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991.
Susan Haase Liliane Ruess Günter Neumann Sven Marhan Ellen Kandeler 《Plant and Soil》2007,301(1-2):151-164
Low amounts of root infestation by plant parasitic nematodes are suggested to increase nutrient supply and in turn enhance
microbial activity and net mineralization rate in the rhizosphere. These effects are generally related to “leakage” of plant-derived
metabolites from damaged roots. Besides leakage, the present study examines other nematode–host interactions such as alterations
in root exudation and morphology, which were almost not considered yet. This includes undamaged root parts in order to assess
systemic plant response. The root-knot nematode Meloidogyne incognita (Kofoid and White 1919; Chitwood 1949) and barley (Hordeum vulgare L. cv. Europa) was used as model system. Host plants were grown in mini-rhizotrons inoculated with 0, 2,000, 4,000 or 8,000 M. incognita for 4 weeks. Root morphology, rhizodeposition (sugars, carboxylates, amino acids), and rhizosphere microbial communities
(PLFAs) were assessed. In treatments with 4,000 nematodes, shoot biomass, total N and P content increased by the end of the
experiment. Generally, an enhanced release of plant metabolites (sugars, carboxylates, amino acids) from the apical root zone
occurred 1 week after inoculation with 4,000 and 8,000 M. incognita, indicating root leakage. Low levels of root herbivory stimulated root hair elongation in both infected and uninfected roots.
These systemic changes in root morphology likely contributed to the increased sugar exudation in uninfected roots in all nematode
treatments at 3 weeks after inoculation. Root-knots formed a separate microhabitat within the root-system. They were characterised
by decreased rhizodeposition and increased fungal to bacterial ratio in the adhering rhizosphere soil. The present study provides
the first evidence that, apart from leakage, nematode root herbivory at background levels induces local and systemic effects
on root morphology and exudation, which in turn may affect plant performance. 相似文献
992.
This study aims to assess the effects of corrections for disturbances such as an increased amount of dead roots and an increase
in volumetric soil water content on the calculation of soil CO2 efflux partitioning. Soil CO2 efflux, soil temperature and superficial soil water content were monitored in two young beech sites (H1 and H2) during a
trenching experiment. Trenching induced a significant input of dead root mass that participated in soil CO2 efflux and reduced the soil dissolved organic carbon content, while it increased superficial soil water content within the
trenched plot. Annual soil CO2 efflux in control plots was 528 g C m−2 year−1 at H1 and 527 g C m−2 year−1 at H2. The annual soil CO2 efflux in trenched plots was 353 g C m−2 year−1 at H1 and 425 g C m−2 year−1 at H2. By taking into account annual CO2 efflux from decaying trenched roots, the autotrophic contribution to total soil CO2 efflux reached 69% at H1 and 54% at H2. The partitioning calculation was highly sensitive to the initial root mass estimated
within the trenched plots. Uncertainties in the remaining root mass, the fraction of root C that is incorporated into soil
organic matter during root decomposition, and the root decomposition rate constant had a limited impact on the partitioning
calculation. Corrections for differences in superficial soil water content had a significant impact on annual respired CO2 despite a limited effect on partitioning. 相似文献
993.
The effect of cellulase and pectinase on bacterial colonization of wheat was studied by three different experiments. In the
first experiment, the root colonization of 3 wheat cultivars (Ghods, Roshan and Omid) by two A. brasilense strains (Sp7 and Dol) was compared using pre-treated roots with cellulase and pectinase, and non-treated with these enzymes
(control). Although the root colonization varied greatly among strain-plant combinations in controls, the pre-treatment of
roots with polysaccharide degrading enzymes significantly increased the bacterial count in roots, regardless of the strain-plant
combination. This might be an indication that cell wall may act as an important factor in plant-Azospirillum interaction. In the second experiment, the root cellulase activity of the same wheat cultivars treated with and without the
two Azospirillum brasilense, strains (Sp7 and Dol) was compared. The pre-treatment of wheat roots with Azospirillum enhanced the cellulase activity of wheat root extracts. Thus, the cellulase activity might participate in the initial colonization
of wheat roots by Azospirillum. The comparison of the cellulase activity of root extracts within inoculated and non-inoculated seedlings showed that the
inoculation had enhanced the cellulase activity in root extracts, but this effect was directly dependent on the strain-plant
combination. Strain Sp7 stimulated the highest cellulase activity in cv. Roshan, but strain Dol induced the highest enzyme
activity in cv. Ghods. In the third experiment, several growth parameters of those 3 wheat cultivars treated with and without
those two bacterial strains (Sp7 and Dol) were compared. The highest magnitude of growth responses caused by Sp7 strain was
in the cv Roshan, but Dol strain stimulated the highest growth in cv Ghods. Therefore, effective colonization may contribute
to more growth responses. 相似文献
994.
Elena Iordanova Vanguelova Stephen Nortcliff Andy J. Moffat Fiona Kennedy 《Plant and Soil》2007,294(1-2):41-54
A manipulated increase in acid deposition (15 kg S ha−1), carried out for three months in a mature Scots pine (Pinus sylvestris) stand on a podzol, acidified the soil and raised dissolved Al at concentrations above the critical level of 5 mg l−1 previously determined in a controlled experiment with Scots pine seedlings. The induced soil acidification reduced tree fine
root density and biomass significantly in the top 15 cm of soil in the field. The results suggested that the reduction in
fine root growth was a response not simply to high Al in solution but to the depletion of exchangeable Ca and Mg in the organic
layer, K deficiency, the increase in NH4:NO3 ratio in solution and the high proton input to the soil by the acid manipulation. The results from this study could not justify
the hypothesis of Al-induced root damage under field conditions, at least not in the short term. However, the study suggests
that a short exposure to soil acidity may affect the fine root growth of mature Scots pine. 相似文献
995.
Mycorrhizal responsiveness of aerobic rice genotypes is negatively correlated with their zinc uptake when nonmycorrhizal 总被引:1,自引:0,他引:1
Xiaopeng Gao Thomas W. Kuyper Chunqin Zou Fusuo Zhang Ellis Hoffland 《Plant and Soil》2007,290(1-2):283-291
Plant Zn uptake from low Zn soils can be increased by Zn-mobilizing chemical rhizosphere processes. We studied whether inoculation
with arbuscular mycorrhizal fungi (AMF) can be an additional or an alternative strategy. We determined the effect of AMF inoculation
on growth performance and Zn uptake by rice genotypes varying in Zn uptake when nonmycorrhizal. A pot experiment was conducted
with six aerobic rice genotypes inoculated with Glomus mosseae or G. etunicatum or without AMF on a low Zn soil. Plant growth, Zn uptake and mycorrhizal responsiveness were determined. AMF-inoculated plants
produced more biomass and took up more Zn than nonmycorrhizal controls. Mycorrhizal inoculation, however, significantly increased
Zn uptake only in genotypes that had a low Zn uptake in the nonmycorrhizal condition. We conclude that genotypes that are
less efficient in Zn uptake when nonmycorrhizal are more responsive to AMF inoculation. We provide examples from literature
allowing generalization of this conclusion on a trade off between mycorrhizal responsiveness and nutrient uptake efficiency. 相似文献
996.
The precursor protein receptor at the chloroplast outer membrane atToc33 is a GTPase, which can be inactivated by phosphorylation in vitro, being arrested in the GDP loaded state. To assess the physiological function of phosphorylation, attoc33 knock out mutants were complemented with a mutated construct mimicking the constitutively phosphorylated state. Our data suggest that the reduced functionality of the mutant protein can be compensated by its upregulation. Chloroplast biogenesis and photosynthetic activity are impaired in the mutants during the early developmental stage, which is consistent with the requirement of atToc33 in young photosynthetic tissues. 相似文献
997.
Summary. Root hairs are tubular cells resulting from a tip-localized growth in which calcium ions play a key role. Hypaphorine, an
indole alkaloid secreted by the fungus Pisolithus microcarpus during the formation of ectomycorrhizae with the host plant Eucalyptus globulus, inhibits root hair tip growth. Hypaphorine-induced inhibition is linked to a transient depolarization of the plasma membrane
and a reorganization of the actin and microtubule cytoskeletons. Here we investigated the activity of hypaphorine on calcium
distribution in E. globulus root hairs with the ratiometric fluorochrome calcium indicator Indo-1. In 85% of actively growing root hairs, a significant
but modest calcium gradient between the apex and the base was observed due to an elevated cytoplasmic calcium concentration
at the apical tip. Following exposure to 1 mM hypaphorine, the apical and basal cytoplasmic Ca2+ concentration increased in 70 and 77% of the hairs, respectively, 10 min after treatment. This led to a reduced calcium gradient
in 81% of the cells. The hypothetical links between calcium concentration elevation, regulation of actin cytoskeleton dynamics,
and root hair growth inhibition in response to hypaphorine treatment are discussed.
Correspondence and reprints: UMR 1136 Interactions Arbres–Microorganismes, Faculté des Sciences, Université Nancy I, BP 239,
54506 Vandoeuvre Cedex, France. 相似文献
998.
Summary. The cytoskeleton in plant cells plays an important role in controlling cell shape and mediating intracellular signalling.
However, almost nothing is known about the reactions of cytoskeletal elements to heat stress, which represents one of the
major environmental challenges for plants. Here we show that living epidermal root cells of Arabidopsis thaliana could cope with short-term heat shock stress showing disruption and subsequent recovery of microtubules and actin microfilaments
in a time-dependent manner. Time-lapse imaging revealed a very dynamic behavior of both cytoskeletal elements including transient
depolymerization and disassembly upon heat shock (40–41 °C) followed by full recovery at room temperature (20 °C) within 1–3
h. Reaction of microtubules, but not actin filaments, to heat shock was dependent on cell type and developmental stage. On
the other hand, recovery of actin filaments, but not microtubules, from heat shock stress was dependent on the same parameters.
The relevance of this adaptive cytoskeletal behavior to intracellular signalling is discussed.
Correspondence and reprints: Institute of Cellular and Molecular Botany, University of Bonn, Kirschallee 1, 53115 Bonn, Federal
Republic of Germany. 相似文献
999.
Zeqiri B 《Progress in biophysics and molecular biology》2007,93(1-3):138-152
This paper provides a review of current metrological capability applied to the characterisation of the acoustic output of equipment used within medical ultrasonic applications. Key measurement devices, developed to underpin metrology in this area, are the radiation force balance, used to determine total output power, and the piezo-electric hydrophone, used to resolve the spatial and temporal distribution of acoustic pressure. The measurement infrastructure in place within the United Kingdom ensuring users are able to carry out traceable measurements of these quantities in a meaningful way, is described. This includes the relevant primary standards, the way international equivalence of national standards is demonstrated and the routes by which the standards are disseminated to the user community. Emerging measurement techniques that may in future lead to improved measurement capability, are also briefly discussed. 相似文献
1000.
In recent years, the use of low-environmental impact biotechnology giving rises to new types of treatment in the textile industry. The use of protease enzymes to improve some physical and mechanical properties such as smoothness, drapeability, dyeing affinity and water absorbency is particularly interesting. In this research, wool yarns were first treated with different concentrations of protease enzymes in water solution including 1, 2, 4 and 6% o.w.f. for 60 min. The dyeing process was then carried out on the treated yarns with madder (50% o.w.f.). Tensile strength of treated yarns was decreased due to enzyme treatment and it continued to decrease with an increase in enzyme concentration in solution. The L* values decreased for the samples treated with enzyme. The wash and light fastness properties of samples were measured according to ISO 105-CO5 and Daylight ISO 105-BO1. The washing fastness properties of treated samples were not changed. In the case of light fastness properties, it was increased a little for 4% and 6% enzyme treated samples. 相似文献