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891.
Rosalyn J. Masterton Anne Roobol Mohamed B. Al‐Fageeh Martin J. Carden C. Mark Smales 《Biotechnology and bioengineering》2010,105(1):215-220
Chinese hamster ovary cells (CHO) are routinely used in industry to produce recombinant therapeutic proteins and a number of studies have reported increased recombinant mRNA levels at temperatures <37°C. Surprisingly, the effect of reduced temperature on mRNA translation in CHO cells has not been investigated despite this process being highly responsive to environmental stresses. The relationship between low temperature culturing of CHO cells and mRNA translation was therefore investigated using labeling studies and dual luciferase reporter gene technology. Global protein synthetic capacity was not greatly affected at 32°C but was diminished at lower temperatures. The expression of both cap‐dependent and cap‐independent (IRES driven) mRNA translated luciferase reporter gene activity was highest at 32°C on a per cell basis and this was partially accounted for by increased mRNA levels. Importantly, post‐translational events appear to proceed with higher fidelity and accuracy at 32 than 37°C resulting in increased yield of active protein as opposed to an increase in total polypeptide synthesis. Therefore at 32°C recombinant cap‐dependent mRNA translation appears sufficient to maintain recombinant protein yields on a per cell basis and this is associated with improved post‐translational processing. Biotechnol. Bioeng. 2010;105: 215–220. © 2009 Wiley Periodicals, Inc. 相似文献
892.
The cold hardiness of two closely related weevil species, Exapion ulicis and E. lemovicinum was studied in relation to their life cycles. These two seed-eating weevils reproduce on Ulex plant species with different fruiting phenologies. E. ulicis lays eggs in spring and overwinters as an adult while E. lemovicinum lays eggs in autumn and overwinters as a larva. Adult weevils were collected in natural populations of Brittany (Western France) and characterized with morphological and molecular tools before experiments. We showed that both weevil species exhibited low supercooling points (SCPs) with mean seasonal values below −17 °C. Fresh mass, moisture content and sex were not correlated to supercooling ability. Weevils died upon freezing and the lower lethal temperatures (LLT) were within the range of SCP, indicating that both species are freezing intolerant. Comparison between species for SCP, LLT and survival to exposure at −8 °C in winter showed a higher cold resistance for E. ulicis than for E. lemovicinum. In addition, the seasonal evolution of cold hardiness differed depending on the species. These features suggest that response to cold of weevils is linked to their life cycles, and thus to the life history of their host plants. 相似文献
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RNase R is an important exoribonuclease that participates in the degradation of structured RNAs in Escherichia coli. In earlier work, it was shown that RNase R levels increase dramatically under certain stress conditions, particularly during cold shock and stationary phase. However, the regulatory processes that lead to this elevation are not well understood. We show here that the increase in RNase R in stationary phase is unaffected by the global regulators, RpoS and (p)ppGpp, and that it occurs despite a major reduction in rnr message. Rather, we find that RNase R is a highly unstable protein in exponential phase, with a half-life of ∼10 min, and that the protein is stabilized in stationary phase, leading to its relative increase. RNase R is also stabilized during cold shock and by growth in minimal medium, two other conditions that lead to its elevation. These data demonstrate that RNase R is subject to regulation by a novel, posttranslational mechanism that may have important implications for our complete understanding of RNA metabolism. 相似文献
897.
Effects of cold‐girdling on flows in the transport phloem in Ricinus communis: is mass flow inhibited? 总被引:1,自引:0,他引:1
The effects of cold girdling of the transport phloem at the hypocotyl of Ricinus communis on solute and water transport were investigated. Effects on the chemical composition of saps of phloem and xylem as well as of stem tissue were studied by conventional techniques and the water flow in the phloem was investigated by NMR imaging. Cold girdling reduced the concentration of sucrose but not that of inorganic solutes or amino acids in phloem saps. The possibility that cold treatment inhibited the retrieval of sucrose into the phloem, following leaching from the sieve tubes along a chemical gradient is discussed. Leaching of other solutes did not occur, as a result of missing promoting gradients in stem tissue. Following 3 d of cold girdling, sugar concentration increased and starch was synthesized and accumulated in stem tissue above the cold girdling region and along the cold-treated phloem pathway due to leaching of sugars from the phloem. Only in the very first period of cold girdling (<15-30 min) was mass flow inhibited, but recovered in the rest of cold treatment period to values similar to the control period before and the recovery period after the cold treatment. It is concluded that cold treatment affected phloem transport through two independent and reversible processes: (1) a permanent leaching of sucrose from the phloem stem without normal retrieval during cold treatment, and (2) a short-term inhibition of mass flow at the beginning of cold treatment, possibly involving P proteins. Possible further mechanisms for reversible inhibition of water flow are discussed. 相似文献
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899.
BACKGROUND: Effects of cooling rates on bud frost hardiness have been studied but there is little information on bud responses to thawing. Since the cell wall pore size has been found to increase with boron (B) deficiency, B deficiency may affect the supercooling ability of buds in winter. METHODS: The effects of duration of thawing time and rate of cooling on bud frost hardiness of Norway spruce (Picea abies) were studied in a B fertilization trial in February 2003 and March 2005. Frost hardiness of apical buds was determined by differential thermal analysis (DTA) and visual scoring of damage. KEY RESULTS: In 2003, the freezing point of primordial shoots of buds (T(f)), i.e. the low-temperature exotherm (LTE), was, on average, -39 degrees C when buds were thawed for less than 3 h and the T(f) increased to -21 degrees C after 18 h of thawing. During the first 4 h of thawing, the rate of dehardening was 6 degrees C h(-1). In 2005, buds dehardened linearly from -39 degrees C to -35 degrees C at a rate of 0.7 degrees C h(-1). In 2003, different cooling rates of 1-5 degrees C h(-1) had a minor effect on T(f) but in 2005 with slow cooling rates T(f) decreased. In both samplings, at cooling rates of 2 and 1 degrees C h(-1), T(f) was slightly higher in B-fertilized than in non-fertilized trees. By contrast, at very short thawing times in 2003, T(f) was somewhat lower in B-fertilized trees. CONCLUSIONS: There was little evidence of reduced frost hardiness in trees with low B status. This study showed that buds deharden rapidly when exposed to above-freezing temperatures in winter, but if cooled again they reharden more slowly. According to this study, rapid dehardening of buds has to be taken into account in assessments of frost hardiness. 相似文献
900.
Effect of long-term and rapid cold hardening on the cold torpor temperature of an aphid 总被引:2,自引:0,他引:2
Abstract. The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature ( CT min ) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min−1 is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min−1 both produce a significant decrease in CT min from 1.5 ± 0.3 to –0.9 ± 0.3 and –1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CT min of the population reared at 10 °C from 0.8 ± 0.1 to –0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CT min of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae , allowing insects to move and continue feeding at lower temperatures than would otherwise be possible. 相似文献