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Barbara Dinkelaker

Bio: Barbara Dinkelaker is an academic researcher from University of Hohenheim. The author has contributed to research in topics: Cluster root & Lupinus. The author has an hindex of 4, co-authored 4 publications receiving 1345 citations.

Papers
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Journal ArticleDOI
TL;DR: The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the Rhizosphere leading to intensive chemical extraction of a limited soil volume.
Abstract: . White lupin (Lupinus albus L.) was grown for 13 weeks in a phosphorus (P) deficient calcareous soil (20% CaCO3, pH(H2O)7.5) which had been sterilized prior to planting and fertilized with nitrate as source of nitrogen. In response to P deficiency, proteoid roots developed which accounted for about 50% of the root dry weight. In the rhizosphere soil of the proteoid root zones, the pH dropped to 4.8 and abundant white precipitates became visible. X-ray spectroscopy and chemical analysis showed that these precipitates consisted of calcium citrate. The amount of citrate released as root exudate by 13-week-old plants was about 1 g plant−1, representing about 23% of the total plant dry weight at harvest. In the rhizosphere soil of the proteoid root zones the concentrations of available P decreased and of available Fe, Mn and Zn increased. The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the rhizosphere leading to intensive chemical extraction of a limited soil volume. In a calcareous soil, citric acid excretion leads to dissolution of CaCO3 and precipitation of calcium citrate in the zone of proteoid roots.

680 citations

Journal ArticleDOI
TL;DR: Proteoid roots and proteoid-like root clusters play an important role in acquisition of P and other mineral nutrients, and in many species these roots excrete large amounts of organic acids and phenolics.
Abstract: Proteoid roots are bottlebrush-like clusters of rootlets which form along lateral roots. They are characteristic of most species of the Proteaceae, which are mainly distributed in Australia and South Africa. Homologous root clusters are present in species of the Casuarinaceae, Mimosaceae, Fabaceae, Myricaceae and Moraceae. Many similarities exist between these species in relation to morphology and function of root clusters. Many are non-mycorrhizal and are highly efficient in phosphorus (P) acquisition. In these species, proteoid roots and proteoid-like root clusters are abundant when grown on infertile soils. Their formation is predominantly affected by the P status of the plants, being induced at low P levels and repressed at high P levels. Proteoid roots and proteoid-like root clusters play an important role in acquisition of P and other mineral nutrients. Although increase in root surface area may be a contributing factor, in many species these roots excrete large amounts of organic acids and phenolics. The excretion of these compounds in a small soil volume gives rise to extensive nutrient mobilization by acidification, reduction and chelation of sparingly soluble forms of P and micronutrients such as Fe and Mn.

400 citations

Journal ArticleDOI
TL;DR: Cluster root formation in white lupin is induced mainly by phosphorus (P) starvation, and seems to be regulated by the endogenous P status of the plant, and inhibitory effects of kinetin application suggest the involvement of endogenous phytohormones (auxins and cytokinins), which may act in an antagonistic manner in the P-starvation response.

326 citations

Book ChapterDOI
01 Jan 1996
TL;DR: Proteoidwurzeln werden als Anpassungen an extrem nahrstoffarme Standorte gedeutet, and ihre Ausbildung wird in erster Linie durch Phosphatmangel induziert.
Abstract: Als Proteoidwurzeln werden Wurzelcluster aus Seitenwurzeln mit begrenztem Wachstum bezeichnet, die oft dicht mit Wurzelhaaren besetzt, „Flaschenbursten“-artig entlang von Seitenwurzeln erster oder hoherer Ordung ausgebildet werden (Abb. 1). Derartige Wurzelcluster sind ein Charakteristikum der Familie der Proteaceae, deren baum- und strauchformige Vertreter vorwiegend in Westaustralien und Sudafrika beheimatet sind (LAMONT, 1982). Homologe Strukturen finden sich aber auch bei anderen Familien, wie z.B. in den Gattungen Casuarina (Casuarinaceae), Lupinus (Fabaceae), Acacia (Mimosaceae), Myrica (Myricaceae) und Ficus (Moraceae). Proteoidwurzeln werden als Anpassungen an extrem nahrstoffarme Standorte gedeutet, und ihre Ausbildung wird in erster Linie durch Phosphatmangel induziert. Aber auch Eisen-, Zink- und Stickstoffmangel werden als Induktionsfaktoren beschrieben (DINKELAKER et al., 1995). Die Wurzelcluster, die eine Langsausdehnung von 1–5 cm, im Extremfall auch bis zu 20 cm erreichen und deren Anteil 40 – 50 % des Gesamtwurzelsystems ausmachen kann, scheiden grose Mengen an Exsudaten ab, die aus organischen Sauren, phenolischen Substanzen und Exoenzymen (saure Phosphatasen) zusammengesetzt sein konnen.

12 citations


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Book
01 Jan 1982
TL;DR: In this article, the Soil as a Plant Nutrient Medium is discussed and the importance of water relations in plant growth and crop production, and the role of water as a plant nutrient medium.
Abstract: 1. Plant Nutrients. 2. The Soil as a Plant Nutrient Medium. 3. Nutrient Uptake and Assimilation. 4. Plant Water Relationships. 5. Plant Growth and Crop Production. 6. Fertilizer Application. 7. Nitrogen. 8. Sulphur. 9. Phosphorus. 10. Potassium. 11. Calcium. 12. Magnesium. 13. Iron. 14. Manganese. 15. Zinc. 16. Copper. 17. Molybdenum. 18. Boron. 19. Further Elements of Importance. 20. Elements with More Toxic Effects. General Readings. References. Index.

4,130 citations

Journal ArticleDOI
TL;DR: Physiological, biochemical, and molecular studies of white lupin and other species response to P-deficiency have identified targets that may be useful for plant improvement, and Genomic approaches involving identification of expressed sequence tags found under low-P stress may also yield target sites for plant improved.
Abstract: Contents I. Introduction 424 II. The phosphorus conundrum 424 III. Adaptations to low P 424 IV. Uptake of P 424 V. P deficiency alters root development and function 426 VI. P deficiency modifies carbon metabolism 431 VII. Acid phosphatase 436 VIII. Genetic regulation of P responsive genes 437 IX. Improving P acquisition 439 X. Synopsis 440 Summary Phosphorus (P) is limiting for crop yield on > 30% of the world's arable land and, by some estimates, world resources of inexpensive P may be depleted by 2050. Improvement of P acquisition and use by plants is critical for economic, humanitarian and environmental reasons. Plants have evolved a diverse array of strategies to obtain adequate P under limiting conditions, including modifications to root architecture, carbon metabolism and membrane structure, exudation of low molecular weight organic acids, protons and enzymes, and enhanced expression of the numerous genes involved in low-P adaptation. These adaptations may be less pronounced in mycorrhizal-associated plants. The formation of cluster roots under P-stress by the nonmycorrhizal species white lupin (Lupinus albus), and the accompanying biochemical changes exemplify many of the plant adaptations that enhance P acquisition and use. Physiological, biochemical, and molecular studies of white lupin and other species response to P-deficiency have identified targets that may be useful for plant improvement. Genomic approaches involving identification of expressed sequence tags (ESTs) found under low-P stress may also yield target sites for plant improvement. Interdisciplinary studies uniting plant breeding, biochemistry, soil science, and genetics under the large umbrella of genomics are prerequisite for rapid progress in improving nutrient acquisition and use in plants.

2,429 citations

Journal ArticleDOI
TL;DR: In this article, a review of the role of organic acids in rhizosphere processes is presented, which includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization).
Abstract: Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress- and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.

2,339 citations

Journal ArticleDOI
TL;DR: In this paper, the authors give an overview of those chemical processes that are directly induced by plant roots and which can affect the concentration of P in the soil solution and, ultimately, the bioavailability of soil inorganic P to plants.
Abstract: In most soils, inorganic phosphorus occurs at fairly low concentrations in the soil solution whilst a large proportion of it is more or less strongly held by diverse soil minerals. Phosphate ions can indeed be adsorbed onto positively charged minerals such as Fe and Al oxides. Phosphate (P) ions can also form a range of minerals in combination with metals such as Ca, Fe and Al. These adsorption/desorption and precipitation/dissolution equilibria control the concentration of P in the soil solution and, thereby, both its chemical mobility and bioavailability. Apart from the concentration of P ions, the major factors that determine those equilibria as well as the speciation of soil P are (i) the pH, (ii) the concentrations of anions that compete with P ions for ligand exchange reactions and (iii) the concentrations of metals (Ca, Fe and Al) that can coprecipitate with P ions. The chemical conditions of the rhizosphere are known to considerably differ from those of the bulk soil, as a consequence of a range of processes that are induced either directly by the activity of plant roots or by the activity of rhizosphere microflora. The aim of this paper is to give an overview of those chemical processes that are directly induced by plant roots and which can affect the concentration of P in the soil solution and, ultimately, the bioavailability of soil inorganic P to plants. Amongst these, the uptake activity of plant roots should be taken into account in the first place. A second group of activities which is of major concern with respect to P bioavailability are those processes that can affect soil pH, such as proton/bicarbonate release (anion/cation balance) and gaseous (O2/CO2) exchanges. Thirdly, the release of root exudates such as organic ligands is another activity of the root that can alter the concentration of P in the soil solution. These various processes and their relative contributions to the changes in the bioavailability of soil inorganic P that can occur in the rhizosphere can considerably vary with (i) plant species, (ii) plant nutritional status and (iii) ambient soil conditions, as will be stressed in this paper. Their possible implications for the understanding and management of P nutrition of plants will be briefly addressed and discussed.

2,120 citations

Journal ArticleDOI
01 Jul 2005
TL;DR: In this paper, molecular, biochemical and physiological factors associated with phosphate acquisition by plants are described. But the authors do not consider the effect of mycorrhizal symbiosis on the ability of plants to acquire Pi.
Abstract: Phosphate (Pi) is considered to be one of the least available plant nutrients in the soil. High-affinity Pi transporters are generally accepted as entry points for Pi in the roots. The physiological, genetic, molecular and biochemical analysis of phosphate starvation response mechanisms highlight the ability of plants to adapt and thrive under phosphate limiting conditions. These responses help them enhance the availability of Pi, increase its uptake and improve the use-efficiency of Pi within a plant. Enhanced ability to acquire Pi appears to be regulated at the level of transcription of high-affinity phosphate transporters. These transporters are encoded by a family of small number of genes having characteristic tissue and organ associated expression patterns. Many of them are strongly induced during phosphate deficiency thus providing plants with enhanced ability to acquire and transfer phosphate. In addition, plants also activate biochemical mechanisms that could lead to increased acquisition of phosphate from both inorganic and organic phosphorus sources in the soil. Furthermore, altered root morphology and mycorrhizal symbiosis further enhance the ability of plants to acquire Pi. Interestingly most of these responses appear to be coordinated by changes in cellular phosphate levels. It is becoming apparent that phosphate acquisition and utilization are associated with activation or inactivation of a host of genes in plants. In this article we describe molecular, biochemical and physiological factors associated with phosphate acquisition by plants.

1,575 citations