Species-specific EcoRI repetitive elements of at least 16 kb in length are present in Lupinus luteus

Summary A genomic DNA library of Lupinus luteus cv. Ventus was constructed in the phage vector EMBL3 using Mb oI-digested DNA. Screening with a 1070 bp labelled repetitive unit from L. luteus yielded several DNA clones. The repetitive family is composed of elements whose length is at least 16 kb. The average copy number of the cloned fragments is 5.0 × 10⁴ per haploid genome and constitutes approximately 3% of the total L. luteus genome. The homologous repeats were found in all ten cultivars of L. luteus tested but were not detected in two cultivars each of the closely related species Lupinus albus and Lupinus angustifolius. The EcoRI family fragments could thus be considered as species-specific DNA elements. These fragments may be useful as molecular markers in the genetic manipulation of L. luteus.     

The formation,morphology and anatomy of cluster root of Lupinus albus L. as dependent on soil type and phosphorus supply

The effect of phosphorus supply on the formation, morphology and anatomy of cluster roots of Lupinus albus L. cv Ultra grown in a loam and two sandy soils was examined relative to its effect on total root length, shoot weight and the phosphorus concentration of the shoots. The loam soil was most conducive to the formation of cluster roots. Cluster roots growing in the sandy soils developed to a lesser extent on plants of an equivalent phosphorus status, suggesting that some biotic or abiotic factors independent of phosphorus supply were also operating. The presence of mature cluster rootlets on a length of lateral root increased the root surface area by 14–22 times of an equal length of lateral roots not bearing cluster rootlets. The application of phosphorus decreased cluster-root length, whereas total root length showed a steady increase. There was an inverse relationship between cluster-root production and phosphorus concentration in shoots ranging from 2 to 8.5 mg g^–1 with the critical phosphorus level for maximum shoot growth being around 2.5 mg g^–1. Cluster roots formed in solution culture were not well developed in comparison with those grown in the loam soil or nutrient solution with added loam soil. The organisation of the cluster rootlet was similar to that of the lateral roots. Mature rootlets lacked an apical meristem and a vascular cambium with a reduced root cap and cortical tissue.     

Investigations into the exploitation of heterogeneous soils by Lupinus albus L. and L. pilosus Murr. and the effect upon plant growth

In calcareous soils, genotypes of Lupinus albus L. generally grow poorly, resulting in stunted plants that often develop lime-induced chlorosis. In contrast, some genotypes of L. pilosus Murr. occur naturally in calcareous soils without developing any visible symptoms of stress. Some genotypic variation for tolerance to calcareous soil does exist in L. albus and the tolerance mechanisms need to be determined. The adaptation through root system morphological plasticity of L. albus and L. pilosus, to heterogeneous limed soil profiles (pH 7.8) containing either patches of acid (non-limed) soil, or vertically split between acid and limed soil, was investigated. When grown in the presence of patches of acid soil, L. albus had a 52% greater shoot dry weight and visibly greener leaves compared with plants grown in the homogeneous limed soil. Total root dry matter in the acid-soil patches was greater than in the control limed-soil patches. This was due to a four-fold increase in the cluster root mass, accounting for 95% of the root dry matter in the acid-soil patch. Although these cluster roots secreted no more citric acid per unit mass than those in the limed soil did, their greater mass resulted in a higher citrate concentration in the surrounding soil. L. pilosus responded to the patches of acid soil in a manner comparable with L. albus. When grown in the homogeneous limed soil, L. pilosus had a greater maximum net CO₂ assimilation rate (P_max) than L. albus, however, the P_max of both species increased after they had accessed a patch of acid soil. Differences were apparent between the L. albus genotypes grown in soil profiles split vertically into limed and acid soil. A genotype by soil interaction occurred in the partitioning between soils of the cluster roots. The genotype La 674 was comparable with L. pilosus and produced over 11% of its cluster roots in the limed soil, whereas the other genotypes produced only 1–3% of their cluster roots in the limed soil. These results indicate L. pilosus is better adapted to the limed soil than L. albus, but that both species respond to a heterogeneous soil by producing mainly cluster roots in an acid-soil patch. This revised version was published online in June 2006 with corrections to the Cover Date.     

武夷山不同海拔黄山松细根性状季节变化

细根作为植物吸收养分和水分的主要器官,其功能性状对森林生态系统功能具有重要影响。以武夷山黄山松为研究对象,通过对不同季节(春季、夏季、秋季和冬季)和不同海拔(1200、1400、1600、1800 m和2000 m)的黄山松细根的功能性状的测定,分析其细根性状特征随海拔和季节变化的规律。结果表明:(1)黄山松细根比根长(SRL),比根面积(SRA)均随海拔先升高后降低,其均值分别为(9.32±0.35) cm/g与(276.41±68.10) cm~2/g;根组织密度(RTD)随海拔先降低后升高,均值为(0.16±0.05) g/cm~3。根平均直径(AvgDiam)随海拔增加变化不显著,均值为(0.097±0.004) mm。SRL和SRA在海拔1600 m处达到最大,而RTD和AvgDiam的最大值出现在海拔1800 m或2000 m处。(2)SRL和SRA在夏季或秋季达到最大,RTD和AvgDiam最大值则出现在冬季或春季。季节和海拔对各细根性状都有显著影响(P0.01),但季节与海拔对根性状并没有产生显著的交互作用(P0.05)。(3)SRL与SRA间的异速生长指数是1.25,显著大于1.0(P0.01);SRL与RTD存在负等速生长关系,而与AvgDiam存在显著负异速生长关系(P0.01);SRA与RTD,以及RTD与AvgDiam间均存在显著负异速生长关系(P0.01),但SRA与AvgDiam之间不存在异速生长关系。黄山松的细根性状在1600 m处倾向于增加比根长和比根面积,而在海拔1800 m或2000 m处则倾向于增加组织密度与根直径,这与黄山松细根性状从夏秋到冬春的季节变化规律相类似。同时,相对于比根面积来说,黄山松的细根在海拔1600 m处和夏秋季节更倾向于投资比根长来增加养分的吸收。     

New Coumaronochromones from White Lupin,Lupinus albus L. (Leguminosae)

A further investigation of the isoflavonoid constituents occurring in roots of the white lupin (Lupinus albus L. cv. Kievskij Mutant) has yielded five new coumaronochromones named lupinalbin A (la), B (2a), C (3), D (4) and E (5). These isoflavonoids were identified by physicochemical methods involving the use of biogenetically related 2′-hydroxyisoflavones as reference compounds. The presence of the rare dihydrofurano-isoflavone, erythrinin C (16), in white lupin roots has also been established.     

Flavonoids in roots of white clover: interaction of arbuscular mycorrhizal fungi and a pathogenic fungus

The effects of two arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. claroideum) and a pathogenic fungus (Pythium ultimum) on the production of eight flavonoids in roots of two white clover (Trifolium repens L.) cultivars were evaluated. Quantification of AM and pathogenic fungi in the roots showed that the AM symbiosis significantly reduced P. ultimum biomass and in some cases prevented infection. The flavonoid productions in clover roots varied depending on the presence of beneficial and/or pathogenic fungi, fungal isolate or plant cultivar. Only plants colonized with G. claroideum showed detectable concentrations of either coumestrol or kaempferol (cultivar-dependant). In addition, inoculation with G. claroideum resulted in significantly higher concentrations of coumestrol in cv. Sonja and medicarpin in cv. Milo. A low production of coumestrol and kaempferol in mycorrhizal plants may be G. mosseae-specific. Only the concentrations of formononetin and daidzein increased in clover roots in response to infection with P. ultimum. These flavonoids are supposedly stress metabolites, synthesized or produced from glycosides in response to pathogen infection. However, the presence of one or both AMF significantly lowered the formononetin and daidzein concentrations, and overruled the inductive effect of P. ultimum. Therefore the antagonistic action of AM against the pathogen must take place through another mechanism.     

Role of bacterial cyanide production in differential reaction of plant cultivars to deleterious rhizosphere pseudomonads

Lettuce and wheat cultivars, differing in reaction to root inoculation with plant growth-inhibitory bacteria, were tested for sensitivity to (i) gaseous metabolites produced by deleterious, cyanogenic isolates of Pseudomonas fluorescens, and to (ii) pure cyanide. Reactions were read as shoot and/or root elongation after exposure of seedlings to the volatiles in vitro. Lettuce cultivar Salad Bowl was significantly less sensitive than cv. Montana, both to bacterial volatiles and to pure cyanide, and a similar difference between these cultivars was also obtained in greenhouse experiments where bacteria were inoculated directly on the roots. Cultivar differences were, however, not recorded, either in vitro or in the greenhouse, when the bacteria were grown on a medium which did not support cyanide production. In wheat, a difference in sensitivity to bacteria-produced volatiles was recorded between two cultivars (Drabant and Besso) differing in reaction to bacterial inoculation, but in contrast to lettuce cultivars, the wheat cultivars tested did not react differentially to pure cyanide. The results suggest that in lettuce differential sensitivity to cyanide is one factor behind cultivar differences in reaction to the bacteria tested, even though bacterial metabolites other than cyanide may contribute to the plant growth inhibition recorded. In wheat, however, differential cultivar responses to these bacteria could not be shown to be related to cyanide.     

The Role of the Stem in Phloem Loading of Minerals in Lupinus albus L. cv. Ultra

Collections of phloem sap made over a 40-day period from a varietyof locations on nodulated white lupin plants (Lupinus albusL. cv. ultra) showed considerable enrichment with K⁺ and Mg²⁺in the phloem streams destined for the shoot apices or fruitsrelative to the streams arising from the leaflets (up to 5.5times). Sodium showed enrichment in the streams destined forthe roots (up to 2.5 times) but only when present in the watersupply at a high level (3 mM). The stem, in view of its centrallocation in the transport pathway, is seen as an organ capableof redistributing minerals in the phloem independently of photosynthate. Lupinus albus L., lupin, phloem loading, magnesium, potassium, sodium, mineral elements     

Oxygen Diffusion in Lupin Nodules: I.VISUALIZATION OF DIFFUSION BARRIER OPERATION

Root nodules of Lupinus albus (L.) cv. Multolupa were subjectedto short- and medium-term stresses by lowering rhizosphere temperaturefrom 25 to 16°C (2 h), detopping plants (3 h), darkeningplants (21 h) or exposing roots to 20 mol m^–3 KNO₃ for4 d. All experimental treatments produced increases in oxygendiffusion resistance, compared with control plants. These correlatedwith structural changes in the nodule cortex, which is describedin detail for the first time. The most noticeable change isthe occlusion of intercellular spaces by a glycoprotein whichwas identified using the monoclonal antibody MAC236. This glycoproteinwas also found surrounding bacteria in intercellular spacesof the cortex of control nodules. Key words: Oxygen diffusion resistance, glycoprotein, nodules, nitrogen fixation, Lupinus albus     

Sorghum root length density and the potential for avoiding striga parasitism

Striga hermonthica is a serious root parasite of sorghum in the semiarid tropics. Successful parasitism is dependent on interactions of Striga seeds and host roots. Several sorghum cultivars have been found which resist parasitism. The basis of resistance is not well known. One possible method for reducing the chances of parasitism is by restricted host root development. This research was conducted to evaluate this hypothesis in sorghum known to possess resistance to parasitism by Striga.Root length density of 21-day-old pot-grown resistant cultivars, Framida, N-13, IS-9830, Tetron and P-967083, were compared to that of the susceptible check, Dabar, using the line intercept method of measuring root length. There was no significant difference between resistant cultivars and the susceptible cultivar Dabar. The RLD of resistant P-967083 however was significantly less than Framida, another resistant cultivar.The RLD of Dabar was compared to that of Framida and P-967083 in USA and Niger field trials. Root length density was determined on soil cores taken at flowering with a Giddings Soil Sampler. Each core was divided into 10-cm fractions for estimating RLD by the line intercept method. In the USA Dabar had significantly greater RLD than the two resistant cultivars in the upper 10-cm portion of the soil profile, but only significantly greater than P-967083 in the 10–20-cm portion. Significant differences in RLD between susceptible and resistant cultivars were not found at depths between 20–60 cm. In field trials in Niger, RLD of Dabar was significantly greater than either resistant cultivar in the (0 to 30 cm) portion of the soil core. These results suggest that part of the Striga resistance of P-967083 and perhaps Framida may be a result of avoiding interactions between parasitic seeds and host roots.     

Effect of Sowing Date and Cultivar on Root System Development in Pea (Pisum sativum L.)

In many species, root system development depends on cultivar and sowing date, with consequences for aerial growth, and seed yield. Most of the peas (Pisum sativum L.) grown in France are sown in spring or in mid-November. We analyzed the effect of two sowing periods (November and February) and three pea cultivars (a spring cultivar, a winter cultivar, a winter recombinant inbred line) on root development in field conditions. For all treatments, rooting depth at various dates seemed to be strongly correlated with cumulative radiation since sowing. Maximum root depth varied from 0.88 to 1.06 m, with the roots penetrating to greater depths for February sowing than for November sowing in very cold winters. The earlier the crop was sown, the sooner maximum root depth was reached. No difference in root dynamics between cultivars was observed. In contrast, the winter recombinant inbred line presented the highest root density in the ploughed layer. These findings are discussed in terms of their possible implications for yield stability and environmental impact.     

Determination of lead in white lupin by anodic stripping voltammetry

An anodic stripping voltammetry method for the simultaneous determination of trace heavy metals in nutrient solutions, soils and plants has been developed at a hydrodynamic electrochemical sensor. Several parameters were optimized in order to enhance sensitivity. Calibration curves in different media are presented. The study of the uptake of lead by white lupin (Lupinus albus L.) was carried out. Toxicity symptoms were observed and compared with levels of lead measured in roots and leaves.     

Different Effect of Humidity on Growth and Salt Tolerance of Two Soybean Cultivars

Two soybean (Glycine max (L.) Merr.) cultivars, Tachiyutaka and Dare, were grown in pots at 30 and 70 % relative humidity (RH) and treated with 0 (control), 40 (moderate), 80 and 120 (severe) mM NaCl for 3 weeks. Increasing RH enhanced growth of salt sensitive cultivar, Tachiyutaka, but had no effect on salt tolerant cultivar, Dare, under control and moderate saline conditions. Both cultivars benefited from elevated humidity under severe saline conditions. Cultivar Tachiyutaka had poorer ability for controlling translocation of Na⁺ to the leaves, lower Na⁺ exclusion ability in the roots, and lower root activity under NaCl treatment, compared with cv. Dare. The increased growth of cv. Tachiyutaka at high RH was consistent with decreased Na⁺ accumulation in the leaves, increased stomatal conductance and root activity, while the unchanged growth of cv. Dare was consistent with similar Na⁺ accumulation in the leaves, and the decreased root activity.     

Secretion activity of white lupin’s cluster roots influences bacterial abundance,function and community structure

White lupin (Lupinus albus L. cv. Amiga) reacts to phosphate deficiency by producing cluster roots which exude large amounts of organic acids. The detailed knowledge of the excretion physiology of the different root parts makes it a good model plant to study plant-bacteria interaction. Since the effect of the organic acid exudation by cluster roots on the rhizosphere microflora is still poorly understood, we investigated the abundance, diversity and functions of bacteria associated with the cluster roots of white lupin, with special emphasis on the influence of root proximity (comparing root, rhizosphere soil and bulk soil fractions) and cluster root growth stages, which are characterized by different excretion activities. Plants were grown for five weeks in microcosms, in the presence of low phosphate concentrations, on acidic sand inoculated with a soil suspension from a lupin field. Plate counts showed that bacterial abundance decreased at the stage where the cluster root excretes high amounts of citrate and protons. In vitro tests on isolates showed that the frequencies of auxin producers were highest in juvenile and mature cluster roots and significantly decreased in senescent cluster roots. However, no significant difference in the frequency of auxin producers was found between cluster and non cluster roots. The diversity and structure of bacterial communities were investigated by DGGE of 16S rDNA and 16S rRNA. The diversity and community structure were mostly influenced by root proximity and, to a lesser extent, by cluster root stage. The richness of bacterial communities decreased with root proximity, whereas the proportion of active populations increased. The high citrate and proton excretion occurring at the mature stage of cluster roots had a strong impact on the structure and richness of the bacterial communities, both in the root and in the rhizosphere soil.     

Muscodor albus, a potential biocontrol agent against plant-parasitic nematodes of economically important vegetable crops in Washington State, USA

The fungus, Muscodor albus, was tested for nematicidal and nematostatic potential against four plant-parasitic nematode species with three different feeding modes on economically important vegetable crops in the Pacific Northwest. Meloidogyne chitwoodi, Meloidogyne hapla, Paratrichodorus allius, and Pratylenchus penetrans were exposed for 72 h to volatiles generated by M. albus cultured on rye grain in sealed chambers at 24 °C in the laboratory. In addition, the nematodes were inoculated into soil fumigated with M. albus, and incubated for 7 days prior to the introduction of host plants under greenhouse conditions. The mean percent mortality of nematodes exposed to M. albus in the chamber was 82.7% for P. allius, 82.1% for P. penetrans, and 95% for M. chitwoodi; mortality in the nontreated controls was 5.8%, 7%, and 3.9%, respectively. Only 21.6% of M. hapla juveniles died in comparison to 8.9% in controls. However, 69.5% of the treated juveniles displayed reduced motility and lower response to physical stimulus by probing, in comparison to the control juveniles. This is evidence of nematostasis due to M. albus exposure. The greenhouse study showed that M. albus caused significant reduction to all nematode species in host roots and in rhizosphere soil. The percent mortality caused by M. albus applied at 0.5% and 1.0% w/w in comparison to the controls was as follows: 91% and 100% for P. allius in the soil; 100% for P. penetrans in bean roots and soil; 85% and 95% for M. chitwoodi in potato roots, and 56% and 100% in the soil; 100% for M. hapla both in pepper roots and soil. In this study, M. albus has shown both nematostatic and nematicidal properties.     

Growth and nutrient allocation in Phaseolus vulgaris L. colonized with endomycorrhizae or Rhizobium

Two cultivars of Phaseolus vulgaris L., one responsive to colonization with microsymbionts (Mexico 309) and one less-responsive (Rio Tibagi) were grown in Leonard jars containing sand/vermiculite under greenhouse conditions. Bean plants were either left non-inoculated (controls) or were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or a strain of Rhizobium leguminosarum bv. phaseoli (UMR-1899). Plants from the Mexico 309 cultivar maintained a higher growth rate, supported proportionately more nodules and mycorrhizae, and assimilated relatively more N or P when colonized by Rhizobium or Glomus, respectively, than did plants of the Rio Tibagi cultivar. Estimated specific nodule activity for Mexico 309 beans was more than twice that of Rio Tibagi, whereas the specific phosphorus uptake rate (SPUR) was 35% greater in the non-inoculated roots of Rio Tibagi compared to Mexico 309. Colonization by G. etunicatum more than doubled the SPUR for each cultivar compared to control roots. New acid phosphatase isozymes appeared in VAM-colonized roots of both cultivars compared to controls. Acid and alkaline phosphatase activities were significantly higher in G. etunicatum-colonized Mexico 309 roots, but not in Rio Tibagi mycorrhizae, compared to uninfected roots. Polyphosphate hydrolase activity was elevated in mycorrhizae of both cultivars compared to control roots. These results indicate that the dependence of a host on a specific endophyte increases when there are limitations to the supply of a nutrient that the endophyte can provide. The greater the increase in absorption or utilization capacity following colonization by the microsymbiont, the greater the dependence by the host. More importantly, identification of enzymatic activities that influence these plant-microbe associations opens the possibility that the specific genes that code for these enzymes could be targeted for future manipulation.     

柠条人工林细根不同分枝根序寿命估计

植物细根在发育结构上表现的形态特征和生理功能异质性影响细根寿命的准确估计,因此了解分枝根序细根寿命差异对于深入认识细根的周转过程和陆地生态系统碳分配具有重要意义。采用微根管(Minirhizotron)技术对晋西北黄土区的五年生柠条(Caragana Korshinskii Kom.)人工林细根的生长过程进行了为期3a(2007—2009年)的追踪观测,分析了不同因素(土层深度、季节变化、空间位置)对一级根和高级根寿命的影响。结果表明:(1)在各土层深度处,一级根的中值寿命均低于高级根中值寿命,其中一级根中值寿命表现随土层深度增加而增加趋势,而高级根除表层0—20 cm中值寿命较短外,各土层间变化趋势不明显,40—60 cm、80—100 cm土层高级根在观测期结束时其累积存活率仍在50%以上;(2)不同季节出生一级根和高级根的中值寿命季节性表现为:秋季夏季春季,并且在各个季节均表现,高级根寿命显著大于一级根寿命(P0.01);一级根仅夏季与秋季差异性不显著(P0.05),而高级根仅春季与秋季存在极显著差异(P0.01);(3)一级根和高级根距树干基部0 cm处细根中值寿命均大于50 cm处一级根和高级根细根的中值寿命。同一位置处高级根寿命要大于一级根寿命。在距树干基部0 cm处和50 cm处,一级根和高级根的寿命均存在极显著差异(P0.01),但高级根却在距树干基部0 cm和50 cm处差异不明显,而一级根却表现极显著差异(P0.01)。     

Alterations in root lipid peroxidation and antioxidative responses in two rice cultivars under NaCl-salinity stress

The comparative alterations of short term NaCl stress and recovery on growth, water relations, ionic composition, lipid peroxidation and antioxidants in roots of two rice cultivars differing in salt tolerance were studied. Exposed for 24 h to increasing (50, 100 and 150 mmol l⁻¹) concentrations of NaCl, roots of 12D Oryza sativa L. cv. Lunishree and cv. Begunbitchi decreased in fresh weight, dry weight and relative water content. Increased Na⁺ and decreased K⁺ ion were determined at increasing NaCl concentrations. Both peroxide content and lipid peroxidation measured in terms of MDA level increased and the ratio was higher in Begunbitchi compared to Lunishree. Recovered roots showed lower peroxide and MDA content. Ascorbate and glutathione contents increased in the stressed and recovered roots of Lunishree, but decreased in Begunbitchi with increasing NaCl concentrations. Although SOD, CAT and GR activities decreased in the stressed roots, CAT activity also increased in recovered roots of both the cultivars. The POX activity increased in stressed and recovered roots of both Lunishree and Begunbitchi. Higher free radicals scavenging capacity and more efficient protection mechanism of Lunishree against salt stress, as revealed by the lower level of lipid peroxidation and improved plant water status as well as activities of some of the antioxidants, suggest that significant cultivar differences in response to salt stress in rice are closely related to differences in the activities of antioxidants and ion content. Another possible conclusion is that improved tolerance to salt stress may be accomplished by increased capacity of antioxidative system.     

The effect of modifying plant structure on the yield and maturity of the white lupin Lupinus albus

Experiments at Rothamsted in the UK and Lusignan in France examined the effect of artificially modifying plant structure on the yield and date of harvest of indeterminate autumn-sown cultivars of Lupinus albus. Experiments in 1989/90 were done on the cv. Lugel at Rothamsted and those in 1990/91 on the cvs Lugel and Lunoble in both the UK and France. At Rothamsted in 1990, when the summer was warm and dry, the indeterminate cv. Lugel ripened at the end of August and yielded 5.2 t grain/ha. At Lusignan in 1991, where summer weather was also warm and dry, the two unpruned indeterminate cultivars ripened in late July and yielded c. 4.9 t grain/ ha. However, at Rothamsted in 1991, in a season which was predominantly cool and wet, the two indeterminate cultivars were not harvested until late October and yielded only 1.5 and 2.4 t/ha. Plants pruned to a semi-determinate form consisting of the mainstem plus the 1^st-order branches yielded approximately the same as the unpruned inde-terminates at Rothamsted and slightly less than the indeterminates at Lusignan. The semi-determinates ripened 10 days earlier than the indeterminates at Rothamsted in 1990 and Lusignan in 1991, and 6 weeks earlier in the UK in 1991. Epigonal plants with only a mainstem inflorescence, ripened even earlier than the semi-determinates but, without branch inflorescences, produced less yield and had poorer yield stability. Where disease was not a factor, as at Rothamsted in 1990 and Lusignan in 1991, epigonal plants ripened 3 weeks earlier than the indeterminates and yielded between 1.6 and 2.6 t/ha. When the pruned epigonal plants were badly infested with Pleiochaeta, as at Rothamsted in 1991, they yielded less than 0.4 t/ha. It is concluded that indeterminate genotypes of L. albus are well adapted to the climatic conditions of Lusignan but lack yield stability further north. For the cooler northern regions of Europe, an autumn-sown, florally-determinate genotype with one order of branching would produce adequate yield and have an acceptably early harvest date and yield stability. Such a genotype would have agricultural and economic value as a new protein break crop with a low requirement for nitrogen fertiliser.     

Proteoid root morphology and function inLupinus albus

Summary Current theories of phosphorus uptake by plants imply that they can augment diffusion to their root axes by the development of abundant root hairs or mycorrhizas. Some phosphorus efficient plants have root morphology with multi-branched roots and localised regions of densely packed root hairs, which we suggest is better suited to the retention of substances exuded by the roots than uptake of substances moving to the root by diffusion. Evidence of substantial exudation by the proteoid roots ofLupinus albus is presented.