Reproductive periodicity and steroid hormone profiles in the sex-changing coral-reef fish, <Emphasis Type="Italic">Plectropomus leopardus</Emphasis>

The reproductive biology of coral trout, Plectropomus leopardus, from the Great Barrier Reef (Australia) was investigated by correlating gonadal condition with plasma levels of gonadal steroids. Female fish were found to be regressed from mid-summer to early spring, after which rapid and cyclical increases in gonado-somatic index (I _G), maximum oocyte diameter (MOD) and plasma concentrations of estradiol-17β and testosterone were detected. Male fish, in contrast, commenced recrudescence slightly earlier in winter and responded with less dramatic increases in both I _G and plasma concentrations of testosterone and 11-ketotestosterone. The mode of oocyte development was multiple group-synchronous, and cyclical fluctuations in reproductive parameters (I _G, MOD and gonadal steroid concentrations) were synchronized with new-moon lunar phases. It is likely, therefore, that individual P. leopardus have the capacity to spawn on multiple occasions, with lunar periodicity. However, evidence suggests that early bouts of reproduction may be more important in terms of reproductive investment than subsequent bouts later in the same season. It is concluded that patterns of gametogenesis and steroidogenesis in P. leopardus are similar to the patterns displayed by other tropical groupers, suggesting that management regimes and propagation protocols developed for these fishes may also be appropriate for use with P. leopardus.     

Characterization of a new flavin metabolite from human urine

A new flavin metabolite comprising approximately 5% of the total flavin of human urine was isolated and characterized using absorption and fluorescence spectra, oxidation-reduction and hydrolysis data, and ninhydrin reactions. The flavin is a derivative associated with a peptide residue in ester linkage from an amino acid carboxyl to the ribityl chain of riboflavin, probably at the 5'-terminus.     

Two Arabidopsis AGC kinases are critical for the polarized growth of pollen tubes

Reproduction of flowering plants requires the growth of pollen tubes to deliver immotile sperm for fertilization. Pollen tube growth resembles that of polarized metazoan cells, in that some molecular mechanisms underlying cell polarization and growth are evolutionarily conserved, including the functions of Rho GTPases and the dynamics of the actin cytoskeleton. However, a role for AGC kinases, crucial signaling mediators in polarized metazoan cells, has yet to be shown in pollen tubes. Here we demonstrate that two Arabidopsis AGC kinases are critical for polarized growth of pollen tubes. AGC1.5 and AGC1.7 are pollen-specific genes expressed during late developmental stages. Pollen tubes of single mutants had no detectable phenotypes during in vitro or in vivo germination, whereas those of double mutants were wider and twisted, due to frequent changes of growth trajectory in vitro . Pollen tubes of the double mutant also had reduced growth and were probably compromised in response to guidance cues in vivo . In the agc1.5 background, downregulation of AGC1.7 using an antisense construct phenocopied the growth defect of double mutant pollen tubes, providing additional support for a redundant function of AGC1.5/1.7 in pollen tube growth. Using the actin marker mouse Talin, we show that pollen tubes of double mutants had relatively unaffected longitudinal actin cables but had ectopic filamentous actin, indicating disturbed control of polarity. Our results demonstrate that AGC1.5 and AGC1.7 are critical components of the internal machinery of the pollen tube leading to polarized growth of pollen tubes.     

High-pressure liquid chromatographic resolution of vitamin A compounds

An electrochemical system has been devised to measure phenol concentrations in aqueous solutions. The unit employs the immobilized enzyme, tyrosinase, to oxidize phenol in the presence of saturating levels of oxygen. The oxidation product, ortho-benzoquinone, is then chemically reduced in the presence of an excess of ferrocyanide ions. The coupled oxidation of ferrocyanide ions to ferricyanide ions results in a measurable potential difference in the electrochemical system. The resulting zero current potentials in these steady-state potentiometric measurements are shown to be directly proportional to the logarithm of phenol concentration over the range of 3.8 × 10^?7 to 1 × 10^?4m. The results of studies carried out with alternate substrates for the enzyme and interfering compounds are also presented.     

Background level of risk determines how prey categorize predators and non-predators

Much of the plasticity that prey exhibit in response to predators is linked to the prey''s immediate background level of risk. However, we know almost nothing of how background risk influences how prey learn to categorize predators and non-predators. Learning non-predators probably represents one of the most underappreciated aspects of anti-predator decision-making. Here, we provide larval damselfish (Pomacentrus chrysurus) with a high or low background risk and then try to teach them to recognize a cue as non-threatening through the process of latent inhibition. Prey from the low-risk background that were pre-exposed to the novel odour cues in the absence of negative reinforcement for 3 days, and then provided the opportunity to learn to recognize the odour as threatening, failed to subsequently respond to the odour as a threat. Fish from the high-risk background showed a much different response. These fish did not learn the odour as non-threatening, probably because the cost of falsely learning an odour as non-threatening is higher when the background level of risk is higher. Our work highlights that background level of risk appears to drive plasticity in cognition of prey animals learning to discriminate threats in their environment.     

Inducible expression of amplified human beta interferon genes in CHO cells.

Plasmid DNA containing the human beta-interferon (IFN-beta) gene and mouse dihydrofolate reductase cDNA was transfected into dihydrofolate reductase-negative Chinese hamster ovary cells. Dihydrofolate reductase-positive transformants were obtained, and cells containing amplified copies of mouse dihydrofolate reductase were selected by exposure to increasing methotrexate concentrations. These cells were found to express high levels of human IFN-beta after polyriboinosinic acid-polyribocytidylic acid superinduction or NDV infection; this was a result of coamplification of the IFN-beta gene. Levels of expression of 1 U/cell per day were achieved on superinduction, giving corresponding titers of up to 10(10) U/liter medium in culture supernatants. Constitutive production of IFN-beta rates of about 0.5% of superinduced rates was observed; cells producing these levels of IFN-beta had acquired resistance to cytotoxic antiviral effects of IFN-beta. Two forms of human IFN-beta were produced; a major glycosylated 23,000-dalton form and an unglycosylated 18,500-dalton form. The latter had greatly reduced antiviral activity. IFN-beta production was very sensitive to cellular growth rate; the highest levels were produced by density-arrested cultures. Regulation of IFN-beta production by polyriboinosinic acid-polyribocytidylic acid or by cell density effects required the presence of DNA sequences 5' to the IFN-beta-coding sequences; replacement of these sequences with the simian virus 40 early promoter resulted in uninducible, density-independent production of IFN-beta.