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Being able to persist in deep shade is an important characteristic of juvenile trees, often leading to a strong dominance of shade-tolerant species in forests with low canopy turnover and a low disturbance rate. While leaf, growth, and storage traits are known to be key components of shade tolerance, their interplay during regeneration development and their influence on juveniles' survival time remains unclear. We assessed the ontogenetic effects of these three traits on the survival time of beech (Fagus sylvatica), and Norway and sycamore maples (Acer pseudoplatanus, Acer platanoides) in a primeval beech forest. Biomass allocation, age, and content of nonstructural carbohydrates (NSC) were measured in the stems and roots of 289 seedlings and saplings in high- and low-vitality classes. Saplings experienced a trade-off between absolute growth rate (AGR) and storage (NSC) as the leaf area ratio (LAR) decreases with biomass development. High LAR but low AGR and low NSC corresponded to beech with a marked ability to persist in deep shade while awaiting canopy release. In turn, a comparably small LAR in combination with a high AGR and higher storage (NSC), as observed in Norway maple and sycamore maple, reduced sapling survival time, thus offering an explanation for beech dominance and maple disappearance in the undergrowth of old-growth beech forests., Ecology and Evolution, 11 (15), ISSN:2045-7758

The key selective pressure shaping the morphology of samaras is seen as enhancing primary wind‐borne dispersal from the parent plant to the ground. However, the consequences of the samara wing of primarily wind‐dispersed tree species for post‐dispersal processes has not been well studied. We explored whether the presence of this wing in Acer pseudoplatanus either deters or promotes predation after dispersal, either by increasing the time and energy required to predate the seed or by increasing the seed's visibility to predators. We found that wing‐removed fruits were preferred, suggesting that the presence of samaras makes seed handling more expensive for granivores. Further, we found that fewer seeds were consumed from treatments that contained the most winged seeds, thus there was no evidence of the samaras making seed finding easier for granivores. We conclude that the presence of the wing may offer an anti‐predatory benefit as well as aiding primary dispersal. Postprint

SUMMARY: In trees, dead and living cells of secondary xylem (wood) function collectively, rendering cell‐to‐cell communication challenging. Water and solutes are transported over long distances from the roots to the above‐ground organs via vessels, the main component of wood, and then radially over short distances to the neighboring cells. This enables proper functioning of trees and integrates whole‐plant activity. In this study, tracer loading, immunolocalization experiments and inhibitor assays were used to decipher the mechanisms enabling transport in wood of Acer pseudoplatanus (maple), Fraxinus excelsior (ash) and Populus tremula × tremuloides (poplar) trees. We show that tracer uptake from dead water‐conducting vessels, elements of the apoplasm, to living vessel‐associated cells (VACs) of the xylem parenchyma of the symplasm system proceeds via the endocytic pathway, including clathrin‐mediated and clathrin‐independent processes. These findings enhance our understanding of the transport pathways in complex wood tissue, providing experimental evidence of the involvement of VACs and endocytosis in radial uptake from vessels.

Hydraulic redistribution (HR) of soil water through plant roots is widely described; however its extent, especially in temperate trees, remains unclear. Here, we quantified HR of five temperate tree species. We hypothesized that both, HR within a plant and into the soil increase with higher water‐potential gradients, larger root conduit diameters and root‐xylem hydraulic conductivities as HR driving factors. Saplings of conifer (Picea abies, Pseudotsuga menziesii), diffuse‐porous (Acer pseudoplatanus) and ring‐porous species (Castanea sativa, Quercus robur) were planted in split‐root systems, where one plant had its roots split between two pots with different water‐potential gradients (0.23–4.20 MPa). We quantified HR via deuterium labelling. Species redistributed 0.39 ± 0.14 ml of water overnight (0.08 ± 0.01 ml/g root mass). Higher pre‐dawn water‐potential gradients, hydraulic conductivities and larger conduits significantly increased HR quantity. Hydraulic conductivity was the most important driving factor on HR amounts, within the plants (0.03 ± 0.01 ml/g) and into the soil (0.06 ± 0.01 ml/g). Additional factors as soil‐root contact should be considered, especially when calculating water transfer into the soil. Nevertheless, trees maintaining high‐xylem hydraulic conductivity showed higher HR amounts, potentially making them valuable ‘silvicultural tools’ to improve plant water status. A free Plain Language Summary can be found within the Supporting Information of this article.

Summary Eutypella canker of maple, caused by Eutypella parasitica (which is native to North America), is reported for the first time from Germany. From 2013 to 2015, this perennial canker disease was recorded on 105 maple trees in Munich. Six maple species were affected: Acer pseudoplatanus, A. campestre, A. platanoides, A. cappadocicum, A. heldreichii ssp. trautvetteri and A. hyrcanum. Occurrence on the latter three species represents new host records for E. parasitica. In Austria, Eutypella canker was newly discovered on two trees at a second locality in 2011, and it is now known to occur on seven A. pseudoplatanus trees at two localities, which are separated nearly 150 km. A. pseudoplatanus was the most frequent host of E. parasitica in Munich and Austria, which is in agreement with previous studies in Europe. The identity of the causative pathogen as E. parasitica was verified by ITS rDNA sequencing of fungal cultures obtained from cankers in Munich and at both Austrian localities. The presence of large and old cankers in both countries suggests that introduction of E. parasitica dates back a long time, probably several decades. The new records of Eutypella canker in Germany and Austria show that the disease is more widely distributed in central Europe than previously recognized.

Background Poisoning with Acer pseudoplatanus L. in horses contradicts the hypothesis of coexistence between plants and vertebrate herbivores being mediated through antipastoral traits as toxins. However, incidental observations showed that horses evaded Acer seedlings with primary leaves. The objective of the present cross-discipline study was (i) to analyse whether developmental stages of A. pseudoplatanus L. differed as to phenolics hypothesised as antipastoral traits, and (ii) to observe systematically the selection behaviour of pastured horses towards A. pseudoplatanus seedlings. Methods Phenolic profiles of five developmental stages from fruits to seedlings of progressing age up to adult leaves of A. pseudoplatanus and Acer campestre L. were characterised. Video recordings of grazing behaviour of 29 pastured horses towards seedlings of A. pseudoplatanus resulted into 117 sequences as additional field data. Results The horses ingested 19.1 per cent of juvenile seedlings with cotyledons (1.65 mg total phenolics/g fresh weight (FW), 82 compounds, 0.02 mg total gallic acid/g FW) yet only 5.46 per cent of older seedlings with primary leaves (8.48 mg total phenolics/g FW, 120 compounds, 3.13 mg total gallic acid/g FW). Conclusion Horses distinguished between seedlings in distinct stages that could be chemically distinguished, too. Acer seedlings with primary leaves provide a strong, but not complete antipastoral effect that correlates with dramatic changes in phenolic compounds.

Plant Biology, 21 (1), ISSN:1435-8603, ISSN:1438-8677

Summary Reasons for performing study Ingestion of sycamore seeds (Acer pseudoplatanus) is the likely source of hypoglycin A in atypical myopathy (AM) but ingestion of seedlings in spring might also contribute to intoxication. Objectives To test for hypoglycin A in seeds and seedlings collected on pastures where AM cases were reported and compare its concentration in serum of affected and healthy horses. Study design Field investigation of clinical cases. Methods Whenever present, samaras (the winged nuts that each contain one seed) and/or seedlings were collected from pastures of 8 AM cases and 5 unaffected horses from different premises. Two AM cases were each co-grazing with an apparently healthy horse. Acylcarnitines and hypoglycin A were quantified in blood samples of all horses involved in the study. Results Hypoglycin A was detected in serum of AM (5.47 ± 1.60 μmol/l) but not in healthy controls pasturing where A. pseudoplatanus trees were not present. However, hypoglycin A was detected at high concentrations (7.98 μmol/l) in serum of a clinically healthy horse grazing a pasture with seedlings and samaras and also in the 2 healthy horses co-grazing with AM cases (0.43 ± 0.59 μmol/l). Hypoglycin A was detected in all samples of seeds and spring seedlings of A. pseudoplatanus. Conclusions Atypical myopathy can be associated with the ingestion of sycamore samaras and also ingestion of seedlings. Hypoglycin A can be detected in the blood of horses with no detectable clinical signs at pasture in which there is A. pseudoplatanus. Determination of hypoglycin A concentration in blood is useful for screening for exposure in suspected cases of AM.

BACKGROUND Hypoglycin A, found in seeds of Acer negundo, appears to cause seasonal pasture myopathy (SPM) in North America and is implicated in atypical myopathy (AM) in Europe. Acer negundo is uncommon in Europe. Thus, the potential source of hypoglycin A in Europe is unknown. HYPOTHESIS AND OBJECTIVES We hypothesized that seeds of Acer pseudoplatanus were the source of hypoglycin A in Europe. Our objective was to determine the concentration of hypoglycin A in seeds of A. pseudoplatanus trees located in pastures where previous cases of AM had occurred. ANIMALS None. METHODS University of Berne records were searched to retrospectively identify 6 farms with 10 AM cases and 11 suspected AM deaths between 2007 and 2011. During October 2012, A. pseudoplatanus seeds were collected from 2 to 6 trees per pasture on 6 AM farms (7 pastures) from trees in or close to 2 pastures on 2 control farms where AM had not been previously reported. Hypoglycin A in seeds was analyzed by GC-MS. RESULTS Acer pseudoplatanus trees were identified on all AM pastures. Hypoglycin A was detected in all A. pseudoplatanus seeds in highly variable concentrations ranging from 0.04 to 2.81 μg/mg (mean 0.69) on AM farms and 0.10 to 9.12 μg/mg (mean 1.59) on control farms. CONCLUSION AND CLINICAL IMPORTANCE Preventing horses from grazing pastures containing A. pseudoplatanus seeds during late fall and early spring might be the best means to prevent AM.

1. At high elevation, temperate trees generally exhibit adaptive genetic differentiation in their morphological and physiological traits. On account of this directional selection, we hypothesized that tree populations growing near their upper cold elevational limits exhibit lower phenotypic plasticity of growth and leaf morphological traits in response to temperature changes than populations growing at lower elevations. 2. Seedlings of six common deciduous tree species originating from low and high elevations were transplanted into eight common gardens along two elevational gradients in the Swiss Alps. The aim of the experiment was to evaluate the genetic differentiation in growth and leaf morphology between populations from low and high elevations and to quantify the phenotypic plasticity of these traits to temperature changes. 3. In contrast to growth that decreased with increasing elevation, leaf mass per area (LMA) showed no significant change with elevation of common garden, except for a decrease in Laburnum alpinum for both low- and high-elevation provenances. Interestingly, leaf density was found to decrease with elevation of the gardens for all species. Genetic differentiation between low- and high-elevation populations was found in both leaf morphology and growth: high-elevation populations tended to have slower growth rate than low-elevation populations, while no consistent trend was found for LMA across species. Interestingly, for Acer pseudoplatanus and Fraxinus excelsior high-elevation populations exhibited a lower phenotypic plasticity of growth in response to temperature compared to lower populations, whereas no interactions between the elevation of a provenance and the elevation of the garden was detected for the four other species. 4. Hence, during young life-stages, the expected increase of tree growth in future warmer climates might be lower in populations living in the coldest part of the species distribution range in temperate species such as Ac pseudoplatanus and Fraxinus excelsior, but similar in other tree species, disregarding other environmental changes.

Summary Reasons for performing study: It is hypothesised that European atypical myopathy (AM) has a similar basis as seasonal pasture myopathy in North America, which is now known to be caused by ingestion of hypoglycin A contained in seeds from the tree Acer negundo. Serum from horses with seasonal pasture myopathy contained the conjugated toxic metabolite of hypoglycin A, methylenecyclopropyl acetic acid (MCPA). Study design: Retrospective study on archived samples. Objectives: 1) To determine whether MCPA-carnitine was present in serum of European horses confirmed to have AM; 2) to determine whether Acer negundo or related Acer species were present on AM pastures in Europe. Methods: Concentrations of MCPA-carnitine were analysed in banked serum samples of 17 AM horses from Europe and 3 diseased controls (tetanus, neoplasia and exertional rhabdomyolysis) using tandem mass spectrometry. Atypical myopathy was diagnosed by characteristic serum acylcarnitine profiles. Pastures of 12 AM farms were visited by experienced botanists and plant species were documented. Results: Methylenecyclopropyl acetic acid-carnitine at high concentrations (20.39 ± 17.24 nmol/l; range 0.95-57.63 nmol/l; reference

• Premise of the study: The picture of how long-distance transport proceeds in trees is still far from being complete. Beside the apoplasmic pathway, transport undoubtedly also takes place within the system of living cells in the secondary xylem and cambial region. Because detailed, thorough studies of the symplasmic routes in woody branches, using direct localization with fluorescent tracers, had not been done, here we focused on the main routes of long-distance symplasmic transport in xylem and cambial tissues and analyzed in detail tracer distribution in the rays on the extended cambial surface in branches of Acer pseudoplatanus and Populus tremula ×P. tremuloides.• Methods: Fluorescent tracers were loaded into branches through the vascular system, then their distribution in xylem and cambial regions was analyzed.• Key results: Tracer signal was present in the symplast of axial and radial xylem parenchyma cells and in both types of cambial cells. The living cells of xylem parenchyma and of the cambium were symplasmically interconnected via xylem rays. Tracer distribution in rays was uneven on the extended cambial surface; cambial regions with intensively or sparsely dyed rays alternated along the vertical axis of analyzed branches.• Conclusions: Symplasmic, long-distance transport is present between the living cells of xylem and the cambial region in woody branches. The uneven distribution of fluorescent tracers in cambial rays along the stems is surprising and suggests the presence of an intrinsic pattern caused by an unknown mechanism.

Couturier, Etienne Brunel, Nicole Douady, Stephane Nakayama, Naomi; Premise of the study: How leaf shape is regulated is a long-standing question in botany. For diverse groups of dicotyledon species, lamina folding along the veins and geometry of the space available for the primordia can explain the palmate leaf morphology. Dubbed the kirigami theory, this hypothesis of fold-dependent leaf shape regulation has remained largely theoretical. Using Acer pseudoplatanus, we investigated the mechanisms behind the two key processes of kirigami leaf development. Methods: Cytological examination and quantitative analyses were used to examine the course of the vein-dependent lamina folding. Surgical ablation and tissue culturing were employed to test the effects of physical constraints on primordia growth. The final morphology of leaves growing without steric constraints were predicted mathematically. Key results: The cytological examination showed that the lamina's abaxial side along the veins grows substantially more than the adaxial side. The abaxial hypergrowth along the veins and the lamina extension correlated with the lamina folding. When a primordium was released from the physical constraints imposed by the other primordia, it rapidly grew into the newly available space, while maintaining the curvature inward. The morphology of such a leaf was predicted to lack symmetry in the lobe shapes. Conclusions: The enhanced growth on the abaxial side of the lamina along the veins is likely to drive lamina folding. The surgical ablation provided clear support for the space-filling nature of leaf growth; thus, steric constraints play a role in determination of the shapes of folded leaves and probably also of the final leaf morphology.

Temperate deciduous forest trees flower in spring, a period that starts when the trees lack leaves and when weather is unpredictable, including frost events, and ends when the forest becomes green and vertical microclimatic gradients are established. This paper asks whether there are spatio-temporal patterns in the development of flowering in trees, and how they relate to reproductive processes. Using a crane, flowering phenology was studied in the crowns of ca. 200 trees of four species, from early spring (ash) through the period of leaf-unfolding (maples) to early summer (lime). Flowering levels in different crown regions were documented quantitatively and repeatedly during the flowering season and compared among individuals and among species. Early-flowering trees displayed a clear and consistent acropetalous and centrifugal flowering pattern, while this pattern disappeared in species that flowered after leaves unfolded. This pattern was superposed on the basic flowering rhythm of each species, and was influenced by effects of direct sunlight, acting at a small scale in early spring and at a large scale in early summer. As this acropetalous centrifugal pattern contrasts the microclimatic gradients that develop only after leaves unfold, it might indicate physiological processes in the ‘awakening’ of trees, as well as evolutionary processes that took place in temperate trees during adaptation to a temperate climate.

To investigate the short-term consequences of direct competition between beech and sycamore maple on root N uptake and N composition, mycorrhizal seedlings of both tree species were incubated for 4 days (i.e. beech only, sycamore maple only or both together) in an artificial nutrient solution with low N availability. On the fourth day, N uptake experiments were conducted to study the effects of competition on inorganic and organic N uptake. For this purpose, multiple N sources were applied with a single label. Furthermore, fine roots were sampled and analysed for total amino acids, soluble protein, total nitrogen, nitrate and ammonium content. Our results clearly show that both tree species were able to use inorganic and organic N sources. Uptake of inorganic and organic N by beech roots was negatively affected in the presence of the competing tree species. In contrast, the presence of beech stimulated inorganic N uptake by sycamore maple roots. Both the negative effect of sycamore maple on N uptake of beech and the positive effect of beech on N uptake of sycamore maple led to an increase in root soluble protein in beech, despite an overall decrease in total N concentration. Thus, beech compensated for the negative effects of the tree competitor on N uptake by incorporating less N into structural N components, but otherwise exhibited the same strategy as the competitor, namely, enhancing soluble protein levels in roots when grown under competition. It is speculated that enhanced enzyme activities of so far unknown nature are required in beech as a defence response to inter-specific competition.

1. The horse-chestnut leaf miner Cameraria ohridella is an invasive moth in Europe and a serious pest of horse-chestnut Aesculus hippocastanum. The moth also occasionally attacks sycamore maple Acer pseudoplatanus, when situated beside infested horse-chestnuts. 2. The main objective of the present study was to provide an overview of the relationship between C. ohridella and A. pseudoplatanus and to determine whether C. ohridella has the potential to shift to this native tree. 3. In the field, females oviposit on different deciduous tree species. Although less frequently attacked than A. hippocastanum, A. pseudoplatanus was clearly preferred for oviposition over 12 other woody species investigated. 4. Surveys in Europe demonstrated that the majority of A. pseudoplatanus trees found beside infested A. hippocastanum had mines of C. ohridella, even though more than 70% of the larvae died within the first two instars. Attack rates and development success greatly varied from site to site. Attack levels on A. pseudoplatanus were not always correlated with those on A. hippocastanum, and mines on A. pseudoplatanus were sometimes observed beside weakly-infested A. hippocastanum. 5. Field observations, experimental exposure of A. pseudoplatanus saplings and rearing trials in a common garden study showed that individual trees may vary in their susceptibility to C. ohridella, whereas there was no evidence that C. ohridella populations vary in their performance on A. pseudoplatanus. 6. To date, there is little evidence that C. ohridella represents a major risk for A. pseudoplatanus.

Violins produced by Antonio Stradivari during the late 17th and early 18th centuries are reputed to have superior tonal qualities. Dendrochronological studies show that Stradivari used Norway spruce that had grown mostly during the Maunder Minimum, a period of reduced solar activity when relatively low temperatures caused trees to lay down wood with narrow annual rings, resulting in a high modulus of elasticity and low density. The main objective was to determine whether wood can be processed using selected decay fungi so that it becomes acoustically similar to the wood of trees that have grown in a cold climate (i.e. reduced density and unchanged modulus of elasticity). This was investigated by incubating resonance wood specimens of Norway spruce (Picea abies) and sycamore (Acer pseudoplatanus) with fungal species that can reduce wood density, but lack the ability to degrade the compound middle lamellae, at least in the earlier stages of decay. Microscopic assessment of the incubated specimens and measurement of five physical properties (density, modulus of elasticity, speed of sound, radiation ratio, and the damping factor) using resonance frequency revealed that in the wood of both species there was a reduction in density, accompanied by relatively little change in the speed of sound. Thus, radiation ratio was increased from 'poor' to 'good', on a par with 'superior' resonance wood grown in a cold climate.

Global data sets provide strong evidence of convergence for leaf structure with leaf longevity such that species having thick leaves, low specific leaf area, low mass-based nitrogen concentrations, and low photosynthetic rates typically exhibit long leaf life span. Leaf longevity and corresponding leaf structure have also been widely linked to plant potential growth rate, plant competition, and nutrient cycling. We hypothesized that selection forces leading to variation in leaf longevity and leaf structure have acted simultaneously and in similar directions on the longevity and structure of the finest root orders. Our four-year study investigated the links between root and leaf life span and root and leaf structure among 11 north-temperate tree species in a common garden in central Poland. Study species included the hardwoods Acer pseudoplatanus L., Acer platanoides L., Fagus sylvatica L., Quercus robur L., and Tilia cordata Mill.; and the conifers Abies alba Mill., Larix decidua Mill., Picea abies (L.) Karst., Pinus nigra Arnold, Pinus sylvestris L., and Pseudotsuga menziesii (Mirbel) Franco. Leaf life span, estimated by phenological observations and needle cohort measurements, ranged from 0.5 to 8 yr among species. Median fine-root life span, estimated using minirhizotron images of individual roots, ranged from 0.5 to 2.5 yr among species. Root life span was not correlated with leaf life span, but specific root length was significantly correlated with specific leaf area. Root nitrogen : carbon ratio was negatively correlated with root longevity, which corroborates previous research that has suggested a trade-off between organ life span and higher organ N concentrations. Specific traits such as thickened outer tangential walls of the exodermis were better predictors of long-lived roots than tissue density or specific root length, which have been correlated with life span in previous studies. Although theories linking organ structure and function suggest that similar root and leaf traits should be linked to life span and that root and leaf life span should be positively correlated, our results suggest that tissue structure and longevity aboveground (leaves) can contrast markedly with that belowground (roots).

Summary • This paper compares the responses to ozone in five woody species: Fagus sylvatica (FS), Acer pseudoplatanus (AP), Fraxinus excelsior (FE), Viburnum lantana (VL) and Ailanthus altissima (AA). The hypothesis being tested was that the strategies that plants adopt to resist oxidative pressure are species-specific. • The study was carried out on field grown plants in an area in Northern Italy characterized by elevated levels of ozone pollution. The observations were made both at ultrastructural (using light and electronic microscopy) and physiological (using chlorophyll a transient fluorescence and microspectral fluorometry) level. • Common responses were: the hypersensitive response (i.e. the death of palisade mesophyll cells) and the formation of callose layers separating injured from healthy cells. FS and AP were capable of thickening the palisade mesophyll cell walls. This thickening process involved changes in cell wall chemical structure, evidenced by the accumulation of yellow autofluorescence compounds. Species-specific behaviours were observed with the fluorescence analysis, with special reference to the photochemical de-excitation constant (Kp). This value increased in FE and AP, and decreased in AA. • The observed responses are interpreted as adaptative strategies against the ozone stress. The increase of Kp indicates that the reaction centres were working as more effective quenchers.

Cadmium is one of the most toxic heavy metals that can be taken up by plants. Although cadmium toxicity in plants is well established, the mechanism of Cd actions at the cell level is not entirely known. The aim of this work was the investigation of Cd effects on cation contents (K, Ca, Mn, Fe, Cu, Zn) and cytological changes in sycamore cells (Acer pseudoplatanus L.). Sycamore cells were treated with 20 μM CdSO 4 , a sub-lethal concentration, for 7 days. Energy-dispersive x-ray fluorescence (EDXRF) spectrometry was applied to quantify cation concentrations in cells. Cd concentration was measured by total reflection x-ray fluorescence (TXRF) spectrometry. The quantification was performed with cells taken directly from the culture and also after being washed in an acidified medium. Light and scanning microscope observations showed several modifications of cadmium-treated cells, namely increased cell volume and vacuolation. Cells exposed to cadmium also showed variations in cation concentrations. An increase in Mn, Fe, Cu and Zn contents and a decrease in K content were observed in Cd-stressed cells. Fe was the most increased element, followed by Mn and Cu and a similar behaviour was observed for Ca and Zn. K was the only cation showing a decreased concentration under Cd stress. The high levels of Cd in cells exposed to Cd are in agreement with the amount of Cd accumulated within the cells. The results obtained allowed differentiation between adsorption of ions on the cell wall and uptake of ions into the intracellular compartments.

The accumulation of carbon (C) and nitrogen (N) was measured on two sites on Rothamsted Farm that had been fenced off some 120 years ago and allowed to revert naturally to woodland. The sites had previously been arable for centuries. One had been chalked and was still calcareous; the other had never been chalked and the pH fell from 7.1 in 1883 to 4.4 in 1999. The acidic site (Geescroft wilderness) is now a deciduous wood, dominated by oak (Quercus robor); the calcareous site (Broadbalk wilderness) is now dominated by ash (Fraxinus excelsior), with sycamore (Acer pseudoplatanus) and hawthorn, (Craetagus monogyna) as major contributors. The acidic site gained 2.00 t C ha(-1) yr(-1) over the 118-year period (0.38 t in litter and soil to a depth of 69 cm, plus an estimated 1.62 t in trees and their roots); the corresponding gains of N were 22.2 kg N ha(-1) year(-1) (15.2 kg in the soil, plus 6.9 kg in trees and their roots). The calcareous site gained 3.39 t C ha(-1) year(-1) over the 120-year period (0.54 t in the soil, plus an estimated 2.85 t in trees and roots); for N the gains were 49.6 kg ha(-1) yr(-1) (36.8 kg in the soil, plus 12.8 kg in trees and roots). Trees have not been allowed to grow on an adjacent part of the calcareous site. There is now a little more C and N in the soil from this part than in the corresponding soil under woodland. We argue from our results that N was the primary factor limiting plant growth and hence accumulation of C during the early stages of regeneration in these woodlands. As soil organic N accumulates and the sites move towards N saturation, other factors become limiting. Per unit area of woodland, narrow strips; that is, wide, hedges with trees, are the most efficient way of sequestering C - provided that they Are not short of N.

Spatial and temporal aspects of overwintering in the holocyclic sycamore aphid Drepanosiphum platanoidis (Schrank) (Homoptera: Callaphididae) were investigated. Eggs of D. platanoidis were principally laid on trunks and branches of Acer pseudoplatanus L., at considerable distances from the buds. Trunks with rough bark, followed by branches with moderate roughness supported more overwintering eggs than the relatively exposed smooth surfaces of twigs and terminal buds. Eggs were aggregated on rough bark. Aspect had no effect on the number of eggs laid. Experimental manipulations varying ovipara densities showed intra-specific competition among oviparae for optimal oviposition sites. Overwintering egg mortality was a function of time, with the greatest mortality rate occurring in late winter. Egg mortality varied from 80.4% to 76.9% on trunks and 83.0% to 65.9% on branches in 1996 and 1997.

1 The arbuscular mycorrhizal (AM) fungi colonizing plants at a woodland site in North Yorkshire (UK) have been characterized from the roots of five plant species (Rubus fruticosus agg. L., Epilobium angustifolium L., Acer pseudoplatanus L., Ajuga reptans L. and Glechoma hederacea L.), and identified using small-subunit rRNA (SSUrRNA) gene amplification and sequencing. 2 Interactions between five plant species from the site and four co-occurring glomalean fungi were investigated in artificial one-to-one AM symbioses. Three of the fungi were isolated from the site; the fourth was a culture genetically similar to a taxon found at the site. Phosphorus uptake and growth responses were compared with non-mycorrhizal controls. 3 Individual fungi colonized each plant with different spatial distribution and intensity. Some did not colonize at all, indicating incompatibility under the conditions used in the experiments. 4 Glomus hoi consistently occupied a large proportion of root systems and outperformed the other fungi, improving P uptake and enhancing the growth of four out of the five plant species. Only G. hoi colonized and increased P uptake in Acer pseudoplatanus, the host plant with which it associates almost exclusively under field conditions. Colonization of all plant species by Scutellospora dipurpurescens was sparse, and beneficial to only one of the host plants (Teucrium scorodonia). Archaeospora trappei and Glomus sp. UY1225 had variable effects on the host plants, conferring a range of P uptake and growth benefits on Lysimachia nummularia and T. scorodonia, increasing P uptake whilst not affecting biomass in Ajuga reptans and Glechoma hederacea, and failing to form mycorrhizas with A. pseudoplatanus. 5 These experimental mycorrhizas show that root colonization, symbiont compatibility and plant performance vary with each fungus-plant combination, even when the plants and fungi naturally co-exist. 6 We provide evidence of physical and functional selectivity in AM. The small number of described AM fungal species (154) has been ascribed to their supposed lack of host specificity, but if the selectivity we have observed is the general rule, then we may predict that many more, probably hard-to-culture glomalean species await discovery, or that members of species as currently perceived may be physiologically or functionally distinct.

Summary In 2015 and 2016, the North American maple tree pathogen Eutypella parasitica was identified in Bohemian and Polish Silesia. To date, the pathogen has been recorded in 35 locations over an area of approximately 400 km2. It has been found primarily in natural stands in Silesia in several types of ravine and alluvial forests, in other natural or commercial forests, in riparian stands and in open landscapes. The proportion of diseased maples ranged between approximately 1% and 50% in certain locations. Acer pseudoplatanus was confirmed as the main host but infections were also detected on A. platanoides and A. campestre. E. parasitica damages the most valuable sycamore timber and represents a clear risk for maple cultivation in the region.

The objectives of this study were (1) to investigate effects of soil acidity on the formation of mycorrhizas in ash and sycamore, and (2) to elucidate if mycorrhization can improve the acquisition of Ca, Mg, and P by these tree species. Soil substrates with different Ca, Mg, and Al saturation were used in pot experiments with mycorrhizal ash and sycamore seedlings and various Ca and Mg fertilization treatments. The development of vesicular-arbuscular-mycorrhizas (VAM) in both species was considerably affected by the chemical soil properties and by the nutritional status of the plants. Mycorrhizal fungi developed well only in plants growing on basalt-derived, Ca and Mg rich loam and in substrates fertilized with Ca and Mg carbonate. In these substrates, the pH value, Ca and Mg supply and growth of the plants were optimal. The mycorrhizas degenerated in an acid loam derived from phyllite, in tertiary sand and in all treatments receiving Ca and Mg sulfate. Ash and sycamore suffered from Ca and Mg (P) deficiency, and partly from Al antagonism against Ca and Mg uptake (sycamore) or Al toxicity (ash). The symbiosis between fungi and the plants was disrupted since the tree species and the VAM fungi (from fertile nursery soils) did not adapt to the acidic experimental soil substrates with high Al activity. Consequently, the fungi lost their function of supporting the plants by improved nutrient uptake and the plants likely did not produce enough organic substances for the fungi. In addition, N fertilization possibly suppressed the development of VA mycorrhizas and inhibited new colonization in acid substrates. Einfluss von bodenchemischen Parametern auf die Entwicklung der VA Mykorrhiza bei Esche (Fraxinus excelsior L.) und Bergahorn (Acer pseudoplatanus L.) in Topfexperimenten Ziel dieser Arbeit war es, (1) die Entwicklung der VA Mykorrhiza bei Esche und Bergahorn in unterschiedlich sauren und nahrstoffreichen Boden zu untersuchen, und (2) zu prufen, ob die Mykorrhiza die Aufnahme der Nahrelemente Ca, Mg und P bei diesen Baumarten verbessern kann. In Gefasversuchen mit Eschen- und Bergahornsamlingen in Boden mit unterschiedlicher Basen- und Al-Sattigung und variierender Ca- und Mg-Dungung wurde die VA Mykorrhiza beider Baumarten einerseits durch den chemischen Bodenzustand, andererseits durch den Ernahrungszustand der Pflanzen stark beeinflusst. Die Mykorrhiza-Pilze, die in den Samlingswurzeln bereits bei Beginn der Experimente vorhanden waren, entwickelten sich nur in den Varianten mit Basaltlehm oder Ca- und Mg-Carbonat-Dungung gut, wo die pH-Werte gunstig und die Ca- und Mg-Gehalte der Boden sowie Wachstum und Ernahrungszustand der Pflanzen hervorragend waren. In sauren Phyllitlehm und Tertiarsand sowie in Dungungsvarianten mit Ca- und Mg-Sulfat mit stark saurer Reaktion degenerierten die Mykorrhizen. Die Eschen und Bergahorne litten gleichzeitig unter Ca- und Mg- (P-) Mangel sowie Al-Antagonismus (Bergahorn) oder Al-Toxizitat (Esche) und ihr Wachstum war erheblich beeintrachtigt. Die Nahrstoffaufnahme durch die Mykorrhizen war offensichtlich gehemmt, ebenso wie die Fahigkeit der Pflanzen, den Pilzen organische Substanzen zur Verfugung zu stellen. Wahrscheinlich hat auch eine N-Dungung die Mykorrhiza-Entwicklung beeintrachtigt und neue Infektionen verhindert.

1. Gas exchange is strongly seasonal in temperate deciduous forests; however, virtually no studies have described measurements made at the leaf scale through the whole growing season. This level of detail is important to understanding processes as substantial differences may occur within the canopy between species and between sun and shade leaves. 2. Gas exchange was measured weekly throughout the growing season in leaves of Oak (Quercus robur) and Sycamore (Acer pseudoplatanus) trees at Wytham Woods, UK. In Q. robur sun, shade and intermediate leaves were sampled on each occasion. 3.Acer pseudoplatanus came into leaf before Q. robur and commenced net assimilation (A) earlier. Maximum irradiance saturated photosynthetic rates (Amax) in Q. robur were reached approximately 50 days after budburst and were maintained until approximately 20 days before abscission. Acer pseudoplatanus lost its leaves before Q. robur in the autumn and showed no seasonal trend in Amax. The lag between budburst and attainment of maximum photosynthetic rate in Q. robur was substantial and represented a quarter of the potential growing season. 4.Amax of A. pseudoplatanus (3·5 μmol m–2 s–1) sun leaves was substantially lower than that of Q. robur (10·4 μmol m–2 s–1) despite A. pseudoplatanus being a fast-growing species. The earlier flushing of A. pseudoplatanus leaves in the spring could not completely compensate for this. It is likely that other variables, such as total leaf area, are responsible for the high growth rate of A. pseudoplatanus, rather than high photosynthetic rates. 5. Shade leaves of Q. robur had lower Amax and mean A than sun leaves; their quantum efficiency was also lower. Consistent with this, sun leaves had a higher nitrogen content per unit area, resulting from a lower specific leaf area (SLA). 6. Week to week variations in solar radiation influenced A; this could be described by a non-rectangular hyperbola. Stomatal conductance (gs) decreased in conditions of high vapour pressure deficit (VPD). However, this did not decrease A as high VPD was associated with high solar radiation and the stimulation of photosynthesis caused by high photosynthetic photon flux density (PPFD) more than compensated for the reduction by VPD.

Water contents in healthy xylem, reaction zones (column boundary layers) and decayed wood were determined in sycamore (Acer pseudoplatanus L.) naturally infected by sooty bark disease (Cryptostroma corticale (Ellis & Everh.) Gregory & Waller) or wound-inoculated with Ustulina deusta (Fr.) Petrak. or Ganoderma adspersum (Schulz) Donk. Water contents determined gravimetrically were greater in reaction zones than in healthy wood by factors of 1.1-2.1 times. Maps of imageable proton density (M 0 ), essentially equivalent to relative water contents, were also calculated from two independent nuclear magnetic resonance (NMR) imaging (MRI) data sets, acquired from T 1 or T 2 -weighted experiments. M 0 values derived from these, corrected for T 2 and T 1 respectively, were in good agreement, and paralleled the results obtained when total water was determined gravimetrically, although the proportional increase in M 0 in reaction zones (1.3-3.7 times) was greater than the corresponding increase in total water. Living wood saturated with water by vacuum infiltration contained approx. 1.3 times more water, determined gravimetrically, than uninfiltrated wood. The proportional increase in M 0 was greater (1.8-2.4 times). This was attributable to the alleviation of magnetic susceptibility effects by elimination of the gas-water interfaces normally present in the uninfiltrated wood. The similarities between infiltrated wood and reaction zone tissues in both total gravimetric water content and NMR-visible water suggest that the biophysical environment of the water might be similar in both. This is compatible with the hypothesis that in reaction zones the gases normally present in the lumens of empty (dead) xylem fibres are replaced by an aqueous solution of phytoalexin-like compounds. This has been confirmed by microscopy. The implications of this in relation to antimicrobial defence and xylem function are discussed. Although contrast in NMR images of lesions was predominantly attributable to changes in M 0 , a decrease in the spin-spin relaxation time (T 2 ) was seen in the vicinity of some lesions. Spin-lattice relaxation times (T 1 ) were not altered to the same extent. Results obtained from both early and late stages of decay were much more variable than those from healthy wood or from reaction zones, and reflected both the low water content of decayed wood (and hence poor signal-to-noise ratios for NMR data) and the changing physical environment as the wood was degraded.

The present work concerns atrazine absorption and metabolism by corn (Zea mays.) seedlings immersed in an aqueous medium in comparison with Acer pseudoplatanus cell cultures. At the point of equilibrium, the apparent concentration inside the A. pseudoplatanus cells (with a moderate lipid content: 0.17% of dry weight) was about twice that of the medium. This equilibrium was probably due to a simple partition process; part of the atrazine was dissolved in the cell water and reached the same concentration as in the external medium while the rest was concentrated inside the cellular lipids. The theoretical calculation of the lipid/water partition, taking into account the value of log P measured not with the lipids but with octanol (log P = 2.5), gave a value of 1.5 for concentration inside the plant material. Such an equilibrium, resulting from a partition process between water and lipids, was also obtained in non-living corn seedlings. In living seedlings, an over-concentration of radioactivity due to [ 14 C]atrazine derivatives was rapidly obtained inside roots and shoots giving concentrations respectively 7- and 12-fold higher than that of atrazine in the external medium. This was due to very rapid chemical transformation of atrazine into its hydroxy derivatives, especially hydroxyatrazine. This hydrolysis of atrazine in corn was due to the presence of high levels of benzoxazinone derivatives in corn seedling cells. The hydroxylated metabolites were able to concentrate in the cells very rapidly and were unable to diffuse freely into the external medium. As a consequence, this process facilitated the penetration of large quantities of atrazine which became rapidly hydroxylated, allowing therefore the passive penetration of atrazine to be further improved, since the concentration C 1 in the receiver compartment was always close to zero. The passive transfer of atrazine, following Fick's law: dq/dt = - Pa (C 0 -C 1 ), was therefore optimized.

Es werden Ergebnisse von dreijahrigen Untersuchungen in einem Agroforestry-Anbausystem, hier bestehend aus Acer pseudoplatanus als Geholzkultur kombiniert mit den Einsaaten “Klee” (Trifolium repens), “Weidelgras” (Lolium perenne) und “ohne Einsaat” (Herbizid), auf einer Parabraunerde aus Los vorgestellt. Der Boden wurde in den vorangegangenen Jahren intensiv landwirtschaftlich genutzt. Bei der Variante “ohne Einsaat” kam es besonders im ersten Jahr nach der Nutzungsanderung, aber auch in den Folgejahren aufgrund der geringen und erst spat in der Vegetationsperiode einsetzenden N-Entzuge durch die Geholze zu Nitratauswaschungen. Die im Boden verbleibende Menge an Mineralstickstoff war fur ein optimales Geholzwachstum ausreichend. Mit der Einsaat von Gras konnte der Boden bereits im ersten Jahr nach der Nutzungsanderung weitgehend an Mineralstickstoff entleert werden, Auswaschungen traten jedoch in der Tiefe 60–90 cm ein. In den Folgejahren blieben die Mineralstickstoffgehalte des Bodens gering, waren aber fur ein optimales Wachstum beider Kulturen nicht ausreichend. Die Wachstumsbedingungen fur die Geholze wurden zusatzlich durch die Wasserkonkurrenz des Grases beeintrachtigt. Bei der Einsaat von Klee lag als Folge der symbiontischen N-Bindung und der anschliesenden N-Mineralisation der Mineralstickstoffgehalt uber der Hohe der Entzuge. Optimales Wachstum der Geholze und der Untersaat ist gewahrleistet, es traten aber Auswaschungsverluste auf. Die auch unter Klee aufgetretenen hohen Wasserspannungen haben das Geholzwachstum nicht beeintrachtigt. In allen drei Jahren kam es bei allen Varianten zu N-Verlagerungen auch im zeitigen Fruhjahr. Das Geholzwachstum unterschied sich bisher nicht zwischen den Varianten “Herbizid” und “Klee” und war bei “Gras” deutlich geringer. Effects of the agroforestry land use system on mineral nitrogen content and water potential in a Haplic Luvisol and on growth of Acer pseudoplatanus Results from three years are presented for an agroforestry system with Acer pseudoplatanus without (bare soil, treated with herbicides) and with undercropping, which was either Lolium perenne or Trifolium repens. The soil, a Haplic Luvisol derived from loess, had been intensively cultivated by agricultural crops before. Without undercropping leaching of nitrate was observed especially in the first, but also in the following years of the experimental period. This is due to the low and late N-demand of trees. Remaining contents of mineral nitrogen in the soil were sufficient for an optimal tree growth. With Lolium perenne as undercrop the mineral nitrogen content in the soil decreased in 0–60 cm depth as a result of N-uptake already in the first year. Leaching was observed from 60–90 cm depth. In the following years mineral nitrogen contents of the soil remained low, and were not sufficient for an optimal tree growth. Tree growth was further affected because of competition for water between gras and trees. With Trifolium repens mineral nitrogen in the soil was much higher than the demand for trees and undercrop due to symbiontic N-fixation by clover with subsequent mineralization. Although low water potentials were recorded similar to gras, competition for water did not diminish tree growth. Hence, optimal tree growth is guaranteed, but leaching of nitrate cannot be avoided. For all treatments leaching of N occured also in early spring. Up to now, there was no difference of tree growth between bare soil and Trifolium repens as undercrop, tree growth was much affected by Lolium perenne as undercrop.

Summary The development of wound periderm after mechanical wounding was examined in the barks of Acer pseudoplatanus, Betula pendula, Fagus sylvatica and Sorbus aucuparia. Following the initial necrosis of cells immediately surrounding the wounds, development of the ligno-suberized barrier zone was detected within 7 days. Suberin deposition was observed in this tissue in A. pseudoplatanus, S. aucuparia and B. pendula 7 days after wounding, but not in F. sylvatica until day 14. By 28 days after wounding, extensive thickening of the walls of these cells had occurred. Differentiation of the wound periderm was detected immediately abutting the ligno-suberized barrier-zone tissues in all species, with extensive development by 28 days. Fifty-six days after wounding, the wound periderm was fully formed and completely confluent with the original periderm. Development of the wound response was similar in all species, with differences only in the timing of first detection of suberin.

summary The wood (xylem) in a living tree is protected from microbial attack by the secondary plant surface (periderm and rhytidome), which provides an effective barrier preventing the entry of most potential pathogens, and by constitutive and induced defence mechanisms in the bark (cortex and phloem). Although a few pathogens are able To penetrate these outer tissues directly, most xylem pathogens gain entry through wounds that expose this tissue and render it more vulnerable to attack. In functional sapwood, microbial colonization might be restricted by active defence mechanisms, or by passive microenvironmental restriction consequent upon the high water content and low availability of O2 in healthy conductive xylem. These factors are not mutually exclusive: indeed, they may operate in concert in many host-pathogen interactions. Sapwood lesions made by wood-decaying fungi are characteristically bounded by multiccllular walls OT barrier zones (compartmentalization wall 4 barriers and reaction zones (column boundary layers)), which may function both as inhibitory or degradation-resistant barriers to further pathogen spread, and as seals to maintain xylem function and prevent the drying and aeration that could predispose to further infection. A range of putative antimicrobial defence mechanisms contributing to the effectiveness of such barriers has been identified in sapwood tissues. This includes cell wall alterations, constitutive and induced antimicrobial compounds, necrotic responses of living cells and the deposition of gummy materials, often resinous or polyphenolic, at the host-pathogen interface. Nutritional, environmental and anatomical features of living wood might also contribute to pathogen restriction. Although there might be differences in detail, the defences operating in gymnospenns and angiosperms are generally similar. Defence responses against a variety of pathogen categories also have much in common. Dynamic studies are crucial in elucidating the roles of the various components of the host-pathogen interaction in the wood of living trees. A model for the protection and defence of xylem tissues in woody angiosperms is suggested, based largely upon results from dynamic studies of host-pathogen interactions in the wood of sycamore (Acer pseudoplatanus L.).

Sycamore (Acer pseudoplatanus L.) is a tetraploid European hardwood tree species. The reproduction system of the insect-pollinated trees and patterns of genetic variation are largely unknown. We isolated and characterized eight polymorphic microsatellite markers for Acer pseudoplatanus L. The high degree of polymorphism observed at these markers makes them useful to observe genetic variation patterns at various spatial scales and to analyse gene flow and the mating system. Primers developed for the amplification of microsatellites in A. pseudoplatanus were tested for 21 different species of genus Acer. Amplification products of the expected size were obtained in most cases.

A 42 kDa anionic peroxidase (EC 1.11.1.7) having a pl of 3.6 was purified from suspension cultures of cells of sycamore maple (Acer pseudoplatanus L.) grown in the dark by a combination of lectin-affinity, anion-exchange and gel permeation chromatography. The enzyme had an amino acid composition similar to that found for other anionic plant peroxidases, but the protein was blocked to amino-terminal protein sequencing. Commercially available antibodies against horseradish peroxidase were shown to cross-react with the sycamore maple enzyme on immunoblots. The purified peroxidase displayed differences in its affinity for each of the three monolignols, and these differences were compared to those found for a commercial preparation of horseradish peroxidase, as well as a laccase (p-diphenol:O2 oxidoreductase: EC 1.10.3.1) purified from sycamore maple cell suspension cultures. These results are discussed with respect to the role played by peroxidases in lignin deposition and host-pathogen response.

Cell suspension cultures of Acer pseudoplatanus L. (Bligny cell line) adapted to growth in the presence of NaCl, are a useful tool for investigating mechanisms for cellular salt tolerance. We compared the activities of vanadate-sensitive (plasma membrane) and nitrate-sensitive (tonoplast) ATPases, and tonoplast K + -stimulated PPase in microsomal fractions (8 000-108 000 g) from unadapted and NaCl-adapted (80 mM) cells of A. pseudoplatanus

The minor veins of small leaf discs, punched out of mature leaves and incubated in 14C-sucrose solution, appear labeled in macro- and microautoradiographs. Discs with a labeled vein pattern and with labeled sieve tubes in microautoradiographs were found in Beta vulgaris, Vicia faba, Gomphrena globosa and Antirrhinum majus. However, in several other plant species, minor veins appeared unlabeled in macroautoradiographs when the discs were incubated in 14C-sucrose. Mesophyll cells (Acer pseudoplatanus, Juglans regia, Fagia, sylvatica, Syringa vulgaris, Laburnum anagyroides), bundle-sheath cells of major veins (Salix viminalis, Robinia pseudoacacia, Commelina communis) or epidermal layers (Ginkgo biloba, Chlorophytum comosum) appeared labeled. Lack of radioactivity in sieve tubes of this latter group was confirmed by microauto-radiography. Using 14C-glucose instead of 14C-sucrose, leaf discs of Beta vulgaris showed no labeled vein pattern and in microautoradiographs the sieve tubes appeared unlabeled. In view of the by-pass phloem loading, this study provides evidence for two pathways of phloem loading.

SUMMARY The growth of Acer pseudoplatanus L. (sycamore) callus tissue on solid and liquid growth media containing elevated copper concentrations was studied in an attempt to understand the responses of trees to metal contamination and to provide an index of tolerance which may show a parallel expression of tolerance to the whole plant. Callus growth on solid media was very variable, but was significantly reduced at 10 mg l−1, with necrosis occurring at 20 mg l−1; copper was readily removed from the media in direct proportion to its concentration. Cell suspension cultures differed in their response to copper according to their site of origin. In cultures originating from uncontaminated sites, growth was inhibited at 12.5 and 15.0 mg l−1 Cu, but cultures originating from mature trees at a metal-contaminated site were not affected by these concentrations. This metal tolerance trait was stable in cell culture through repeated sub-culturing on uncontaminated media for periods of more than 12 months. The trait was not present in a culture derived from a (non-tolerant) seedling at the metal-contaminated site, but it was induced in one non-tolerant culture by repeated exposure to high metal levels. The significance of these findings is discussed in the context of the possession of appropriate genetic variation in trees for surviving the impact of metal contamination.

SUMMARY Seeds and seedlings of Acer pseudoplatanus L. (sycamore) were collected at sites contaminated by metals, originating either from mining spoil or from aerial deposition from metal processing industry, and at a number of relatively uncontaminated sites. Seedling growth was examined in relation to site of origin, both in nutrient solutions with elevated metal concentrations and in reciprocal transplant experiments in soils from the sites. Metal tolerance was not detected and there was no significant difference between plants from the different sites of origin. It was found, however, that roots could proliferate in uncontaminated zones of the soil and that, even in contaminated soils, most seedlings used in growth tests survived for at least three years despite impaired growth. Seedlings growing at the contaminated sites showed phytotoxic symptoms associated with high metal levels, but apparently healthy seedlings and saplings of different ages were also found. Some form of low level innate tolerance may be involved but it is suggested that phenotypic plasticity is more important than previously thought, potentially allowing survival until favourable conditions are encountered either temporally or spatially.

Semiprotoplasts were produced from suspension-cultured Acer pseudoplatanus (sycamore maple) cells prior to cell disruption by passing them through a 60 μm nylon screen. Cell membranes from homogenates were separated by ultracentrifugation on linear sucrose density gradients. Samples were collected by gradient fractionation and subcellular fractions were assayed for membrane markers and glycosyl transferase activities. Results of standard marker assays (cytochrome c reductase for endoplas-mic reticulum. uridine and inosine diphosphatases for Golgi. and eosin-5′-maleimide binding for plasma membrane) showed partial separation of these three membrane types. Golgi and plasma membrane markers overlapped in most gradients. Incorporation of 14C-labeled sugars from UDP-glucose and UDP-xylose into ethanol precipitated polysaccharides was used to detect glucan synthases I & II (glucosyl transferases) and xylosyl transferase activities in Golgi membrane fractions. All three glycosyl transferases overlapped in fractions corresponding to both Golgi and plasma membrane markers, although peak activities for all three occurred in different fractions. More than one peak of glucan synthase I activity was found. Glucan synthase II, associated with s-l.3 glucan (cullose) synthesis in plasma membranes, was also detected and exhibited a 10-fold stimulation in the presence of Ca2+.

This work was undertaken to verify whether surface NADH oxidases or peroxidases are involved in the apoplastic reduction of Fe(III). The reduction of Fe(III)-ADP, linked to NADH-dependent activity of horseradish peroxidase (HRP), protoplasts and cells of Acer pseudoplatanus, was measured as Fe(II)-bathophenanthrolinedisulfonate (BPDS) chelate formation. In the presence of BPDS in the incubation medium (method 1), NADH-dependent HRP activity was associated with a rapid Fe(III)-ADP reduction that was almost completely inhibited by superoxide dismutase (SOD), while catalase only slowed down the rate of reduction. A. pseudoplatanus protoplasts and cells reduced extracellular Fe(III)-ADP in the absence of exogenously supplied NADH. The addition of NADH stimulated the reduction. SOD and catalase only inhibited the NADH-dependent Fe(III)-ADP reduction. Mn(II), known for its ability to scavenge O−2, inhibited both the independent and NADH-dependent Fe(III)-ADP reduction. The reductase activity of protoplasts and cells was also monitored in the absence of BPDS (method 2). The latter was added only at the end of the reaction to evaluate Fe(II) formed. Also, in this case, both preparations reduced Fe(III)-ADP. However, the addition of NADH did not stimulate Fe(III)-ADP reduction but, instead, lowered it. This may be related to a re-oxidation of Fe(II) by H2O2 that could also be produced during NADH-dependent peroxidase activity. Catalase and SOD made the Fe(III)-ADP reduction more efficient because, by removing H2O2 (catalase) or preventing H2O2 formation (SOD), they hindered the re-oxidation of Fe(II) not chelated by BPDS. As with the result obtained by method 1, Mn(II) inhibited Fe(III)-ADP reduction carried out in the presence or absence of NADH. The different effects of SOD and Mn(II), both scavengers of O−2, may depend on the ability of Mn(II) to permeate the cells more easily than SOD. These results show that A. pseudoplatanus protoplasts and cells reduce extracellular Fe(III)-ADP. Exogenously supplied NADH induces an additional reduction of Fe(III) by the activity of NADH peroxidases of the plasmalemma or cell wall. However, the latter can also trigger the formation of H2O2 that, reacting with Fe(II) (not chelated by BPDS), generates hydroxyl radicals and converts Fe(II) to Fe(III) (Fenton's reaction).

Summary A laccase-type polyphenoloxidase (EC 1.10.3.2.), abundantly secreted by suspension-cultured sycamore (Acer pseudoplatanus) cells was purified to homogeneity. This laccase form is a glycoprotein (molecular weight 110000) with high mannose and complex glycans. The polypeptide moiety has a molecular weight of 66 000, indicating that the glycoprotein is 40% carbohydrate. Laccase is abundantly present in both the cell wall and the culture medium of suspension-cultured sycamore cells, but it is not detected in the cytoplasm, indicating that this large protein is efficiently secreted by the cells. Polyclonal rabbit antiserum was raised against the deglycosylated protein and was used to probe extracts of sycamore stem tissues. A second laccase form (molecular weight 56 000), antigenically related to laccase from cell cultures, is abundant in the epidermis of sycamore stems. In addition, this 56 kDa laccase form co-localizes with lignin precursors on tissue prints from sycamore stems. A polypeptide (molecular weight 50 000-56 000), antigenically related to sycamore laccase, was also immunodetected in most plant organs previously described in the literature as polyphenoloxidase-rich.

Herbivores, whether sucking such as aphids or chewers such as lepidopterans, impose an important drain on plant resources (Dixon 1971, Leather 1988). Plants have evolved a number of responses to minimise the effects of such parasites, although the herbivores have fought back in a variety of ingenious ways. For example, it is well known that individual trees within a species show significant variation in budburst date (Jones 1959, Leather 1996a) and it is traditionally assumed that early flushing trees suffer higher rates of herbivory from leaf chewing insects than those that flush later (Varley and Gradwell 1968). There is, however, conflicting evidence to support this assumption (Crawley and Akhteruzzaman 1988, Watt and MacFarlane 1991, Hunter 1992). These and other studies (e.g. Watt 1987, Hunter 1990) although recognizing the importance of synchrony between herbivore and host plant have not considered either within-tree variability or the fact that plant phenology may be altered by, or in response to, insect attack. Although sycamore and other trees show consistent variability in herbivore loads from year to year, i.e. a good tree for herbivores one year is a good tree for herbivores the following year (Leather 1986, Crawley and Akhteruzzaman 1988), the intra-tree distribution of these herbivores is not uniform (Leather 1996b). For example, in sycamore, Acer pseudoplatanus, some branches support much higher populations of the sycamore aphid, Drepanosiphum platanoidis, than others. Field observations suggest that those branches that supported high aphid populations in the preceding year, have an accelerated budburst compared to those branches that had few aphids on them the preceding year (Leather 1996b) and as a consequence escape the aphids hatching from the overwintering eggs. The tree thus ensures, that although aphid numbers may be high on the tree as a whole, not all branches suffer equally damaging levels of aphids. Losses due to aphid feeding, which can exceed 15% reductions in volume increment (Dixon 1971) are thus minimised. Is this a widespread phenomenon or does it apply only to phloem feeding herbivores and/or sycamores in particular? The important and puzzling question is how does the tree engineer accelerated budburst in those particular branches?

Ammonium supplied to Acer cells incubated in Tricine buffer raised net dark incorporation of 14C-bicarbonate by 1.5 to 3.3 fold; this stimulation was not abolished by prior inhibition of glutamine synthetase by methionine sulphoximine. With cells in phosphate buffer, ammonium gave a smaller 1.15 to 1.3 fold stimulation which was abolished when glutamine synthetase was inhibited. Ammonium had no direct effect on the activities of phosphoenolpyruvate carboxylase and pyruvate kinase assayed in partially purified extracts or on the enzymes catalysing release of label.

summary The dynamics of the seasonal internal cycling of nitrogen (N) in Acer pseudoplatanus were studied in relation to N supply and leaf demography. Trees were grown in sand culture, and throughout 1988, supplied with either 1.0 mol N m −3(Low N) or 6.0 mol N m −3(High N), labelled with 15N to 5.0 atom %, in order to precondition their growth and capacity for N storage over the winter period. In 1989, the initial spring growth of leaves was independent of the current N supply at either 1.0 or 6.0 mol N m−3, and depended only upon the N supplied in 1988. A net loss of 15N from perennial tissues and recovery of 15N in the growing leaves confirmed that the current N supply had no effect on the remobilization of N from winter stores in the roots and stem. After 22 May 1989, remobilization of stored N for leaf growth had ceased and leaf demography was influenced by the current N supply. Plants preconditioned to 6.0 mol N m −3in 1988, but receiving only 1.0 mol N m−3in 1989, were unable to sustain previous leaf growth after 22 May and there was a decrease in leaf mass and area due to leaf abscission. In contrast, trees preconditioned with 1.0 mol N m−3in 1988, but receiving 60 mol N m−3in 1989 greatly increased their leaf growth after 22 May. This was a consequence of the stimulation by N uptake of growth of many small leaves on axillary shoots at the base of the canopy. Although leaf number increased, mean area per leaf decreased. The trees were inefficient at withdrawing N from senescing leaves in both years, allowing most of the N to fall from the tree with the leaves. The spring remobilization of N, therefore, was dependent largely upon the direct uptake of N into the stem and roots, in late summer and autumn, for storage over the winter period. The results are discussed in relation to leaf demography and the nitrogen use efficiency of deciduous trees.

The impact of leaf-feeding nymphs of the horse chestnut scale insect, Pulvinaria regalis Canard (Hem., Coccidae), was investigated by manipulating population densities on young sycamore, lime and horse chestnut trees under experimental conditions. The effects of sap feeding on leaves by scale nymphs during the summer on shoot elongation and diameter, plus root biomass, were considered. Sycamores exhibited dramatic reductions in leader, lateral and bottom shoot elongation in the prescence of Pulvinaria nymphs in both years of the investigation. However, neither limes nor horse chestnuts showed significant changes, although data for limes qualitatively suggested increased growth when infested. In the main, diameter growth was unaffected. All three host tree species suffered significant reductions in root dry weight biomass when infested with scale nymphs. Zusammenfassung Zum Einflus des Befalls von Pulvinaria regalis Canard (Hom., Coccidae) auf junge Wirtsbaume Der Einflus der Saugschaden an Blattern junger Wirtsbaume (Ahorn, Linde und Roskastanie) durch Schildlausnymphen (Pulvinaria regalis) wurde bei unterschiedlichen Populationsdichten untersucht. Es wurden die Auswirkungen des Sommerbefalls auf Trieblange, Durchmesser und Wurzelbiomasse aufgenommen. In beiden Beobachtungsjahren zeigte sich bei Ahorn eine dramatische Reduktion der Leit- und Seitentriebe. Dagegen zeigten sich bei Linde und Roskastanie keine Veranderungen, obwohl die Daten fur Linde zunachst den Eindruck einer Wachstumsforderung durch Schildlausbefall erweckten. Das Durchmesserwachstum blieb meist unbeeinflust, dagegen verursachte der Schildlausbefall bei allen drei Wirtsbaumen eine signifikante Reduktion der Trockenbiomasse der Wurzeln.

SUMMARY Differences in maturation drying and desiccation tolerance during seed development were detected between the two contrasting Acer spp., Norway maple (Acer platanoides L.), which shows orthodox seed storage behaviour, and sycamore (A. pseudoplatanus L.), which shows recalcitrant seed storage behaviour. In both species, the onset of germinability (150 d tests at 5 °C) occurred after percentage seed moisture content had begun to decline, but before net loss in seed moisture. The onset of germinability in Norway maple occurred 4 wk before physiological maturity (i.e. 4 wk before the end of the increase in seed dry matter), whereas in sycamore it occurred some ten weeks before physiological maturity when the seeds were only 60 % filled. Seeds of Norway maple were able to tolerate enforced rapid desiccation to 10% moisture content (f. wt) at physiological maturity, when maturation-drying had reduced seed moisture content to 54 %. Between 2 and 4 wk later seed moisture content rapidly declined naturally to 25 %, at which value the fruits were shed. In contrast, a constant rate of maturation-drying was observed in sycamore. The seeds were shed at 58 % moisture content and, in almost all cases, the seeds were intolerant of rapid desiccation to c. 10 % moisture content throughout seed development. A very small proportion of sycamore seeds did survive rapid desiccation when harvested between 6 September and 4 October, but no seeds survived desiccation to 5 % moisture content or below. A comparison of the germination of sycamore seeds harvested on four dates and dried to various moisture contents showed that the seeds tolerated greater desiccation as they matured between 12 July and 20 September, but there was no further change thereafter. The results are therefore compatible with previous classifications of seed storage behaviour in each species, and with the view that the initial decline in seed moisture content stimulates the developmental switch which results in the onset of germinability in both orthodox and recalcitrant seeds.

Filtration stress, consisting in the rapid filtration of Acer pseudoplatanus L. cell suspension cultures, resulted in significant differences between the peroxidases (EC 1.11.1.7) released during cell growth and those released after filtered cells were resuspended in fresh medium (recovery medium). These differences concerned mainly modifications of (i) the pH optimum of peroxidase activity (guaiacol as electron donor), (ii) the number and the pI values of the peroxidase isoenzymes as shown by isoelectric focusing, and (iii) the molecular weights of the different peroxidase fractions determined by gel filtration chromatography. The presence of 1 mM Li+ in the recovery medium inhibited the release of peroxidase and this effect was partially reversed by K+. The release of peroxidase by stressed cells was also strongly inhibited by Na2CO3 in the recovery medium. The results presented are consistent with the proposal that the characteristic isoperoxidase patterns induced by filtration stress might be used as a model to study the response of plant cells to stress.