Multiregional Evaluation of the SimPlate Heterotrophic Plate Count Method Compared to the Standard Plate Count Agar Pour Plate Method in Water

A new SimPlate heterotrophic plate count (HPC) method (IDEXX Laboratories, Westbrook, Maine) was compared with the pour plate method at 35°C for 48 h. Six laboratories tested a total of 632 water samples. The SimPlate HPC method was found to be equivalent to the pour plate method by regression analysis (r = 0.95; y = 0.99X + 0.06).     

Transmission and perception of acoustic signals in the desert clicker,Ligurotettix coquilletti (Orthoptera: Acrididae)

Males of the desert clicker, Ligurotettix coquilletti (Acrididae: Orthoptera) defend a femalerequired resource, the creosote bush Larrea tridentata, in desert habitats of the southwestern United States. Males signal acoustically to each other as well as to searching females. The call is produced by tegminal/femoral stridulation where one or both legs are used for sound production. Sound pressure levels, measured laterally, are influenced by the intervening tegmen between the stridulating leg and the microphone. Differences in measured sound pressure levels between sides can vary up to 7 dB. When clicks are produced multiply,these multiple clicks may be 4 dB louder than single clicks. We examine the structure of the call and the effective broadcast area of single males by monitoring acoustic ascending neurons of the ventral nerve cord in the neck. By taking the neurophysiological preparation into the field, we were able to map the broadcast area of isolated males and also of males calling within aggregations. The distance over which the signal of isolated males could be detected was 8–14 m, whereas neural representation of the calls of males within aggregation were detectable within 4–6 m. The sound spectrum of the song, although having a major lower-frequency component around 10 kHz, has extensive power in the ultrasonic range. The tuning characteristics of the ascending auditory neuron matched the overall structure of the male call. The importance of the acoustic cue, as compared to visual cues, is discussed in relation to female attraction.     

Growth regulation of the interstitial cell population in hydra : I. Evidence for global control by nerve cells in the head

The interstitial cells of hydra form a multipotent stem cell system, producing terminally differentiated nerve cells and nematocytes during asexual growth. Under well-fed conditions the interstitial cell population doubles in size every 4 days. We have investigated the possible role of nerve cells in regulating this behavior. Nerve cells are normally found in highest concentrations in the head region of hydra, while interstitial cells are primarily located in the body column. Our experimental approach was to construct, by grafting, animals in which the density of nerve cells varied in (1) the head region, or (2) the body column. The growth of the interstitial cell population was then measured in these hydra. The results indicate that differences in head nerve cell density are closely correlated with how fast the interstitial cell population increases in size. Variations in the level of either nerve cells or interstitial cells in the body column showed no such correlation. These findings suggest the existence of a signaling mechanism in the head region. This signal, which is a function of the density of head nerve cells, emanates from the head tissue and exerts global control on the growth of the interstitial cell population in the body column.     

Interleukin-1 binding, internalization, and processing in a murine osteoblastic cell line, MC3T3.E1.

We have investigated the interaction of IL-1 and its receptor on a murine osteoblastic cell line, MC3T3.E1, with regard to binding, internalization, and the fate of the receptor-ligand complex following internalization. Binding experiments indicated that this cell line possesses a high affinity receptor (Kd 1.02 x 10(-10) M) that binds both IL-1 alpha and IL-1 beta, and has approximately 6500 receptors per cell. Cross-linking experiments indicated that the receptor has a molecular weight of 100,000 daltons. Binding of IL-1 to the receptor is inhibited by the Interleukin Receptor Antagonist Protein (IRAP). These characteristics suggest that the murine osteoblastic receptor resembles that found on T lymphocytes and fibroblasts. Internalization experiments showed that this process is fairly rapid and results in degradation of the ligand and subsequent loss of degraded IL-1 from the cell. In this respect, processing of the receptor-ligand complex mimics that observed with IL-1 receptors on murine bone marrow cells, pre-B cells, and macrophages. Although the reasons for these differences are unclear, it may be that, unlike fibroblasts, osteoblasts may function as an effector cell which rapidly removes IL-1 from the immediate environment via ligand degradation while at the same time initiating bone resorption via stimulation of osteopontin biosynthesis.     

Molecular Variability in the Replicase Gene of Viruses Causing Tomato Leaf Curl Disease in India

Tomato Leaf Curl Virus (ToLCV)-infected samples collected from four different ecological zones of India: Northern zone, NewDelhi (IARI) [ToLCNDV-IARI]; Central zone, Jabalpur [ToLCV-Jb], Raipur [ToLCV-Rp] and Southern zone, Dharwad [ToLCV-Dh] were maintained by whitefly transmission into tomato cv Pusa Early Dwarf. Replicase gene coding for replication initiator protein (Rep) was amplified by PCR using gene specific primers, yielding an amplicon of 1086 bp for all the isolates. Sequence analysis of the rep amplicons of all the Indian isolates of ToLCV causing the disease clearly shows the presence oftwo subgroups irrespective of their geographical evolution. Isolates belonging to subgroup I comprising of tomato leaf curl virus-New Delhi (ToLCV-NDe) having bipartite genome are conserved within themselves and showed 94–95% nucleotide sequence homology. Second subgroup comprising of tomato leaf curl virus-Bangalore (ToLCBV) having monopartite genome and conserved among themselves, but showed only 73-75% homology with the subgroup I. In phylogenetic tree analysis, ToLCV-NDe appeared in a different cluster than ToLCV-Ban. All the four isolates used in this study fall in ToLCV-NDe group based on their replicase gene sequences. The specificity determinant located at N terminal suggests ToLCV-NDe and ToLCV-Rp as mild isolates.     

Settlement Patterns of Mediterranean Fruit Flies in the Tree Canopy: An Experimental Analysis

Males of the Mediterranean fruit fly, Ceratitis capitata (medfly), defend individual leaves of host and non-host trees as mating territories and attract females via production of a sex pheromone (a behavior termed ‘calling’). Males tend to aggregate within the tree canopy, and the present study examined the influence of (1) location and (2) resources on female visitation to male aggregations. Males were placed in screen-covered containers, which were suspended on field-caged trees at two locations selected to differ in only one of the following parameters: height above ground (low versus high), leaf density (sparse versus dense), distance to main trunk (canopy edge versus center), proximity to a food source (bird feces absent or present), and proximity to a host fruit (oranges absent or present). Females were released, and we periodically recorded the number of calling males in each of the test aggregations as well as the number of females sighted within 15 cm of each male aggregation. Male calling did not differ between treatments in any of the experiments. However, females were more frequently sighted near males calling (1) in dense foliage, (2) near the central trunk, (3) near bird feces, and (4) near oranges. In an additional experiment, we compared male settlement (in the absence of females) on leaves in the same sites used previously to determine the degree of congruence between the sexes in microhabitat use. Aside from the lack of center-edge effect, males displayed the same settlement patterns as females. In a final experiment, we found no effect of male calling on the distribution of other males: released males were sighted with equal frequency near cups containing mature, calling males and cups containing immature, non-calling males. Medfly lek behavior is discussed in light of these findings.     

Zymosan-activated plasma-mediated thromboxane production by the perfused rabbit liver and isolated hepatocytes: involvement of calcium

The present study investigates the mechanism of zymosan-activated plasma (ZAP)-mediated eicosanoid production by the isolated, perfused rabbit liver and described ZAP-mediated eicosanoid stimulation in cultured hepatocytes. Perfused livers receiving untreated plasma demonstrated no significant changes in portal venous pressure or the rates of release of lactic dehydrogenase or acid phosphatase activity (indicators of cellular injury). The control group livers demonstrated stable rates of release for 6-keto PGF1 alpha and thromboxane B2 (TXB2). In contrast, the infusion of ZAP alone resulted in a rapid but transient release of TXB2 from the livers. No significant changes in perfusion pressure or enzyme release were observed following ZAP administration. Perfusion of livers with a calcium-free buffer decreased the basal rates of both 6-keto PGF1 alpha and TXB2 production and significantly, but not completely, attenuated the ZAP-mediated increase in hepatic TXB2 production. Perfusion of livers with nifedipine (3 microM) had no effect on ZAP-mediated TXB2 production in this model. Isolated hepatocytes responded to ZAP-treatment with significant increases in TXB2 production. These data suggest that activated fluid phase complement components induce thromboxane production by specific cells within the liver and that this stimulation is partially dependent upon the release of intracellular calcium but independent of complement-mediated cellular injury.