A split-root growth system was used to study photosynthate partitioning to developing nodules and roots of soybean (Glycine max L., Merr.). Opposite sides of the root systems were inoculated with Bradyrhizobium japonicum at 8 and 12 d after planting (early/delayed inoculation treatment) or, alternatively, only one side was inoculated 8 d after planting (early/uninoculated treatment). Plants were incubated with 14CO2 at 24-h intervals from early inoculation until the onset of N2 fixation (acetylene reduction). After staining with Eriochrome black, root and nodule meristematic structures were excised under a dissecting microscope and their radioactivity determined by scintillation counting. The specific radioactivity of nodule structures increased with nodule development, and was as much as 4 times higher in early nodules than in roots and nodules on half-roots receiving delayed inoculation. By the time that N2 fixation could be measured in the first mature nodules, the early inoculated half-root contained over 70% of the radioactivity recovered from the entire root systems of both early/delayed and early/uninoculated treatments. These results suggest that developing nodules create a strong sink for photosynthate, and that nodules and roots compete for current photosynthate. Early initiated nodules might develop at the expense of late initiated nodules, as well as at the expense of the roots themselves.

The gelatinous layer (G-layer) of tension-wood fibres in reaction wood of beech showed alterations as a result of the physiological processes involved in the conversion of sapwood into false heartwood or reaction-zone tissue. Using transmitted-light, fluorescence and UV microscopy, polyphenolic compounds were found to infiltrate and encrust the cellulose microfibrils within the G-layer. Experiments with naturally infected and artificially inoculated wood showed that these processes affect the rate and mode of degradation by wood-decaying fungi. Thus, although the ascomycete Ustulina deusta was able to degrade the G-layer from within the lumina of tension-wood fibres in unaltered sapwood, it failed to do so for a prolonged period within false heartwood and reaction zones. In both situations, however, there was some degradation of the underlying secondary wall in the form of erosion troughs which can be attributed to soft rot ‘type II’, and internal cavity formation typical for ‘type I’ attack. The present study indicates that not only cell type, but also alterations in the cell wall structure, affect the activity and degradation mode of decay fungi in beech.

The effects of prolonged simulated acid rain on percentage cover of ground vegetation, and on growth and reproduction of two dominating dwarf shrubs (Empetrum nigrum and Vaccinium vitis-idaea) were examined in a field experiment in the Finnish Subarctic, in an area with low ambient levels of sulphur and nitrogen deposition. Acid rain treatments included moderate (pH 3·8) and high (pH 2·9) concentrations of either H2SO4, or HNO3, or a mixture of them, and were compared with irrigated (pH 6) and dry control plots.

Long-term application of acid rain caused significant alteration in the cover and composition of ground vegetation. Effects of acid rain depended on the accompanying anion and on pH. Sub-plots under different canopy tree species differed in responses indicating that spatial heterogeneity is important in predicting the effect of acidifying pollution on this plant community.

In the bottom layer, acid rain caused significant reduction in cover of the cyanobacterial lichens Nephroma arcticum and Peltigera spp. Decrease in cover of fruticose lichens, mainly composed of Cladina spp., more likely resulted from additional watering.

In the field layer, acid rain containing moderate concentrations of NO3− caused an increase in cover of graminoid species. There were only slight alterations in growth and cover of the two dominant evergreen dwarf shrubs, E. nigrum and V. vitis-idaea, indicating that these species are tolerant to acid rain of as low as pH 3. Even some positive responses of dwarf shrubs were observed, depending on canopy tree. Application of acid rain of pH 3 to plots under pine trees caused an increase in cover of V. vitis-idaea and, when the nitric acid only was applied, a short-term increase in the number of new shoots of E. nigrum.

In contrast to vegetative growth, reproduction of the dwarf shrubs was more strongly affected by acid rain, but this also depended on local conditions and anion composition of acid rain. On ‘pine’ plots, rain of pH 3 reduced the number of berries and flower buds on terminal current shoot of E. nigrum, however, this was partially compensated by an increase in berry production at the ramet level. Simulated acid rain had mainly negative effects on berry production by V. vitis-idaea.

During the initial phases of elongation of pea internodes, oat and rice coleoptiles, oat mesocotyls, soybean hypocotyls and dandelion peduncles, net transverse orientation of cellulose wall microfibrils (Mfs) was found in the outer epidermal wall. This paper demonstrates that in all these axes, with the exception of rice coleoptile, net longitudinal orientation of microfibrils occurs in the outer epidermal wall in portions of the axes that were still elongating at the time of sampling. The timing of the transition to net longitudinal orientation and whether the transition proceeded acropetally or basipetally varied with the type of axis under study. The variability of the relationship between extension and the transition from net transverse to net longitudinal orientation suggests that factors other than extension are important in determining the transition. Layers of longitudinal wall microfibrils may be added to the extending epidermal wall to bolster its tensile strength commensurate with its function during and after extension. Attention is drawn to the parallels between the concept of tissue tension in growing axes and the concept that the epidermis functions as a stressed skin in the support of mature plant parts in primary growth.

The effect of colonization of tissue-cultured strawberry (Fragaria × ananassa Duch. cv. Kent) plantlets in vitro by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices on plantlet response to poly(ethylene glycol) (PEG)-8000-induced water stress was investigated. The plantlets were inoculated axenically and co-cultured with the AMF for 4 wk, then transferred to 15% PEG-8000 solutions for 4, 8 and 12 h. Relative water content, water potential, osmotic potential, leaf conductance for water vapour diffusion and photosynthetic efficiency as estimated by chlorophyll a fluorescence were all affected by the PEG treatment and its duration but not by the presence of the intraradical phase of the AMF. However, distinct differences in PEG-induced changes in amino acid content were observed between nonmycorrhizal and mycorrhizal plantlets. In the latter, the treatment with PEG caused a substantial decrease in asparagine levels in leaves that was accompanied by a marked increase in asparagine concentration in roots. The opposite was observed in nonmycorrhizal plantlets. Furthermore, concentrations of aspartic acid, serine, threonine, amino-N-butyric acid, alanine and starch increased in roots of mycorrhizal and decreased in nonmycorrhizal plantlets. Our results suggest the presence of a mobile pool of asparagine that can be translocated from leaves to roots or vice versa in response to PEG-induced water stress, depending on the mycorrhizal status of the plantlets. These opposite patterns suggest different strategies of mycorrhizal and nonmycorrhizal plantlets to water stress, which seem to involve different adjustments in nitrogen and carbon metabolism.

The morphology and anatomy of ectomycorrhizas of Rhizopogon arctostaphyli, R. ellenae, R. flavofibrillosus, R. occidentalis, R. rubescens, R. smithii, R. subcaerulescens and R. truncatus synthesized on Ponderosa pine (Pinus ponderosa) in glasshouse conditions using spore slurries, are described and compared. All species produced a well-developed Hartig net, and a well-developed fungal mantle. The mantles of R. arctostaphyli, R. smithii and R. subcaerulescens ectomycorrhizas were two-layered with outer mantle hyphae of wider diameter than inner mantle hyphae. The mantle of R. subcaerulescens ectomycorrhizas also had distinctive peg-like structures (cystidia) along peripheral hyphae. Rhizopogon truncatus ectomycorrhizas were tuberculate in morphology and had a rind-like mantle enclosing adjacent roots. In addition, several species exhibited crystal inclusions in the outer mantle, presumably at the interface between mantle and soil.

The development of fruits of blackcurrant (Ribes nigrum) cv. Ben Alder from flower to maturity was studied non-invasively by nuclear magnetic resonance (NMR) microscopy, using attached and detached fruits, and the images were compared with those from low temperature scanning electron microscopy (LTSEM) and conventional resin histology. The NMR images derived from 2-D and 3-D datasets showed the previously unreported growth of arillar tissues to the extent that they almost completely occlude the locular cavity, but LTSEM and resin histology revealed that no fusion occurs between the arillar tissues and the gelatinous sheath surrounding each seed, or between the arillar tissues and the endocarp. The discontinuities between these tissues cause magnetic inhomogenities which result in these structures being clearly resolved by gradient echo imaging sequences. During seed maturation the endosperm changed from high (bright) to low (dark) signal intensity as lipid reserves formed and solidified, whereas the gelatinous sheath had high signal intensity throughout maturation. The high lipid concentration in the seed was manifested by chemical shift effects in the images and the increasing viscosity of the endosperm was reflected in the decrease in spin–lattice (T1) relaxation times. The funiculi, throughout development of seeds, appeared in NMR images with low signal intensity and 3-D surface-rendered reconstructions illustrated the complexity of the spatial array of seeds and funiculi arising from parietal placentas within the loculus. All other vascular tissues in the pericarp and placentas were resolved as a small bright core surrounded by a dark region, within a matrix of moderate signal intensity. Conventional microscopical studies then showed that the bright core discernible by NMR imaging encompassed an entire vascular bundle whereas the darker surrounding region represented small parenchyma cells with pronounced intercellular gas spaces. Other regions of the pericarp which included extremely large parenchyma cells, however, had few intercellular spaces and consequently gave rise to brighter regions of the image.

The hydration of selected lichens (Cladonia mitis, Cladonia bellidiflora, Cetraria islandica, Parmelia saxatilis, and Xanthoria parietina) was investigated using gravimetry and proton magnetic free induction decays (FIDs).

The hydration from gaseous phase and dehydration to gaseous phase showed first-order kinetics. The amount of water which was non-removable in the air-dry state (relative humidity p/p0=9%) did not depend significantly on the lichen species and was found to be 5·6±1·0% of the d. wt.

The proton FID Gaussian component from the solid matrix of thallus structure, and two (or, depending on lichen species, one averaged) liquid signals coming from water tightly bound on the surface of thallus solid matrix and from loosely bound or free water, were recorded. The bound-water component was distinguished by its motional properties and by its proximity to endogenous paramagnetic centres present in solid matrix (presumably PS II reaction centres of the photobiont). Mild dehydration (from gaseous phase) could completely remove the loosely bound water fraction, leaving the system below the water percolation threshold and below the water clustering point, emphasizing the passivity of lichen response to desiccation shock. In the species in which the one average liquid component was recorded, bound water behaved similarly.

The hydration at which free water pool vanishes (ΔM/m0) and the relative (scaled to water) proton densities of solid matrix of lichen (β) were evaluated for all lichens investigated.

Brassica rapa L. (rapid-cycling Brassica), was grown in environmentally controlled chambers to determine the interactive effects of ozone (O3) and increased root temperature (RT) on biomass, reproductive output, and photosynthesis. Plants were grown with or without an average treatment of 63 ppb O3. RT treatments were 13°C (LRT) and 18°C (HRT). Air temperatures were 25°C/15°C day/night for all RT treatments.

Ozone affected plant biomass more than did root temperature. Plants in O3 had significantly smaller total plant d. wt, shoot weight, leaf weight, leaf area and leaf number than plants grown without O3. LRT plants tended to have slightly smaller total plant d. wt, shoot weight, root weight, leaf weight, leaf area, and leaf number than HRT plants. For all variables, LRT plants grown in O3 had the smallest biomass, and plants grown in HRT without O3 had the largest biomass.

Ozone reduced both fruit weight and fruit number; LRT also reduced fruit weight but had no effect on fruit number. Ozone reduced photosynthesis but RT had no effect. Conductance and internal CO2 were unaffected by O3 or RT.

These studies indicate that plant growth with LRT might be more reduced in the presence of O3 than growth in plants with HRT, which might be able to compensate for O3-caused reductions in photosynthesis to avoid decreased biomass and reproductive output.

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 aim of this paper is to review the present knowledge of the main aspects of differentiation of Acetabularia, a unicellular, eukaryotic organism, and to underline the multiple control pathways modulated by circadian rhythmicity. Growth and morphogenesis are sequentially programmed. Timing of cap differentiation is highly dependent on external conditions. The importance of the sequence of processes is shown by experimental disregulation.

The alga is a highly polarized cell, both in morphology and in the relative concentrations of a number of the molecules it contains. Apical cap differentiation is regulated at the post-transcriptional level and could also depend in part on polyamines and on proteolytic activity.

Chickweed plants (Stellaria media Vill.), either inoculated with cucumber mosaic virus (CMV) or not, were grown to reproductive maturity at a range of densities, both in monoculture and in mixture. CMV infection did not influence the vegetative growth of plants grown in monoculture. Similarly, the total vegetative production of a population containing infected and healthy plants was the same as that of a monoculture of healthy plants. However, infected plants were disadvantaged when in competition with healthy plants, the disadvantage increasing with density and the proportion of healthy plants. Investment in sexual reproduction was reduced in infected plants at all densities and in healthy plants at high densities. In very hard conditions, plants did not even produce seeds.

For the first time the well known drought stress hormone abscisic acid, which is involved in regulating processes increasing desiccation tolerance in many plant systems, was analysed in lichens. ABA was detected in all 26 species investigated. In contrast to higher plants and liverworts, the ABA content increased after hydration of air dry lichen thalli and decreased in desiccating lichen material. Experiments with Baeomyces rufus (Huds.) Rebent indicated that the mycobiont might be the major site of ABA biosynthesis. After incubation of hydrated lichen thalli with radioactive ABA for up to 72 h no metabolism to phaseic acid and dihydrophaseic acid could be detected. Fluctuations of internal ABA might be a result of ABA release to the external medium.

This paper describes a developing approach for correlating molecular markers with phenotypic expression in barley, and research examples are given. This approach is intended to elucidate the connection between defined parts of the barley genome and their physiological expressions. To illustrate our approach (up to the point of marker correlation), the materials, methods and results of an experiment are presented. Briefly, the natural abundance levels of carbon and nitrogen isotopes (δ13C and δ15N) serve as the primary screening tools for assessing barley genotypes for their responses to imposed abiotic stresses. The isotopic responses are then correlated with molecular markers as the first step in identifying the mechanisms relating genetic variation with phenotypic expression.

A well-described mechanistic model exists for interpreting plant δ13C, and this enables partitioning of the physiological processes contributing to the whole plant δ13C. Although plant δ15N appears to be equally well correlated with genotype and environment, there is no mechanistic model explaining this isotopic signature. Hence, δ15N is used empirically and in parallel with attempts to understand its underlying mechanism(s).

A new group of darkly pigmented root-infecting fungi was isolated from cereal roots obtained from six different locations in northeastern Germany. Similar random amplified polymorphic DNA(RAPD) patterns and restriction profiles of amplified rDNA were used as a basis for classifying the isolates in a separate group. The isolates demonstrating mycelial and infection characteristics typical of Gaeumannomyces graminis could be differentiated from the varieties of G. graminis as well as from Gaeumannomyces cylindrosporus/Phialophora graminicola using RAPD Polymerase chain reaction (PCR) and rDNA Restriction-fragment length polymorphism (RFLP) analysis. Phylogenetic analysis of the Internal transcribed spacer (ITS) regions suggests that the isolates form a distinct group (named group ‘E’) situated within the Gaeumannomyces–Phialophora complex between the branch of the G. graminis varieties and Gaeumannomyces incrustans/Magnaporthe poae. Isolates of group E produced lobed hyphopodia and were shown in biotests to be non-pathogenic to wheat, oats, Italian Ryegrass and Chewings Fescue, suggesting it is a benign parasite which colonizes cereals or grasses without destroying vascular tissue. Furthermore, curved phialospores could be found. Summarizing the results presented, this new group could be classified as a new species of Phialophora. Although isolates of group E were found at only six of the 32 investigated locations, they composed up to 50% of total isolates of the Gaeumannomyces–Phialophora complex at these sites. Because of the non-pathogenic behaviour, the new group may be of value as biological control agents for pathogenic fungi.

The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO2 concentrations (350 and 550 μmol mol−1). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root[ratio ]shoot ratios) and within tissues[ratio ]infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO2. Elevated CO2 stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO2 on growth, with infected plants showing a greater response, such that elevated CO2 partly alleviated the effects of the parasite on host growth. Elevated CO2 did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO2 but was unaffected by O. minor. There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO2 in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO2 on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO2.

To clarify the role of the fungal nitrate assimilation pathway in nitrate reduction by mycorrhizal plants, nitrate reductase (NR)-deficient (NR−) mutants of the ectomycorrhizal basidiomycete Hebeloma cylindrosporum Romagnesi have been selected. These mutants were produced by u.v. mutagenesis on protoplasts originating from homokaryotic mycelia belonging to complementary mating types of this heterothallic tetrapolar species. Chlorate-resistant mutants were first selected in the presence of different nitrogen (N) sources in the culture medium. Among 1495 chlorate resistant mycelia, 30 failed to grow on nitrate and lacked a detectable NR activity. Growth tests on different N sources suggested that the NR activity of all the different mutants is specifically impaired as a result of mutations in either the gene coding for NR apoprotein or genes controlling the synthesis of the molybdenum cofactor. Furthermore, restoration of NR activity in some of the dikaryons obtained after crosses between the different mutant mycelia suggested that not all the selected mutations mapped in the same gene. Utilization of N on a NH415NO3 medium was studied for two mutant strains and their corresponding wild-type homokaryons. None of the mutants could use nitrate whereas 15N enrichment values indicated that 13–27% of N present in 13-d-old wild-type mycelia originated from nitrate. Apparently, the mutant mycelia do not compensate their inability to use nitrate by a more efficient use of ammonium. These different NR mutants still form mycorrhizas with the habitual host plant, Pinus pinaster (Ait.), making them suitable for study of the contribution of the fungal nitrate assimilation pathway to nitrate assimilation by mycorrhizal plants.

Frictional resistance to a penetrating body can account for more than 80% of the total resistance to penetration of soil. We measured the frictional resistance between growing root caps of maize and pea and ground and smooth glass surfaces, which was linearly correlated to load, allowing calculation of the coefficient of kinetic friction and adhesion. Coefficients of kinetic friction between the root caps and the ground and smooth glass surfaces were approximately 0.04 and 0.02, respectively, the first measurements of the frictional properties of root tips at rates approaching those of root elongation, and an order of magnitude smaller than those previously reported. Results suggest that roots are well designed for penetrating soil, and encounter only small frictional resistance on the root cap. These data provide important parameters for modelling soil stresses and deformation around growing root tips.

Arbuscular mycorrhizas are a widespread symbiosis between soil fungi and plant roots. Flow cytometry, after DNase I partial digestion and DAPI staining, and light and electron microscopy were used to analyse chromatin condensation and nuclear conditions in mycorrhizal and control roots of Allium porrum. The 2C peak, detected by flow cytometry, split into two peaks representing two populations of nuclei, one more resistant and one more susceptible to the enzyme action. The microscopic analyses showed the presence of pyknotic and chromatolytic nuclei, two typical features of senescence. In order to quantify the senescing process, a terminal deoxynucleotidyl transferase assay was performed on extracted nuclei, later analysed by flow cytometry. The numbers of senescing nuclei and their DNA cleavage were higher in control plants. Our results show the existence of senescing nuclei in cortical cells of the bulbous monocotyledon A. porrum and the delaying effect of arbuscular mycorrhizas on senescence.

In an experiment to determine the influence of mycorrhizal colonization on root development, fertilized seedlings of cotton were grown in long tubular pots. Inoculation of soil with an isolate of Glomus mosseae at 10, 25 or 40 cm below the soil surface resulted in spread of arbuscular mycorrhizas up and down the root system, and localized elongation of roots following colonization. Specific root length was not influenced by colonization. Increases in local root density at the point of inoculation were observed, though total root mass in relation to shoot mass declined following initiation of mycorrhizas.