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41.
Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots 总被引:2,自引:1,他引:1
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The recent proposal of Tipton and Thowsen (Plant Physiol 79: 432-435) that iron-deficient plants reduce ferric chelates in cell walls by a system dependent on the leakage of malate from root cells was tested. Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean (Phaseolus vulgaris L. var Prélude) plants. The role of O2 in the reduction of ferric chelates by roots of iron-deficient bean plants was also tested. The rate of Fe(III) reduction was the same in the presence and in the absence of O2. However, in the presence of O2 the reaction was partially inhibited by superoxide dismutase (SOD), which indicates a role for the superoxide radical, O2[unk], as a facultative intermediate electron carrier. The inhibition by SOD increased with substrate pH and with decrease in concentration of the ferrous scavenger bathophenanthroline-disulfonate. The results are consistent with a mechanism for transmembrane electron transport in which a flavin or quinone is the final electron carrier in the plasma membrane. The results are discussed in relation to the ecological importance that O2[unk] may have in the acquisition of ferric iron by dicotyledonous plants. 相似文献
42.
The activity of enzymes involved in the conversion of sucrose to starch together with the distribution of 14C-labelled photosynthate and 4C-sucrose was studied in potato tubers showing a range of growth rates and growth patterns. Within a particular tuber the uptake of 14C from labelled photosynthate and the conversion to ethanol-insoluble 14C was greatest in the apical tissue where both the rate of production of new storage cells and starch synthesis were likely to be greatest. Uptake and conversion of 14C was lowest in the older tissue of the tuber base. Pre-treatment of tubers with gibberellic acid reduced the total input of 14C from labelled photosynthate, reversed the gradient in 14C uptake between apical and basal tuber tissue, increased the amount of 14C per g fresh weight in the basal tissue and decreased the conversion of labelled sugars to starch. For tubers with different growth rates both the total uptake of 14C from labelled photosynthate and the ratio ethanol-insoluble 14C/ethanol-soluble 14C appeared to be correlated with growth rate. In contrast when tubers were fed directly with 14C-sucrose via the tuber surface, total uptake was independent of growth rate but the correlation between growth rate and the ratio ethanol-insoluble 14C/ethanol-soluble 14C persisted. Within a particular tuber there was a decreasing gradient in sucrose synthetase activity between youngest tissue of the tuber apex and the older tissue at the tuber base but there was no clear correlation between mean enzyme activity and tuber growth rate. ADPG-pyrophosphorylase and the ratio ADPG-pyrophosphorylase/starch phosphorylase showed some correlation with tuber growth rate. Starch synthase, starch phosphorylase and UDPG-pyro-phosphorylase activities per g fresh weight of tuber tissue appeared to be relatively constant. The results suggest that the transport of sugar from the phloem sieve tubes to the tuber storage parenchyma cells, in particular the phloem unloading step, and the conversion of sugar into starch are subject to separate regulation in the potato tuber. 相似文献
43.
Effects of salinity and replacement of K+ by Na+ on lipid composition in two sugar beet inbred lines
The effects of NaCl and replacement of K+ by Na+ on the lipid composition of the two sugar beet inbred lines FIA and ADA were studied (a) with increasing additions of NaCl to the basal medium, and (b) with increasing replacement of K+ by Na+ at the same total concentration as in the basal medium. Direct relations were noted between NaCl concentration of the nutrient solution and the phospholipid concentration in the roots of FIA, the genotype characterized by a low K+ /Na+ ratio, as well as between NaCl in the medium and the phospholipid concentration in the shoots of ADA, the genotype with a high K + /Na + ratio. The sulfolipid level in the roots of FIA was maintained at higher NaCl concentrations, while it was decreased in ADA. The glycolipid concentration in the shoots of ADA and the degree of unsaturation of the fatty acids of the total lipid fraction were decreased by salinity, indicating reduced biosynthesis of chloroplast glycolipids and/or accelerated oxidation of these lipids in the presence of NaCl.
In the Na+ for K+ replacement experiment a low content of K+ in the medium resulted in decreased levels of total lipids, phospholipids and sulfolipid in the roots of both genotypes, which did not relate to root growth. K+ -leakage from the roots at low K+ -level in the medium may be reduced by the increase in saturation of the lipids. In the shoots of ADA increased levels of total lipids, phospholipids and Sulfolipid were noted at a low K+ -concentration of the nutrient solution. 相似文献
In the Na
44.
45.
Extension of the phosphorus depletion zone in VA-mycorrhizal white clover in a calcareous soil 总被引:23,自引:2,他引:21
To examine the influence of vesicular-arbuscular (VA) mycorrhizal fungi on phosphorus (P) depletion in the rhizosphere, mycorrhizal
and non-mycorrhizal white clover (Trifolium repens L.) were grown for seven weeks in a sterilized calcareous soil in pots with three compartments, a central one for root growth
and two outer ones for hyphae growth. Compartmentation was accomplished by a 30-μm nylon net. The root compartment received
a uniform level of P (50 mg kg−1 soil) in combination with low or high levels of P (50 or 150 mg kg−1 soil) in the hyphal compartments. Plants were inoculated withGlomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or remained uninfected.
Mycorrhizal inoculation doubled P concentration in shoot and root, and increased dry weight, especially of the shoot, irrespective
of P levels. Mycorrhizal contribution accounted for 76% of total P uptake at the low P level and 79% at the high P level,
and almost all of this P was delivered by the hyphae from the outer compartment. In the non-mycorrhizal plants, the depletion
of NaHCO3-extractable P (Olsen-P) extended about 1 cm into the outer compartment, but in the mycorrhizal plants a uniform P depletion
zone extended up to 11.7 cm (the length of the hyphal compartment) from the root surface. In the outer compartment, the mycorrhizal
hyphae length density was high (2.5–7 m cm−3 soil) at the various distances (0–11.7 cm) from the root surface. Uptake rate of P by mycorrhizal hyphae was in the range
of 3.3–4.3×10−15 mol s−1 cm−1. 相似文献
46.
47.
The effect of application of the fungicide pentachloronitrobenzene (PCNB) at levels between 2 and 50 mg kg–1 soil on root growth, mycorrhizal infection and P uptake was studied in pot culture with oats (Avena sativa cv. Alfred) growing in a rendzina soil low in available P. The soil had been partially sterilized by X-ray, and half of the pots were inoculated with spores of the VAM-fungusGlomus mosseae (indigenous species).Soil irradiation (0.5 Mrad) did not decrease the levels of infection by VAM. Application of PCNB decreased the VAM-infected root length, at 50 mg PCNB kg–1 soil VAM-infected root length was about 12% of the controls. Total root length, however, increased to about 126% of control values at PCNB rates up to 20 mg kg–1 soil, but decreased to 89% of the controls at 50 mg kg–1 soil. Total P-uptake decreased with increasing levels of PCNB and was linearly correlated with infected root length (r=0.92).The stimulation of root growth by PCNB at rates up to 20 mg kg–1 soil is regarded as an indirect effect, brought about by suboptimal P-supply due to inhibition of VA-mycorrhiza. Conversely, the reduction of total root length at 50 mg PCNB kg–1 soil is most likely a direct effect. Due to the phytotoxicity of the fungicide, the contribution of the indigenous VA-mycorrhiza to plant P uptake under field conditions cannot be determined by soil application of PCNB at rates sufficient for complete inhibition of VAM.As inhibition or absence of VAM may lead to compensatory root growth, mycorrhizal dependency ought to be calculated from the amounts of P taken up per unit root length in mycorrhizal and nonmycorrhizal plants, respectively. 相似文献
48.
Roginski Ana Cristina Zemniaçak Ângela Beatris Marschner Rafael Aguiar Wajner Simone Magagnin Ribeiro Rafael Teixeira Wajner Moacir Amaral Alexandre Umpierrez 《Journal of bioenergetics and biomembranes》2022,54(4):203-213
Journal of Bioenergetics and Biomembranes - Propionic acid (PA) predominantly accumulates in tissues and biological fluids of patients affected by propionic acidemia that may manifest chronic renal... 相似文献
49.
Background and aims
Phosphorus and nitrogen availability and forms are affected by soil properties as well as by plant species and further modulated by soil microbes. Additionally, close contact of the roots of two plant species may affect concentrations and forms of N and P. The aim of this study was to assess properties related to N and P cycling in the rhizosphere of wheat and legumes grown in monoculture or in wheat/legume mixtures in three soils differing in pH.Methods
Faba bean, white lupin and wheat were grown in three soils differing in pH (4.8, 7.5 and 8.8) in monoculture or in mixed culture of wheat and legumes. Rhizosphere soil was collected at flowering and analyzed for P pools by sequential fractionation, available N as well as community structure of bacteria, fungi, ammonia oxidizers, N2-fixers and P mobilizers by polymerase chain reaction (PCR)—denaturing gradient gel electrophoresis (DGGE).Results
Soil type was the major factor determining plant growth, rhizosphere nutrient dynamics and microbial community structure. Among the crop species, only faba bean had a significant effect on nitrification potential activity (PNA) in all three soils with lower activity compared to the unplanted soil. Soil type and plant spieces affected the community composition of ammonia-oxidizing archaea (AOB), ammonia-oxidizing archaea (AOA), N2-fixers (nifH), P mobilizers (ALP gene) and fungi, but not that of bacteria. Among the microbial groups, the AOA and nifH community composition were most strongly affected by crop species, cropping system and soil type, suggesting that these groups are quite sensitive to environmental conditions. All plants depleted some labile as well as non-labile P pools whereas the less labile organic P pools (NaOH extractable P pools, acid extractable P pools) accumulated in the rhizosphere of legumes. The pattern of depletion and accumulation of some P pools differed between monoculture and mixed culture as well as among soils.Conclusions
Plant growth and rhizosphere properties were mainly affected by soil type, but also by crop species whereas cropping system had the least effect. Wheat and the legumes depleted less labile inorganic P pools in some soils whereas less labile organic P pools (NaOH extractable P, acid extractable P) accumulated in the rhizosphere of legumes. 相似文献50.