Impact of <Emphasis Type="Italic">Heterobasidion</Emphasis> root-rot on fine root morphology and associated fungi in <Emphasis Type="Italic">Picea abies</Emphasis> stands on peat soils

We examined differences in fine root morphology, mycorrhizal colonisation and root-inhabiting fungal communities between Picea abies individuals infected by Heterobasidion root-rot compared with healthy individuals in four stands on peat soils in Latvia. We hypothesised that decreased tree vitality and alteration in supply of photosynthates belowground due to root-rot infection might lead to changes in fungal communities of tree roots. Plots were established in places where trees were infected and in places where they were healthy. Within each stand, five replicate soil cores with roots were taken to 20 cm depth in each root-rot infected and uninfected plot. Root morphological parameters, mycorrhizal colonisation and associated fungal communities, and soil chemical properties were analysed. In three stands root morphological parameters and in all stands root mycorrhizal colonisation were similar between root-rot infected and uninfected plots. In one stand, there were significant differences in root morphological parameters between root-rot infected versus uninfected plots, but these were likely due to significant differences in soil chemical properties between the plots. Sequencing of the internal transcribed spacer of fungal nuclear rDNA from ectomycorrhizal (ECM) root morphotypes of P. abies revealed the presence of 42 fungal species, among which ECM basidiomycetes Tylospora asterophora (24.6 % of fine roots examined), Amphinema byssoides (14.5 %) and Russula sapinea (9.7 %) were most common. Within each stand, the richness of fungal species and the composition of fungal communities in root-rot infected versus uninfected plots were similar. In conclusion, Heterobasidion root-rot had little or no effect on fine root morphology, mycorrhizal colonisation and composition of fungal communities in fine roots of P. abies growing on peat soils.     

Positive association between mycorrhiza and foliar endophytes in Poa bonariensis, a native grass

The interaction between mycorrhiza and leaf endophytes (Neotyphodium sp.) was studied in three Poa bonariensis populations, a native grass, differing significantly in endophyte infection. The association between endophytes and mycorrhizal fungi colonisation was assessed by analysing plant roots collected from the field. We found that roots from endophyte-infected populations showed a significantly higher frequency of colonisation by mycorrhizal fungi and that soil parameters were not related to endophyte infection or mycorrhiza colonization. In addition, we did not observe significant differences in the number of AM propagules in soils of the three populations sites. We also report the simultaneous development of Paris-type and Arum-type mycorrhiza morphology within the same root systems of P. bonariensis. The co-occurrence of both colonisation types in one and the same root system found in the three populations, which differed in Neotyphodium infection, suggests that foliar endophytes do not determine AM morphology. The percentage of root length colonised by different types of fungal structures (coils, arbuscules, longitudinal hyphae and vesicles) showed significant and positive differences in arbuscular frequency associated with endophyte infection, whereas the much smaller amounts of vesicles and hyphal coils did not differ significantly.     

Plant growth, nutrient acquisition and mycorrhizal symbioses of a waterlogging tolerant legume (Lotus glaber Mill.) in a saline-sodic soil

Seedlings of Lotus glaberMill., were grown in a native saline-sodic soil in a greenhouse for 50 days and then subjected to waterlogging for an additional period of 40 days. The effect of soil waterlogging was evaluated by measuring plant growth allocation, mineral nutrition and soil chemical properties. Rhizobiumnodules and mycorrhizal colonisation in L. glaberroots were measured before and after waterlogging. Compared to control plants, waterlogged plants had decreased root/shoot ratio, lower number of stems per plant, lower specific root length and less allocation of P and N to roots. Waterlogged plants showed increased N and P concentrations in plant tissues, larger root crown diameter and longer internodes. Available N and P and organic P, pH and amorphous iron increased in waterlogged soil, but total N, EC and exchangeable sodium were not changed. Soil waterlogging decreased root length colonised by arbuscular mycorrhizal (AM) fungi, arbuscular colonisation and number of entry points per unit of root length colonised. Waterlogging also increased vesicle colonisation and Rhizobium nodules on roots. AM fungal spore density was lower at the end of the experiment in non-waterlogged soil but was not reduced under waterlogging. The results indicate that L. glaber can grow, become nodulated by Rhizobium and colonised by mycorrhizas under waterlogged condition. The responses of L. glaber may be related its ability to form aerenchyma.     

MycoRed: Betalain pigments enable in vivo real-time visualisation of arbuscular mycorrhizal colonisation

Arbuscular mycorrhiza (AM) are mutualistic interactions formed between soil fungi and plant roots. AM symbiosis is a fundamental and widespread trait in plants with the potential to sustainably enhance future crop yields. However, improving AM fungal association in crop species requires a fundamental understanding of host colonisation dynamics across varying agronomic and ecological contexts. To this end, we demonstrate the use of betalain pigments as in vivo visual markers for the occurrence and distribution of AM fungal colonisation by Rhizophagus irregularis in Medicago truncatula and Nicotiana benthamiana roots. Using established and novel AM-responsive promoters, we assembled multigene reporter constructs that enable the AM-controlled expression of the core betalain synthesis genes. We show that betalain colouration is specifically induced in root tissues and cells where fungal colonisation has occurred. In a rhizotron setup, we also demonstrate that betalain staining allows for the noninvasive tracing of fungal colonisation along the root system over time. We present MycoRed, a useful innovative method that will expand and complement currently used fungal visualisation techniques to advance knowledge in the field of AM symbiosis.

Arbuscular mycorrhiza are mutualistic interactions formed between soil fungi and plant roots. This study presents the MycoRed system, which uses red plant pigments derived from beetroot to reveal how fungi establish symbiosis with living legume and wild tobacco roots.     

Root traits and taxonomic affiliation of nine herbaceous species grown in glasshouse conditions

This study examines whether root traits differed between three major plant families (Asteraceae, Fabaceae and Poaceae) and whether they are related to root respiration and exudation. Nine traits related to biomass allocation, root topology, morphology, chemical composition and mycorrhizal colonisation were examined for nine C₃ herbaceous species grown in controlled conditions. Poaceae differed from Fabaceae for the whole set of root traits examined except mycorrhizal colonisation, while Asteraceae showed intermediate characteristics. As compared to Fabaceae, Poaceae allocated more biomass to roots; showed a more sparsely branched root system with a small average root diameter, a high root dry matter content and a low nitrogen concentration. Root respiration was weakly related to root mass ratio and root dry matter content; no significant relationship was found between root functions and root architecture or morphology. This study shows that plant classification based on taxonomic affiliation reflects differences in root system traits and functions. Whole root system traits do not allow strong predictions of root respiration and exudation, perhaps because these processes are more linked to fine root than to whole root system traits.     

Plant Growth Substances Produced by Azospirillum brasilense and Their Effect on the Growth of Pearl Millet (Pennisetum americanum L.)

Azospirillum brasilense, a nitrogen-fixing bacterium found in the rhizosphere of various grass species, was investigated to establish the effect on plant growth of growth substances produced by the bacteria. Thin-layer chromatography, high-pressure liquid chromatography, and bioassay were used to separate and identify plant growth substances produced by the bacteria in liquid culture. Indole acetic acid and indole lactic acid were produced by A. brasilense from tryptophan. Indole acetic acid production increased with increasing tryptophan concentration from 1 to 100 μg/ml. Indole acetic acid concentration also increased with the age of the culture until bacteria reached the stationary phase. Shaking favored the production of indole acetic acid, especially in a medium containing nitrogen. A small but biologically significant amount of gibberellin was detected in the culture medium. Also at least three cytokinin-like substances, equivalent to about 0.001 μg of kinetin per ml, were present. The morphology of pearl millet roots changed when plants in solution culture were inoculated. The number of lateral roots was increased, and all lateral roots were densely covered with root hairs. Experiments with pure plant hormones showed that gibberellin causes increased production of lateral roots. Cytokinin stimulated root hair formation, but reduced lateral root production and elongation of the main root. Combinations of indole acetic acid, gibberellin, and kinetin produced changes in root morphology of pearl millet similar to those produced by inoculation with A. brasilense.     

Regulation of defence responses in avocado roots infected with Phytophthora cinnamomi (Rands)

Phytophthora cinnamomi occurs worldwide and has a host range in excess of 1,000 plant species. Avocados (Persea americana Mill) have been described as highly susceptible to this soil-borne pathogen. Here, the regulation of defence responses in avocado root seedlings inoculated with P. cinnamomi mycelia is described. A burst of reactive oxygen species (ROS) was observed 4 days after inoculation. The higher physiological concentration of H₂O₂ induced by P. cinnamomi on avocado roots had no effect on in vitro growth of the oomycete. Total phenols and epicathecin content showed a significant decrease, but lignin and pyocianidins exhibited no changes after inoculation. Also, increased nitric oxide (NO) production was observed 72 h after treatment. We studied the effects of one NO donor [sodium nitroprusside (SNP)], and one NO scavenger [2- to 4-carboxyphenyl-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (CPTIO)] to determine the role of NO during root colonisation by P. cinnamomi mycelia. Pretreatment of the roots with CPTIO, but not with SNP, inhibited root colonisation suggesting an important role for NO production during the avocado–P. cinnamomi interaction. Our data suggest that although defence responses are activated in avocado roots in response to P. cinnamomi infection, these are not sufficient to avoid pathogen invasion.     

Functional aspects of root architecture and mycorrhizal inoculation with respect to nutrient uptake capacity

The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisation on root morphology and nitrogen uptake capacity of carob ( Ceratonia siliqua L.) under high and low nutrient conditions. The experimental design was a factorial arrangement of presence/absence of mycorrhizal fungus inoculation ( Glomus intraradices) and high/low nutrient status. Percent AM colonisation, nitrate and ammonium uptake capacity, and nitrogen and phosphorus contents were determined in 3-month-old seedlings. Grayscale and colour images were used to study root morphology and topology, and to assess the relation between root pigmentation and physiological activities. AM colonisation lead to a higher allocation of biomass to white and yellow parts of the root. Inorganic nitrogen uptake capacity per unit root length and nitrogen content were greatest in AM colonised plants grown under low nutrient conditions. A better match was found between plant nitrogen content and biomass accumulation, than between plant phosphorus content and biomass accumulation. It is suggested that the increase in nutrient uptake capacity of AM colonised roots is dependent both on changes in root morphology and physiological uptake potential. This study contributes to an understanding of the role of AM fungi and root morphology in plant nutrient uptake and shows that AM colonisation improves the nitrogen nutrition of plants, mainly when growing at low levels of nutrients.     

Arbuscular mycorrhizal symbiosis elicits proteome responses opposite of P-starvation in SO4 grapevine rootstock upon root colonisation with two Glomus species

Although plant biotisation with arbuscular mycorrhizal fungi (AMF) is a promising strategy for improving plant health, a better knowledge regarding the molecular mechanisms involved is required. In this context, we sought to analyse the root proteome of grapevine rootstock Selection Oppenheim 4 (SO4) upon colonisation with two AMF. As expected, AMF colonisation stimulates plant biomass. At the proteome level, changes in protein amounts due to AMF colonisation resulted in 39 differentially accumulated two-dimensional electrophoresis spots in AMF roots relative to control. Out of them, 25 were co-identified in SO4 roots upon colonisation by Glomus irregulare and Glomus mosseae supporting the existence of conserved plant responses to AM symbiosis in a woody perennial species. Among the 18 proteins whose amount was reduced in AMF-colonised roots were proteins involved in glycolysis, protein synthesis and fate, defence and cell rescue, ethylene biosynthesis and purine and pyrimidine salvage degradation. The six co-identified proteins whose amount was increased had functions in energy production, signalling, protein synthesis and fate including proteases. Altogether these data confirmed that a part of the accommodation program of AMF previously characterized in annual plants is maintained within roots of the SO4 rootstock cuttings. Nonetheless, particular responses also occurred involving proteins of carbon metabolism, development and root architecture, defence and cell rescue, anthocyanin biosynthesis and P remobilization, previously reported as induced upon P-starvation. This suggests the occurrence of P reprioritization upon AMF colonization in a woody perennial plant species with agronomical interest.     

Mycorrhizal colonisation in plants from intermittent aquatic habitats

Several plant species with amphibious characteristics from intermittent aquatic habitats were examined for colonisation with arbuscular mycorrhizal fungi (AM), dark septate endophytes (DSE) and the ratio of aerenchyma in root tissue. We studied submerged specimens of Alisma plantago-aquatica, Mentha aquatica, Myosotis scorpioides, Oenanthe fistulosa, Gratiola officinalis, Glyceria fluitans, Sium latifolium and Teucrium scordium. In the first four, we also examined the emerged growth forms, which were grown under experimental conditions. Roots of all species were mycorrhizal and showed AM and DSE colonisation. The results suggest that AM colonisation may also be abundant in plants of aquatic environment. Arbuscules were not found in submerged specimens of M. aquatica, O. fistulosa and S. latifolium. The AM colonisation was generally higher in emerged specimens as compared to submerged ones. The aerenchyma ratio in root cross-sections ranged from 10 to 50% and in most cases did not differ between submerged and emerged specimens. No clear relationship between AM colonisation and aerenchyma ratio was recognized, while a positive correlation between AM and plant available phosphorous was established.     

Influence of colonisation by an arbuscular mycorrhizal fungus on the growth of seedlings of<Emphasis Type="Italic"> Banksia ericifolia</Emphasis> (Proteaceae)

Tap and primary lateral roots of seedlings of the putatively non-mycorrhizal Banksia ericifolia became marginally colonised when grown in an established mycelium of an arbuscular mycorrhizal (AM) fungus in the laboratory. A similar degree of colonisation was found in seedlings from an open woodland. All colonies lacked arbuscules. Two factors influencing colonisation and associated growth of host plants were examined experimentally: concentration of P in the soil and organic energy associated with the fungus. While some inoculated seedlings were slightly smaller when colonised by AM fungi, the results were inconsistent and never statistically significant. Seedlings take up insignificant quantities of soil P during early growth, even in the presence of abundant added P. Though colonisation was minor in all cases, an existing mycelium, whether or not connected to a companion plant, slightly increased the amount of root of B. ericifolia colonised by an AM fungus. All seedlings grew slowly. Shoots were significantly larger than roots, until the initiation of proteoid roots which commenced at about 40 days after germination, with both relatively high and low P supply.     

Genetic variation for root architecture, nutrient uptake and mycorrhizal colonisation in Medicago truncatula accessions

Sustainable agriculture strives for healthy, high yielding plants with minimal agronomic inputs. Genetic solutions to increase nutrient uptake are desirable because they provide ongoing improvements. To achieve this it is necessary to identify genes involved in uptake and translocation of nutrients. We selected Medicago truncatula L. as a model because of its: i) close genetic relationship to food legumes, ii) use as a pasture legume in southern Australia and iii) availability of mapping populations generated from genetically diverse accessions. We discovered statistically significant differences between eight accessions for: root architecture in growth pouches, % root colonisation with the arbuscular mycorrhizal (AM) fungus Glomus intraradices, and plant tissue concentration of most macro- and micronutrients. Mycorrhizal colonisation had a significant effect on P concentration in roots but not shoots, Mg concentration in both roots and shoots, and the concentration of various micronutrients in shoots including Fe, Ca, but not Zn. Comparison of micronutrient uptake between root and shoot tissues showed that some M. truncatula accessions were more efficient at mobilisation of nutrients from roots to shoots. We are now in a position to use existing mapping populations of M. truncatula to identify quantitative trait loci important for human health and sustainable agriculture.     

Growth and morphology of eucalypt seedling-roots, in relation to soil strength arising from compaction

Information on the response of root growth and morphology to soil strength is useful for testing suitability of existing and new tillage methods and/or for selecting plants suitable for a specific site with or without tillage. Although there is extensive published information on the root growth-soil strength relationships for annual agricultural plants, such information is scarce for woody, perennial tree species. The purpose of this study is to examine growth and morphology of the root systems of 17-day-old eucalypt seedlings with respect to variation in soil strength. Soil strength in this study was varied by compaction of a well-aggregated clay soil to bulk densities of 0.7–1.0 Mg m^-3 whilst maintaining adequate water availability and aeration for plant growth. Lengths and tip-diameters of primary and lateral roots were measured on the excavated root systems of seedlings.With increase in bulk density and also soil strength (expressed as penetrometer resistance), total length of primary and lateral roots decreased. There were 71 and 31% reduction in the lengths of primary and lateral roots respectively with an increase in penetrometer resistance from 0.4 to 4.2 MPa. This indicated primary roots to be more sensitive to high soil strength than the lateral roots. Average length of lateral roots and diameters of both primary and lateral root tips increased with an increase in soil strength as well. There was greater abundance of lateral roots (no. of lateral roots per unit length of primary root) and root hairs with increased soil strength. The observed root behaviour to variable soil strength is discussed in the context of compensatory growth of roots and overall growth of plants.     

Mycorrhizal C costs and nutritional benefits in developing grapevines

Arbuscular mycorrhizal (AM) C-costs in grapevines were investigated. Dormant vines rely on stored C for initial growth. Therefore AM colonisation costs would compete with plant growth for available C reserves. One-year-old grapevines, colonised with Glomus etunicatum (Becker and Gerdemann), were cultivated under glasshouse conditions. The C-economy and P utilisation of the symbiosis were sequentially analysed. AM colonisation, during the 0–67 day growth period, used more stem C relative to root C, which resulted in lower shoot growth. The decline in AM colonisation during the period of 67–119 days coincided with stem C replenishment and higher shoot growth. Construction costs of AM plants and root C allocation increased with root P uptake. The efficiency of P utilisation was lower in AM roots. The reliance of AM colonisation on stem C declined with a decrease in colonisation, providing more C for the refilling of stem carbohydrate reserves and shoot growth. Once established, the AM symbiosis increased P uptake at the expense of refilling of root C reserves. Although higher root C allocation increased plant construction costs, AM roots were more efficient at P utilisation.     

Comparative analysis of Cd and Zn impacts on root distribution and morphology of Lolium perenne and Trifolium repens: implications for phytostabilization

Backgrounds and aims

The phytostabilization potential of plants is a direct function of their root systems. An experimental design was developed to investigate the impact of Cd and Zn on the root distribution and morphology of Lolium perenne and Trifolium repens.

Methods

Seedlings were transplanted into columns filled with washed quartz and irrigated daily with Cd- or Zn-containing nutrient solutions during 1 month. Root biomass, root length density (RLD) and diameter were subsequently quantified as a function of depth. Pot experiments were also performed to quantify metal, lignin and structural polysaccharides concentrations as well as cell viability.

Results

Lolium perenne accumulated Cd and Zn in the roots whereas T. repens was unable to restrict heavy metal translocation. Cadmium and Zn reduced rooting depth and RLD but induced thick shoot-borne roots in L. perenne. Cd-induced root swelling was related to lignification occurring in the exodermis and parenchyma of central cylinder. Hemicelluloses and lignin did not play a key role in root metal retention. Cadmium slightly reduced mean root cell viability whereas Zn increased this parameter in comparison to Cd.

Conclusions

Even though plant species like Lolium perenne and Trifolium repens may appear suitable for a phytostabilization scheme based on their shoot metal tolerance, exposure to toxic heavy metals drastically impairs their root distribution. This could jeopardize the setting up of phytostabilization trials. The metal-induced alterations of root system properties are clearly metal- and species-specific. At sites polluted with multiple metals, it is therefore recommended to first test their impact on the root system of multiple plant species so as to select the most appropriate species for each site.     

Molecular dialogues between Trichoderma and roots: Role of the fungal secretome

Trichoderma species are opportunistic fungi residing primarily in soil, tree bark and on wild mushrooms. Trichoderma is capable of killing other fungi and penetrating plant roots, and is commonly used as both a biofungicide and inducer of plant defence against pathogens. These fungi also exert other beneficial effects on plants including growth promotion and tolerance to abiotic stresses, primarily mediated by their intimate interactions with roots. In root–microbe interactions (both beneficial and harmful), fungal secreted proteins play a crucial role in establishing contact with the roots, fungal attachment, root penetration and triggering of plant responses. In Trichoderma–root interactions, the sucrose present in root exudates has been demonstrated to be important in fungal attraction. Attachment to roots is mediated by hydrophobin-like proteins, and secreted swollenins and plant cell wall degrading enzymes facilitate internalization of the fungal hyphae. During the early stage of penetration, suppression of plant defence is vital to successful initial root colonisation; this is mediated by small soluble cysteine-rich secreted proteins (effector-like proteins). Up to this stage, Trichoderma's behaviour is similar to that of a plant pathogen invading root structures. However, subsequent events like oxidative bursts, the synthesis of salicylic acid by the plants, and secretion of elicitor-like proteins by Trichoderma spp. differentiate this fungus from pathogens. These processes induce immunity in plants that help counter subsequent invasion by plant pathogens and insects. In this review, we present an inventory of soluble secreted proteins from Trichoderma that might play an active role in beneficial Trichoderma–plant interactions, and review the function of such proteins where known.     

指数施肥对楸树无性系生物量分配和根系形态的影响

为探求楸树不同无性系生物量分配和根系形态的差异,2011年3-8月在甘肃省天水市小陇山林科所,以2年生楸树无性系1-4、7080和015-1组培苗为试验材料,设置了CK、6、10、14 g尿素/株4个处理,研究指数施肥对楸树无性系生物量分配和根系形态的影响.结果表明:(1)同一无性系中,10 g尿素/株的根、茎、叶生物量及总生物量、根长、根表面积、根体积和根平均直径均高于其它处理.无性系015-1的生物量和根系形态参数整体上高于无性系1-4和7080.无性系015-1在10 g尿素/株的根、茎、叶生物量及总生物量分别为89.44 g、61.30 g、79.97 g、230.71 g,是CK的1.48、1.52、2.09、1.66倍;根长、根表面积和根体积为22667 cm、6260 cm2、578.14 cm3,是CK的1.94、1.54、2.43倍.(2)指数施肥和无性系的遗传差异明显影响楸树不同无性系生物量的分配格局.适量施氮明显促进3个楸树无性系生物量的积累,而氮素缺乏或过量均不利于生物量的积累.8月同一无性系的根冠比均随施氮量的增加而降低;同一处理下无性系7080的根冠比高于无性系1-4和015-l.无性系1-4和7080的生物量主要向叶和茎分配,而无性系015-1主要向叶分配.(3)指数施肥在6月和7月主要促进细根根长和根表面积的增加;指数施肥在8月主要促进细根、中等根和粗根体积的急剧增加,分别比7月高达36.88％、124.96％、154.79％.这利于根系在中后期吸收更多养分,从而引起生物量分配格局的变化.(4)生物量参数和根系形态参数关系密切.根生物量、地上生物量、总生物量分别和根长、根表面积、根体积、根平均直径极显著正相关;根冠比和根长、根表面积、根体积、根平均直径极显著负相关;比根长和地上生物量、总生物量显著正相关,和根冠比极显著负相关.     

Birch effects on root fungal colonisation of crowberry are uniform along different environmental gradients

Changes in plant–fungal interactions were often suggested as one of possible mechanisms behind facilitative plant–plant effects in harsh environments. We asked how the mycorrhizal and dark septate endophyte (DSE) colonisations of understorey crowberry (Empetrum nigrum ssp. hermaphroditum) are affected by proximity to mature mountain birch trees (Betula pubescens ssp. czerepanovii) along three abiotic stress gradients (pollution, elevation, seashore) in the Kola peninsula, NW Russia. Stress level affected shoot growth and reproduction in crowberry, but had no effect on root fungal colonisation. In contrast, proximity to a mountain birch tree had no effect on either growth or reproduction of crowberry, but changed all characteristics of root colonisation. The mycorrhizal coil colonisation of crowberry was on average 21% higher near a birch tree, whereas other parameters were higher outside of canopy area (hyaline hyphae: 12%; DSE hyphae: 16%; DSE sclerotia: 42%). Effects of birch tree on root fungal colonisation in crowberry did not depend on the level of abiotic stress. Although we detected a weak positive association between growth of crowberry and its mycorrhizal coil colonisation, we conclude that mycorrhizal and DSE colonisations of crowberry are primarily affected by the abiotic environment. None of the detected patterns was consistent with the patterns expected from the theories concerning stress effects on plant–plant interactions.     

Early changes in root characteristics of maize (Zea mays) following seed inoculation with the PGPR Azospirillum lipoferum CRT1

The effect of direct inoculation of seeds with the plant growth promoting rhizobacteria (PGPR) Azospirillum lipoferum CRT1 was assessed on maize (Zea mays) grown for 35 days after sowing (d.a.s.) in controlled conditions (greenhouse) in a luvisol soil from south-eastern France. WhinRhizo^® software was used to describe the following changes in the root system morphology for each plant: distribution and average root diameter, root surface and the number of tips. The stress at breakage and stiffness of the roots in tension were also determined. Evaluation of biochemical components of roots was achieved by direct Attenuated Total Reflectance (or reflection) (ATR)-Fourier transform infrared (FTIR) on root section. Inoculated roots exhibited significantly larger numbers of tips and extending surface to rhizosphere when compared to controls. Measured mechanical parameters of inoculated roots showed a slight increase in rupture stress up to the largest diameter (1.2 mm) when compared to controls. Stiffness (Young’s modulus) values were nearly constant for inoculated plants with higher values than for non-inoculated plants at day 26 and day 35. Using Principal Components Analysis of ATR-FTIR profiles, the polysaccharide enrichment of inoculated roots compared to controls was found at day 35. Noticeable absorbance at wavenumber specific to aromatic ether (lignin) was observed in control plants. All these data had a pattern of immature root properties, when maize was inoculated with Azospirillum lipoferum CRT1. Observed modifications of root development are possibly conducive to unseen beneficial effects, like water retention, resistance to mechanical stress, or root litter quality. Studies on more mature plants are required to assess if the differences between inoculated and control plants would persist or become accentuated with time until harvest.     

Contribution of an arbuscular mycorrhizal fungus to the uptake of cadmium and nickel in bean and maize plants

Two experiments were carried out in pots with three compartments, a central one for root and hyphal growth and two outer ones which were accessible only for hyphae of the arbuscular mycorrhizal fungus, Glomus mosseae ([Nicol. and Gerd.] Gerdemann and Trappe). In the first experiment, mycorrhizal and nonmycorrhizal bean (Phaseolus vulgaris L.) plants were grown in two soils with high geogenic cadmium (Cd) or nickel (Ni) contents. In the second experiment, mycorrhizal and nonmycorrhizal maize (Zea mays L.) or bean plants were grown in a non-contaminated soil in the central compartment, and either the Cd- or Ni-rich soil in the outer compartments. In additional pots, mycorrhizal plants were grown without hyphal access to the outer compartments. Root and shoot dry weight was not influenced by mycorrhizal inoculation, but plant uptake of metals was significantly different between mycorrhizal and nonmycorrhizal plants. In the first experiment, the contribution of mycorrhizal fungi to plant uptake accounted for up to 37% of the total Cd uptake by bean plants, for up to 33% of the total copper (Cu) uptake and up to 44% of the total zinc (Zn) uptake. In contrast, Ni uptake in shoots and roots was not increased by mycorrhizal inoculation. In the second experiment, up to 24% of the total Cd uptake and also up to 24% of the total Cu uptake by bean could be attributed to mycorrhizal colonisation and delivery by hyphae from the outer compartments. In maize, the mycorrhizal colonisation and delivery by hyphae accounted for up to 41% of the total Cd uptake and 19% of the total Cu uptake. Again, mycorrhizal colonisation did not contribute to Ni uptake by bean or maize. The results demonstrate that the arbuscular mycorrhizal fungus contributed substantially not only to Cu and Zn uptake, but also to uptake of Cd (but not Ni) by plants from soils rich in these metal cations. Deceased 21 September 1996 Deceased 21 September 1996