Showing papers by "University of Hohenheim published in 1991"

The role of phytosiderophores in acquisition of iron and other micronutrients in graminaceous species: An ecological approach

Abstract: Phytosiderophores (PS) are released in graminaceous species (Gramineae) under iron (Fe) and zinc (Zn) deficiency stress and are of great ecological significance for acquisition of Fe and presumably also of Zn. The potential for release of PS is much higher than reported up to now. Rapid microbial degradation during PS collection from nutrient solution-grown plants is the main cause of this underestimation. Due to spatial separation of PS release and microbial activity in the rhizosphere a much slower degradation of PS can be assumed in soil-grown plants. Concentrations of PS up to molar levels have been calculated under non-sterile conditions in the rhizosphere of Fe-deficient barley plants.

Contribution of the VA mycorrhizal hyphae in acquisition of phosphorus and zinc by maize grown in a calcareous soil

Abstract: An investigation was carried out to test whether the mechanism of increased zinc (Zn) uptake by mycorrhizal plants is similar to that of increased phosphorus (P) acquisition. Maize (Zea mays L.) was grown in pots containing sterilised calcareous soil either inoculated with a mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe or with a mixture of mycorrhizal fungi, or remaining non-inoculated as non-mycorrhizal control. The pots had three compartments, a central one for root growth and two outer ones for hyphal growth. The compartmentalization was done using a 30-μm nylon net. The root compartment received low or high levels of P (50 or 100 mg kg−1 soil) in combination with low or high levels of P and micronutrients (2 or 10 mg kg−1 Fe, Zn and Cu) in the hyphal compartments. Mycorrhizal fungus inoculation did not influence shoot dry weight, but reduced root dry weight when low P levels were supplied to the root compartment. Irrespective of the P levels in the root compartment, shoots and roots of mycorrhizal plants had on average 95 and 115% higher P concentrations, and 164 and 22% higher Zn concentrations, respectively, compared to non-mycorrhizal plants. These higher concentrations could be attributed to a substantial translocation of P and Zn from hyphal compartments to the plant via the mycorrhizal hyphae. Mycorrhizal inoculation also enhanced copper concentration in roots (135%) but not in shoots. In contrast, manganese (Mn) concentrations in shoots and roots of mycorrhizal plants were distinctly lower, especially in plants inoculated with the mixture of mycorrhizal fungi. The results demonstrate that VA mycorrhizal hyphae uptake and translocation to the host is an important component of increased acquisition of P and Zn by mycorrhizal plants. The minimal hyphae contribution (delivery by the hyphae from the outer compartments) to the total plant acquisition ranged from 13 to 20% for P and from 16 to 25% for Zn.

Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [ Picea abies (L.) Karst.]

Abstract: Relationships between root zone temperature, concentrations and uptake rates of NH 4 + and NO 3 − were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH 4 + and NO 3 − uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (Cmin) range of 100–150 μM uptake rates of NH 4 + were 3–4 times higher than those of NO 3 − The preference for NH 4 + uptake was also reflected in the minimum concentration (Cmin) values. Supplying NH4NO3, the rate of NO 3 − uptake was very low until the NH 4 + concentrations had fallen below about 100 μM. The shift from NH 4 + to NO 3 − uptake was correlated with a corresponding shift from net H+ production to net H+ consumption in the external solution. The uptake rates of NH 4 + were correlated with equimolar net production of H+. With NO 3 − nutrition net consumption of H+ was approximately twice as high as uptake rates of NO 3 − In the forest stand the NO 3 − concentration in the soil solution was more than 10 times higher than the NH 4 + concentration (<100 μM), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO 3 − uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium.

Phosphorus depletion and pH decrease at the root–soil and hyphae–soil interfaces of VA mycorrhizal white clover fertilized with ammonium

Abstract: summary To study phosphorus (P) depletion and soil pH changes at the root–soil interface (rhizosphere) and at the hyphaesoil interface, mycorrhizal and non-mycorrhizal white clover (Trifolium repens L.) plants were grown for 7 wk in two sterilized soils (Luvisol and Cambisol) in pots comprising five compartments: a central one for root growth, two adjacent compartments, separated from the central compartment by a nylon net of 30 μm mesh size, for growth of vesicular-arbuscular (VA) mycorrhizal [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] hyphae (hyphal compartments), and two outer compartments, separated from the hyphal compartments by a 0.45 μm membrane, which neither roots nor hyphae could penetrate (bulk soil compartments). Phosphorus was supplied as Ca(H2PO4)2 at a rate of 50 mg P kg−1 soil in the root compartment and 150 mg P kg−1 soil in the hyphal and bulk soil compartments. Nitrogen was supplied as (NH4)2SO4 at the rate of 300 mg N kg−1 soil uniformly to all compartments. In both soils, shoot dry weight and P uptake were much higher in mycorrhizal plants compared with non-mycorrhizal plants. Hyphae of VA mycorrhizal fungi contributed 70% (Cambisol) or 80% (Luvisol) to total P uptake of mycorrhizal plants. In the hyphal compartments, concentrations of both H2O-extractable soil P (Cambisol and Luvisol) and NaHCO3-extractable soil P (Luvisol) were decreased drastically. Soil P depletion profiles developed not only at the root-soil interface (rhizosphere), but also at the hyphae-soil interface and extended several millimetres from the hyphae surface into the soil. Likewise, the soil pH was decreased at the root-soil interface, in the hyphal compartment and also at the hyphae-soil interface. The results demonstrate that, similarly to roots, hyphae of VA mycorrhizal fungi have the ability to form a P depletion zone and a zone of altered pH in the adjacent soil. Thus, as well as at the root-soil interface, soil conditions at the hyphae–soil interface may also differ considerably from conditions in the bulk soil.

Survival of pathogenic micro-organisms and parasites in excreta, manure and sewage sludge.

Abstract: The causative agents of many infectious diseases are excreted by the faecal route and also with other excretions or secretions of the body. Some pathogens are also excreted from clinically healthy animals, from those with latent infections and in cases of transmissible multifactorial diseases. In all types of livestock housing, the pathogens finally reach the floor with the installations for collecting manure as a solid or liquid. Under these conditions livestock owners do not realise that manure may contain pathogens, and therefore do not take precautions against possible spread of diseases by utilisation of manure. The pathogens do not survive very long in stored farmyard manure because of the temperatures and biological and biochemical activities prevailing in the middens. But the conditions in slurry are different because the temperature does not rise and biochemical activity is low. Therefore the pathogens survive for rather long periods in slurry. To avoid disease transfer by utilisation of manure and slurry as fertilisers, certain precautions are necessary and these are described in detail. The agricultural utilisation of municipal sewage sludge is common in many countries. However, these sludges contain pathogens which are excreted by the human population served by the sewers and sewage treatment plants. In the sewage purification processes most of the pathogens are reduced in number but not completely eliminated. They are enriched by sedimentation processes in the sewage sludge. To protect the livestock of farms utilising sewage sludge as fertiliser or for amending soils it is necessary to sanitise hygienically dubious sludges prior to their use. The epidemiological aspects of agricultural sludge utilisation are discussed and details of the available sanitation technologies are given.

Effect of a vesicular–arbuscular mycorrhizal fungus and rhizosphere micro-organisms on manganese reduction in the rhizosphere and manganese concentrations in maize (Zea mays L.)

Abstract: summary Maize (Zea mays L. ev. Tau) plants were grown in a calcareous soil for six weeks in pots having separate compartments for growth of roots and vesicular-arbuscular (VA) mycorrhizal fungal hyphae. Soil was sterilized and either left non-inoculated (sterile treatment), or was inoculated with rhizosphere micro-organisms only (MO–VA) or with rhizosphere micro-organisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol & Gerd.) Gerdemann & Trappe (MO +VA)]. Concentrations of Mn in roots and shoots, as well as exchangeable Mn in rhizosphere soil, decreased in the order MO–VA < MO + VA < sterile treatment. In all treatments, the concentration of exchangeable Mn was lower in the rhizosphere soil (0–5 mm distance from the root surface) than in the bulk soil (5–15 or 15–25 mm distance from the root surface). In the rhizosphere soil, the total microbial population was similar in mycorrhizal (MO + VA) and non-mycorrhizal (MO–VA) treatments, but the proportion of Fe- or Mn-reducers was 20- to 30-fold higher in the non-mycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The Mn+Iv-reducing potential (net balance between reduction and oxidation) in the rhizosphere soil was also distinctly lower in mycorrhizal treatment compared to non-mycorrhizal treatment. In the sterile treatment, low Mn+IV-reducing potential and correspondingly low concentration of exchangeable Mn in soil, compared to the other treatments, indicates the importance of micro-organisms in Mn reduction in soil and acquisition of Mn by plants. Therefore, the lower Mn concentrations in mycorrhizal plants are most probably caused by a shift in composition and activity of rhizosphere micro-organisms. As a side effect of the treatments, improved soil aggregation, as indicated by soil adhering to the nylon net (facing hyphal compartments) after plant harvest, occurred in non-mycorrhizal and sterile treatments but not in the mycorrhizal treatment.

Stable isotopes in tree ring cellulose and climatic change

Abstract: Relationships between the stable isotope contents ( δ 2 H, δ 13 C) in dendrochronologically dated tree rings of firs (Abies alba, Black Forest) and air temperature, relative humidity, as well as precipitation rate were investigated for the period 1959 to 1980. Only the late wood of each ring was used, since isotope data from early wood, grown during spring, does not unambiguously reflect the climate of the respective growth season. The δ 13 C-values, but not the δ 2 H-values show significant correlations with temperature, humidity, and precipitation. Based on this observation, δ 13 C-values were used to construct a paleoclimatic record for the past millenium. This required correction for anthropogenic 13 C -inputs since about 1850. The reconstructed temperatures are largely in agreement with presently-accepted variations in the recent past, whereby a “climatic optimum” appears during the Early Middle Ages with August temperatures about 0.5 °C higher than today. DOI: 10.1034/j.1600-0889.1991.t01-2-00005.x

Reduction of nitroaromatic compounds by different Pseudomonas species under aerobic conditions

Abstract: Pseudomonas sp. CBS3 converted various nitro-aromatic compounds under aerobic resting-cell conditions to the corresponding amino compounds. Mononitro-compounds were reduced to anilines. 1-Chloro-2,4-dinitrobenzene was reduced via the two possible chloronitroanilines to 4-chloro-1,3-diaminobenzene. In the case of 2,4,6-trinitrotoluene, two monoaminodinitrotoluenes and one diaminomononitrotoluene were obtained. In addition to the reduction, in most cases the amines were partially acetylated. In experiments under an argon atmosphere conversion of the nitro-compounds was as fast as under aerobic conditions. Cells of Pseudomonas sp. CBS3 cultivated on complex medium showed higher nitro-reducing activity than those cultivated on mineral salts medium with 4-chlorobenzoate as substrate, which is normally used as medium for this strain. Several other Pseudomonas species (ATCC 4359, ATCC 23937, ATCC 15005, ATCC 17933) also showed nitro-reducing activities. In crude cell-free extracts of Pseudomonas sp. CBS3 an enzyme catalysing the reduction of nitro-aromatics was detected. The enzyme was inactivated by dialysis and was reactivated by the addition of NADH or NADPH. NADPH was the more efficient co-substrate.

Diurnal rhythm of release of phytosiderophores and uptake rate of zinc in iron-deficient wheat

Abstract: The diurnal rhythm of release of phytosiderophores and uptake rate of zinc (Zn) was studied in iron (Fe) deficient wheat (Triticum aestivum L. cv. Ares) plants grown in nutrient solution under controlled environmental conditions. Different forms of Zn (e.g. ZnSO4, ZnEDTA) were used to obtain different degrees of loading of the root apoplasmic pool with Zn. In the Fe-deficient plants the release of phytosiderophores from the roots followed a distinct diurnal rhythm with a steep peak about 4 h after the onset of the light period. These plants also showed a similar pattern in the rates of Zn uptake over the 24 h day-night cycle. During the light period there was a steep transient peak (factor 3.8) in Zn uptake rate in the Fe-deficient plants supplied with ZnSO4. This transient peak was much less distinct in plants supplied with ZnEDTA (factor 1.8) and absent in plants supplied with ZnEDTA plus free chelator (+ NaEDTA) in excess. The peak in Zn uptake coincided with the maximum rate of phytosideropho...

Role of the Root Apoplasm for Iron Acquisition by Wheat Plants

Abstract: The role of the root apoplasm for iron acquisition was studied in wheat (Triticum aestivum L. cv Ares) grown in nutrient solution under controlled environmental conditions. To obtain different levels of Fe in the root apoplasm, plants were supplied in the dark for 5 hours (preloading period) with various (59)Fe-labeled Fe compounds [Fe(III) hydroxide; microbial siderophores: Fe rhodotorulic acid (FeRDA) and ferrioxamin (FeDesferal(3)), and synthetic Fe chelate (FeEDDHA)], each at a concentration of 5 micromolar. Large pools of apoplasmic Fe were formed after supplying Fe(III) hydroxide or FeRDA, but no such pools were observed after supplying FeDesferal or FeEDDHA. Depending on plant Fe nutritional status (preculture +/- 0.1 millimolar FeEDTA), apoplasmic Fe was used to different extent for translocation to the shoot. Under Fe deficiency, a much greater fraction of the apoplasmic Fe was utilized than in Fe-sufficient plants, as a result of the different rates of phytosiderophore release. Because of the diurnal rhythm in release of phytosiderophores in Fe-deficient plants, the utilization of the apoplasmic Fe for translocation into the shoot started 2 hours after onset of the light period and was dependent on the concentration of Fe in the apoplasm, which followed the order: Fe(III) hydroxide >> FeRDA >> FeDesferal = FeEDDHA. From these results, it can be concluded that in soil-grown plants the apoplasmic Fe pool loaded by various indigenous Fe compounds such as siderophores in the soil solution can be an important Fe source in graminaceous species, particularly during periods of limited Fe supply from the soil.

Degradation of 2,4,6-trichlorophenol by Azotobacter sp. strain GP1.

Abstract: A bacterium which utilizes 2,4,6-trichlorophenol (TCP) as a sole source of carbon and energy was isolated from soil. The bacterium, designated strain GP1, was identified as an Azotobacter sp. TCP was the only chlorinated phenol which supported the growth of the bacterium. Resting cells transformed monochlorophenols, 2,6-dichlorophenol, and 2,3,6-trichlorophenol. Phenol and a number of phenolic compounds, including 4-methylphenol, all of the monohydroxybenzoates, and several dihydroxybenzoates, were very good carbon sources for Azotobacter sp. strain GP1. The organism utilized up to 800 mg of TCP per liter; the lag phase and time for degradation, however, were severely prolonged at TCP concentrations above 500 mg/liter. Repeated additions of 200 mg of TCP per liter led to accelerated degradation, with an optimum value of 100 mg of TCP per liter per h. TCP degradation was significantly faster in shaken than in nonshaken cultures. The optimum temperature for degradation was 25 to 30 degrees C. Induction studies, including treatment of the cells with chloramphenicol prior to TCP or phenol addition, revealed that TCP induced TCP degradation but not phenol degradation and that phenol induced only its own utilization. Per mol of TCP, 3 mol of Cl- was released. 2,6-Dichloro-p-benzoquinone was detected in the resting-cell medium of Azotobacter sp. strain GP1. By chemical mutagenesis, mutants blocked in either TCP degradation or phenol degradation were obtained. No mutant defective in the degradation of both phenols was found, indicating separate pathways for the dissimilation of the compounds. In some of the phenol-deficient mutants, pyrocatechol was found to accumulate, and in some of the TCP-deficient mutants, 2,6-dichlorohydroquinone was found to accumulate.

A comparative study on rumen fermentation of energy supplements in vitro

Abstract: Zusammenfassung Eine vergleichende in vitro-Untersuchung zur Fermentation von energiereichen Zulagen im Pansen Eine Methode zur Inkubation von Futtermitteln mit Inoculum aus Panseninhalt (Menke et al. 1979) wurde eingesetzt, um Fermentationsraten von Weizen, Gerste, Tapioka, Sorghum, Hafer, Roggen, einer Konzentratmischung, Heu und Haferstroh zu bestimmen. Wahrend der Inkubationsdauer von 96 Stunden wurde die Gasproduktion in verschiedenen Zeitintervallen gemessen. Die Fermentationsrate (k) wurde mittels nichtlinearer Regression geschatzt, wobei mathematische Modelle mit und ohne anfanglicher Verzogerung (1) der Fermentation verwendet wurden. Die Schatzwerte fur k variierten zwischen 0,024 und 0,140 bzw. 0,035 und 0,135 wenn das Modell die Verzogerung ein- bzw. ausschlos. Es werden Probleme diskutiert, welche sich im Zusammenhang mit der Schatzung und Interpretation von 1 sowie deren Einflus auf Schatzungen von k ergeben. Die Anwendung von k- und l-Werten zur Vorhersage der Pansenverdauung werden ebenfalls diskutiert.

Genetic diversity among progenitors and elite lines from the Iowa Stiff Stalk Synthetic (BSSS) maize population: comparison of allozyme and RFLP data

Abstract: Data for restriction fragment length polymorphisms (RFLPs) of 144 clone-enzyme combinations and for 22 allozyme loci from 21 U.S. Corn Belt maize (Zea mays L.) inbreds were analyzed. The genetic materials included 14 progenitors of the Iowa Stiff Stalk Synthetic (BSSS) maize population, both parents of one missing BSSS progenitor, four elite inbreds derived from BSSS, and inbred Mo17. Objectives were to characterize the genetic variation among these 21 inbreds for both allozymes and RFLPs, to compare the results from both types of molecular markers, and to estimate the proportion of unique alleles in the BSSS progenitors. Genetic diversity among the 21 inbreds was substantially greater for RFLPs than for allozymes, but the percentages of unique RFLP variants (27%) and unique allozyme alleles (25%) in the BSSS progenitors were similar. Genetic distances between inbreds, estimated as Rogers' distance (RD), were, on average, twice as large for RFLP (0.51) as for allozyme data (0.24). RDs obtained from allozyme and RFLP data for individual line combinations were only poorly correlated (r = 0.23); possible reasons for discrepancies are discussed. Principal component analysis of RFLP data, in contrast to allozyme data, resulted in separate groupings of the ten BSSS progenitors derived from the ‘Reid Yellow Dent’ population, the four BSSS elite lines, and Mo17. The remaining six BSSS progenitors were genetically rather diverse and contributed a large number of rare alleles to BSSS. The results of this study corroborate the fact that RFLPs are superior to allozymes for characterizing the genetic diversity of maize breeding materials, because of (1) the almost unlimited number of markers available and (2) the greater amount of polymorphisms found. In particular, RFLPs allow related lines and inbreds with common genetic background to be identified, but a large number of probe-enzyme combinations is needed to estimate genetic distances with the precision required.

Fully automated high-performance liquid chromatographic separation of DL-amino acids derivatized with o -phthaldialdehyde together with N -isobutyryl-cysteine. Application to food samples

Abstract: A method is presented that enables the fully automated precolumn derivatization of mixtures of DL-amino acids (DL-AA) witho-phthaldialdehyde together withN-isobutyryl-L(orD)-cysteine. HPLC on a 250 mm×4 mm i.d. column packed with Shandon Hypersil ODS, 5 μm, and a linear gradient formed from 23 mM sodium acetate (pH 6.0) and methanol/acetonitrile (600 ml+50 ml) separates completely an AA standard composed of 17 pairs of DL-AA (including Asn and Gln), Gly and the internal standard L-homo-Arg, within 75 min at a flow rate at 1 ml/min. Applications are shown of the determination of free D-AA isolated from an orange juice concentrate and from soy sauce, and the detection of D-AA in a gelatine total hydrolysate. In the case of these foodstuffs fluorescence detection (excitation at 230 nm, emission at 445 nm) allows the routine detection of 5–10 pmol per AA; and approx. 0.2–1% D-AA, in an excess of L-AA, are quantifiable.

High-resolution flow cytometry of nuclear DNA in higher plants

Abstract: High-resolution flow cytometry of nuclear DNA in higher plants has been performed from chopped plant tissues and plant protoplasts. A preparation and staining procedure with the DNA specific fluorochrome DAPI, successfully employed for precise flow cytometric DNA analysis of animal and human cells has been used in a slightly modified manner for the DNA analysis of plant cell material. High-resolution DNA histograms coefficients of variation about 1–1.5% have been obtained routinely from plant species with different DNA content. Staining of nuclei with DAPI in combination with the protein fluorochrome sulforhodamine 101 allows bi-parametric analysis of nuclear DNA and protein. The described simple and precise method might be very promising for the analysis of DNA in basic and applied cytogenetic investigations of plant cell research.

Mobilization of iron by phytosiderophores as affected by other micronutrients

Abstract: It has been shown previously (Treeby et al., 1989) that phytosiderophores, released by roots of iron deficient grasses (Gramineae), mobilize from calcareous soils not only iron (Fe) but also zinc (Zn), manganese (Mn) and copper (Cu). Mobilization of Fe may therefore be impaired by other micronutrient cations. This has been studied in both, model experiments with Fe hydroxide and with a calcareous soil (15% CaCO3, pH 8.6) amended with micronutrients as sulfate salts.

Complete nucleotide sequences and comparison of the structural genes of two 2-haloalkanoic acid dehalogenases from Pseudomonas sp. strain CBS3.

Abstract: The nucleotide sequences of two DNA segments from Pseudomonas sp. strain CBS3 that code for two different haloalkanoic acid halidohydrolases were determined. Two open reading frames with coding capacities of 227 amino acids (corresponding to a molecular mass of 25,401 Da) and 229 amino acids (corresponding to a molecular mass of 25,683 Da) were identified as structural genes of 2-haloalkanoic acid dehalogenases I (dehCI) and II (dehCII) by comparison with the N-terminal amino acid sequences of these enzymes. Comparison of the two sequences revealed 45% homology on the DNA level and 37.5% homology on the amino acid level. No homology with other known protein or nucleotide sequences was found.

Root system parameters determining water uptake of field crops

Abstract: The distribution of a crop rooting system can be defined by root length density (RD), root length (RL) per soil layer of depth Δz, sum of root length (SRL) in the soil profile (total root length) or rooting depth (z r . The combined influence of these root system parameters on water uptake is not well understood. In the present study, field data are evaluated and an attempt is made to relate a daily “maximum water uptake rate” (WUmax) per unit soil volume as measured in different soil layers of the profile to relevant parameters of the root system. We hypothesize that local uptake rate is at its maximum when neither soil nor root characteristics limit water flow to, and uptake by, roots. Leaf area index and the potential evapotranspiration rate (ET p ) are also important in determining WUmax, since these quantities influence transpiration and hence total crop water uptake rate. Field studies in Germany and in Western Australia showed that WUmax depends on RD. In general, there was a strong correlation between the maximum water uptake rate of a soil layer (LWUmax) normalized by ET p and RL normalized by SRL. The quantity LWUmax · ET was linearly related to (RL/SRL)1/2. The data show that the single root model will not predict the influence of RD on WUmax correctly under field conditions when water-extracting neighboring roots may cause non-steady-state conditions within the time span of sequential observations. Since the rooting depth z r was linearly related to (SRL)1/2, the relation: LWUmax · ET = f (RL1/2/z r ) holds. Furthermore it was found that the maximum “specific” uptake rate per cm root length URmax was inversely related to RD1/2 and to SRL1/2 or z r of the profile. Observed high specific uptake rates of shallow rooted crops might be explained not only by their lower RD-values but also by the additional effect of a low z r . The relations found in this paper are helpful for realistically describing the “sink term” of dynamic water uptake models. Growing plants extract water from the soil to meet transpiration needs. Rates of transpiration and of water uptake are set by evaporative demand and by plant and soil factors which influence capacity to meet that demand. These factors include crop canopy size and leaf characteristics, root system characteristics and hydraulic properties of the soil and the soil-root interface. Soil and root system properties vary with depth and all factors vary in time, so that parameters related to them require constant updating over a crop season. Dynamic simulation models describe water uptake by root systems under field conditions as a function of soil depth and time. Many of these simulation approaches are based on Gardner's (1960) single root model (Feddes 1981). These simulation procedures follow the assumption that water uptake is proportional to a difference in water potential between the bulk soil and the root surface or the plant interior, to the hydraulic conductivity of the soil-plant system and to the “effectiveness” of competing roots in water uptake. The effectiveness factor accounts more or less empirically for the influence of various root system parameters on water uptake such as percentage of “active” roots absorbing water, root surface permeability, root length density determining the distance between neighbouring roots, or total root length and depth of the root system. Such models however, will not always reflect correctly the influence of root system characteristics on water uptake since these assumptions have rarely been tested under field conditions. In many instances, there is better agreement between simulated and measured total water use of plants than between predicted and observed water depletion by roots within individual layers of the soil profile (Alaerts et al. 1985). Water uptake by an expanding root system as a function of depth and time has been studied under field conditions for several crops (listed in Herkelrath et al. 1977a; Feddes 1981; Hamblin 1985). They show that the dynamics of water uptake depend on root length density and the “availability” of soil water. However, the combined influence of root length density, total root length and rooting depth on the water uptake pattern has not been assessed. An evaluation of root system parameters with respect to soil water extraction should aid our understanding of how roots perform under field conditions and may assist our efforts to formulate the water uptake function of roots in dynamic simulation studies more realistically. The aim of the present investigation is to develop an approach that relates measured water uptake rates to relevant parameters of the root systems. This approach will be confined to situations where water uptake in a soil layer is not restricted by unfavorable soil conditions, such as in wet soil, by insufficient aeration and, in dry soil, by reduced water flow towards roots or by increased contact resistance (Herkelrath et al. 1977b). We will define a maximum water uptake rate WUmax that is neither soil-limited nor appreciably limited by the decreasing permeability of aging roots. This WUmax will be related to relevant root system parameters as they exist when WUmax is observed. Hence, water uptake by roots in a very wet, as well as in a dry soil, has been excluded from consideration.

Methodical improvements in rye anther culture.

Abstract: The crucial problem in anther culture of rye (Secale cereale L.) is the very low regeneration capacity. Our study was conducted to overcome this restriction. The plant material used included a doubled haploid line (DH), two single crosses between DH Unes, and a tetraploid Secale cereale L. population. The factors carbohydrate source, post-plating temperature treatment, and gelling agent were investigated. Substantial progress was achieved by substituting maltose for sucrose. Top rates of 49 % responding anthers and 20 % green plants were obtained from one of the single crosses after a post-plating cold treatment on geirrte solidified medium. We consider our results a methodical step forward in rye anther culture.

Patterns of Organic Matter Accumulation in Soils of the Semiarid Argentinian Pampas

Abstract: A-horizons of 48 Haplic Phaeozems and Kastanozems in plain sites of the Semiarid Argentinian Pampas under three contrasting management systems (virgin bushland, permanent pasture and continuous agriculture) were studied. Morphological characteristics, organic carbon and total nitrogen levels and E4:E6 ratios were determined on the assumption that both quantity and quality of organic matter should be related to soil texture of parent materials in this region since other soil forming factors are uniform. The more intensive land use produced an averaged decrease of 7 cm in A-horizon thickness and degradation of soil structure, but little changes in color and properties of boundaries to AC horizons. In virgin soils organic carbon and nitrogen contents correlate with silt + clay fractions (r = 0,92 and 0,99, respectively), while E4:E6-ratios are related to clay contents (r = −0.69*) confirming the strong influence of soil texture. Agricultural-management and pasture use of soils lead to dispersion of these correlations probably because of differential influence of varying intensities of land use within each management system. Soils under continuous agriculture show lower organic carbon contents than virgin soils only at clay + silt > 40%. Eragrostis curvula-pastures seems to be more effective in restoring organic matter and nitrogen levels in sandy but not in loamy soils with respect to virgin soils. This may be due to a better efficiency of E. curvula-roots in coarse than in fine textured soils to produce humificable residues than the autochthonous grass species. Humusverteilung in Boden der semiariden argentinischen Pampas Die A-Horizonte von 48 Haplic Phaeozems und Kastanozems in ebener Lage der semiariden argentinischen Pampas wurden untersucht. Sie verteilten sich unter die drei unterschiedlichen Landnutzungssysteme naturliches Buschland, Dauerweide und permanenter Ackerbau. Die morphologischen Eigenschaften, die organischen Kohlenstoff- und Gesamtstickstoffgehalte sowie die E4:E6-Verhaltnisse wurden bestimmt unter der Annahme, das sowohl Quantitat wie auch Qualitat der organischen Substanz zur Bodenart des Ausgangssubstrats und Bodennutzung in diesem Gebiet in Beziehung stehen, alle anderen bodenbildenden Faktoren konnen als einheitlich betrachtet werden. Die intensivere Landnutzung erzeugte im Durchschnitt eine Abnahme der Machtigkeit der A-Horizonte von 7 cm und eine Degradierung der Bodenstruktur, aber nur geringe Veranderungen der Bodenfarbe und der Ausbildung der Grenze zu den AC-Horizonten. Die org. Kohlenstoff- und Stickstoffgehalte korrelieren mit den Schluff + Tongehalten (r = 0,92 bzw. 0,99), wahrend die E4:E6-Quotienten nur mit der Tonfraktion in den jungfraulichen Boden in Beziehung stehen (r = −0,69). Dies bestatigt die Eingangshypothese. In ackerbaulich und weidewirtschaftlich genutzten Boden nimmt die Straffheit dieser Korrelationen ab; wahrscheinlich, weil der Einflus verschiedener Intensitaten der Landnutzung innerhalb eines Landnutzungssystems differenzierend wirkt. Die Eragrostis curvula-Weiden waren effektiv im Erhalten der organischen Substanz und des Stickstoffniveaus in sandigen aber nicht in lehmigen Boden, wiederum bezogen auf die jungfraulichen Boden. Wahrscheinlich sind Eragrostis curvula-Wurzeln in groberen eher als in feineren Boden in der Lage, mehr humifizierbare Ruckstande zu bilden als die autochthonen Graser.

Differentiation of primary and secondary fibroblasts in cell culture systems.

Abstract: As a function of the advancing development of Valo chicken, C3H mice, BN rats, and man in the embryonic, juvenile, adolescent, and senescent phases, stem cells and fibroblasts in the connective tissues of skin and lung differentiate along an 11-stage differentiation sequence in five compartments of the fibroblast stem cell system, when studied in primary ex vivo-in vitro systems. In the fibroblast stem cell system, three stem cells develop in the stem cell compartment along the cell lineage S1-S2-S3, three mitotic fibroblasts (MF) differentiate along the sequence MF I-MF II-MF III in the fibroblast progenitor compartment, three postmitotic fibroblasts (PMF) proceed in the fibroblast maturing compartment along the row PMF IV-PMF V-PMF VI. PMF VI is the terminally differentiated end cell of the fibroblast stem cell system. After a species- and tissue-specific period of high metabolic activity, PMF VI either dies as PMF VIIa in the fibroblast apoptosis compartment or transforms as PMF VIIb in the fibroblast transforming compartment. The reiterated appearance of the 11 cell types in primary stem cell and fibroblast populations and the reiterated age-related changes in the cell type composition of the primary stem cell and fibroblast populations make it very likely that stem cell, mitotic and postmitotic fibroblast equivalents exist in vivo and that age-related changes of the frequencies of the stem cell and fibroblast equivalents result from the progressing differentiation of stem cell, mitotic, and postmitotic fibroblast equivalents along the 11 stage differentiation sequence in the fibroblast equivalent stem cell system in vivo. Secondary fibroblast populations derived from connective tissue of prenatal and postnatal skin of Valo chicken, C3H mice, BN rats, and man, including the normal embryonic human lung fibroblast cell line WI38, were also found to develop along a terminal stem cell sequence. Thus, secondary fibroblast populations in vitro constitute a representative material for studies of general and special issues of cell biology, such as terminal differentiation, aging, apoptosis, and transformation, as long as stem cell system-specific concepts and methods are employed in such investigations.