SYSTEMATICS OF ANADYOMENE SPECIES (ANADYOMENACEAE,CHLOROPHYTA) IN THE TROPICAL WESTERN ATLANTIC1

Three new species of Anadyomene are described. Anadyomene lacerata has pinnately branched veins and a unique lacerated margin formed by elongated vein cells. Anadyomene linkiana consists of a perforate blade arising by polychotomous branching from a distinct stripe, and A. howei has an eperforate, delicate blade of polychotomously branched cells and a smooth margin of elongated vein cells. Distinguishing features of the five previously described species are clarified, and all eight taxa are illustrated. Observations in the field and from more than 400 herbarium specimens form the basis for a discussion of Indo-Pacific affinities, ecological adaptations, cell division, reproduction, and ordinal status. A phylogenetic analysis based on 17 equally weighted characters produced a cladistic gradation, indicating that Anadyomene is a monophyletic genus. The most basal species (A. saldanhae, A. linkiana, A. howei, A. menziesii) show only polychotomous branching. In contrast, the distal group (A. pavonina, A. stellata, A. rhizoidifera, A. lacerata) have pinnate interstitial cells along the veins in addition to polychotomous branching at the vein apices.     

Macroalgal blooms on southeast Florida coral reefs: I. Nutrient stoichiometry of the invasive green alga Codium isthmocladum in the wider Caribbean indicates nutrient enrichment

Invasive blooms of the siphonaceous green algae Codium spp. have been considered a symptom of coastal eutrophication but, to date, only limited biochemical evidence supports a linkage to land-based nutrient pollution. Beginning in the summer of 1990, spectacular blooms of unattached Codium isthmocladum developed on deep coral reef habitats in southern Palm Beach County and northern Broward County, and in subsequent years, attached populations formed on reefs in northern Palm Beach County.To better understand the nutrition of these HABs, we collected C. isthmocladum and other reef macroalgae from various locations in southeast Florida as well as the wider Caribbean region for tissue C:N:P analysis in order to gauge variability in the type and degree of N- and/or P-limited growth. Widespread nutrient enrichment in floridian C. isthmocladum populations was evidenced by significantly higher tissue P (0.06% versus 0.04% of dry weight) and lower C:N (12 versus 19), C:P (425 versus 980), and N:P (35 versus 50) ratios compared to more nutrient-depleted Caribbean populations. To determine nutrient availability on southeast Florida's reefs, we sampled near-bottom waters at a variety of locations for DIN (NH₄⁺ + NO₃⁻ + NO₂⁻) and SRP analysis. In general, concentrations of NH₄⁺, NO₃⁻and SRP were all high on southeast Florida's reefs compared to values reported for Caribbean coral reefs. Although summertime upwelling provides episodic NO₃⁻ and SRP enrichment to reefs in southeast Florida, these transient nutrient pulses have not historically supported C. isthmocladum blooms.We suggest that the widespread P enrichment of C. isthmocladum tissue and water column DIN:SRP ratios <16:1 in southeast Florida drive this system toward N limitation where low level NH₄⁺ enrichment becomes of paramount importance. Hence, the recent C. isthmocladum blooms appear to be supported by increasing land-based nutrient pollution, particularly, sewage that is enriched in NH₄⁺ and SRP at a low N:P ratio (<10:1) critical to sustaining balanced growth during bloom formation.     

Polo-box domains confer target specificity to the Polo-like kinase family

Polo-like kinases (Plks) contain a conserved Polo-box domain, shown to bind to phosphorylated Ser-pSer/pThr-Pro motifs. The Polo-box domain of Plk-1 mediates substrate interaction and plays an important role in subcellular localization. Intriguingly, the major interactions between the PBD and the optimal recognition peptide are mediated by highly conserved residues in the PBD, suggesting there is little target specificity conveyed by the various PBDs. However, here we show that the affinity of the purified Plk1-3 PBDs to both a physiological Cdc25C derived phospho-peptide and an optimal recognition phospho-peptide differs significantly among family members. To decipher the role of the PBDs and kinase domains in inferring Plk specificity, we exchanged the PBD of Plk1 (PBD1) with the PBD of Plk2, 3, or 4 (PBD2-4). The resulting hybrid proteins can restore bipolar spindle formation and centrosome maturation in Plk1-depleted U2OS cells to various degrees. In these experiments PBD2 was most efficient in complementing PBD-function. Using the MPM2 antibody that recognizes a large set of mitotic phospho-proteins, we could show that PBD1 and PBD2 display some limited overlap in target recognition. Thus, PBDs convey a significant deal of target specificity, indicating that there is only a limited amount of functional redundancy possible within the Plk family.     

Comparison of vertebrate and invertebrate CLIC proteins: the crystal structures of Caenorhabditis elegans EXC-4 and Drosophila melanogaster DmCLIC

The crystal structures of two CLIC family members DmCLIC and EXC-4 from the invertebrates Drosophila melanogaster and Caenorhabditis elegans, respectively, have been determined. The proteins adopt a glutathione S-transferase (GST) fold. The structures are highly homologous to each other and more closely related to the known structures of the human CLIC1 and CLIC4 than to GSTs. The invertebrate CLICs show several unique features including an elongated C-terminal extension and a divalent metal binding site. The latter appears to alter the ancestral glutathione binding site, and thus, the invertebrate CLICs are unlikely to bind glutathione in the same manner as the GST proteins. Purified recombinant DmCLIC and EXC-4 both bind to lipid bilayers and can form ion channels in artificial lipid bilayers, albeit at low pH. EXC-4 differs from other CLIC proteins in that the conserved redox-active cysteine at the N-terminus of helix 1 is replaced by an aspartic acid residue. Other key distinguishing features of EXC-4 include the fact that it binds to artificial bilayers at neutral pH and this binding is not sensitive to oxidation. These differences with other CLIC family members are likely to be due to the substitution of the conserved cysteine by aspartic acid.     

FUNCTIONAL SIMILARITY AMONG ISOMORPHIC LIFE-HISTORY PHASES OF POLYCAVERNOSA DEBILIS (RHODOPHYTA,GRACILARIACEAE) 1

Morphologically identical but different life-history phases of the red alga Polycavernosa debilis (Forsskål) Fredericq and J. Norris showed no conspicuous differences in physiological or ecological performances. The costs and benefits of ploidy level, as measured by net photosynthesis, calorific content, structural makeup and resistance to predation, were not sufficient to result in statistically significant differences (P > 0.05 ANOA) for the various reproductive phases [haploid male or female (including cystocarps) and diploid tetrasporic]. The lack of measurable functional responses leads to two hypotheses: (1) that adaptive ecological-physiological differences between life-history phases are subtle, or (2) that predominantly genetic / reproductive factors are implicated in maintaining isomorphic life-history phases.     

Human atrial and ventricular myosin light-chains subunits in the adult and during development.

1. Myosin was isolated from human right- and left-atrial and -ventricular myocardium, and examined both in adult subjects and at different stages during pre- and post-natal development. 2. The myosin light-chain subunits in the atria and ventricles were different when characterized by isoelectric focusing and subsequent two-dimensional poly-acrylamide-gel electrophoresis. 3. No differences were observed between the light-chain subunits in the right and left ventricle at any stage of development. 4. The foetal ventricle contained a characteristic light chain that was a major component throughout the latter half of gestation. This foetal light chain, which disappeared in the postnatal period, could not be distinguished from adult atrial light chain 1 on two-dimensional electrophoresis. 5. Myosin in the adult atria, particularly the left, contained components similar to ventricular light-chain components. 6. The possible stimuli for the observed changes in myosin light-chain expression are discussed in relation to the known physiological changes occurring during development.     

Distinct cold tolerance traits independently vary across genotypes in Drosophila melanogaster

Cold tolerance, the ability to cope with low temperature stress, is a critical adaptation in thermally variable environments. An individual's cold tolerance comprises several traits including minimum temperatures for growth and activity, ability to survive severe cold, and ability to resume normal function after cold subsides. Across species, these traits are correlated, suggesting they were shaped by shared evolutionary processes or possibly share physiological mechanisms. However, the extent to which cold tolerance traits and their associated mechanisms covary within populations has not been assessed. We measured five cold tolerance traits—critical thermal minimum, chill coma recovery, short- and long-term cold tolerance, and cold-induced changes in locomotor behavior—along with cold-induced expression of two genes with possible roles in cold tolerance (heat shock protein 70 and frost)—across 12 lines of Drosophila melanogaster derived from a single population. We observed significant genetic variation in all traits, but few were correlated across genotypes, and these correlations were sex-specific. Further, cold-induced gene expression varied by genotype, but there was no evidence supporting our hypothesis that cold-hardy lines would have either higher baseline expression or induction of stress genes. These results suggest cold tolerance traits possess unique mechanisms and have the capacity to evolve independently.