excised plants, polysomal mRNA has also been isolated from leaves of plants over a time-course of 2, 4, 10 and 24 h after PIIF-treatment. Changes in the pattern of ³⁵S-translation products indicates that the events induced by PIIF resemble those induced by mechanical injury, rather than those induced by the endogenous systemic signal.Abbreviations IFF isoelectric focussing - PI proteins proteinase inhibitor proteins - PIIF proteinase-inhibitor-inducing factor - ssRubisco small subunit of ribulose-1,5-bisphosphate carboxylase     

Chemotaxis in Methanospirillum hungatei

Methanospirillum hungatei gave a positive chemotactic response to acetate.     

Control of respiratory motor pattern by sensory neurons in spinal cord of lamprey

Summary Extracellular stimulation over the dorsal funiculus in the spinal cord of lampreys was found to selectively activate prolonged episodes of fictive arousal respiration (Figs. 1, 3). The induced episodes showed comparable increases in cycle frequency and motoneuron burst duration to the spontaneous arousal pattern observed in isolated brain preparations (Fig. 2). Intracellular stimulation of primary sensory neurons with axons in the dorsal funiculus, called dorsal cells, also elicited the arousal pattern (Fig. 4). Mechanoreceptive dorsal cells respond to cutaneous stimulation. When mechanical stimuli were applied to the skin of intact lampreys (Fig. 6) or to lampreys with ipsilateral vagotomy, arousal respiration was induced (Figs. 7, 8). Bilateral, but not unilateral, trigeminal lesion blocked dorsal cell induction of the arousal response (Fig. 5). Spontaneous arousal respiration was recorded from intact, unrestrained lampreys (Fig. 9). These results suggest that fictive arousal respiration is the in vitro correlate of natural arousal respiration in lampreys, and that one mechanism leading to arousal respiration may be the activity of sensory dorsal cells. A model for respiratory motor pattern switching in lamprey is proposed. The model suggests that the normal and arousal patterns are produced by separately engaging rostral or caudal pattern generators in the medulla, rather than by modifying one pattern generator (Fig. 10).     

Segmentation and moral status in vivo and in vitro: a scientific perspective

A basic consideration in research on human embryos is the controversy about when the embryo acquires moral status. The author refutes the contention that segmentation is the determinant of moral status. She notes that segmentation, as a stage in embryonic development, does not coincide with the development of "irreversible individuality" upon which the segmentation argument depends. Dawson also finds a lack of clarity in the meaning of "individuality." These problems, she maintains, prevent segmentation from being morally important and render the proposed 14-day limit on embryo research unnecessary. Dawson concludes that to introduce a time restriction on embryo research is premature because it is based on an inadequate philosophical argument.     

In vitro detachment of bacteria from ruminal digesta by buffered sodium oleate solutions

The effectiveness of a buffered sodium oleate solution was evaluated for detaching bacteria from ruminal digesta samples. A response surface derived from an octagonal design was used to determine the pH and concentration combination for maximum detachment of total and cellulolytic bacteria. The total number of bacteria detached increased up to 81% over control with treatment of a pH 8.8 and 1.5% sodium oleate solution. The recovery of cellulolytic bacteria was decreased to 35% of control with treatment of a pH 9.0 and 0.1% sodium oleate solution. Attempts to improve the recovery of viable bacteria exposed to sodium oleate solutions were unsuccessful. This response surface design identified an optimal pH and concentration that were consistent with existing information regarding detachment of total bacteria, and suggested that sodium oleate, at the concentrations tested, was toxic to the cellulolytic population of the rumen.     

Class II genes of miniature swine

Class II genes of miniature swine have been characterized by restriction fragment length polymorphism (RFLP) analysis and by analysis of a series of clones isolated from a lymphocyte genomic library. For RFLP analysis, DNA samples from three independent major histocompatibility complex homozygous lines and three intra-MHC recombinant lines were digested with a variety of restriction enzymes and analyzed in Southern blots using human cDNA probes for DP, DQ, DR, and DZ alpha genes, and DP, DQ, DR, and DO beta genes. One, or at most two, unique fragments were detected by hybridization with each of the human probes tested. In contrast, multiple bands (five to six for most enzymes examined) were detected by each of the human probes tested, the majority of which were found to cross-react with at least three of these probes under conditions of moderate stringency. Genomic DNA from the SLA ^c haplotype was cloned into an EMBL-3 bacteriophage vector, and the corresponding genomic library was screened with each of these human cDNA probes. The class II genes thereby isolated from this library showed characteristics consistent with those anticipated from the RFLP analysis. Thus, unique genes were obtained which showed no evidence of cross-hybridization, while genes showed extensive cross-hybridization and were frequently detected in the library by more than one human gene probe. These data are consistent with early evolutionary divergence of a genes, prior to mammalian speciation, and with continuing evolution of genes, with possible shared usage of these genes by different a loci. The data also imply that genes can readily be assigned to loci homologous to their human counterparts, but that genes will require further mapping and/or sequence analysis to confirm assignments.