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921.
A survey was conducted of natural populations of the sleepy lizard Tiliqua rugosa in South Australia to determine whether infestation by ectoparasitic ticks reduced their fitness. Between 1982 and 1990,
2183 captures of 824 individual lizards were made in an area where they were infested by the tick Aponomma hydrosauri, and 3668 captures of 586 individual lizards were made in an area where they were infested with the tick Amblyomma limbatum. Lizards with high tick loads in one year tended to have high loads the next year. Longevity of lizards in the study was
either not correlated with tick load, or positively correlated. Size achieved was greater amongst lizards with greatest tick
load, and lizards in mating pairs had higher tick loads than those never found in pairs. The data do not support the hypothesis
that tick load diminishes host fitness. 相似文献
922.
Differential thermal analysis (DTA) was used to determine the exothermic responses in dormant stems and excised lengths of stem of Salix dasyclados Wimmer subjected to artificial freezing treatments.
The presence of ice on the surfaces of intact stems restricted the mechanism of freezing avoidance to temperatures above –4°C. In contrast, excised lengths of stem started to freeze as soon as the ambient temperature fell below –2°C, demonstrating that extracellular ice formation takes place earlier if cut surfaces are present. Exposure of dormant excised lengths of stem to subfreezing temperatures for more than 8 weeks did not alter their nucleation temperature not their exothermic differential responses. Early extracellular crystallisation of freezable cellular water provides conditions that allow dormant Salix dasyclados stems or excised lengths of stem to survive extreme freezing stress.
Crystallisation of extracellular and cellular water took place in the cortex, and did not result in visual damage or reduced survival. This nucleation of extracellular water took place over the same temperature range whether the excised dormant lengths of stem were partly (bark only) or completely thawed. Exposure of dormant tissue to 20°C for up to 24 h did not alter the level of freezing tolerance, nor did it increase the susceptibility of excised lengths of stem to damage by extreme temperature fluctuations. 相似文献
The presence of ice on the surfaces of intact stems restricted the mechanism of freezing avoidance to temperatures above –4°C. In contrast, excised lengths of stem started to freeze as soon as the ambient temperature fell below –2°C, demonstrating that extracellular ice formation takes place earlier if cut surfaces are present. Exposure of dormant excised lengths of stem to subfreezing temperatures for more than 8 weeks did not alter their nucleation temperature not their exothermic differential responses. Early extracellular crystallisation of freezable cellular water provides conditions that allow dormant Salix dasyclados stems or excised lengths of stem to survive extreme freezing stress.
Crystallisation of extracellular and cellular water took place in the cortex, and did not result in visual damage or reduced survival. This nucleation of extracellular water took place over the same temperature range whether the excised dormant lengths of stem were partly (bark only) or completely thawed. Exposure of dormant tissue to 20°C for up to 24 h did not alter the level of freezing tolerance, nor did it increase the susceptibility of excised lengths of stem to damage by extreme temperature fluctuations. 相似文献
923.
Maxine B. Nichols Marie-Odile Bancal Michael E. Foley Jeffrey J. Volenec 《Physiologia plantarum》1993,88(2):221-228
Nonstructural carbohydrates were determined in both embryo and endosperm of dormant (nongerminating) and afterripened (germinating) intact caryopses of wild oat ( Avena fatua L.). No changes in endosperm starch or soluble sugar were observed at the onset of germination (18 h). No changes in glucose, fructose, sucrose or starch within dormant or afterripened embryos correlated with onset of visual germination. In afterripened embryos, depletion of raffinose (18 h), stachyose (18 h) and galactose (24 h) was correlated with germination. In contrast, raffinose-family oligosaccharide levels in dormant embryos remained constant for 7 days following imbibition. Germination of isolated dormant embryos on 88 m M galactose-containing media was accompanied by decreased endogenous levels of raffinose and stachyose. Isolated embryos from dormant caryopses incorporated 14 C from 14 C-fructose into both raffinose and stachyose during 24 h of imbibition. In contrast, no 14 C incorporation into stachyose was observed in embryos from afterripened caryopses. No 14 C incorporation into raffinose was observed at 18 and 24 h. When in vitro activities of α galactosidase were measured, no temporal differences between dormant or afterripened caryopses were detected in either embryo or endosperm tissue. Although the mechanism associated with differences in utilization of raffinose and stachyose is yet unidentified, alterations in raffinose-family oligosaccharide metabolism in the embryo appear to be a unique prerequisite for afterripening-induced germination. 相似文献
924.
Effects of erosion on ecto- and VA-mycorrhizal inoculum potential of soil following forest fire in southwest Oregon 总被引:1,自引:0,他引:1
The Longwood Complex wildfire in the Siskiyou Mountains of southern Oregon in August 1987 created an opportunity to study erosion and its effects on mycorrhizal fungus inoculum potential of a forest soil on steep slopes. As measured by the erosion-bridge method, most erosion occurred in a single, intense storm in December after the fire and amounted to an estimated 2 to 4 cm of surface soil. Captured eroded soil had a higher pH and P and Mg levels than residual soil. Seedlings ofLibocedrus decurrens andPseudotsuga menziesii were planted on eroded plots with additions of captured eroded soil (ET) or pasteurized eroded soil (PET) transferred to the planting holes. After one growing season,Libocedrus seedlings formed nearly 4 times the vesicular-arbuscular mycorrhizae in ET treatments and more than twice as much in PET treatments than in controls. Survival and basal area growth were significantly better in ET than in the other treatments, and both ET and PET produced more seedling shoot growth than did controls.Pseudotsuga seedlings did not differ in measured characteristics between treatments; ectomycorrhiza formation was slight, evidently the result of reduced inoculum potential resulting from the fire. 相似文献
925.
Nitrate limitation of N2O production and denitrification from tropical pasture and rain forest soils
William F. J. Parsons Martin E. Mitre Michael Keller William A. Reiners 《Biogeochemistry》1993,22(3):179-193
Nitrous oxide production was measured in intact cores taken from active pasture and old-growth forest Inceptisols in the Atlantic Lowlands of Costa Rica. Following additions of aqueous KNO3 or glucose, or the two combined amendments, the cores were incubated in the laboratory to determine if N2O production rates were either N-limited or C-limited in the two land use types. Differences in rates of denitrification (N22O + N2 production) among amended forest and pasture soils were determined by addition of 10% C2H2.The forest soils were relatively insensitive to all amendment additions, including the acetylene block. Forest N2O production rates among the treatments did not differ from the controls, and were consistently lower than those of the pasture soils. With the addition of glucose plus nitrate to the forest soils, production of N2O was three times greater than the controls, although this increase was not statistically significant. On the other hand, the pasture soils were definitely nitrogen-limited since N2O production rates were increased substantially beyond controls by all the amendments which contained nitrate, despite the very low N level (5 mg N kg–1 soil) relative to typical fertilizer applications. With respect to the nitrate plus glucose plus acetylene treatment, denitrification was high in the pasture soils; N2O production in the presence of C2H2 was 150% of the rate of N2O production measured in the absence of the acetylene block. The results are discussed in relation to the effects of agricultural land use practices and subsequent impacts of disturbance on N2O release. 相似文献
926.
Michael J. Gasson 《FEMS microbiology reviews》1993,12(1-3):3-19
Abstract: Current activities and future prospects for the biotechnology of lactic acid bacteria are reviewed. Genetic engineering technology, including advances and limitations of plasmid vectors and chromosomal integration strategies are discussed together with the status of gene expression and the importance of in vivo gene transfer systems and transposition. Areas of biotechnological application considered include proteolysis and flavour generation, bacteriophage resistance, antimicrobials, metabolic engineering and the possible uses of lactic acid bacteria in relation to health. 相似文献
927.
Russell B. Lingham Keith C. Silverman Gerald F. Bills Carmen Cascales Manual Sanchez Rosalind G. Jenkins Suzanne E. Gartner Isabel Martin Maria T. Diez Fernando Peláez Sagrario Mochales Yu-Lin Kong Richard W. Burg Maria S. Meinz Leeyuan Huang Mary Nallin-Omstead Scott D. Mosser Michael D. Schaber Charles A. Omer David L. Pompliano Jackson B. Gibbs Sheo B. Singh 《Applied microbiology and biotechnology》1993,40(2-3):370-374
Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella.
Correspondence to: R. B. Lingham 相似文献
928.
The Golgi complexes of animal cells are said to become vesicular during cell division in order to allow the equal partitioning of organelles between daughter cells (Warren, 1985). However, in the epidermis of fifth stage larval Calpodes ethlius (Lepidoptera, Hesperi idae), cutical deposition is concurrent with cell division in preparation for pupation. We therefore looked at the Golgi complexes of these epidermal cells to see if they maintained their interphase form to allow them to continue to function during cell division. Dividing cells were recognized by changes in the nucleus and nuclear envelope, the form of the cell cortex and cell surface, and by the disposition of microtubules. Epidermal Golgi complexes consist of 3-5 cisternae capped by endoplasmic reticulum with transfer vesicles and rings of GC beads next to the cis face, and secretory vesicles on the trans face. Golgi complexes of dividing cells are structurally indistinguishable from those in interphase, their beads are in the rings characteristic of active GCs, and cuticle continues in uninterrupted lamellae above the apical microvilli. The observations suggest that Golgi complexes in dividing insect cells differ from those of most vertebrates by remaining functional through mitosis. 相似文献
929.
Summary The pH-value and the stirrer speed during cultivation of the thermophilic fungus Thermomyces lanuginosus were found to have a pronounced influence on xylanase production using corn cobs as carbon source. The highest xylanase activity of 32500 nkat/ml was produced in labscale fermentation within 118 hours at a stirrer speed of 50 rpm and a controlled pH-value of 7.5. 相似文献
930.