Resurrection plants are a perennial fascination to botanists. The transformation, within a few hours (or even minutes) of supplying them with water, from a plant that has all the appearances of being dead – dry, brown, crisp and shrivelled – to a plant that is obviously living and functioning – turgid, green, pliable and growing – suggests the miraculous. Studies of the complex processes of restoration and repair have been made on a number of resurrection plants, and at many levels of organization from molecules through membranes, organelles and cells to the whole plant (Gaff, 1989). The woody South African shrub Myrothamnus is the most extreme example of such plants, in that it has the highest level of organization to be repaired. It is transformed from lifeless-looking sticks with a water content below 5% to a flourishing bush in a day after its roots receive water. Two papers in this issue from Ulrich Zimmermann's group in Würzburg concentrate on the restoration of the functioning hydraulic systems of the stems (see pp. 221–238, and 239–255).

Extended areas of new crops to produce not only food, but also energy and materials, was one of the visions when the EU agricultural policy was reformed in 1992. However, this vision remains unfulfilled. The perennial C4 grass Miscanthus, originating from eastern Asia, was one of the crops that caught major interest as a potential biomass crop due to its high productivity even in cool northern European conditions (Beale & Long, 1995). However, even very large initial programmes on Miscanthus were conducted almost exclusively within one genotype, namely the sterile, triploid, interspecific hybrid M. × giganteus, and ran into significant problems of low first winter survival and prohibitive high costs of vegetative establishment. Thus, despite the many encouraging results on Miscanthus productivity (van der Werf et al., 1993), environmental acceptability (Christian & Riche, 1998) and harvest and storage suitability (Venturi et al., 1998), it is clear that the introduction of a new crop into agriculture is not simple, and that basic ecophysiological understanding is important to support commercial exploitation. The results in this issue from Clifton-Brown & Lewandowski (see pp. 287–294) contribute to this vital, basic understanding, revealing that low frost tolerance of M. × giganteus rhizomes is probably the cause of low winter survival in cool parts of Europe, but that within the genus Miscanthus better frost tolerance exists.

Summary 196

I. INTRODUCTION 196

1. The neglected dimension 196

2. Basic concepts 197

(a) The heuristic notion of vessel-tiers 197

(b) Ohm's law 199

(c) Conductances, resistances and resistivities 199

(d) Lumen and pit resistances 199

(e) The importance of conduit radius and length in conductance 199

II. EVOLUTIONARY TRENDS IN CONDUIT DIMENSIONS 199

1. Nature and origin of xylem conduits 199

2. Increasing hydraulic conductance with increasing diameter and length 200

(a) Evolutionary trends in tracheid dimensions 200

(b) Origin of the vessel 200

3. Functional limitations to increasing vessel length 201

(a) Safety versus efficiency 201

(b) Containment of cavitation and embolism 202

III. MAXIMUM XYLEM TRANSPORT IN THE PRESENCE OF CAVITATION 203

1. Cavitation is linked to the driving force for transport 203

2. Transport models and extreme assumptions about conduit length 203

(a) Unitary cavitation response (n = 1) 203

(b) Infinitely partitioned response (n = ∞) 204

(c) ΔP and cavitation containment 204

IV. INCLUDING VESSEL LENGTH IN A TRANSPORT MODEL 205

1. Framing questions of optimal conduit length 205

2. A numeric model for flow through n conduit tiers 205

(a) Model structure 205

(b) Model solution 206

3. Optimization when f(P) is linear 206

(a) Isolating the effects of n on cavitation containment 206

(b) Optimal conduit tier-length distributions (OCLDs) 207

(c) Abrupt changes in conduit length 208

(d) Optimal frequency of end walls: incorporating Rpit 208

4. Optimization when f(P) is curvilinear 210

V. CONDUIT LENGTH IN MODERN TAXA: IMPLICATIONS FOR TRANSPORT 210

1. Limitations to the concept of conduit tiers 210

(a) Vessel ends are randomly distributed 210

(b) Dispersion around mean length within each ‘tier’ 210

2. Is the xylem optimally partitioned? 211

(a) Optimal number of end walls 211

(b) Conduit length distribution along the pathway 211

3. Hydraulic segmentation 212

(a) Segmentation in hydraulic resistance 212

(b) Segmentation in cavitation vulnerability 212

VI. CONCLUSIONS 212

1. Anatomy 212

2. Modelling flow 213

VII. APPENDIX: ANALYTICAL SOLUTIONS AND PROOFS 213

1. Analytic solution for Qmaxwith a single tier 213

2. The general case for n tiers 214

3. Analytic solution for Qmaxwith two tiers 214

4. Matric flux and n = ∞ 215

5. Rpit, variable pathway resistance and OCLD 215

6. Proof of Eqn 15 describing limited cavitation containment 215

Acknowledgements 216

References 216

Vascular plants have shown a strong evolutionary trend towards increasing length in xylem conduits. Increasing conduit length affects water transport in two opposing ways, creating a compromise that should ultimately define an optimal conduit length. The most obvious effect of increased length is to decrease the sequential number of separate conduits needed to traverse the entire pathway, and thereby to reduce the number of wall-crossings and the hydraulic resistance to flow within the xylem. This is an essential evolutionary pressure towards the development of the vessel, a conduit of multicellular origin whose length is not restricted by developmental constraints. The vessel has been an essential component in all plant lineages, achieving transport tissues with very high specific conductivity. A countering effect, however, arises from the partitioning of the cavitation response, a process whereby individual xylem conduits drain of water and lose conducting capacity. Flow in the xylem is down a gradient of negative pressure, which is necessarily most negative in the distal regions (i.e. near the foliage). Cavitation can be caused directly by negative pressures, and results in a total loss of the hydraulic conductance of the individual conduits within which it occurs. If cavitation is triggered by low pressure experienced only at the very distal end of a long conduit, the conduit nevertheless loses its conducting capacity along its entire length. Pathways composed of long conduits will therefore suffer greater total conductance loss for equivalent pressure gradients, because the effects of cavitation are not effectively restricted to the tissue regions within which the cavitation events are generated. By contrast, short conduits can restrict cavitation to distal regions, leaving trunk and root tissues less seriously affected. The increased total conductance loss of a system made entirely of very long conduits translates into a lower maximum rate of water transport in the xylem. The loss in hydraulic capacity associated with failure to partition the flow pathway fully, and locally contain the effects of cavitation, theoretically reaches a maximum of 50% for the extreme case in which a single set of conduits traverses the entire pathway. Shorter conduits confine individual cavitation events to smaller regions and permit the pathway as a whole to have a more gradual conductance loss in conjunction with the pressure gradient. A compromise exists between (1) minimizing total conductance loss from cavitation via fine partitioning of the pathway with many tiers of short conduits, and (2) reducing total wall resistance via coarse partitioning with a few tiers of long conduits. An analysis is presented of the optimal number of end walls (i.e. mean conduit length relative to total pathway length) to maximize transport capacity. The principle of optimal containment of cavitation also predicts that conduits should not be of equal length in all portions of the pathway. The frequency of end walls should rather be proportional to the magnitude of the water-potential gradient at each point, and conduits should be longest in the basal portion (roots) and progressively shortened as they move up the stems to the foliage. These concepts have implications for our understanding of the contrasting xylem anatomies of roots and shoots, as well as the limits to evolution for increased hydraulic conductance per xylem cross-sectional area. They also indicate that to model the hydraulic behaviour of plants accurately it is necessary to know the conduit length distribution in the water flux pathway associated with species-specific xylem anatomy.

The acropetal water refilling kinetics of the dry xylem of branches (up to 80 cm tall) of the resurrection plant Myrothamnus flabellifolia were determined with high temporal resolution by observation of light refraction at the advancing water front and the associated recurving of the folded leaves. To study the effect of gravity on water rise, data were acquired for cut upright, horizontal and inverted branches. Water rise kinetics were also determined with hydrostatic and osmotic pressure as well as at elevated temperatures (up to 100 °C) under laboratory conditions and compared with those obtained with intact (rooted) and cut branches under field conditions. Experiments in which water climbed under its capillary pressure alone, showed that the axial flow occurred only in a very few conducting elements at a much higher rate than in many of the other ones. The onset of transpiration of the unfolded and green leaves did not affect the rise kinetics in the ‘prominent’ conducting elements. Application of pressure apparently increased the number of elements making a major contribution to axial xylem flow. Analysis of these data in terms of capillary-pressure-driven water ascent in leaky capillaries demonstrated that root pressure, not capillary pressure, is the dominant force for rehydration of rooted, dry plants. The main reasons for the failure of capillary forces in xylem refilling were the small, rate-limiting effective radii of the conducting elements for axial water ascent (c. 1 μm compared with radii of the vessels and tracheids of c. 18 μm and 3 μm, respectively) and the very poor wetting of the dry walls. The contact (wetting) angles were of the order of 80 ° and decreased on root or externally applied hydrostatic pressure. This supported our previous assumption that the inner walls of the dry conducting elements are covered with a lipid layer that is removed or disintegrates upon wetting. Consistent with this, potassium chloride and, particularly, sugars exerted an osmotic pressure effect on axial water climbing (reflection coefficients > zero, but small). Although the osmotically active solutes apparently suppressed radial water spread through the tissue to the leaf cells, they reduced the axial water ascent rather than accelerating it as predicted by the theory of capillary-driven water rise in leaky capillaries. Killing cells by heat treatment and removal of the bark, phelloderm, cortex and phloem also resulted in a reduction of the axial rise rate and final height. These observations demonstrated that radial water movement driven by the developing osmotic and turgor pressure in the living cells was important for the removal of the lipid layer from the walls of those conducting elements that were primarily not involved in water rise. There is some evidence from field measurements of the axial temperature gradients along rooted branches that interfacial (Marangoni) streaming facilitated lipid removal (under formation of vesicle-like structures and lipid bodies) upon wetting.

The axial and radial refilling with water of cut dry branches (up to 80 cm tall) of the resurrection plant Myrothamnus flabellifolia was studied in both acro- and basipetal directions by using 1H-NMR imaging. NMR measurements showed that the conducting elements were not filled simultaneously. Axial water ascent occurred initially only in a cluster of a very few conducting elements. Refilling of the other conducting elements and of the living cells was mainly achieved by radial extraction of water from these initial conducting elements. With time, xylem elements in a few further regions were apparently refilled axially. Radial water spread through the tissue occurred almost linearly with time, but much faster in the acropetal than in the basipetal direction. Application of hydrostatic pressure (up to 16 kPa) produced similar temporal and spatial radial refilling patterns, except that more conducting elements were refilled axially during the first phase of water rise. The addition of raffinose to the water considerably reduced axial and radial spreading rates. The polarity of water climbing was supported by measurements of the water rise in dry branches using the ‘light refraction’ (and, sometimes, the ‘leaf recurving’) method. Basipetal refilling of the xylem conduit exhibited biphasic kinetics; the final rise height did not exceed 20–30 cm. Three-cm-long branch pieces also showed a directionality of water climbing, ruling out the possibility that changes in the conducting area from the base to the apex of the branches were responsible for this effect. The polarity of water ascent was independent of gravity and also did not change when the ambient temperature was raised to c. 40 °C. At external pressures of 50–100 kPa the polarity disappeared, with basipetal and acropetal refill times of the xylem conduit of tall branches becoming comparable. Refilling of branches dried horizontally (with a clinostat) or inverted (in the direction of gravity) showed a pronounced reduction of the acropetal water rise to or below basipetal water climbing level (which was unaffected by this treatment). Unlike water, benzene and acetone climbing showed no polarity. In the case of benzene, the rise kinetics (including the final heights) were comparable with those measured acropetally for water, whereas with acetone the rise height was less. Transmission electron microscopy of dry branches demonstrated that the inner surfaces of the conducting tracheids and vessels were lined with a continuous osmiophilic (lipid) layer, as postulated by the kinetic analysis and light microscopy studies. The thickness of the layer varied between 20 and 80 nm. The parenchymal and intervessel pits as well as numerous tracheid corners contained opaque inclusions, presumably also consisting of lipids. Electron microscopy of rehydrated plants showed that the lipid layer was either thinned or had disintegrated and that numerous vesicle-like structures and lipid bodies were formed (together with various intermediate structural elements). These, many other data and the physical–chemical literature imply that several (radial) driving forces (such as capillary condensation, Marangoni forces, capillary, osmotic and turgor pressure forces) operate when a few conducting elements become axially refilled with water. These forces apparently lead to an avalanche-like radial refilling of most of the conducting elements and living cells, and thus to the removal of the ‘internal cuticle’ and of the hydrophobic inclusions in the pits. The polarity of water movement presumably results from high resistances in the basipetal direction, which are created by local gradients in the thickness of the lipid film as a result of draining under gravity in response to drought. There are striking similarities in morphology and function between the xylem-lining lipid film and the lung surfactant film lining the pulmonary air spaces of mammals.

The gradients in photosynthetic and carbohydrate metabolism which persist within the fully expanded second leaf of barley (Hordeum vulgare) were examined. Although all regions of the leaf blade were green and photosynthetically active, the basal 5 cm, representing approximately 20% of the leaf area, retained some characteristics of sink tissue. The leaf blade distal from the leaf sheath exhibited characteristics typical of source tissue; the activities of sucrolytic enzymes (invertase and sucrose synthase) were relatively low, whilst that of sucrose phosphate synthase was high. These regions of the leaf accumulated sucrose throughout the photoperiod and starch only in the second half of the photoperiod whilst hexose sugars remained low. By contrast the leaf blade proximal to the leaf sheath retained relatively high activities of sucrolytic enzymes (especially soluble, acid invertase) whilst sucrose phosphate synthase activity was low. Glucose, as well as sucrose, accumulated throughout the photoperiod. Although starch accumulated in the second half of the photoperiod, a basal level of starch was present throughout the photoperiod, by contrast with the rest of the leaf. The 14CO2 feeding experiments indicated that a constant amount of photosynthate was partitioned towards starch in this region of the leaf irrespective of irradiance. These findings are interpreted as the base of the leaf blade acting as a localized sink for carbohydrate as a result of sucrose hydrolysis by acid invertase.

Because recalcitrant seeds are not desiccation-tolerant they must be stored moist. Their limited storage potential presents significant practical problems, but the cause of viability loss is not known. It has been suggested that a stress-induced metabolic imbalance can develop during storage that results in free-radical generation and consequent damage. To investigate this hypothesis, the presence of a stable free radical, lipid peroxidation and representative enzymatic and nonenzymatic protection mechanisms against oxidative attack were monitored in nondormant recalcitrant seeds during moist storage. A comparison was made between seeds of a short-lived sub-tropical species (Avicennia marina) and two longer-lived temperate species (Quercus robur and Castanea sativa). As a test of the hypothesis, seeds of both temperate species were held under conditions of elevated temperature and oxygen concentration to develop different rates of respiration during storage. The number of normal seedlings produced from seeds of the two temperate species declined during storage, but viability remained high, so effects of ageing were not confounded with an increasing proportion of dead seeds in the population. Under these conditions, lipid peroxidation changed little over the storage period, although there was evidence of accumulation of a stable free radical in Q. robur axes. However, this response was not affected by storage conditions that elevated respiration rates. In the shorter-lived A. marina seeds viability declined soon after the start of storage, but the significant increase in free radicals shown by EPR measurement was only evident when an increasing percentage of the seed population was no longer viable. Changes in the activity of scavenging enzymes and the concentration of antioxidants were time-dependent and not related to respiration rates. Therefore, in the present work, no consistent evidence was found to show that metabolism-induced free-radical activity was a significant contributing factor to pre-mortem deterioration in moist-stored recalcitrant seeds.

The ability of seeds to germinate and establish seedlings in a predictable manner under a range of conditions has a direct contribution to the economic success of commercial crops, and should therefore be considered in crop improvement. We measured traits associated with seed vigour and pre-emergence seedling growth in a segregating population of 105 doubled haploid Brassica oleracea lines. The germination traits measured were: mean germination times for unstressed germination; germination under water stress or germination after a heat treatment; and conductivity of seed leachate. The seedling growth traits measured were: seed weight; seedling growth rate; and seedling size at the end of the exponential growth phase. There were some correlations, notably among germination traits, and between seed weight and pre-emergence seedling growth. Heritability of the various traits was typically in the 10–15% range, with heritability of conductivity and mean germination time under water stress 25 and 24% respectively. Collectively the results indicate that germination and pre-emergence seedling growth are under separate genetic control. Quantitative trait loci analyses were carried out on all measurements and revealed significant loci on linkage groups O1, O3, O6, O7 and O9. We suggest that genes at these loci are important in determining predictable seed germination and seedling establishment in practice.

Miscanthus, a perennial rhizomatous C4 grass, is a potential biomass crop in Europe, mainly because of its high yield potential and low demand for inputs. However, until recently only a single clone, M. × giganteus, was available for the extensive field trials performed across Europe and this showed poor overwintering in the first year after planting at some locations in Northern Europe. Therefore, field trials with five Miscanthus genotypes, including two acquisitions of Miscanthus × giganteus, one of M. sacchariflorus and two hybrids of M. sinensis were planted in early summer 1997 at four sites, in Sweden, Denmark, England and Germany. The field trials showed that better overwintering of newly established plants at a site was not apparently connected with size or early senescence. An artificial freezing test with rhizomes removed from the field in January 1998 showed that the lethal temperature at which 50% were killed (LT50) for M. × giganteus and M. sacchariflorus genotypes was −3.4 °C. However, LT50 in one of the M. sinensis hybrid genotypes tested was −6.5 °C and this genotype had the highest survival rates in the field in Sweden and Denmark. Although the carbohydrate content of rhizomes, osmotic potential of cell sap and mineral composition were not found to explain differences in frost tolerance adequately, moisture contents correlated with frost hardiness (LT50) in most cases. The results obtained form a basis for identifying suitable Miscanthus genotypes for biomass production in the differing climatic regions of Europe.

The period of active growth for spring ephemeral plants coincides with the period of high light, water and nutrient availability between snow melt and canopy closure in the understorey of deciduous forests in eastern North America. However, low temperatures prevail during this period and might restrict the performance of these plants. Remarkably, this peculiar phenology is extremely rare among annual plants. To understand better the role of light and water availability and of temperature in the phenology of spring ephemeral plants, we investigated the effects of two temperature regimes (low: 16/7 °C and high: 21/14 °C), three water availability levels (saturated, control and drought), and three photosynthetically active photon flux densities: low (85–100 μmol m−2 s−1); intermediate (182–196 μmol m−2 s−1); high (437–454 μmol m−2 s−1) on the growth and reproduction of the annual Floerkea proserpinacoides. Total biomass, total leaf area and flower and seed production increased with increasing temperature, water availability and light intensity. Total leaf area and total biomass were reduced in plants that were stressed under drought. However, at high temperatures, this reduction was less pronounced when droughted plants were partially shaded. At low temperatures, plants began to senesce after approximately 9 wk, whereas at higher temperatures, signs of senescence appeared after only 7 wk of growth. Despite shorter longevity, total biomass was approximately 1.5 times higher in the control water treatment at higher than at lower temperatures as a result of greater above-ground growth, and plants allocated a significantly greater proportion of mass gain to seed production. Although F. proserpinacoides can tolerate low temperatures such as those typical of early spring, higher temperatures such as those of late spring/early summer are more favorable for growth and reproduction as long as water and light are not limiting. Spring ephemeral annuals might be rare because low temperatures reduce growth rate and extend the life cycle. An annual plant might not have time to reproduce before resource availability deteriorates with canopy closure unless reproduction begins early in the life cycle of the species.

The purpose of this study was to describe morph-specific patterns of stigma–anther separation and style curling in the distylous Jasminum fruticans. We also examined whether variation in floral traits is correlated with variation in seed production. Stigma–anther separation is more variable in short-styled plants than in long-styled plants. In all populations studied, some plants bear flowers that lack any stigma–anther separation. These plants have the pollen characteristics (size and number) and compatibility relations of short-styled plants. Comparison with other distylous species illustrates that the variability of stigma–anther separation in short-styled plants is a novel finding for a distylous species. Long-styled plants have greater stigma–anther separation than short-styled plants, styles are often curled and protrude from the corolla, and anthers are placed well within the corolla tube. The frequency of long-styled plants with curled styles and the mean degree of style curling were significantly correlated with style length. Short-styled plants have larger corollas than long-styled plants and never have curled styles. Morph ratios are always 50[ratio ]50 in natural populations. Mean values of each floral trait in the two morphs were significantly correlated among populations. There were no consistent differences in fecundity of the two morphs nor any correlation between floral traits and seed set for each morph in natural populations. We discuss the potential causes and significance of the two morph-specific patterns we describe; reduced stigma–anther separation in short-styled plants and the presence of curled styles in long-styled plants.

A lacustrine sequence from Lake Sedmo Rilsko (altitude 2095 m) in the northwest of Rila Mountain, Bulgaria, was analysed on the basis of 84 pollen spectra and three 14C accelerator mass spectrometry dates. The lower part of the sequence (413–530 cm) corresponds to the Late-glacial. Three phases, two stadial and one interstadial, are characterized by the dominance of mountain–steppe herb vegetation composed of Artemisia, Chenopodiaceae and Poaceae, with single trees of Pinus and shrub land of Juniperus and Ephedra. The identification of pollen grains of Abies, Quercus robur-type, Corylus, Acer, Fagus and other mesophilous trees suggests that they survived the harsh Late-glacial conditions in refuges below an altitude of 1000 m, where moisture was sufficient for their growth. In the early Holocene period, Betula forests at high altitudes and, below them, closed deciduous forests with Quercus, Tilia, Ulmus and Corylus, occurred from 11800 until approx. 6700 cal. BP. The formation of the coniferous belt dominated by Pinus sylvestris, Pinus peuce and Abies alba lasted from between 6700 and 5000 cal. BP. The forest dynamics in the Subboreal and the Subatlantic ended with the invasion of Fagus sylvatica and Picea abies after approx. 4500 and 3300 cal. BP, respectively. Indications of anthropogenic activities, expansion of agriculture in the lowland foothills, and livestock grazing in the mountain meadows and pastures, are clearly evident from the pollen diagram from 2400 cal. BP onwards.

A lectin with hemagglutinating activity has been isolated from an aqueous extract of the symbiotic phenotype of Dictyonema glabratum and its cyanobacterial photobiont Scytonema sp. The purified lectin had a pI of 6.8 and its molecular mass was investigated by electrospray ionization mass spectrometry, gel filtration and SDS-PAGE, which indicated its native conformation as a dimer formed by two identical subunits of 16540 Da. The lectin is a glycoprotein with a low degree of glycosylation, containing galactose, xylose, glucose and mannose as neutral monosaccharides, in addition to glucosamine, which could indicate both N- and O-linkages. Amino acid analysis showed the predominance of nonpolar residues such as phenylalanine. Agglutination of human erythrocytes required divalent cations, which is affected by addition of EDTA. The lectin was more stable at 30 °C or less for at least 1 h and between pH 5.0 and 7.0. Among the various compounds tested for hemagglutination inhibition, N-acetylgalactosamine was the most active. The potential role of this lectin in recognition of the compatible cyanobacterial photobiont is discussed.

Sarcodes sanguinea and Pterospora andromedea (Ericaceae, Monotropoideae) are nonphotosynthetic myco-heterotrophic plants. Recent studies have shown that the roots of the adult plants are always associated with closely related but exclusive sets of Rhizopogon species (Basidiomycota, Boletales) from section Amylopogon. We have isolated Rhizopogon species that were associated with the adult plants and used them to germinate seeds under gnotobiotic conditions. All Rhizopogon species isolated from either plant species were capable of stimulating seed germination in both Sarcodes and Pterospora. Under the primary conditions used, germination varied from 9 to 73% in the case of Sarcodes and 0 to 13% in that of Pterospora. The single Rhizopogon strain that failed to elicit germination in Pterospora under these conditions did stimulate germination under slightly different conditions. By contrast, seeds failed to germinate on all media which lacked these Rhizopogon species, or in the presence of six other genera of basidiomycetes. Seed germination could be stimulated either through cellophane or at the edge of fungal colonies without direct fungus–seed contact. These results suggest that a diffusible or volatile compound that is unique to Rhizopogon stimulates germination of these plant seeds. Seed lots of Sarcodes from two successive years had similar germination levels. Sarcodes seeds that had overwintered under natural conditions were also stimulated to germinate. These results demonstrate the potential for long-term dormancy. We suggest that a combination of dormancy and the use of specific germination cues might increase the opportunities of these plants for recruitment. In addition, the specific germination response explains at least a part of the specialized associations observed in the adult plants. Nevertheless, the seeds respond to a slightly broader range of Rhizopogon species than has been observed to be associated with the adult plants; thus other factors must also be involved with specificity under natural conditions.

Some mycorrhizal plants exhibit greater resistance than nonmycorrhizal plants to aluminium toxicity. This has not yet been shown for banana despite its importance as a cash and food crop in tropical regions, although bananas are sensitive to aluminium stress. We studied the effects of the arbuscular mycorrhizal fungus Glomus intraradices in alleviating aluminium toxicity in the banana cultivar Grande Naine grown in a continuous-nutrient-flow cultivation system using dilute solution. The micropropagated plants, some of which were inoculated with arbuscular mycorrhizal fungus, were grown for 40 d in pots filled with sand, and continuously irrigated with a nutrient solution containing up to 180 μM of aluminium. Water and nutrient uptake were measured once a week for 24 h, and root arbuscular mycorrhizal fungal colonization, biomass production, and mineral content of roots and shoots were measured at harvest. The root arbuscular mycorrhizal fungal colonization was large, and not significantly influenced by aluminium treatment. The effects of aluminium on both mycorrhizal and nonmycorrhizal plants were: decrease in biomass production, water and nutrient uptake, and magnesium content of roots and shoots; greater aluminium content in roots than in shoots; and increase in potassium and phosphorus content, particularly in roots. A significant positive effect of arbuscular mycorrhizal fungi on plant growth was observed with aluminium treatment, and was most pronounced at the highest concentration. The benefits, compared with nonmycorrhizal plants, included: increase in shoot dry weight, uptake of water and of most nutrients, and in calcium, magnesium and phosphorus content, particularly in roots; decrease in aluminium content in root and shoot; and delay in the appearance of aluminium-induced leaf symptoms. These results indicate that arbuscular mycorrhizal fungi could be effective in alleviating aluminium toxicity to banana plants.