INTERACTIONS AMONG IRRADIANCE,OXYGEN EVOLUTION AND NITRITE UPTAKE BY CHLAMYDOMONAS (CHLOROPHYCEAE)1,2

Nitrite uptake and oxygenic photosynthesis by cultures of Chlamydomonas sp. isolated from Lake Superior were measured at different irradiances in order to compare predictive models of nitrite uptake and to assess the proportion of photoreductant (measured as oxygen evolution, mol × 4 eq. mol^?1) that is allocated to nitrite assimilation (measured as nitrite uptake, mol × 6 eq. mol^?1). These measurements are analogous to measurements of carbon fixation (CO₂ uptake) at different irradiances and photosynthetic activities. Nitrite uptake as a function of irradiance did not follow Michaelis-Menten kinetics as proposed for nitrate by MacIsaac and Dugdale (1972) because of inhibition at high irradiances. The Haldane equation described nitrite uptake better. Nitrite uptake as a function of oxygenic photosynthesis followed Michaelis-Menten kinetics. Irradiance-dependent (Haldane) and photosynthesis-dependent models described nitrite uptake equally well. We suggest that nitrite is taken up and assimilated in response to intracellular concentrations of photoreductant that are directly proportional to photosynthetic activity and are related indirectly to irradiance. This contention is supported by photosynthesis-dependent nitrite uptake (Michaelis-Menten) at both light-limited and photoinhibited photosynthetic activities. This is consistent conceptually with deactivation of light traps at high irradiance levels. The proportion of photoreductant allocated to nitrite uptake and assimilation increased markedly at low irradiance levels. This indicates that cells synthesize important N-containing biomolecules across a broader range of irradiance levels than fixation of carbon for synthesis of energy storage and structural products.     

Thermophilic fungi in the mycoflora of man and environmental air

The objective of this study was to determine if thermophilic fungi exist in the mycoflora of man and in the aeroflora of his environment.Humicola lanuginosa andHumicola grisea were isolated from 5 of 55 samples of outside air. Three thousand cultures were taken from the nasal mucosae, skin surfaces and recta of 570 children. Cultures were incubated at 50°C. Thermophilic fungi were isolated from 6 of 287 children receiving immunosuppressive therapy for malignancies and from 1 of 283 normal children.H. lanuginosa was recovered from the skin of one, the rectum of one and the nasal mucosae of three patients.Mucor pusillus was isolated from the nasopharynges of two patients.Further studies are now indicated to determine the pathogenicity of these organisms with respect to tissue invasive disease, antigenicity and metabolite toxicity.Supported by General Research Support Grant RR-05584 from National Institutes of Health; Cancer Research Center Grant CA-08480 and Training Grant CA-05176 from the National Cancer Institute, National Institutes of Health and by ALSAC.     

Comparative cytomolecular analyses reveal karyotype variability related to biogeographic and species richness patterns in Bombacoideae (Malvaceae)

Bombacoideae is one out of nine subfamilies of Malvaceae and encompasses 160 tree species. The subfamily is karyotypically characterized by small and numerous chromosomes and is traditionally known by a remarkable inter- and intraspecific chromosome number variation. We conducted a comparative cytogenetic analysis to investigate karyotype diversity and chromosome evolution within Bombacoideae. To achieve this, we performed new chromosome counts, CMA/DAPI double staining, genome size estimations, and localization of 5S and 45S rDNA by fluorescence in situ hybridization for 21 species distributed across the Bombacoideae phylogeny. We performed ancestral states reconstruction analyses to elucidate chromosome evolution and provide insights into the systematics and evolution of Bombacoideae in comparison with other Malvaceae species. Newly generated data on chromosome number on Bombacoideae revealed diploids (Ochroma (2n = 84), Cavanillesia, Pochota, Pseudobombax (2n = 88), and Pachira (2n = 92)) and polyploids (Adansonia digitata (2n = 160) and Eriotheca species (2n = ca. 194 and 2n = 276)). For most species, in situ hybridization revealed karyotype, with two pairs of 45S rDNA sites co-located with CMA⁺ bands, and 5S rDNA sites in only one chromosome pair. Taken together, our results provide support to the hypothesis of karyotypic stability in Bombacoideae. Only the Pachira s.l. clade displayed some variability in ploidy level, number of CMA⁺ bands and 45S rDNA sites, and genome size compared to other Bombacoideae clades. The Striated bark clade was characterized by comparatively small genomes and low cytomolecular variability. Karyotypic data were related to biogeographic and species richness patterns of Bombacoideae.     

Terrigenous sediment-dominated reef platform infilling: an unexpected precursor to reef island formation and a test of the reef platform size–island age model in the Pacific

Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr⁻¹) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.