Estimation of desmosponge (Porifera,Demospongiae) larval settlement rates from short-term recruitment rates: Preliminary experiments

During a study of the spatial and temporal patterns of desmosponge (Porifera, Demospongiae) recruitment on rocky and coral reef habitats of Santa Marta, Colombian Caribbean Sea, preliminary attempts were made to estimate actual settlement rates from short-term (1 to a few days) recruitment censuses. Short-term recruitment rates on black, acrylic plastic plates attached to open, non-cryptic substratum by anchor screws were low and variable (0–5 recruits/plate in 1–2 days, sets of n=5–10 plates), but reflected the depth and seasonal trends found using mid-term (1 to a few months) censusing intervals. Moreover, mortality of recruits during 1–2 day intervals was low (0–12%). Thus, short-term censusing intervals can be used to estimate actual settlement rates. To be able to make statistical comparisons, however, it is necessary to increase the number of recruits per census by pooling data of n plates per set, and to have more than one set per site or treatment.     

The bull shark (Carcharhinus leucas) and largetooth sash (Pristis perotteti) in Lake Bayano,a tropical man-made impoundment in Panama

Synopsis The Río Bayano in eastern Panama is one of many tropical rivers in which bull sharks (Carcharhinus leucas) and largetooth sawfish (Pristis perotteti) have been known to occur. Since both species can osmoregulate in fresh water throughout life, theoretically, both could survive in landlocked situations for many years.P. perotteti reproduces in fresh water, butC. leucas ordinarily does not, so only the former would appear to have the potential for establishing a breeding stock in such a landlocked freshwater body.The damming of the Rio Bayano and the creation of a large impoundment in 1976 provides a test of the ability of members of both species trapped there to survive and to establish breeding stocks. In 1980 and 1981 three mature femaleC. leucas were found dead in Lake Bayano and three sub-adult femaleP. perotteti were taken by trammel net. These events confirm the ability of both to survive in fresh water for long periods, but the establishment of breeding stocks appears doubtful and the question may not be answered for many years.     

Structural Characteristics of the Short-Tail Fibers of T4 Bacteriophage

The characteristics of pure preparations of short-tail fibers of bacteriophage T4 have been studied in the optical and electron microscope. Three main structures were observed: 1) spheres of 8.1 nm diameter; 2) fibers 43 nm long and 3.8 nm thick; and 3) fibers 54 nm long and 3.2 nm thick. Both types of fibers exhibited a regular beaded appearance. The 43-nm fibers were the most abundant structure. During the process of purification of the short-tail fibers, the formation of aggregates was observed each time the material containing the short-tail fibers was dialyzed against saline solutions. These aggregates became increasingly fibrous (as observed in the optical microscope) as the material used was increasingly enriched in short-tail fibers. Finally, most of the aggregates were of the fibrous type when they were formed from a purified preparation of short-tail fibers. In the electron microscope, it was found that the filamentous aggregates were organized in well-defined bundles. The amino acid composition of the highly purified short-tail fibers was also determined. Among the known fibrous proteins, the ones that most resemble the amino acid composition of the short-tail fibers are actin and fibrinogen. These observations are discussed in relation to the T4 short-tail fiber structure and their localization on the hexagonal baseplate of the T4 tail structure.     

Plant tumor reversal associated with the loss of foreign DNA

Summary Transformation of plant tissues into crown gall tumors has been associated with the transfer of a portion of a tumor-inducing plasmid (Ti-plasmid) into plant DNA. Various laboratories have regenerated normal-appearing plants from a number of crown gall tumors. This study investigates the fate of the foreign DNA in a series of tissues derived from various parts of a plant regenerated from the tumor BT-37 by Braun and his coworkers. It was found that all the foreign DNA sequences were lost from tissues that had lost all their tumorous traits; whereas the plasmid DNA sequences were still present in tissues that appeared normal but still exhibited tumorous traits when returned to tissue culture media. From these studies it would appear that the presence of the Ti-plasmid sequences in the plant DNA is required for the maintenance of the transformed state. Presented in the Symposium on Gene Transfer, Differentiation and Neoplasia in Plant and Animal Cells at the 30th Annual Meeting of the Tissue Culture Association, Seattle, Washington, June 10–14, 1979. This symposium was supported in part by Grant CA 26748 from the National Cancer Institute, DHEW, and Grant RD-67 from the American Cancer Society.     

Heavy metal composition of polysomal fractions following cadmium challenge

Endogeneous levels of zinc and copper were found to be 1.2±0.1×10⁻² and 0.3±0.1×10⁻² μg/A260 unit, respectively, in polysomal fractions from control animals; cadmium, however, was undetectable. In experimental animals (injected with cadmium) zinc, copper, and cadmium were found in polysomal fractions isolated by two different methods. One hour after a cadmium injection there was a rise in both the zinc and copper content of the polysomal fractions, which then declined steadily to below control levels by 16 h. Neither zinc nor cadmium were dialyzable from these fractions by a TRIS buffer; however, addition of 0.01M EDTA to the buffer resulted in removal of 75% of the zinc and all of the detectable cadmium. The addition of cadmium (CdCl₂) to control supernatants (adjusted to the cadmium concentration present in supernatants 6 h after in vivo exposure) resulted in metal binding to polysomal fractions in levels comparable to those observed after in vivo exposures to the metal. When cadmium was added in the form of cadmium thionein, a smaller fraction of the metal was isolated with the polysomal fraction. Cadmium bound to polysomal fractions in vivo (24 h after exposure) was sensitive to release by protease digestion, but insensitive to release by ribonuclease digestion.     

Marker rescue transformation by linear plasmid DNA in Bacillus subtilis

Although plasmid-free Bacillus subtilis cannot be transformed for markers carried by linear or nicked plasmid DNA, a resident plasmid can rescue a marker on such damaged DNA under certain conditions. Linearized chimeric plasmid DNA has been used to transform cultures carrying a resident plasmid which is homologous with a portion of the donor. This system has revealed the following properties of the marker rescue process: (1) It is recE dependent. (2) It requires the presence in the resident plasmid of sequences which are homologous to the donor. (3) When the selected marker is on a nonhomologous segment it must be flanked by segments which are homologous to the resident plasmid. (4) The efficiency of rescue varies in a regular way with the position of the linearizing cut. (5) Marker rescue is first order with respect to DNA concentration. These properties and other data are interpreted as providing a strong indication that marker rescue occurs by recombination, although an alternative explanation involving recE-dependent recircularization of the donor plasmid has not been eliminated. Our results also suggest that if the major pathway of marker rescue is by recombination, an average of 0.15 Mdal (single strand) must be removed from each donor DNA molecule or otherwise rendered unavailable for recombination and that the exchange frequency during transformational recombination is approximately 0.2 to 0.5 Mdal⁻¹.     

Interactions of cardiac glycosides with cells and membranes Properties and structural aspects of two receptor sites for ouabain in erythrocytes

The existence of two types of binding sites for ouabain in human erythrocyte membranes is described. Receptor sites designated as ‘type I’, which may be identical to the K⁺-insensitive sites of intact cells, were detected at concentrations of ouabain as low as 10⁻⁷ M. The ‘type II’ receptor sites require the inclusion of Mg²⁺ + P_i to form complexes with ouabain; they may be identical to the K⁺-sensitive sites of intact cells. These sites were saturated at approx. 5 · 10⁻⁷ M ouabain but could not be detected at higher concentrations. The range of ouabain concentrations at which ‘type I’ receptors start to predominate (i.e. 5 · 10⁻⁸–5 · 10⁻⁷ M) was termed ‘critical digitalis concentrations’. The process of binding reached equilibrium within 1 and 4 h for ‘type I’ and ‘type II’ sites, respectively. The dissociation constant for ‘type II’ receptor-ouabain complexes was 7.6 · 10⁻⁹ M.Under similar experimental conditions, rat erythrocyte membranes exhibited only non-saturable sites.Alterations in the proportions of the two types of receptors were demonstrated by preincubation of the membranes, in the presence or absence of Mg²⁺ + P_i, prior to the addition of ouabain. In the first case, ‘type II receptor-ouabain’ complexes were stabilized at about 50% of the untreated membranes and ‘type I-ouabain’ complexes slowly approached equilibrium over a period of 24 h. In the latter instance, ‘type I’ receptors were not detected, and only ‘type II-ouabain’ complexes prevailed.     

Periovulatory changes in ovarian prostaglandin formation and their hormonal control in the rat

The concentration of prostaglandins of the E-group (PGE) and F-group (PGF) and the activity of prostaglandin-synthetase in rat ovaries increased on the evening of the day of proestrus and reached a peak at 5.00 h on the following morning, i.e. about the time of ovulation. Enzyme activity and PG concentrations receded to basal levels by 10.00 h on the day of estrus. These changes were prevented when the proestrous gonadotropin surge was blocked by administration of nembutal, and could be restored by administration of either LH or of FSH freed of LH contamination. The spontaneous preovulatory rise in prostaglandin concentration was about 6-fold for PGF and 30-fold for PGE, compared with values observed during the remainder of the cycle, whereas the rise in prostaglandin synthetase activity was only about 1.7-fold. The LH effect on PG accumulation had a latency of 2–4 h, which argues for enzyme synthesis rather than activation of preformed enzyme as the mechanism responsible. The small magnitude of the change in enzymic activity suggests that LH may, in addition, augment the availability of PG precursors. The results are compatible with the concept that prostaglandins play a physiological role in the gonadotropin-induced process of follicular rupture.