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101.
The osmotic tolerance of microbial cells of different microorganisms was investigated as a function of glycerol concentration and temperatures. Cells displayed specific sensitivity to dehydration in glycerol solutions. The viability of Gram-negative strains (Escherichia coli, Bradyrhizobium japonicum), Gram-positive strains (Lactobacillus plantarum, L. bulgaricus), and yeasts (Saccharomyces cerevisiae, Candida utilis) decreased with increasing osmotic pressure. For each strain, a characteristic osmotic pressure threshold causing a loss of 40% of the population at the growth temperature was determined: 26-40 MPa for E. coli, 15-25 MPa for B. japonicum, 7-15 MPa for L. bulgaricus, 40-133 MPa for L. plantarum, 50-100 MPa for S. cerevisiae, and 15-26 MPa for C. utilis. Because this threshold varies with temperature, it was possible to construct a diagram that could be helpful to the determination of the sensitivity of each strain to osmotic stress as a function of osmotic pressure and temperature. 相似文献
102.
Thompson AJ Jackson AC Parker RA Morpeth DR Burbidge A Taylor IB 《Plant molecular biology》2000,42(6):833-845
Two genes encoding enzymes in the abscisic acid (ABA) biosynthesis pathway, zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED), have previously been cloned by transposon tagging in Nicotiana plumbaginifolia and maize respectively. We demonstrate that antisense down-regulation of the tomato gene LeZEP1 causes accumulation of zeaxanthin in leaves, suggesting that this gene also encodes ZEP. LeNCED1 is known to encode NCED from characterization of a null mutation (notabilis) in tomato. We have used LeZEP1 and LeNCED1 as probes to study gene expression in leaves and roots of whole plants given drought treatments, during light/dark cycles, and during dehydration of detached leaves. During drought stress, NCED mRNA increased in both leaves and roots, whereas ZEP mRNA increased in roots but not leaves. When detached leaves were dehydrated, NCED mRNA responded rapidly to small reductions in water content. Using a detached leaf system with ABA-deficient mutants and ABA feeding, we investigated the possibility that NCED mRNA is regulated by the end product of the pathway, ABA, but found no evidence that this is the case. We also describe strong diurnal expression patterns for both ZEP and NCED, with the two genes displaying distinctly different patterns. ZEP mRNA oscillated with a phase very similar to light-harvesting complex II (LHCII) mRNA, and oscillations continued in a 48 h dark period. NCED mRNA oscillated with a different phase and remained low during a 48 h dark period. Implications for regulation of water stress-induced ABA biosynthesis are discussed. 相似文献
103.
Aggregation pheromones are used by fruit flies of the genus Drosophila to assemble on breeding substrates, where they feed, mate and oviposit communally. These pheromones consist of species-specific blends of chemicals. Here, using a phylogenetic framework, we examine how differences among species in these pheromone blends have evolved. Theoretical predictions, genetic evidence, and previous empirical analysis of bark beetle species, suggest that aggregation pheromones do not evolve gradually, but via major, saltational shifts in chemical composition. Using pheromone data for 28 species of Drosophila we show that, unlike with bark beetles, the distribution of chemical components among species is highly congruent with their phylogeny, with closely related species being more similar in their pheromone blends than are distantly related species. This pattern is also strong within the melanogaster species group, but less so within the virilis species group. Our analysis strongly suggests that the aggregation pheromones of Drosophila exhibit a gradual, not saltational, mode of evolution. We propose that these findings reflect the function of the pheromones in the ecology of Drosophila, which does not hinge on species specificity of aggregation pheromones as signals. 相似文献
104.
The effects of compression and pulverization on the dehydration kinetics and hardness of creatine monohydrate tablets were
studied using a variety of kinetic equations and physical models. The dehydration behavior of unpulverized and pulverized
tablets was investigated by using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The hardness
of both unpulverized and pulverized monohydrate tablets was significantly decreased after dehydration. The relationship between
the degree of dehydration and the tablet hardness of both unpulverized and pulverized monohydrate tablets formed a straight
line. The results suggest that the reduction in tablet hardness is dependent on the dehydration of crystal water, and the
values of the slopes indicate that the bonding energy of the unpulverized sample was stronger than that of the pulverized
sample. The dehydration kinetics of the unpulverized and pulverized monohydrate tablets were evaluated by analyzing the fit
of the isothermal DSC data using a variety of solid-state kinetic models. The dehydration of the unpulverized tablets at various
levels of compression pressure followed the 3-dimensional growth of nuclei mechanism. In contrast, although the dehydration
kinetics of pulverized monohydrate tablets compressed at 500 and 750 kg/cm2 followed the 3-dimensional diffusion mechanism, those compressed at 1000 kg/cm2 followed the 3-dimensional growth of nuclei mechanism. The PXRD analysis indicated that the diffraction intensity of the
pulverized monohydrate powder was significantly lower than that of the unpulverized powder. The diffraction peaks of the (h00)
planes and the micropore structure of the unpulverized monohydrate tablets were affected by pulverization and compression
force, respectively.
Published: October 26, 2005 相似文献
105.
Haoru Tang Zhenglong Ren Gari Krczal 《In vitro cellular & developmental biology. Plant》2000,36(1):47-50
Summary Well-developed somatic embryos were selected from a repetivively somatic embryo line derived from embryonic axes of immature
zygotic embryos of English walnut ‘No. 120’ (Juglans regia L.) for germination and conversion studies. In germinating dishes, somatic embryos germinated into only shoots, only roots,
or both shoots and roots. Without any pretreatment, 28% somatic embryos germinated, while those treated with 2.5–5.0 mg 1−1 (7.2–14.4 μmol) gibberellic acid (GA3) germinated at 25–28% and those receiving a cold treatment of 2–3 mo. at 3–4°C germinated at 30–43%. However, only 4–19%
of the germinating embryos showed both shoots and roots. Treated with desiccation, either with CaCl2·6H2O or Ca(NO3)2·4H2O at 20°C in the dark for 3 d, somatic embryos germinated at 85–91%, 57–69% of which had both shoots and roots. Treatment
with 2 mo. cold storage in combination with desiccation using Ca(NO3)2·4H2O resulted in 92% of somatic embryos germinating, 70% of which showed both shoots and roots. No significant differences were
observed between solid and liquid germination media. After transferring the germinating embryos to plantlet development media,
52–63% of those with both shoots and roots developed into plantlets while 11% with only shoots or 9% with only roots converted
into plantlets. Plantlet development was improved by using lower medium salts and sucrose concentrations. The addition of
activated charcoal enhanced root development, particularly root branching. Of 131 plants transplanted, 91 plants were acclimatized
to a greenhouse. 相似文献
106.
E. Pacini 《Plant Systematics and Evolution》2000,222(1-4):19-43
The events and processes occurring between pollen maturation, opening of the anther and presentation of pollen to dispersing agents are described. In the final phases of pollen development, starch is always stored; this occurs before the anther opens. Depending on the species, this starch may be totally or partially transformed into: (a) other types of polysaccharides (fructans and rarely callose); (b) disaccharides (sucrose); (c) monosaccharides (glucose and fructose, all situated in the cytoplasm. While awaiting dispersing agents and during dispersal, polysaccharides, especially fructans, and sucrose may be interconverted to control osmotic pressure and prevent loss and uptake of water. Opening of the anther is preceded by disappearance of the locular fluid and in many cases by partial dehydration of the pollen. Pollen generally has a water content between 5 and 50%. Pollen with a high water content may or may not be able to control water retention during pollen exposure and dispersal. Pollen may be dispersed in monads or grouped in pollen dispersing units by the following mechanisms: (i). tangling of filamentous pollen; (ii). adhesion by viscous substances (pollenkitt, tryphine, elastoviscin) derived from the tapetum; (iii). common walls. When the anther opens, the pollen may be dispersed immediately, remain until dispersed (primary presentation), or be presented to pollinators in another part of the flower (secondary presentation). 相似文献
107.
Fluorescence induction kinetics was used to investigate the effects of dehydration and rehydration on photosynthesis of detached leaves of the desiccation-tolerant, resurrective plant Boea hygrometrica (Bunge) R. Br. In comparison with the desiccation-intolerant plant Chirita heterotricha Merr., the PSⅡphotochemical activity of Boea hygrometrica was characterized by a faster decline during dehydration and a much higher capacity of recovery during rehydration. By means of native PAGE, it was further shown that the thylakoid pigment-protein complexes of Boea hygrometrica were highly stable during dehydration and rehydration. These features may contribute to the extreme desiccation resistance of photosynthesis apparatus of resurrective plant Boea hygrometrica. 相似文献
108.
M. F. Tobin R. B. Pratt A. L. Jacobsen M. E. De Guzman 《Plant biology (Stuttgart, Germany)》2013,15(3):496-504
Vulnerability to cavitation curves describe the decrease in xylem hydraulic conductivity as xylem pressure declines. Several techniques for constructing vulnerability curves use centrifugal force to induce negative xylem pressure in stem or root segments. Centrifuge vulnerability curves constructed for long‐vesselled species have been hypothesised to overestimate xylem vulnerability to cavitation due to increased vulnerability of vessels cut open at stem ends that extend to the middle or entirely through segments. We tested two key predictions of this hypothesis: (i) centrifugation induces greater embolism than dehydration in long‐vesselled species, and (ii) the proportion of open vessels changes centrifuge vulnerability curves. Centrifuge and dehydration vulnerability curves were compared for a long‐ and short‐vesselled species. The effect of open vessels was tested in four species by comparing centrifuge vulnerability curves for stems of two lengths. Centrifuge and dehydration vulnerability curves agreed well for the long‐ and short‐vesselled species. Centrifuge vulnerability curves constructed using two stem lengths were similar. Also, the distribution of embolism along the length of centrifuged stems matched the theoretical pressure profile induced by centrifugation. We conclude that vulnerability to cavitation can be accurately characterised with vulnerability curves constructed using a centrifuge technique, even in long‐vesselled species. 相似文献
109.
110.