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Threefold Difference (threefold + difference)
Selected AbstractsThe effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South AfricaJOURNAL OF APPLIED ECOLOGY, Issue 4 2006NAVASHNI GOVENDER Summary 1Fire is important for the maintenance and conservation of African savanna ecosystems. Despite the importance of fire intensity as a key element of the fire regime, it is seldom measured or included in fire records. 2We estimated fire intensity in the Kruger National Park, South Africa, by documenting fuel loads, fuel moisture contents, rates of fire spread and the heat yields of fuel in 956 experimental plot burns over 21 years. 3Individual fires were conducted in five different months (February, April, August, October and December) and at five different return intervals (1, 2, 3, 4 and 6 years). Estimated fire intensities ranged from 28 to 17 905 kW m,1. Fire season had a significant effect on fire intensity. Mean fire intensities were lowest in summer fires (1225 kW m,1), increased in autumn fires (1724 kW m,1) and highest in winter fires (2314 kW m,1); they were associated with a threefold difference between the mean moisture content of grass fuels in winter (28%) and summer (88%). 4Mean fuel loads increased with post-fire age, from 2964 kg ha,1 on annually burnt plots to 3972 kg ha,1 on biennial, triennial and quadrennial burnt plots (which did not differ significantly), but decreased to 2881 kg ha,1 on sexennial burnt plots. Fuel loads also increased with increasing rainfall over the previous 2 years. 5Mean fire intensities showed no significant differences between annual burns and burns in the biennial, triennial and quadrennial categories, despite lower fuel loads in annual burns, suggesting that seasonal fuel moisture effects overrode those of fuel load. Mean fire intensity in sexennial burns was less than half that of other burns (638 vs. 1969 kW m,1). 6We used relationships between season of fire, fuel loads and fire intensity in conjunction with the park's fire records to reconstruct broad fire intensity regimes. Changes in management from regular prescribed burning to ,natural' fires over the past four decades have resulted in a decrease in moderate-intensity fires and an increase in high-intensity fires. 7The highest fire intensities measured in our study (11 000 , > 17 500 kW m,1) were significantly higher than those previously reported for African savannas, but were similar to those in South American cerrado vegetation. The mean fire intensity for late dry season (winter) fires in our study was less than half that reported for late dry season fires in savannas in northern Australia. 8Synthesis and applications. Fire intensity has important effects on savanna vegetation, especially on the dynamics of the tree layer. Fire intensity varies with season (because of differences in fuel moisture) as well as with fuel load. Managers of African savannas can manipulate fire intensity by choosing the season of fire, and further by burning in years with higher or lower fuel loads. The basic relationships described here can also be used to enhance fire records, with a view to building a long-term data set for the ongoing assessment of the effectiveness of fire management. [source] Consequences of insect herbivory on grape fine root systems with different growth ratesPLANT CELL & ENVIRONMENT, Issue 7 2007T. L. BAUERLE ABSTRACT Herbivory tolerance has been linked to plant growth rate where plants with fast growth rates are hypothesized to be more tolerant of herbivory than slower-growing plants. Evidence supporting this theory has been taken primarily from observations of aboveground organs but rarely from roots. Grapevines differing in overall rates of new root production, were studied in Napa Valley, California over two growing seasons in an established vineyard infested with the sucking insect, grape phylloxera (Daktulosphaira vitifoliae Fitch). The experimental vineyard allowed for the comparison of two root systems that differed in rates of new root tip production (a ,fast grower', Vitis berlandieri × Vitis rupestris cv. 1103P, and a slower-growing stock, Vitis riparia × Vitis rupestris cv. 101,14 Mgt). Each root system was grafted with a genetically identical shoot system (Vitis vinifera cv. Merlot). Using minirhizotrons, we did not observe any evidence of spatial or temporal avoidance of insect populations by root growth. Insect infestations were abundant throughout the soil profile, and seasonal peaks in phylloxera populations generally closely followed peaks in new root production. Our data supported the hypothesis that insect infestation was proportional to the number of growing tips, as indicated by similar per cent infestation in spite of a threefold difference in root tip production. In addition, infested roots of the fast-growing rootstock exhibited somewhat shorter median lifespans (60 d) than the slower-growing rootstock (85 d). Lifespans of uninfested roots were similar for the two rootstocks (200 d). As a consequence of greater root mortality of younger roots, infested root populations in the fast-growing rootstock had an older age structure. While there does not seem to be a trade-off between potential growth rate and relative rate of root infestation in these cultivars, our study indicates that a fast-growing root system may more readily shed infested roots that are presumably less effective in water and nutrient uptake. Thus, differences in root tip production may be linked to differences in the way plants cope with roots that are infested by sucking insects. [source] Charges dispersed over the permeation pathway determine the charge selectivity and conductance of a Cx32 chimeric hemichannelTHE JOURNAL OF PHYSIOLOGY, Issue 10 2008Seunghoon Oh Previous studies have shown that charge substitutions in the amino terminus of a chimeric connexin, Cx32*43E1, which forms unapposed hemichannels in Xenopus oocytes, can result in a threefold difference in unitary conductance and alter the direction and amount of open channel current rectification. Here, we determine the charge selectivity of Cx32*43E1 unapposed hemichannels containing negative and/or positive charge substitutions at the 2nd, 5th and 8th positions in the N-terminus. Unlike Cx32 intercellular channels, which are weakly anion selective, the Cx32*43E1 unapposed hemichannel is moderately cation selective. Cation selectivity is maximal when the extracellular surface of the channel is exposed to low ionic strength solutions implicating a region of negative charge in the first extracellular loop of Cx43 (Cx43E1) in influencing charge selectivity analogous to that reported. Negative charge substitutions at the 2nd, 5th and 8th positions in the intracellular N-terminus substantially increase the unitary conductance and cation selectivity of the chimeric hemichannel. Positive charge substitutions at the 5th position decrease unitary conductance and produce a non-selective channel while the presence of a positive charge at the 5th position and negative charge at the 2nd results in a channel with conductance similar to the parental channel but with greater preference for cations. We demonstrate that a cysteine substitution of the 8th residue in the N-terminus can be modified by a methanthiosulphonate reagent (MTSEA-biotin-X) indicating that this residue lines the aqueous pore at the intracellular entrance of the channel. The results indicate that charge selectivity of the Cx32*43E1 hemichannel can be determined by the combined actions of charges dispersed over the permeation pathway rather than by a defined region that acts as a charge selectivity filter. [source] N-linked glycosylation is an important parameter for optimal selection of cell lines producing biopharmaceutical human IgGBIOTECHNOLOGY PROGRESS, Issue 1 2009Patrick H. C. van Berkel Abstract We studied the variations in N-linked glycosylation of human IgG molecules derived from 105 different stable cell lines each expressing one of the six different antibodies. Antibody expression was based on glutamine synthetase selection technology in suspension growing CHO-K1SV cells. The glycans detected on the Fc fragment were mainly of the core-fucosylated complex type containing zero or one galactose and little to no sialic acid. The glycosylation was highly consistent for the same cell line when grown multiple times, indicating the robustness of the production and glycan analysis procedure. However, a twofold to threefold difference was observed in the level of galactosylation and/or non-core-fucosylation between the 105 different cell lines, suggesting clone-to-clone variation. These differences may change the Fc-mediated effector functions by such antibodies. Large variation was also observed in the oligomannose-5 glycan content, which, when present, may lead to undesired rapid clearance of the antibody in vivo. Statistically significant differences were noticed between the various glycan parameters for the six different antibodies, indicating that the variable domains and/or light chain isotype influence Fc glycosylation. The glycosylation altered when batch production in shaker was changed to fed-batch production in bioreactor, but was consistent again when the process was scaled from 400 to 5,000 L. Taken together, the observed clone-to-clone glycosylation variation but batch-to-batch consistency provides a rationale for selection of optimal production cell lines for large-scale manufacturing of biopharmaceutical human IgG. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] | ||||||||||