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991.
Root water uptake of field-growing plants indicated by measurements of natural-abundance deuterium 总被引:1,自引:0,他引:1
Measurements of stable-isotope ratios of water extracted from stems and, in some studies, soils are increasingly being used to study the integrated root function of field-growing plants. This study explored if additional measurements on water extracted from roots could indicate the activity of roots in different areas of the soil profile and their influence on canopy water sources, so providing advantages over more common sampling strategies. Studies were conducted on trees and shrubs located in diverse habitats: a saline, semi-arid floodplain, a subhumid mountain-range front and a cold desert. At each site, roots, soil immediately surrounding the roots, and plant stems were sampled. Roots were taken from different depths in the soil, to approximately 2 m at one site. Overall, 80% of roots sampled had H isotope ratios different from the surrounding soil. The differences up to 37, were significant (p<0.05) at two of the sites. Thus water in most of the roots sampled did not come entirely, if at all, from the surrounding soil, illustrating movement and possible mixing of water within the root system. This condition was not simply related to the availability of water surrounding the soil, which was also measured. There were also differences in root and stem H isotope ratios (up to 17) in 67% of samples, although the difference was only significant in shallow samples from the floodplain. The general similarity in stem and root 2H values indicates that most roots sampled were involved in the main supply of water to the canopy. Patterns of root function varied between the individual sites. Trees were primarily using groundwater at the floodplain and mountain front sites, as the surface soils had mean matric potentials of-1800 kPa. At the mountain front site, the surface roots were transporting groundwater to the canopy in isolation form the surrounding soil. In contrast, surface roots at the floodplain were taking up water from the surrounding soil, although this water was not a significant source in the trees' overall water supply. This activity of surface roots would not have been evident from the 2H data without the root samples. At the cold desert the roots in moist surface soil provided the main source of water for the shrubs. There too the root data indicated different water uptake patterns than otherwise would have been assumed. The root data showed that groundwater could not have been a water source, a conclusion which had been reached in a previous study. Thus measurements of stable isotope ratios in root water may be a valuable tool in assessing water uptake patterns and root function. 相似文献
992.
James Whelan Marie Hugosson Elzbieta Glaser David A. Day 《Plant molecular biology》1995,27(4):769-778
Import of the synthetic precursor of the alternative oxidase from soybean was shown to be dependent on a membrane potential and ATP. The membrane potential in soybean mitochondria may be formed either by respiration through the cytochrome pathway, or through the alternative oxidase pathway with NAD+-linked substrates. Import of the alternative oxidase precursor in the presence of succinate as respiratory substrate was inhibited by KCN. Import in the presence of malate was insensitive to KCN and SHAM added separately, but was inhibited by KCN and SHAM added together (inhibitors of the cytochrome and alternative oxidases respectively). Import of the alternative oxidase was accompanied by processing of the precursor to a single 32 kDa product in both cotyledon and root mitochondria. This product had a different mobility than the two alternative oxidase bands detected by immunological means (34 and 36 kDa), suggesting that the enzyme had been modified in situ. When the cDNA clone of the alternative oxidase was modified by a single mutation (–2 Arg changed to –2 Gly), the processing of the precursor was inhibited. 相似文献
993.
Phosphorus limitation of forest leaf area and net primary production on a highly weathered soil 总被引:11,自引:0,他引:11
We tested the hypothesis that P was the nutrient limiting net primary production of a nativeMetrosideros polymorpha forest on a highly weathered montane tropical soil in Hawaii. A factorial experiment used all combinations of three fertilizer treatments: nitrogen (N), phosphorus (P) and a mix of other essential nutrients (OE), consisting primarily of mineral derived cations and excluding N and P. P addition, but not N or OE, increased leaf area index within 12 months, foliar P concentration measured at 18 months, and stem diameter increment within 18 months. Stem growth at 18 months was even greater when trees fertilized with P also received the OE treatment. N and P additions increased leaf litterfall and N and P in combination further increased litterfall. The sequence of responses suggests that increased available P promoted an increase in photosynthetic area which led to increased wood production. P was the essential element most limiting to primary production on old volcanic soil in contrast to the N limitation found on young volcanic soils. 相似文献
994.
Abstract: The combined effect of hydrostatic pressure and heat shock on thermotolerance was examined in the deep-sea hyperthermophilic archaeon Pyrococcus strain ES4. Pressure equivalent to the depth of isolation (22 MPa) enhanced ES4's survival at super-optimal temperatures (101–108°C) relative to low pressure (3 MPa). Pressure also raised the temperature at which a putative heat-shock protein (98 kDa) accumulated. ES4 grown at 95°C and 3 MPa displayed immediate enhanced thermotolerance to 105°C after being shifted to 22 MPa. Cultures grown at 95°C and 22 MPa and then heat shocked at 105°C and 3 MPa retained enhanced thermotolerance after decompression. These results suggest that this deep-sea hyperthermophile has developed pressure-induced responses that include increased survival to hyperthermal conditions. 相似文献
995.
Reactions of Cr(CO)3(η6-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)2Re(THF), where Cp′ = η5-C5H5 or η5-C5Me5, give the products Cp′(CO)2Re(η2:η6-μ2-BT)Cr(CO)3 in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)2Re(η2:η6-μ2-BT)Cr(CO)3 (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)2Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η2) or the sulfur (η1(S)). Thus, the electron-withdrawing Cr(CO)3 group in 3 stabilizes the 2,3-η2 mode of BT coordination to the Cp′(CO)2Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group . 相似文献
996.
The reversible equilibrium conversion under H2 of [RuCl(dppb) (μ-Cl)]2 (1) to generate (η2-H2) (dppb) (μ-Cl)3RuCl(dppb) in CH2Cl2 (dppb = Ph2P(CH2)4PPh2) has been studied at 0–25 °C by UV-Vis and 31P{1H} NMR spectroscopy, and by stoppe kinetics; the equilibrium constant and corresponding thermodynamic parameters, and the forward and reverse rate constants at 25 °C have been determined. A measured ΔH° value of 0 kJ mol−1 allows for an estimation of an exothermicity of 60 kJ mol−1 for binding an η2-H2 at an Ru(II) centre; a ΔS° value of 60 J mol−1 K−1 indicates that in solution 1 contain s coordinated CH2Cl2. The kinetic and thermodynamic data are compared to those obtained from a previously studied hydrogenation of styrene catalyzed by 1. Preliminary findings on related systems containing Ph2P(CH2)3PPh2 and (C6H11)2P(C6H11)2 are also noted. 相似文献
997.
Gonzlez E.M.; Gordon A.J.; James C.L.; Arrese-lgor C. 《Journal of experimental botany》1995,46(10):1515-1523
Experiments were carried out to investigate the effects of droughtstress on enzymatic activities related to carbon and nitrogenmetabolism in soybean nodules. Gradual drought stress, imposedby withholding water nutrients, resulted in declines in thewater potential of leaves and nodules consistent with a significantdecline in N2 fixation. However, the amounts of nitrogenasecomponents 1 and 2 were virtually unaffected by drought stress.Similarly, no significant changes could be detected in aspartateaminotransferase, phosphoenolpyruvate carboxylase, glutaminesynthetase or alkaline invertase activities throughout the experiment.In contrast, sucrose synthase (SS), one of the enzymes involvedin sucrose metabolism in legume nodules, declined dramaticallyin activity and in content within a few days of withholdingwater. Coincident with this decline in SS activity were significantincreases in the nodule contents of sucrose, total free aminoacids and ureides. The amounts of proline, however, did notincrease until some days later. It is suggested that SS mayplay a key role in the regulation of nodule carbon metabolismand, therefore, of nitrogen fixation under drought stress conditions. Key words: Glycine max, soybean, nodule metabolism, drought stress, sucrose synthase 相似文献
998.
David M. Barnes Destiny B. Sykes James J. Smith David S. Miller 《Journal of cellular physiology》1995,164(2):304-314
The insulin mimic, peroxide of vanadate (pervanadate), stimulated 35S-methionine incorporation into Xenopus oocyte protein in a Mg2+-dependent manner. Reducing the extracellular Mg2+ concentration from 1.0 to 0.1 mM decreased the pervanadate-stimulated component of incorporation by 35%; with 0.01 mM Mg2+ or lower, the pervanadate-stimulated component was abolished. In addition, reducing extracellular Mg2+ to 0.01 mM inhibited about 50% of the insulinstimulated component of methionine incorporation. Mg2+ depletion had no effects on incorporation in controls or when protein synthesis was stimulated by Zn2+ or bovine growth hormone. Thus, not all substances that stimulated protein synthesis showed a dependence on extracellular Mg2+. Reducing extracellular Ca2+ had no effects on methionine incorporation in control cells or in cells stimulated by pervanadate or insulin. When oocytes maintained in a paraffin oil medium were brought into contact with a 0.5 m?I droplet of buffer containing the Mg2+ indicator dye, mag-fura-2, and pervanadate, apparent droplet Mg2+ decreased rapidly, indicating net uptake by the cells. Insulin also caused a net uptake of Mg2+. In contrast, apparent extracellular Mg2+ was constant when cells were in contact with droplets containing no effectors. Together, these data indicate that extracellular Mg2+, but not Ca2+, is involved in the stimulation of protein synthesis by pervanadate, and to a lesser extent by insulin. Pervanadate appears to induce a net uptake of Mg2+, and this change in membrane transport may be an early event in signalling the increase in translation. © 1995 Wiley-Liss, Inc. 相似文献
999.
1000.
Abstract: Fetal alcohol syndrome produces defects that parallel abnormalities associated with early iron deficiency. Hence, we examined the effects of prenatal exposure to ethanol on iron, transferrin, and ferritin concentrations. The subjects were the offspring of pregnant rats fed an ethanol-containing diet (Et), pair-fed an isocaloric control diet (Ct), or fed chow and water. The amounts of iron, transferrin, and ferritin were assessed in three CNS regions (cerebral cortex, subcortical forebrain, and brain-stem). In all three segments of the control rats, iron, transferrin, and ferritin levels decreased during the first 2 postnatal weeks, reached a minimum during week 3, and then rose to adult levels. This pattern was delayed by ethanol treatment, e.g., the minimal concentrations in iron, transferrin, and ferritin in the Et-treated rats were achieved later (3 days, 7 days, and 2 weeks, respectively) than they were in the Ct-treated rats. Ethanol-induced alterations in iron homeostasis persisted into adulthood; iron concentration was reduced, transferrin concentration was unaffected, and ferritin concentration was increased. The net result was that the timely delivery and bioavailability of iron were compromised by ethanol exposure. The defects in iron regulation are permanent and may underlie ethanol-induced abnormalities in iron-dependent growth processes such as myelination. 相似文献