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  • 1
    Electronic Resource
    Electronic Resource
    Hg2+-induced leakage of electrolytes and inhibition of NO3 − utilization inNostoc calcicola (1990)
    Springer
    BioMetals 3 (1990), S. 208-212 
    Details
    ISSN: 1572-8773
    Keywords: Hg2+ toxicity ; Nostoc calcicola ; Electrolyte leakage ; NO3 − uptake ; Nitrate reductase ; Metal interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of mercury (Hg2+) in the absence and presence of methylmercury (CH3Hg+), cadmium (Cd2+), copper (Cu2+), nickel (Ni2+) and calcium (Ca2+) on Nostoc calcicola Bréb. has been studied in terms of electrolyte leakage, NO3 − uptake and in vivo nitrate reductase (NR) activity to discover any possible correlation among such parameters under Hg2+ stress. Leakage of electrolytes from Hg2+-treated cyanobacterial cells was directly proportional to Hg2+ concentrations and exposure time. In comparison to NO3 − uptake, an about 60-fold slower rate of NR activity was observed in the untreated cultures, the former being five times more Hg2+-sensitive. A non-competitive synergistic interaction of Hg2+ with CH3Hg+ or Cd2+ and antagonistic with that of Ni2+ or Ca2+ has been observed for both the processes of NO3 − utilization. The antagonistic interaction of Cu2+ with Hg2+ in terms of NO3 − uptake and synergistic with respect to NR activity, has been attributed to the dual bonding preference of Cu2+ for cellular ligands. These findings suggest that (a) a statistically significant correlation exists among such parameters; (b) Hg2+ predominantly attacks the cyanobacterial cell membrane; (c) Hg2+ inhibits NO3 − utilization; (d) the presence of other cations increases or decreases the inhibitory actions of Hg2+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01140581
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  • 2
    Electronic Resource
    Electronic Resource
    Assessment of Hg2+ toxicity to a N2-fixing cyanobacterium in long- and short-term experiments (1992)
    Springer
    BioMetals 5 (1992), S. 149-156 
    Details
    ISSN: 1572-8773
    Keywords: Hg2+ toxicity ; cyanobacterium ; Nostoc calcicola ; growth ; photopigments ; nucleic acids ; photosynthesis ; membrane integrity ; nutrient uptake ; enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Toxicological responses of the filamentous N2-fixing cyanobacteriumNostoc calcicola Bréb. towards Hg2+ were studied to enumerate the decisive lethal events. In low-dose, long-term experiments (0.05–0.25 μm Hg2+, 10 days), photoautotrophic growth was severely inhibited with concurrent loss of photosynthetic pigments (phycocyanin〉chlorophyll α〉carotenoids) and nucleic acids. The termination of growth after a day 4 exposure to 0.25 μm Hg2+ has been attributed to the complete inhibition ofin vivo photosynthetic activity in the cyanobacterium (O2 evolution〉14CO2 incorporation). The elevated Hg2+ concentrations irreversibly damaged the cell membrance as observed under light microscopy, and as indicated by the leakage of intracellular electrolytes and phycocyanin. In high-dose, short-term experiments (0.5–20.0 μm Hg2+, up to 6 h), thein vivo activities of selected enzymes (glutamine synthetase 〉 nitrate reductase 〉 nitrogenase) were less inhibited by Hg2+ than the uptake of nutrient ions (NH 4 + 〉NO 3 − 〉PO 4 3− ).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01061321
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  • 3
    Electronic Resource
    Electronic Resource
    Certain phenological characters of the shrub layer of Kumaun Himalayan forests (1985)
    Springer
    Plant ecology 63 (1985), S. 113-119 
    Details
    ISSN: 1573-5052
    Keywords: Flowering ; Fruiting ; Leafdrop ; Leaf flushing ; Kumaun Himalayan forest ; Phenology ; Shrub layer phenology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phenology of 49 shrub species in five forest types occurring along an altitudinal gradient (350–2150 m) in Kumaun Himalaya has been studied. The evergreen leaf-exchanging taxa accounted for nearly half of the species, the remaining half was nearly equally divided between an evergreen continual leaf drop type and deciduous taxa. The percentage of species with lengthy leaf drop increased with elevation and finally leveled off. At each site the maximum leaf drop period coincided with the warm dry period. Percentage of species with multiple leaf flushing was low for all forests. The degree of extended leafing decreased with increasing elevation along which summer dryness also decreased. Earliest leaf initiation was observed for evergreen continual leaf drop species, followed by evergreen leaf-exchanging, and deciduous types. For each forest, two peaks of flowering activity occurred, one during the warm dry period and the other in the warm wet period. The percentage of species with multiple flowering increased with increasing elevation. Nearly half of the species bore fleshy fruits. The mature fruit retention period for different forests ranged from about 2–3 months. The proportion of deciduous species was similar in trees and shrubs; leaf drop was common during the summer season for trees, while it was common during the winter season for shrubs; the proportion of species with multiple leafings was greater and leaf initiation earlier in shrubs than trees; and generally shrubs showed two flowering peaks and trees only one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00044061
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  • 4
    Electronic Resource
    Electronic Resource
    Phenological characteristics of the tree layer of Kumaun Himalayan forests (1985)
    Springer
    Plant ecology 60 (1985), S. 91-101 
    Details
    ISSN: 1573-5052
    Keywords: Flowering ; Forest ; Fruiting ; Kumaun Himalaya ; Leafdrop ; Leaf flushing ; Phenology ; Phenological activity level ; Treelayer phenology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phenology of tree components of natural forests occurring between 350 and 2150 m in Kumaun Himalaya is descibed. All forests had more evergreen than deciduous taxa. The degree of evergreenness increased with increasing elevation and decreasing summer dryness. For most species (including all dominants) concentrated leafdrop and simultaneous leafing occurred during the warm-dry period of the year. About half of the species showed multiple leafing. All species had a sharp flowering peak in April. Wet-season flowering was rare. Most of the species flowered synchronously. In the sal- (Shorea robusta) and pine (Pinus roxburghii) forests a single peak of fruit maturation occurred in summer, while in other forests there also was a secondary peak in autumn.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00040351
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