盐胁迫下两草种SOD和POD及脯氨酸动态研究

在NaCl、KCl、MgSO₄及其复合盐胁迫下, 研究草坪草-金牌美达丽(Lolium perenne)和猎狗(Fesluca elata) 中脯氨酸含量、超氧化物歧化酶和过氧化物酶活性的变化。结果表明:不同盐分、不同浓度胁迫下脯氨酸含量呈波动式变化, 其峰值出现在较高浓度下, 说明在一定范围内盐胁迫强度越大脯氨酸积累越明显;SOD 的最高值出现在低浓度下, 而最低值无此特点, 不同盐胁迫下的最高值、最低值相差不多, 说明L.perenne 和F.elata 相差不明显;POD 活性随盐浓度增加呈波动性变化, L.perenne (除KCl)和F.elata (除MgSO₄)最高值均出现在低浓度下, L.perenne 的最低值集中在高浓度, 而F.elata 的最低值则集中在低浓度, F.elata在高浓度胁迫下, 处于一个比较稳定的水平, 高于或接近CK, 且各值比较接近, 而在L.perenne 中却没有这一结果。     

Root uptake and distribution of radiocaesium from contaminated soils and the enhancement of Cs adsorption in the rhizosphere

Uptake by roots from contaminated soil is one of the key steps in the entry of radiocaesium into the food chain. We have measured the uptake by roots of radiocaesium and its transfer to shoots of a heathland grass, sheep fescue (Festuca ovina L.) from two contrasting agricultural soils, a sandy podzol and a clayey calcareous soil. A culture device which keeps the roots separate from the soil was used thus allowing rhizosphere soil to be obtained easily and enhancing the effect of root action. Biomass production and ¹³⁷Cs in shoots and roots were recorded. Cs adsorption was studied on both the initial, nonrhizosphere soil and on rhizosphere soil in dilute soil suspension. Cs desorption was measured by resuspending subsamples of contaminated soil in solutions containing various concentrations of stable Cs. The proportion of Cs fixed, i.e. not readily desorbable, was calculated by comparison of the adsorption and desorption isotherms. Uptake by roots varied considerably between soils and did not appear to be diffusion limited. Root-to-shoot transfer did not differ for the two soils studied. Root action considerably enhanced Cs adsorption on the soils, particularly the in sandy podzol with a low Cs affinity. The value of K_d was increased by up to an order of magnitude. A large proportion of adsorbed Cs was found to be fixed, the K_d was up to seven times greater on desorption than adsorption, indicating that up to 80% of adsorbed Cs was not readily exchangeable. Root action had little effect on the fixed fraction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Chlorophyll a fluorescence, enzyme and antioxidant analyses provide evidence for the operation of alternative electron sinks during leaf senescence in a stay-green mutant of Festuca pratensis

Mutation of the sid gene in Festuca pratensis prevents chlorophyll degradation. The senescing leaves retain their chlorophyll complement and stay green. Nevertheless, CO2 assimilation and ribulose-bisphosphate carboxylase/oxygenase content decline in both mutant and wild-type plants. Photosynthesis and chlorophyll a fluorescence measurements were performed in air and at low oxygen to prevent photorespiration. The maximum extractable activity of ribulose 1,5 bisphosphate carboxylase was higher in the senescent mutant leaves than in those of the wild-type control hut Mas much lower than that observed in the mature leaves of either genotype. The activation state of this enzyme was similar in mutant and wild-type lines at equivalent stages of development. Analysis of chlorophyll a fluorescence quenching with varying irradianco showed similar characteristics for mature leaves of the two genotypes. Genotypic variations in photosystem II (I'SII) efficiency were observed only in the senescent leaves. Photochemical quenching and the quantum efficiency of PSII were greater in the senescent mutant leaves than in (he wild type at a given irradiance. The calculated electron flux through PSII was substantially higher in the mutant with a greater proportion of electrons directed to photorespiration. Maximum catalytic activities of ascorbate peroxidase decreased in senescent compared to mature leaves of both genotypes, while glutathione reductase and monodehydroascorbate reductase were unchanged in both cases. Superoxide dismutase activity was approximately doubled and dehydroascorbate reductase activity was three times higher in senescent leaves compared with the mature leaves of both genotypes. In no case was there a difference in enzyme activities between mutant and wild type at equivalent growth stages. The pool of reduced ascorbate was similar in the mature leaves of the two genotypes, whereas it was significantly higher in the senescent leaves of the mutant compared with the wild type. Conversely, the hydrogen peroxide content was significantly higher in the mature leaves of the wild type than in those of the mutant, but in senescent leaves similar values were obtained. In leaves subjected to chilling stress the reduced ascorbate pool was higher in both mature and senescent leaves of the mutant than in their wild-type counterparts. Similarly, the hydrogen peroxide pool was significantly lower in both mature and senescent leaves of the mutant than in the wild type. We conclude that, in spite of deceased CO₂ assimilation, the mutant is capable of high rates of electron Slow. The high ascorbate/hydrogen peroxide ratio observed in the mutant, particularly at low temperatures, suggests that the senescent leaves are not subject to enhanced oxidative stress.     

Seasonal distribution of topsoil ammonium and nitrate under legume-grass and grass swards

Losses of soil N through leaching and N₂ fixation by legumes often are related to soil nitrate concentration. The seasonal distribution of soil ammonium and nitrate concentrations under ungrazed legume-grass and grass swards were evaluated on two experiments that were established in 1983 (Exp. 1) and in 1984 (Exp. 2). Treatments were white clover (Trifolium repens L.) (WC), red clover (Trifolium pratense L.) (RC), and birdsfoot trefoil (Lotus corniculatus L.) (BT), each grown with tall fescue (Festuca arundicacea Schreb.) (TF) at two legume proportions, and a pure stand of TF. The concentrations of both forms of N were measured in the top 20-cm layer during 2 years in Exp. 1 and for 1 year in Exp. 2. The concentrations of nitrate and ammonium were least in winter and spring, and greatest in summer. The concentration of nitrate for the mixtures decreased in the order WC-TF, RC-TF, and BT-TF in both summers of Exp. 1 but there were no mixture differences in Exp. 2. The concentration of soil ammonium was not affected by the treatments applied. We conclude that the concentration of soil nitrate usually was small for these swards but became greater and often dependent on species and legume proportion during summer. The concentration of soil ammonium also was greater in summer but was not affected by species or legume proportion. Journal of Paper no. J.-13359 of the Iowa Agric. and Home Econ. Exp Stn., Ames. Project 2281. Supported in part by the Facultad de Agronomía, Montevideo, Uruguay. Journal of Paper no. J.-13359 of the Iowa Agric. and Home Econ. Exp Stn., Ames. Project 2281. Supported in part by the Facultad de Agronomía, Montevideo, Uruguay.     

Leaf senescence in Festuca pratensis: accumulation of lipofuscinlike compounds

Fluorescent compounds (FCs) with spectral properties comparable to those of lipofuscin-like compounds are present in aqueous methanolic extracts of senescent meadow fescue, Festuca pratensis Huds., leaves. An HPLC system for the separation of FC from other fluorescent materials was developed. The chromatograms suggest that the FC-fraction consists of a large number of chemically related compounds. FCs are accumulated during senescence in leaves of a yellowing genotype, cv. Rossa. In leaves of a non-yellowing genotype, Bf 993, only traces of FCs appear at advanced stages of senescence.
FCs are regarded as final products of lipid peroxidation. Since both yellowing and non-yellowing genotypes are competent with regard to the degradation of galactolipids (the potential sources of polyunsaturated fatty acids) as well as regarding lipoxygenase (EC 1.13.11.12; a key enzyme of lipid peroxidation), and since incompentence to degrade chlorophyll is associated with lack of FC accumulation in the mutant genotype, it is hypothesized that the polar FCs present in senescent F. pratensis leaves represent catabolites of chlorophyll.     

Ecotypic differentiation within Festuca rubra L. occurring in a heterogeneous coastal environment

In order to study the genetic differentiation between Festuca rubra L. individuals growing in a heterogeneous environment, indices of salt tolerance, mean relative growth rates and the numbers of tillers formed by plants grown in a Hoagland solution, were determined. It was found that plants from salt marsh sites have a high index of salt tolerance, a high mean relative growth rate and numerous tillers; plants from coastal sand dunes are less tolerant, grow slowly and form few tillers; plants from the inland polder sites are rather salt sensitive, fast growing and form a high number of tillers. The heritability of the mean relative growth rate and the tiller number appeared to differ from zero. Apparently, these characters have been under recent selection and thus give a picture of the adaptations of individual plants to the different environments encountered. An indication of gene flow has been found, although the effect of gene flow seems to be small in the face of the force of selection. It was concluded that the distinction of three ecotypes within the species F. rubra is insufficient to describe the differentiation found. Considering the differences observed, it seems more reasonable to speak of ecotypic variation.     

Compensatory light utilization of Phalaris arundinacea within the Phalaris arundinacea–Phragmites australis compound community

This study investigated the light utilization characteristics of Phalaris arundinacea within the Phalaris arundinacea-Phragmites australis compound community. The investigation was based on the response curve equation of the net photosynthetic rate-photosynthetic photon flux density (Pn-PPFD) of P. arundinacea and on the distribution of PPFD on the surface canopy of P. arundinacea within the compound community. Results showed that P. arundinacea was able to compensate for substantial reduction in available light, and utilize the weak light within the lower part of the compound community. On the one hand, the density of P. australis within the compound community determined the compensatory light utilization rate (CLUR) of P.arundinacea. On the other hand, the CLUR amplitude of P. arundinacea within the compound community with the same P. australis density was relatively small in a day. The results can help people to regulate P. arundinacea-P. australis compound communities to maintain a long-term, stable coexistence in the constructed wetlands.

Abbreviations: CK – control; CLUR, compensatory light utilization rate; LER, light extinction rates; Pn, net photosynthetic rate; PPFD, photosynthetic photon flux density.     

A novel method for characterisation and quantification of plant root exudates

A microcosm unit is described which readily allows manipulation of experimental conditions to enable the subsequent impact on root exudation release to be monitored with time. Festuca ovina and Plantago lanceolata seedlings were grown in this microcosm unit over a 34 day experimental period under conditions of high (3.75 mol m^–3 N) or low (1.25 mol m^–3 N) nitrate-nitrogen treatment. At the end of the experimental period the seedlings in the microcosms were labelled with [¹⁴C]-CO₂ and the fate of the label within the plant and its release by the roots monitored. Total organic carbon (TOC) content of the collected exudate material was measured throughout the experimental period as well as during the ¹⁴C-chase period and comparison of plant C budgets using these two measurements is discussed. Nitrogen treatment as found to have a greater effect on exudate release by F. ovina than by P. lanceolata seedlings as indicated by both the total organic carbon and ¹⁴C results. The use and applications of the microcosm unit are discussed.