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Dive into the research topics where Peter R. Ryan is active.

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Featured researches published by Peter R. Ryan.


Plant Physiology | 1995

Aluminum toxicity and tolerance in plants

Emmanuel Delhaize; Peter R. Ryan

Aluminum (Al) is the most abundant metal in the earths crust, comprising about 7% of its mass. Since many plant species are sensitive to micromolar concentrations of Al, the potential for soils to be Al toxic is considerable. Fortunately, most of the Al is bound by ligands or occurs in other nonphytotoxic forms such as aluminosilicates and precipitates. However, solubilization of this Al is enhanced by low pH and Al toxicity is a major factor limiting plant production on acid soils. Soil acidification can develop naturally when basic cations are leached from soils, but it can be accelerated by some farming practices and by acid rain (Kennedy, 1986). Strategies to maintain production on these soils include the application of lime to raise the soil pH and the use of plants that are tolerant of acid soils. Although Al toxicity has been identified as a problem of acid soils for over 70 years, our knowledge about the primary sites of toxicity and the chain of events that finally affects plant growth remains largely speculative. In this paper we review recent progress that has been made in our understanding of Al toxicity and the mechanisms of Al tolerance in plants.


Trends in Plant Science | 2001

Aluminium tolerance in plants and the complexing role of organic acids

Jian Feng Ma; Peter R. Ryan; Emmanuel Delhaize

The aluminium cation Al(3+) is toxic to many plants at micromolar concentrations. A range of plant species has evolved mechanisms that enable them to grow on acid soils where toxic concentrations of Al(3+) can limit plant growth. Organic acids play a central role in these aluminium tolerance mechanisms. Some plants detoxify aluminium in the rhizosphere by releasing organic acids that chelate aluminium. In at least two species, wheat and maize, the transport of organic acid anions out of the root cells is mediated by aluminium-activated anion channels in the plasma membrane. Other plants, including species that accumulate aluminium in their leaves, detoxify aluminium internally by forming complexes with organic acids.


Plant Physiology | 1993

Aluminum Tolerance in Wheat (Triticum aestivum L.) (II. Aluminum-Stimulated Excretion of Malic Acid from Root Apices).

Emmanuel Delhaize; Peter R. Ryan; Peter J. Randall

We investigated the role of organic acids in conferring Al tolerance in near-isogenic wheat (Triticum aestivum L.) lines differing in Al tolerance at the Al tolerance locus (Alt1). Addition of Al to nutrient solutions stimulated excretion of malic and succinic acids from roots of wheat seedlings, and Al-tolerant genotypes excreted 5- to 10-fold more malic acid than Al-sensitive genotypes. Malic acid excretion was detectable after 15 min of exposure to 200 [mu]M Al, and the amount excreted increased linearly over 24 h. The amount of malic acid excreted was dependent on the external Al concentration, and excretion was stimulated by as little as 10 [mu]M Al. Malic acid added to nutrient solutions was able to protect Al-sensitive seedlings from normally phytotoxic Al concentrations. Root apices (terminal 3–5 mm of root) were the primary source of the malic acid excreted. Root apices of Al-tolerant and Al-sensitive seedlings contained similar amounts of malic acid before and after a 2-h exposure to 200 [mu]M Al. During this treatment, Al-tolerant seedlings excreted about four times the total amount of malic acid initially present within root apices, indicating that continual synthesis of malic acid was occurring. Malic acid excretion was specifically stimulated by Al, and neither La, Fe, nor the absence of Pi was able to elicit this response. There was a consistent correlation of Al tolerance with high rates of malic acid excretion stimulated by Al in a population of seedlings segregating for Al tolerance. These data are consistent with the hypothesis that the Alt1 locus in wheat encodes an Al tolerance mechanism based on Al-stimulated excretion of malic acid.


Plant and Soil | 2011

Plant and microbial strategies to improve the phosphorus efficiency of agriculture

Alan Richardson; Jonathan P. Lynch; Peter R. Ryan; Emmanuel Delhaize; F. Andrew Smith; Sally E. Smith; Paul R. Harvey; Megan H. Ryan; Erik J. Veneklaas; Hans Lambers; Astrid Oberson; Richard A. Culvenor; Richard J. Simpson

BackgroundAgricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. In fertilised and intensive systems, P-efficient plants are required to minimise inefficient use of P-inputs and to reduce potential for loss of P to the environment.ScopeThree strategies by which plants and microorganisms may improve P-use efficiency are outlined: (i) Root-foraging strategies that improve P acquisition by lowering the critical P requirement of plant growth and allowing agriculture to operate at lower levels of soil P; (ii) P-mining strategies to enhance the desorption, solubilisation or mineralisation of P from sparingly-available sources in soil using root exudates (organic anions, phosphatases), and (iii) improving internal P-utilisation efficiency through the use of plants that yield more per unit of P uptake.ConclusionsWe critically review evidence that more P-efficient plants can be developed by modifying root growth and architecture, through manipulation of root exudates or by managing plant-microbial associations such as arbuscular mycorrhizal fungi and microbial inoculants. Opportunities to develop P-efficient plants through breeding or genetic modification are described and issues that may limit success including potential trade-offs and trait interactions are discussed. Whilst demonstrable progress has been made by selecting plants for root morphological traits, the potential for manipulating root physiological traits or selecting plants for low internal P concentration has yet to be realised.


Planta | 1995

Characterisation of Al-stimulated efflux of malate from the apices of Al-tolerant wheat roots

Peter R. Ryan; Emmanuel Delhaize; Peter J. Randall

Aluminium (Al) stimulates the efflux of malate from the apices of wheat (Triticum aestivum L.) roots (Delhaize et al. 1993, Plant Physiol. 103, 695–702). The response was five to tenfold higher in Al-tolerant seedlings than Al-sensitive seedlings and the capacity for Al-stimulated malate efflux was found to co-segregate with Al tolerance in a pair of near-isogenic wheat lines differing in Al-tolerance at a single dominant locus. We have investigated this response further using excised root apices. Half-maximal efflux of malate from apices of Al-tolerant seedlings was measured with 30 μM Al in 0.2 mM CaCl2, pH 4.2, while saturating rates of 2.0 nmol·apex−1·h−1 occurred with concentrations above 100 μM Al. The stimulation of malate efflux by Al was accompanied by an increase in K+ efflux which appeared to account for electroneutrality. The greater stimulation of malate efflux from Al-tolerant apices compared to Al-sensitive apices could not be explained by differences in the activities of phosphoenolpyruvate carboxylase or NAD-malate dehydrogenase. Several other polyvalent cations, including gallium, indium and the tridecamer Al13, failed to elicit malate efflux. Aluminium-stimulated efflux of malate was correlated with the measured concentration of total monomeric Al present, and with the predicted concentrations of Al3+ and AlOH2+ ions in the solution. Several antagonists of anion channels inhibited Al-stimulated efflux of malate with the following order of effectiveness: niflumic acid≈NPPB>IAA-94≈A-9-C>ethacrynic acid. Lanthanum, chlorate, perchlorate, zinc and α-cyano-4-hydroxycinnamic acid inhibited malate release by less than 30% at 100 μM while 4,4′-diisothiocyanatostilbene-2,2′-disulphonate (DIDS) had no effect. These results suggest that the Al3+ cation stimulates malate efflux via anion channels in apical cells of Al-tolerant wheat roots.


Plant Physiology | 2009

A Second Mechanism for Aluminum Resistance in Wheat Relies on the Constitutive Efflux of Citrate from Roots

Peter R. Ryan; Harsh Raman; Sanjay Gupta; Walter J. Horst; Emmanuel Delhaize

The first confirmed mechanism for aluminum (Al) resistance in plants is encoded by the wheat (Triticum aestivum) gene, TaALMT1, on chromosome 4DL. TaALMT1 controls the Al-activated efflux of malate from roots, and this mechanism is widespread among Al-resistant genotypes of diverse genetic origins. This study describes a second mechanism for Al resistance in wheat that relies on citrate efflux. Citrate efflux occurred constitutively from the roots of Brazilian cultivars Carazinho, Maringa, Toropi, and Trintecinco. Examination of two populations segregating for this trait showed that citrate efflux was controlled by a single locus. Whole-genome linkage mapping using an F2 population derived from a cross between Carazinho (citrate efflux) and the cultivar EGA-Burke (no citrate efflux) identified a major locus on chromosome 4BL, Xcec, which accounts for more than 50% of the phenotypic variation in citrate efflux. Mendelizing the quantitative variation in citrate efflux into qualitative data, the Xcec locus was mapped within 6.3 cM of the microsatellite marker Xgwm495 locus. This linkage was validated in a second population of F2:3 families derived from a cross between Carazinho and the cultivar Egret (no citrate efflux). We show that expression of an expressed sequence tag, belonging to the multidrug and toxin efflux (MATE) gene family, correlates with the citrate efflux phenotype. This study provides genetic and physiological evidence that citrate efflux is a second mechanism for Al resistance in wheat.


FEBS Letters | 2007

The roles of organic anion permeases in aluminium resistance and mineral nutrition

Emmanuel Delhaize; Benjamin D. Gruber; Peter R. Ryan

Soluble aluminium (Al3+) is the major constraint to plant growth on acid soils. Plants have evolved mechanisms to tolerate Al3+ and one type of mechanism relies on the efflux of organic anions that protect roots by chelating the Al3+. Al3+ resistance genes of several species have now been isolated and found to encode membrane proteins that facilitate organic anion efflux from roots. These proteins belong to the Al3+‐activated malate transporter (ALMT) and multi‐drug and toxin extrusion (MATE) families. We review the roles of these proteins in Al3+ resistance as well as their roles in other aspects of mineral nutrition.


Plant and Soil | 2011

Strategies and agronomic interventions to improve the phosphorus-use efficiency of farming systems

Richard J. Simpson; Astrid Oberson; Richard A. Culvenor; Megan H. Ryan; Erik J. Veneklaas; Hans Lambers; Jonathan P. Lynch; Peter R. Ryan; Emmanuel Delhaize; F. Andrew Smith; Sally E. Smith; Paul R. Harvey; Alan E. Richardson

Phosphorus (P)-deficiency is a significant challenge for agricultural productivity on many highly P-sorbing weathered and tropical soils throughout the world. On these soils it can be necessary to apply up to five-fold more P as fertiliser than is exported in products. Given the finite nature of global P resources, it is important that such inefficiencies be addressed. For low P-sorbing soils, P-efficient farming systems will also assist attempts to reduce pollution associated with P losses to the environment. P-balance inefficiency of farms is associated with loss of P in erosion, runoff or leaching, uneven dispersal of animal excreta, and accumulation of P as sparingly-available phosphate and organic P in the soil. In many cases it is possible to minimise P losses in runoff or erosion. Uneven dispersal of P in excreta typically amounts to ~5% of P-fertiliser inputs. However, the rate of P accumulation in moderate to highly P-sorbing soils is a major contributor to inefficient P-fertiliser use. We discuss the causal edaphic, plant and microbial factors in the context of soil P management, P cycling and productivity goals of farms. Management interventions that can alter P-use efficiency are explored, including better targeted P-fertiliser use, organic amendments, removing other constraints to yield, zone management, use of plants with low critical-P requirements, and modified farming systems. Higher productivity in low-P soils, or lower P inputs in fertilised agricultural systems can be achieved by various interventions, but it is also critically important to understand the agroecology of plant P nutrition within farming systems for improvements in P-use efficiency to be realised.


The Plant Cell | 2003

Genes encoding proteins of the cation diffusion facilitator family that confer manganese tolerance.

Emmanuel Delhaize; Tatsuhiko Kataoka; Diane M. Hebb; Rosemary G. White; Peter R. Ryan

The yeast Saccharomyces cerevisiae expressing a cDNA library prepared from Stylosanthes hamata was screened for enhanced Mn2+ tolerance. From this screen, we identified four related cDNAs that encode membrane-bound proteins of the cation diffusion facilitator (CDF) family. One of these cDNAs (ShMTP1) was investigated in detail and found to confer Mn2+ tolerance to yeast by internal sequestration rather than by efflux of Mn2+. Expression of ShMTP1 in a range of yeast mutants suggested that it functions as a proton:Mn2+ antiporter on the membrane of an internal organelle. Similarly, when expressed in Arabidopsis, ShMTP1 conferred Mn2+ tolerance through internal sequestration. The ShMTP1 protein fused to green fluorescent protein was localized to the tonoplast of Arabidopsis cells but appeared to localize to the endoplasmic reticulum of yeast. We suggest that the ShMTP1 proteins are members of the CDF family involved in conferring Mn2+ tolerance and that at least one of these proteins (ShMTP1) confers tolerance by sequestering Mn2+ into internal organelles.


Journal of Experimental Botany | 2011

The identification of aluminium-resistance genes provides opportunities for enhancing crop production on acid soils

Peter R. Ryan; Stephen D. Tyerman; Takayuki Sasaki; Takuya Furuichi; Yoko Yamamoto; Wen-Hao Zhang; Emmanuel Delhaize

Acid soils restrict plant production around the world. One of the major limitations to plant growth on acid soils is the prevalence of soluble aluminium (Al(3+)) ions which can inhibit root growth at micromolar concentrations. Species that show a natural resistance to Al(3+) toxicity perform better on acid soils. Our understanding of the physiology of Al(3+) resistance in important crop plants has increased greatly over the past 20 years, largely due to the application of genetics and molecular biology. Fourteen genes from seven different species are known to contribute to Al(3+) tolerance and resistance and several additional candidates have been identified. Some of these genes account for genotypic variation within species and others do not. One mechanism of resistance which has now been identified in a range of species relies on the efflux of organic anions such as malate and citrate from roots. The genes controlling this trait are members of the ALMT and MATE families which encode membrane proteins that facilitate organic anion efflux across the plasma membrane. Identification of these and other resistance genes provides opportunities for enhancing the Al(3+) resistance of plants by marker-assisted breeding and through biotechnology. Most attempts to enhance Al(3+) resistance in plants with genetic engineering have targeted genes that are induced by Al(3+) stress or that are likely to increase organic anion efflux. In the latter case, studies have either enhanced organic anion synthesis or increased organic anion transport across the plasma membrane. Recent developments in this area are summarized and the structure-function of the TaALMT1 protein from wheat is discussed.

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Emmanuel Delhaize

Commonwealth Scientific and Industrial Research Organisation

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Alan E. Richardson

Commonwealth Scientific and Industrial Research Organisation

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Meixue Zhou

University of Tasmania

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Diane M. Hebb

Commonwealth Scientific and Industrial Research Organisation

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Harsh Raman

Charles Sturt University

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