RAPID PROCEDURE FOR DETECTING CIGUATOXINS IN FISH

Flesh and viscera/gill tissues of six amberjacks (Seriola dumerilii), suspected positive for ciguatoxins, were each extracted and the toxins partially purified. Both flesh and viscera/gill of only five fish were toxic to mice exhibiting ciguatoxins (CTX) symptoms. The methanol extracts of the five fish were pooled and concentrated, the volume of flesh extract was 50.0 mL (129.4 mg toxins/mL) and viscera/gill had 25.0 mL (25.5 mg toxins/mL). Pooled extracts exhibited CTX symptoms in mice but only flesh killed mice in 6 h and the LD₅₀ was 1.72 mg toxins. The lethal potencies of the pooled flesh killed mice in 6 h and the LD₅₀ was 1.72 mg toxins. The lethal potencies of the pooled flesh was 198.17 g fish, equivalent to 58.3 mouse unit. An efficient fractionation and purification procedure was developed for the extracts using an HPTLC and silica gel 60 plate with a chromatographic solvent mixture of chloroform:methanol:water (60:35:8, v/v). The system yielded 10 fractions for flesh and 9 for viscera/gill. Scanned plates were subdivided into three equal zones, each scraped, methanol extracted and tested in mice. The 2nd zone (R_f fractions between 0.40 and 0.66) was very toxic to mice compared to 1st or 3rd zones and the mice had CTX symptoms. The scanner for this 2nd zone had a cluster of minor peaks on both sides of the major one with a sum total area of 62.47% indicating multiplicity of CTX in amber-jack fish. The major peak, at retention time of 1.48 s and a single area of 43.28%, is believed to be the main ciguatoxins present. The HPTLC is a rapid and sensitive procedure for ciguatoxins in fish flesh extracts with a detection limit of 40.0 ± 1.9 picogram toxins.     

Changes in a deep lake following sewage diversion – a challenge to the orthodoxy of external phosphorus control as a restoration strategy?

1. The restoration of deep lakes has traditionally focused on reducing the external phosphorus loading. 2. Following the diversion of sewage effluent, that led to marked reductions in nutrient concentrations in its main inflow, Rostherne Mere has shown no reduction in phosphorus or chlorophyll a concentrations. A shallow lake upstream (Little Mere), however, has shown a marked response to effluent diversion. 3. Nutrient budgets for Rostherne Mere reveal that sewage effluent was by far the most significant external source of total phosphorus and that diffuse drainage from the catchment was the most significant external source of dissolved inorganic nitrogen. Phosphorus loads from groundwater and a bird roost were insignificant. Internal sources of phosphorus were, however, considerable and were largely responsible for the observed delay in recovery. 4. Phosphorus limitation of phytoplankton biomass may never be attainable because of substantial internal and diffuse sources of phosphorus, combined with a long retention time. Nitrogen is likely to be more important in limiting phytoplankton biomass. Control of diffuse nitrogen sources may therefore be more effective in the restoration of the deeper lakes of this region.     

The Fate of L-Tyrosine-UL−14C in Shoot-Forming Tobacco Callus

Tobacco callus fed L-tyrosine-UL^?14C was sampled at 3-day intervals for 15 days, homogenized and studied with respect to distribution of incorporated radioactivity. The supernatant obtained by centrifuging of the homogenates at 270 g contained the bulk of the radioactivity although significant activity was also detected in the pellet. Sucrose density gradient centrifugation of the supernatant showed over 90% of the recovered label to be associated with a fraction designated as “less dense than mitochondria”, with the remainder being found in the fraction identified as “mitochondria”. During tissue culture, virtually all of the radioactivity in the fraction “less dense than mitochondria” was recovered in the supernatant obtained by centrifugation at 100,000 g. From 4 to 18% of the labeling in the 100,000 g supernatant fraction was attributable to tyrosine-containing protein, and the rest to free tyrosine and unidentified anionic constituents. The highest proportions of radio-activity in the 270 g pellet were associated with substances extractable with NaCl, pronase, 4.6 N NaOH, and acetolyzing reagent. Low but substantial labeling characterized the extracts obtained with Triton X-100 and 1 N NaOH. The final unextractable residue contained 20% of the 270 g pellet radioactivity.     

Seasonal and diurnal variations in the energetics and foraging activities of the brown honey eater,Lichmera indistincta

In general, the brown honeyeater, Lichmera indistincta, flies more and expends more energy when visiting flowers in the early morning than at other times. Floral nectar is most abundant early in the day, and nectar energy intake by L. indistincta is greatest at that time. It appears as if birds can only store excess energy during the early part of the day, incurring energy deficits at other times. Unit perching and flight costs are greatest for L. indistincta in winter and spring. As a result, peak total energy expenditures and requirements occur at these times, birds apparently being unable to reduce energy demands by employing nocturnal torpor. Estimates of probable energy uptake by L. indistincta from the plant species studied exceed predicted requirements in all seasons except winter, when it is apparent that birds would need to be especially selective in the plants that they used as major energy sources.     

Hybridization between tetraploid species of Alopecurus L. (Poaceae): chromosome behaviour of natural and artificial hybrids

The meiotic behaviour of plants from mixed populations of Alopecurus pratensis × A. geniculatus and of A. pratensis × A. arundinaceus ( 2n = 4×(= 28) is reported together with observations on some artificially produced hybrids. This meiotic behaviour is correlated with the degree of hybridity as shown by the hybrid index values of the plant. In A. pratensis × A. geniculatus hybrids there are marked differences between populations in the degree of meiotic disturbance and in one population there was an almost complete breakdown of meiosis. Alopecurus pratensis × A. arundinaceus hybrids show fairly regular meiotic pairing but in most plants there are a few univalent chromosomes at metaphase I. Artificially produced hybrids of A. pratensis × A. aequalis gave meiotic configurations that suggest that the genomes of the parent species are very similar. Taken together with the results from artificially produced hybrids of A. pratensis × A. geniculatus , it is suggested that bivalent-promoting mechanisms reduce multivalent formation both in the species and the hybrids. The interaction of different genotypes involved in the control of meiosis may account for the variation in meiotic behaviour in the different populations of hybrids. Pollen fertility is reduced in most populations of hybrids and likely to be an important factor permitting introgressive hybridization.     

Light and Electron Microscope Study of Dunaliella primolecta Butcher (Volvocida)*

SYNOPSIS. Light and electron microscope observations on Dunaliella primolecta Butcher from logarithmic and stationary phases of batch cultures are correlated. Except for the lack of a cell wall the fine structure has typical volvocid features. The transition from logarithmic to stationary phase is marked by changes in content and size of cytoplasmic vacuoles, accumulation of cytoplasmic lipid, accumulation of starch in the plastid matrix, and by the formation of autophagosome-like bodies. The organelles in stationary-phase flagellates are closely packed together because of the cytoplasmic lipid and starch-distended chloroplast. Organisms from logarithmic phase have an abundant ribosome-packed groundplasm supporting the organelles. In the cytochemical demonstration of acid phosphatase activity, Golgi cisternae and smooth and coated Golgi vesicles contain Gomori reaction product. The possible roles of the Golgi apparatus in this flagellate are discussed.     

Effect of Gibberellic Acid on Rate of Extension and Maturation of Pea Internodes

Gibberellic acid (GA) does not delay maturation of pea internodes;on the con-trary, maturation (i.e. cessation of extension) takesplace slightly earlier. Thus the increased length of internodesresulting from GA treatment is due entirely to increased rateof extension. In this experiment, GA treatment of plants accelerated the visibleproduction of the first flower bud by about 4 days: the nodebearing the first flower was not altered. The total number offlower buds produced by the end of the experiment was increasedas a result of GA treatment, but many of those first formedon plants receiving high doses (I-IOµg.) withered beforeopening.