We investigated interactions between the effects of elevated atmospheric carbon dioxide concentrations ([CO2]) and soil water availability on root biomass, root length and nutrient uptake by spring wheat (Triticum aestivum cv. Tonic). We grew plants at 350 and 700 µmol mol−1 CO2 and with frequent and infrequent watering (‘wet’ and ‘dry’ treatments, respectively). Water use per plant was 1·25 times greater at 350 than at 700 µmol CO2 mol−1, and 1·4 times greater in the ‘wet’ than in the ‘dry’ treatment. Root biomass increased with [CO2] and with watering frequency. Elevated [CO2] changed the vertical distribution of the roots, with a greater stimulation of root growth in the top layers of the soil. These data were confirmed by the video data of root lengths in the ‘dry’ treatment, which showed a delayed root development at depth under elevated [CO2]. The apparent amount of N mineralized appeared to be equal for all treatments. Nutrient uptake was affected by [CO2] and by watering frequency, and there were interactions between these treatments. These interactions were different for N, K and P, which appeared to be related to differences in nutrient availability and mobility in the soil. Moreover, these interactions changed with time as the root system became larger with [CO2] and with watering frequency, and as fluctuations in soil moisture contents increased. Elevated [CO2] affected nutrient uptake in contrasting ways. Potassium uptake appeared to be reduced by the smaller mass flow of water reaching the root surface. However, this might be countered with time by the greater root biomass at elevated [CO2], by the greater soil moisture contents at elevated [CO2], enabling faster diffusion, or both. Phosphorus uptake appeared to be increased by the greater root biomass at elevated [CO2]. We conclude that plant nutrient uptake at elevated [CO2] is affected by interactions with water availability, though differences between nutrients preclude generalizations of the response.

Unifoliated plants of Lolium temulentum L. cv. Ceres, a qualitative long-day grass, were induced to flower by one 24-h long day (LD) or by one 8-h short day (SD) advanced by 12 h in the normal regime, so-called ‘displaced short day’ (DSD). Standard light for SD and DSD was a mixture of fluorescence and incandescence at 400 μmol m−2 s−1 whereas the extension period of the 24-h LD was solely incandescence at 10–15 μmol m−2 s−1. The DSD system was first characterized by the timings of floral induction, stimulus translocation and apical development. Carbohydrates in the blade tissues and in leaf exudate were analysed comparatively in vegetative and induced plants.

Fructans were not detected in the leaf tissues whereas sucrose and starch were found to be present in similar amounts. In SD, their contents exhibited a diurnal fluctuation and were not in large excess. The common change observed during the two inductive treatments was that starch remained at a high level during the LD extension, even though the lighting was unsuitable for photosynthesis, and increased transiently in DSD.

Sucrose was the major sugar contained in the leaf exudate. Its content increased when flowering was induced, but not at the same time in the two systems. In LD, sucrose exudation rose when plants were returned to standard light after the inductive cycle, i.e. after the LD stimulus had left the leaf blade. By contrast, during the DSD, sucrose was transported at the same time as the floral stimulus. Results are discussed together with the methods used to time stimulus translocation and their implications.

Topology is an important component of the architecture of whole root systems. Unfortunately, most commonly applied indices used for characterizing topology are poorly correlated with one another and thus reflect different aspects of topology. In order to understand better how different methods of characterizing topology vary, this paper presents an exploration of several different methods for assigning order within branched root systems on the basis of (a) developmental (centrifugal) vs. functional (centripetal) ordering sequences and (b) whether orders are assigned to individual links or groups of adjacent links (segments). For each ordering system, patterns of scaling in relation to various aspects of link and segment size are explored using regression analyses. Segment-based ordering systems resulted in better fits for simple scaling relationships with size, but these patterns varied between developmental vs. functional ordering as well as the different size metrics examined. The functional (centripetal), link-based ordering system showed complex, non-linear scaling in relation to numbers of links per order. Using a simple simulation model of root growth, it is demonstrated that this method of characterizing root topology in relation to root size might be a more powerful tool for characterizing root system architecture than in the use of simple, single-index characterizations of topology.

The genus Phillyrea includes woody shrub species of Mediterranean maquis which can be found occasionally in saline soils or areas exposed to salt aerosols. To test salinity tolerance in Phillyrea latifolia L., plants were grown in 1-l containers and exposed to different levels of salinity in a glasshouse over two growing seasons. Plants survived exposure to NaCl concentrations of up to 500 mM NaCl for 4 months. Analysis of the growth response to increasing salinity showed that shoot elongation was inhibited by 50% at 123 and 135 mM external NaCl after 31 and 123 d of salt treatment, respectively. Growth parameters were completely inhibited by treatment with 300 mM external NaCl for 64 d. High salt tolerance in Phillyrea plants was the result of both exclusion and secretion mechanisms. Secretion of ions occurred via salt glands present mainly on the abaxial surface of the leaf. Salt glands occurred alone or in pairs and were typically formed by a highly vacuolated collecting cell, a stalk cell and a group of 10–16 secretory cells. The mean diameter of the glands was 54 μm and the average density was 6·1 mM−2 (abaxial side). Peaks of Cl, K, Ca, Na, Si, Mg, Fe and Cu were detected in salt crystals near glands by X-ray microprobe analysis. This is the first report of salt glands in the Oleaceae family and of their role in salinity tolerance in Phillyrea species.

The effects of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolium perenne L. cv. Parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at two levels of nitrogen (N) supply (no additional N and 200 kg N ha−1) and at season-long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations, in open-top chambers. Stands were cut four times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measured. In addition, plant height of both species at harvest dates and during several regrowth periods was monitored.

Results indicate that both species made demand on different resources and profited from growth in a mixed sward. CO2-related yield increase amounted to 16–42% for white clover whereas the effect of high CO2 on ryegrass yield ranged between −33% and +9% depending on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was significantly enhanced by CO2 enrichment at many harvests in both N supply treatments. Without additional N supply, shoot competition for light was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petioles grew longer and ryegrass was shorter at elevated CO2. With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. Since clover and total yield were increased by CO2 enrichment, nutrient requirements were also increased and potassium deficiency and increased intraspecific competition of clover for K was observed in the mixtures under elevated CO2 which had the highest nutrient withdrawal. Although white clover profited much more from CO2 enrichment in both N fertilization treatments, the suppression of ryegrass in mixed swards could only be observed under low N conditions.

Generally, the effect of N fertilization on competitive interference between both species was much greater than the effect of CO2 enrichment and it is suggested that the effect of elevated CO2 on the balance of species and the outcome of competition in a grass/clover sward is mainly dependent on the N status.

The possible involvement of polyamines in the tobacco mosaic virus (TMV)-induced hypersensitive reaction (HR) in Nicotiana tabacum (L.) cv. Samsun NN, which bears the N resistance gene, was investigated. Concentrations of free and conjugated polyamines, as well as the activities of their biosynthetic enzymes ornithine decarboxylase (ODC) and arginine decarboxylase (ADC), were analysed in the necrotic area (I, internal zone) and in the two concentric zones surrounding it (M, middle zone; E, external zone) during the progression of the HR (1, 3 and 5 d from TMV inoculation). Results were compared with those obtained in control plants (mock-inoculated) and with the pattern in susceptible TMV-infected tobacco plants.

In the HR, concentration increased towards zone I for free putrescine and spermidine. Highest concentrations in zones M and I occurred on day 3. Conjugated polyamines similarly showed an increasing concentration gradient towards zone I, with maximum accumulation on day 5. ODC and ADC activities also showed an increasing gradient towards zone I that could be related to the increase in free and conjugated polyamines. By contrast, in control plants concentrations of free and conjugated polyamines decreased from day 1 to day 5, ODC activity increased slightly, whereas ADC activity did not show significant changes. In the TMV-infected susceptible tobacco plants, polyamines tended to remain in the free state instead of being conjugated as infection progressed. These results suggest that polyamines could play a role in mechanisms of resistance to biotic stress.

Traits associated with leaf energy balance are especially important for desert plants because decoupling leaf and ambient temperatures can be critical for maximizing productivity and survival in these hot, dry regions. Deserts are also one of the most climatically unpredictable and heterogeneous biomes; thus, variation of energy balance characters due either to plasticity or genetic differentiation might also be crucial to the success of desert plant species. In a common garden environment we examined variation in the traits associated with energy balance and productivity in Encelia farinosa A. Gray (brittlebush) plants. Comparing two populations from contrasting rainfall and drought climates, we found that plants from the wetter site (Superior, Arizona) always maintained higher leaf absorptances than plants from the more xeric region (Oatman, Arizona) when at similar water potentials. Superior plants also increased stomatal conductance and photosynthesis in response to mid-spring rainfall, whereas Oatman plants did not. Oatman plants, however, tended to have greater leaf areas and continuous spring growth, which made them larger than Superior plants, yet both populations produced the same number of flower heads. The differences for these traits, and the associations among them, agree with predictions based on the contrasting drought and rainfall environments of these two populations. Our results suggest that the differences might represent alternative suites of characters of selective importance for maximizing carbon gain over the climatically variable range of this widespread species. Furthermore, these differences, detected in common environment conditions, might have a genetic basis, which might contribute to a greater potential for local adaptation in this species.

Fructan: fructan fructosyltransferase (FFT) activity was purified about 300-fold from leaves of Lolium rigidum Gaudin by a combination of affinity chromatography, gel filtration, anion exchange and isoelectric focusing. The FFT activity was free of sucrose: sucrose fructosyltransferase and invertase activities. It had an apparent pI of 4·7 as determined by isoelectric focusing, and a molecular mass of about 50000 (gel filtration). The FFT activity utilized the trisaccharides 1-kestose and 6G-kestose as sole substrates, but was not able to use 6-kestose as sole substrate. The FFT activity was not saturated when assayed at concentrations of 1-kestose, 6G-kestose or (1,1)-kestotetraose of up to 400 mM. The rate of reaction of the FFT activity was most rapid when assayed with 1-kestose and was less rapid when assayed with 6G-kestose, (1,1)-kestotetraose or (1,1,1)-kestopentaose. The FFT activity when assayed at a relatively high concentration of enzyme activity (approximately equivalent to about half the activity in crude extracts per gram fresh mass) did not synthesize fructan of degree of polymerization > 6, even during extended assays of up to 10 h. When assayed with a combination of 1-kestose and uniformly labelled [14C]sucrose as substrates, the major reaction was the transfer of a fructosyl residue from 1-kestose to sucrose resulting in the re-synthesis of 1-kestose. Tetrasaccharide and 6G-kestose were also synthesized. When assayed with 6G-kestose and [14C]sucrose as substrates, the major reaction of the FFT activity was the synthesis of tetrasaccharide. However, some synthesis of 1-kestose and re-synthesis of 6G-kestose also occurred. When 6G-kestose was the sole substrate for the FFT activity, synthesis of tetrasaccharide was 2·7 to 3·4-fold slower than when 1-kestose was used as the sole substrate. Owing to differences in the fructan [ratio ] sucrose fructosyltransferase activity of the FFT with each of the trisaccharides, net synthesis of tetrasaccharide by the FFT was altered significantly in the presence of sucrose. The magnitude of this effect depended on the concentration of the trisaccharides. In the presence of sucrose, 6G-kestose could be a substrate of equivalent importance to 1-kestose for synthesis of tetrasaccharide.

The products formed by a fructan [ratio ] fructan fructosyltransferase (FFT) activity purified from Lolium rigidum Gaudin were identified after gas chromatography-mass spectrometry of partially methylated alditol acetates, electrospray ionization-mass spectrometry and reversed-phase high-performance liquid chromatography. The FFT activity synthesized oligofructans up to degree of polymerization (DP) 6, but did not synthesize fructans of DP > 6 even when assayed with (1,1,1)-kestopentaose for up to 10 h. The FFT activity when assayed with 1-kestose or 6G-kestose synthesized fructan with fructosyl residues almost exclusively linked by β-2,1-glycosidic linkages. When assayed with 1-kestose, the FFT activity synthesized tetrasaccharides and pentasaccharides with an internal glucosyl residue. The predominant tetrasaccharide was (1&6G)-kestotetraose and the predominant pentasaccharide was (1&6G,1)-kestopentaose. By comparison, tetrasaccharides and pentasaccharides extracted from L. rigidum also contained predominantly β-2,1-glycosidic linked fructans with an internal glucosyl residue. The only exception was that one of the pentasaccharides contained β-2,1- and β-2,6-glycosidic linked fructosyl residues. This pentasaccharide was not synthesized by the FFT activity. The role of this FFT activity in formation of oligofructans in L. rigidum is discussed.

The potential to improve the salt tolerance of white clover (Trifolium repens L.) was evaluated in populations developed by selecting plants within the cv. Haifa which had high and low concentrations of Cl− in the shoots. Under saline conditions (40 mm NaCl), the low-Cl populations consistently maintained lower concentrations of both Na and Cl in all plant parts and produced more dry matter than the original parent cultivar (Haifa), or the high-Cl populations. Under non-saline conditions, there were no differences between populations for these characters. In young seedlings, concentrations of Cl− in the shoots of the low-Cl and high-Cl populations started to diverge after 4 d exposure to saline conditions and there were significant differences between populations after 6 d growth at 40 mm NaCl. Results using 36Cl suggested that the salt-tolerant low Cl population was better able to retain 36Cl in the roots and to limit its translocation to the leaves and petioles than the high-Cl population. Realized heritability values for shoot Cl− concentration were found to be moderate in the first cycle of selection (0·24 and 0·37 for high and low Cl− concentrations respectively), but were substantially lower (0·10 and 0·09 respectively) in the second selection cycle. We propose that it is possible to increase levels of salt tolerance in white clover by selecting for low shoot Cl− concentrations under saline conditions and that this criterion could be used at very early stages of exposure to NaCl (i.e. day 4 or 6).

Pathozone behaviour of soil-borne plant pathogenic fungi is characterized by curves for the change in probability of infection with distance of inoculum from a host. We identify three major components that give rise to the pathozone profile for infection efficiency: the germinability of inoculum, given that it occurs in the pathozone (P1), the growth of the resulting fungal colony outwards to make contact with the host (P2), and the infectivity of mycelium once contact is made (P3). The probability of infection (P) is then given by the product, P1 × P2 × P3. Using Raphanus sativus and two contrasting types of inoculum of Rhizoctonia solani as a model experimental system, we measured each of the three components by quantifying germinability, colony architecture (to determine the chance of contact by one or more hyphae) and the change in susceptibility over time as a measure of infectivity as mycelium arrives from different distances away. The germinability of inoculum is uniform across the pathozone whereas the probability of contact declines with distance, and the net effect of host susceptibility and infectivity increases. The characteristics of these components result in pathozone profiles that vary in shape. Infection efficiency can decline in an exponential or sigmoidal fashion with increasing distance from the host or follow a curve that rises close to the host and then falls asymptotically to zero with increasing distance. Colony architecture was summarized by the distribution of the furthest extent of hyphal growth amongst colonies growing out from single inoculum units (described, because of its asymmetrical pattern, by a gamma distribution) and by the radial density of hyphae on concentric circles at different distances from the centre of the colony (described by a negative binomial distribution with parameters changing with distance).

The mechanistic model for the components of pathozone behaviour is tested by comparing the magnitude and shape of pathozone profiles predicted by the model with independent estimates for P obtained by placing inoculum at fixed distances from the host, and measuring the proportion of successful infections. The shape depends on the relative magnitudes and change with distance of the three components, P1, P2 and P3, which differed between the two types of inoculum. The profiles could be reproduced accurately when the probability of contact was based on the distribution and density of hyphae reaching the host rather than on the furthest extent of hyphal growth amongst colonies. The model is used to analyse the effects of replication and stochastic variability in the components of pathozone behaviour on the comparison of treatments for disease control.

This study investigated the mechanisms which control the partitioning between roots and shoots in plants subjected to changes in environment. Two types of analyses were used: firstly, an examination of the cost and revenue associated with investment in different plant parts, and secondly, a test of the principle of functional equilibrium between roots and shoots, i.e. whether root dry matter × root specific activity balances shoot dry matter × shoot specific activity. Measurements were made on individual plants of Lolium perenne in sunlit controlled environments, grown from germination to canopy closure under optimal nitrogen supply. At the final harvest, increased air temperature (+4 °C above ambient) reduced whole-plant dry matter by 12% relative to the control, whereas elevated CO2 mole fraction (700 μmol mol−1) led to a 38% gain. The combined treatment yielded an intermediate result (+19%). Plants grown at +4 °C maintained balanced activity between roots and shoots throughout the experimental period, irrespective of CO2 concentration. This required enhanced allocation to roots in young plants to compensate for a strong negative effect of higher temperature on root specific activity, which suggests that plants conserve balanced activity by adjusting dry matter partitioning. The extra cost involved with the adjustment at +4 °C significantly enhanced the cost[ratio ]revenue ratio of plant investment. In ambient temperature, the balance between roots and shoots departed from equilibrium, slightly at ambient but substantially at elevated CO2: the plants accumulated excess carbon relative to nitrogen, and this imbalance increased with plant age. At elevated CO2, the cost[ratio ]revenue ratio increased in young plants but this was later reversed owing to loss of root specific activity, which explains the gradually declining CO2 stimulation with time. The strategies in equilibrating root and shoot functioning observed in the different treatments are discussed in the light of whole plant performance.

Plants known as hyperaccumulators take up and sequester high concentrations of potentially toxic elements from metalliferous soils. We tested the hypothesis that zinc hyperaccumulation benefits plants by deterring herbivory. In laboratory feeding trials, three species of herbivores were allowed to choose between Thlaspi caerulescens (Brassicaceae) plants grown in low-Zn and Zn-amended culture solution. Locusts (Schistocerca gregaria), slugs (Deroceras caruanae), and caterpillars (Pieris brassicae) all showed significant preferences for plants with lower foliar Zn concentrations. Such differential feeding could result in selection pressures favouring the evolution of hyperaccumulation. The findings are also relevant to current proposals to exploit hyperaccumulation as a means of remediating metal-contaminated soils.

Leaves of Lolium temulentum L. contain both low and high pI acid invertases. Immunoblot analysis of a highly purified preparation of these forms suggested that they both possess a subunit molecular weight of 68 kDa. Protoplasts and their derived vacuoles were isolated from leaf blades and contained sufficient acid invertase activity to account for all the activity found in the soluble fraction of crude homogenates of leaf blades. Alkaline invertase was present in the basal region of leaves and, unlike acid invertase, did not bind to Con A-Sepharose, suggesting that the acid invertase was a glycoprotein and that the alkaline invertase was not. Fructose inhibited both acid and alkaline invertases. The hypothesis is discussed that activity in vivo could be modulated by the concentration of free fructose.

To assess adverse effects of ambient ozone on injury and yield, EDU (ethylenediurea) and non-EDU-treated plants of bean (Phaseolus vulgaris L. cv. Lit) were exposed to ambient air at four rural sites in the Netherlands in 1994. After 6 wk of exposure, the proportion of leaves injured in non-EDU-treated plants was higher than that in plants treated with the antioxidant. A maximal degree of 35% injury was observed. The highest ozone levels accumulated at each site for three consecutive days before injury clearly exceeded the proposed short-term critical level for injury development. Both injury in untreated plants and the protective effect of EDU differed between sites and were not related to the measured ozone levels. EDU increased the d. wt of dry (mature) pods after 11 wk of exposure but not of green (marketable) pods after 6 wk. The effect of EDU in enhancing dry pod yield did not differ between sites and was 20% on average. The proportional yield increases in EDU-treated plants compared with those of non-EDU-treated plants at the sites were not correlated with the measured ozone levels known to adversely affect bean yield. The available evidence, however, suggests that ambient ozone was involved in the observed yield increase by EDU. When the dry pods were harvested, EDU-treated plants had more leaves than non-EDU-treated ones. The effect of EDU in delaying senescence appears to be an important factor to consider when attempting to evaluate the effect of ambient ozone on pod weight in beans using the EDU approach.

Spring ephemerals have evolved specific growth strategies that take advantage of the high photon fluence rates of early spring. These strategies involve a sequential growth of different organs. Erythronium americanum (Ker-Gawl), a common spring ephemeral of northern maple forests, produces its roots in the autumn, although stems and leaves develop in the spring. Mycorrhizal infection of the root system occurs very rapidly and intensively. The fungi thus depend on carbohydrate reserves accumulated in the corm (underground reserve organ) for their growth and development through the winter. We found that the presence of mycorrhizas drastically decreases root growth during the cold period and is more costly of carbohydrate reserves than root growth alone. However, during the spring, the presence of mycorrhizas fully benefits the plant: we measured an annual growth rate of mycorrhizal plants twice that of fungicide-treated plants which were non-mycorrhizal. We suspect that E. americanum is highly susceptible to water stress during the growing season and might rely on its mycorrhizas for water supply to a greater extent than for nutrient supply. Nutrient uptake might occur mainly in the autumn when arbuscules are at their most abundant.

In Plantago lanceolata L. the effect of Cu(II) additions to the nutrient solution on root-associated Fe(III) reductase was studied in a factorial design with different Cu(II) and Fe(III) concentrations. Iron starvation resulted in approx. an eightfold increase in root Fe reduction at the level of intact plants and twofold enhancement in the specific activity of both NADH-linked FeEDTA reductase and H+-ATPase in isolated root plasma membrane vesicles. In plants exposed to low (0·3–0·7 μM) Cu and suboptimal Fe levels, reduction activity at the root surface was further increased and associated with more severe interveinal chlorosis than plants grown in Cu-free medium. In Fe-sufficient plants, withholding Cu over a prolonged period slightly enhanced the reduction activity.

Addition of high (5 μM) Cu concentrations to Fe-free medium inhibited the induction of the physiological responses by Fe-deficiency stress. In plants without Fe supply but with adequate Cu supply, short-term application of 5 μM CuSO4 completely inhibited the reduction activity. Neither incubation of the plasma membrane vesicles before measurement nor incubation of intact plants with Cu before isolation caused a significant decrease in reductase activity. The results are interpreted as indicating different mechanisms underlying Cu-induced alterations in iron nutrition.

The fructan-β-fructosidase activity (1-FEH; EC 3.2.1.80) that degrades inulin in tubers of Helianthus tuberosus L. appears to be developmentally regulated; it was low in growing tubers but increased during dormancy and sprouting. In spite of relatively high 1-FEH activity in vitro, fructose concentration was very low in developing and dormant tubers and increased markedly only during sprouting. A fructan-β-fructosidase from such sprouting tubers was purified 41-fold to a single protein band on one-dimensional sodium dodecylsulphate–polyacrylamide gels. The purification procedure included ammonium sulphate precipitation, lectin-affinity chromatography on concanavalin A, anion-exchange and cation-exchange chromatography. The enzyme had an apparent molecular mass of 75000 measured by size-exclusion chromatography, and 79000 measured by one-dimensional sodium dodecylsulphate-polyacrylamide gel electrophoresis. It exhibited a high substrate specificity, hydrolysing terminal β-(2-1)-fructosyl-fructose-linkages in linear and branched fructan oligomers; β-(2-6)-linkages were hardly hydrolysed. Hydrolysis of inulin oligomers followed normal saturation kinetics: Km values for 1,1-kestotetraose and 1,1,1-kestopentaose were 8·3 mM and 12 mM, respectively. Fructosyl residues were hydrolysed from inulin oligomers by a multi-chain mechanism. The fructan-β-fructosidase showed optimal enzyme activity at pH 5·2, and it retained its full activity after pre-incubation for 1 h at up to 40 °C. The release of fructose from 5 mM 1,1-kestotetraose was reduced by 25% when 1-FEH was assayed in the presence of 10 mM sucrose. It is proposed that the inhibition of 1-FEH activity by sucrose is a mechanism for controlling fructan degradation in planta.

The response of epicuticular wax of Scots pine (Pinus sylvestris L.) needles to dry- and wet- deposited sulphur and heavy metals was investigated at six sites located 10–110 km from the Monchegorsk Cu-Ni smelter on the Kola Peninsula, North-West Russia, and in a long-term irrigation experiment where pines were exposed over four growing seasons (1991–1994) to either acid rain treatment at pH 3·1 (H2SO4), metal treatment at pH 5·7 (Cu and Ni) or a combination of these at pH 3·1. Needle wettability exhibited a closer relationship with epistomatal wax tube distribution (WTD) than with chemical composition of epicuticular wax. Water droplet contact angles (DCA) decreased towards the smelter, and significant differences due to site were noted for 26-month-old and 38-month-old needles. Significant differences due to site were determined for secondary alcohols, dehydroabietic acid and hydroxy fatty acids, the proportions of which ranged from 22·5 to 48·9%, 6·2 to 22·4% and 0·6 to 2·6% respectively, depending on site and needle age class. The proportion of dehydroabietic acid increased towards the smelter, but no gradient was observed in the proportion of secondary alcohols or hydroxy fatty acids. No major effect of experimentally applied pollutants on the chemical composition or structure of the epicuticular wax was observed. The effect of treatment on DCA was significant in 1993 and 1994 due to a 6·5–13·2 degree greater wettability of the 37–49-month-old acid-treated needles relative to the irrigated or dry controls. Sulphuric acid at pH 3·1 did not increase needle wettability when combined with copper and nickel sulphate in similar concentrations. These data indicate that S deposition, especially H2SO4, plays a more important role in needle surface deterioration than Cu and Ni. Pollutant-induced changes in epicuticular wax structure and needle wettability mimic natural wax ageing, but at an accelerated rate. Changes in wax chemical composition might also be caused by pollutant-induced metabolic changes in elongating needles.

Arabidopsis thaliana (L.) Heynh. was exposed to various concentrations of SO2 during almost the entire life cycle. No negative effects of SO2 on shoot biomass production were observed. There was a linear relation between the deposition of SO2 and the atmospheric SO2 concentration. Sulphur accumulated substantially in the shoots upon SO2 exposure. SO2 was either oxidized to sulphate or converted into extra organic sulphur compounds in a sulphate to organic sulphur ratio of 3[ratio ]1, independently of the atmospheric SO2 concentration. Exposure to SO2 resulted in an increase in water soluble non-protein sulphydryl content and a slight increase in the amount of glucosinolates, but both of these play a minor role as sinks for the excess sulphur. The ratio of total nitrogen to total sulphur decreased upon SO2 exposure as a result of the increased sulphate content. The organic nitrogen to organic sulphur ratio did not change upon SO2 exposure, indicating no changes in the composition of sulphur-containing compounds.