Seed germination and seedling emergence of three annuals growing on desert sand dunes in China.
(73/427)
BACKGROUND AND AIMS: Information on the initial growth characteristics of annuals found in Chinese deserts is very limited. The aim of this study was to investigate seed germination and interactive effects of irrigation and seed burial depth in sand on seedling emergence and seedling survival in three annuals (Agriophyllum squarrosum, Bassia dasyphylla and Aristida adscensionis) commonly growing on sand dunes in these regions. METHODS: Effects of temperature, light and polyethylene glycol-6000 on seed germination were examined by irrigating seeds sown on filter paper in Petri dishes. Seedling emergence was examined for seeds sown on the surface of, or at different depths (5, 10, 20, 30, 40 and 50 mm) in, sand-filled pots, which were irrigated under different regimes. For seeds buried at a depth of 50 mm, seed viability was examined after irrigation of the pots. KEY RESULTS: Seeds of three species germinated at most temperatures recorded between spring and autumn in their native habitats. No seed dormancy was found in any species. For all three species, seedling emergence was most favoured when seeds were buried at a depth of 10 mm. When seeds sown on the sand surface were irrigated, seed germination was considerably suppressed due to water deficiency, but many seeds remained viable. For A. squarrosum and B. dasyphylla, many seeds that were deeply buried and irrigated remained ungerminated but viable, while for A. adscensionis deeply buried seeds germinated, but the seedlings did not emerge due to unfavourable seedling growth in deep sand. CONCLUSIONS: Precipitation is the most crucial factor in determining the seasonal emergence of seedlings of the three tested species in the field. The vertical distribution of seeds in sand determines the proportion of seeds that germinate after precipitation and acts to maintain seed banks over multiple years. (+info)
Citricoccus alkalitolerans sp. nov., a novel actinobacterium isolated from a desert soil in Egypt.
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An actinobacterium, strain YIM 70010T, which was isolated from a desert soil sample collected in Egypt, was subjected to a polyphasic taxonomy study. The organism was alkalitolerant and its optimum growth occurred at pH 8.0-9.0. The isolate contained chemotaxonomic markers that were characteristic of the genus Citricoccus, i.e. the peptidoglycan type Lys-Gly-Glu (variation A4alpha), the predominant menaquinone MK-9(H2) and a polar lipid profile consisting of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and two unknown glycolipids. The major fatty acids were anteiso-C(15 : 0) and iso-C(15 : 0). The G+C content of the genomic DNA was 63.8 mol%. Strain YIM 70010T exhibited a 16S rRNA gene sequence similarity of 99.6 % and DNA-DNA relatedness value of 56 % with Citricoccus muralis DSM 14442T. The phenotypic characteristics and DNA-DNA relatedness data indicate that strain YIM 70010T can be distinguished from C. muralis (DSM 14442T). Therefore, on the basis of the polyphasic taxonomic data presented, a novel species of the genus Citricoccus, Citricoccus alkalitolerans sp. nov. (type strain, YIM 70010)=CCTCC AA 203008T=DSM 15665T=KCTC 19012T) is proposed. (+info)
Planococcus stackebrandtii sp. nov., isolated from a cold desert of the Himalayas, India.
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The taxonomic position of a bacterium isolated from a cold desert of the Himalayas, India, was analysed by using a polyphasic approach. The isolated strain, designated K22-03T, had phenotypic characteristics that matched those of the genus Planococcus and it represents a novel species. The almost-complete 16S rRNA gene sequence (1464 bases) of the novel strain was compared with those of previously studied Planococcus type strains and confirmed that the strain belongs to the genus Planococcus. 16S rRNA gene sequence analysis indicated that strain K22-03T differs from all other species of Planococcus by at least 2.5 %. DNA-DNA hybridization showed that it had low genomic relatedness with Planomicrobium mcmeekinii (MTCC 3704T, 23 %), Planococcus psychrophilus (MTCC 3812T, 61 %), Planococcus antarcticus (MTCC 3854T, 45 %) and Planomicrobium okeanokoites (MTCC 3703T, 51 %), the four species with which it was most closely related based on 16S rRNA gene sequence analysis (97-97.5 % similarity). Therefore, strain K22-03T should be recognized as a novel species, for which the name Planococcus stackebrandtii sp. nov. is proposed. The type strain is K22-03T (=MTCC 6226T=DSM 16419T=JCM 12481T). (+info)
Selection on leaf ecophysiological traits in a desert hybrid Helianthus species and early-generation hybrids.
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Leaf ecophysiological traits related to carbon gain and resource use are expected to be under strong selection in desert annuals. We used comparative and phenotypic selection approaches to investigate the importance of leaf ecophysiological traits for Helianthus anomalus, a diploid annual sunflower species of hybrid origin that is endemic to active desert dunes. Comparisons were made within and among five genotypic classes: H. anomalus, its ancestral parent species (H. annuus and H. petiolaris), and two backcrossed populations of the parental species (designated BC2ann and BC2pet) representing putative ancestors of H. anomalus. Seedlings were transplanted into H. anomalus habitat at Little Sahara Dunes, Utah, and followed through a summer growing season for leaf ecophysiological traits, phenology, and fitness estimated as vegetative biomass. Helianthus anomalus had a unique combination of traits when compared to its ancestral parent species, suggesting that lower leaf nitrogen and greater leaf succulence might be adaptive. However, selection on leaf traits in H. anomalus favored larger leaf area and greater nitrogen, which was not consistent with the extreme traits of H. anomalus relative to its ancestral parents. Also contrary to expectation, current selection on the leaf traits in the backcross populations was not consistently similar to, or resulting in evolution toward, the current H. anomalus phenotype. Only the selection for greater leaf succulence in BC2ann and greater water-use efficiency in BC2pet would result in evolution toward the current H. anomalus phenotype. It was surprising that the action of phenotypic selection depended greatly on the genotypic class for these closely related sunflower hybrids grown in a common environment. We speculate that this may be due to either phenotypic correlations between measured and unmeasured but functionally related traits or due to the three genotypic classes experiencing the environment differently as a result of their differing morphology. (+info)
The effect of the Dead Sea environment on uveitis.
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BACKGROUND: Uveitis is an acute or chronic inflammatory process of the uvea caused by a number of etiologies. In many patients the etiology is unknown. OBJECTIVE: To investigate the effect of the Dead Sea environment (climatotherapy) on the signs, symptoms and clinical course of chronic uveitis. METHODS: Fifty-five patients with chronic uveitis were examined at the beginning and end of a 3-4 week stay at the Dead Sea region and on repeat visits to the region. Study data included demographic information, medical history, etiology, diagnosis, medication, and a complete ophthalmic examination. RESULTS: Statistically significant improvements were seen between the two examinations within each visit in four parameters (negative values indicate improvement): a) visual acuity for near and far: Jaeger (-0.98 +/- 0.18, P < or = 0.001) and best corrected visual acuity (-0.22 +/- 0.04, P < or = 0.0001); b) anterior chamber flare (-0.18 +/- 0.06, P < or = 0.01); c) anterior chamber cells (-0.12 +/- 0.03, P < or = 0.0001); and d) vitreous cells (-0.17 +/- 0.05, P < or = 0.001). There was a significant mean improvement during visits to the Dead Sea area and a slight dissipation of the effect during the intervals between visits. Sixty-four percent of the patients reported that they required less medication and had fewer and milder attacks of uveitis following the visits. CONCLUSIONS: The results of this study provide evidence of short- and possibly long-term improvement in the signs and symptoms of uveitis following exposure to the Dead Sea environment. (+info)
Jiangella gansuensis gen. nov., sp. nov., a novel actinomycete from a desert soil in north-west China.
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A novel actinomycete strain, designated YIM 002(T), was isolated from a desert soil sample in Gansu Province, north-west China. This actinomycete isolate formed well-differentiated aerial and substrate mycelia. In the early stages of growth, the substrate mycelia fragmented into short or elongated rods. Chemotaxonomically, it contained ll-2,6-diaminopimelic acid in the cell wall. The cell-wall sugars contained ribose and glucose. Phospholipids present were phosphatidylinositol mannosides, phosphatidylinositol and diphosphatidylglycerol. MK-9(H(4)) was the predominant menaquinone. The major fatty acids were anteiso C(15 : 0) (35.92 %), anteiso C(17 : 0) (15.84 %), iso C(15 : 0) (10.40 %), iso C(16 : 0) (7.07 %) and C(17 : 1)omega8c (9.37 %). The G+C content of the DNA was 70 mol%. Phylogenetic analysis and signature nucleotide data based on 16S rRNA gene sequences showed that strain YIM 002(T) is distinct from all recognized genera of the family Nocardioidaceae in the suborder Propionibacterineae. On the basis of the phenotypic and genotypic characteristics, it is proposed that isolate YIM 002(T) be classified as a novel species in a new genus, Jiangella gansuensis gen. nov., sp. nov. The type strain is YIM 002(T) (=DSM 44835(T)=CCTCC AA 204001(T)=KCTC 19044(T)). (+info)
Vertical distribution of the free-living amoeba population in soil under desert shrubs in the Negev desert, Israel.
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A field study was designed to examine the effect of desert shrubs on the dynamics of free-living amoebae in arid soil. Soil samples from 0- to 50-cm depths were collected at 10-cm intervals in each of the four seasons. The vertical distributions of the four main morphological types of amoebae, grouped according to their mobility, and of small flagellate populations were measured under the canopies of Hammada scoparia and Atriplex halimus, shrubs belonging to the chloride-absorbing xerohalophytes. The result obtained from the field study demonstrated that the total number of protozoa was significantly higher during the wet seasons (winter and spring) than during the dry seasons. The protozoan population was more diverse under the canopy of H. scoparia during the wet seasons, reaching 8,000 individuals per 1 g of dry soil, whereas during the dry seasons, the populations were higher under the canopy of A. halimus, with a mean of 250 individuals. The protozoan population in the deeper layers (40 to 50 cm) was found to be as active as that in the upper layers, demonstrating that, in the desert, soil columns below 20 cm are fertile and worth studying. The type 1 amoebae (e.g., Acanthamoeba and Filamoeba spp.) were the most abundant throughout the study period, and their numbers were significantly higher than those of the other amoeba types. (+info)
Comparing genomes of Helicobacter pylori strains from the high-altitude desert of Ladakh, India.
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The genomic diversity of Helicobacter pylori from the vast Indian subcontinent is largely unknown. We compared the genomes of 10 H. pylori strains from Ladakh, North India. Molecular analysis was carried out to identify rearrangements within and outside the cag pathogenicity island (cag PAI) and DNA sequence divergence in candidate genes. Analyses of virulence genes (such as the cag PAI as a whole, cagA, vacA, iceA, oipA, babB, and the plasticity cluster) revealed that H. pylori strains from Ladakh are genetically distinct and possibly less virulent than the isolates from East Asian countries, such as China and Japan. Phylogenetic analyses based on the cagA-glr motifs, enterobacterial repetitive intergenic consensus patterns, repetitive extragenic palindromic signatures, the glmM gene mutations, and several genomic markers representing fluorescent amplified fragment length polymorphisms revealed that Ladakhi strains share features of the Indo-European, as well as the East Asian, gene pools. However, the contribution of genetic features from the Indo-European gene pool was more prominent. (+info)