Changes in soluble sugars in relation to desiccation tolerance and effects of dehydration on freezing characteristics of Acer platanoides and Acer pseudoplatanus seeds

The role of soluble sugars in desiccation tolerance was investigated in seeds of two species from the genus Acer: Norway maple (Acer platanoides L.) — tolerant and sycamore (Acer pseudoplatanus L.) — intolerant to dehydration. During two years of observations it was found that seeds of Norway maple acquire desiccation tolerance at the end of August i.e. about 125 days after flowering (DAF). During seed development, the transition from intolerant to tolerant state in Norway maple seeds was accompanied by the accumulation in seed tissues of raffinose, stachyose and sucrose. The sucrose/raffinose ratio in Norway maple seeds was lower than in sycamore. In mature Norway maple seeds sucrose and raffinose contents were higher than in sycamore. It was concluded, that soluble sugars such as sucrose, raffinose and stachyose may play an important role in desiccation tolerance and/or intolerance of Norway maple and sycamore seeds. Differential thermal analysis (DTA) was used to study the relationship between desiccation sensitivity and the state of water in seed tissues. The level of non-freezable water was the same in both analysed seed species, but the temperature of water crystallization during desiccation was lower in sycamore seeds.     

Changes in abscisic acid levels in embryo axes of Norway maple and sycamore seeds during maturation and dehydration

Changes in the abscisic acid (ABA) levels in embryo axes of seeds, belonging to the orthodox (Norway maple — Acer platanoides L.) and recalcitrant (sycamore — Acer pseudoplatanus L.) categories, were investigated throughout maturation using an ELISA (enzyme-linked immunosorbent assay) test. Concentration of ABA in embryo axes substantially differed depending on species and sampling date. ABA was always higher in Norway maple except at the end of seed maturation when ABA content was similar in both species. During maturation ABA decreased in both species but the decline was more marked in Norway maple than in sycamore (11 vs. 3 fold). These species also differed in the pattern of ABA changes, which in sycamore embryo axes was very regular, while in Norway maple a sharp decrease was recorded after acquisition by the seeds of tolerance to desiccation. Dehydration of embryo axes of Norway maple caused a further significant decrease of ABA level. In contrast, in dehydrated sycamore embryo axes ABA content did not decrease, but slightly increased. The role of ABA in desiccation tolerance and dormancy of Norway maple and sycamore seeds is discussed.     

The expression of dehydrin proteins in desiccation-sensitive (recalcitrant) seeds of temperate trees

Proteins that have homology with dehydrins have been identified immunologically in the desiccationsensitive (recalcitrant) seeds of English oak (Quercus robur L.), European chestnut (Castanea sativa L.), horse chestnut (Aesculus hippocastanum L.), sycamore (Acer psuedoplatanus L.) and silver maple (Acer saccharinum L.), and in the desiccation-tolerant seeds of Norway maple (Acer platanoides L.). The mRNA for a late embryogenesis abundant (LEA) protein (dehydrin) was also detected by Northern blotting, using a cDNA clone (D11) from cotton embryos, in the recalcitrant and orthodox seeds. Medium-stringency washing was required to detect this hybridization. InQ. robur the amount of dehydrin protein increased during seed development, andLEA mRNA was induced by limited desiccation and by abscisic acid. Confirmation of the presence of dehydrin mRNA in matureQ. robur andC. sativa seeds was obtained by in-vitro translation of the extracted polyadenylated RNA followed by analysis of the immunoprecipitation products. Thus the presence of dehydrin proteins is not sufficient to confer desiccation tolerance on truly recalcitrant seeds, nor can their presence or absence be used as clear criteria for identification of recalcitrant seeds.     

Nuclear Replication Activity During Seed Development, Dormancy Breakage and Germination in Three Tree Species: Norway Maple (Acer platanoidesL.), Sycamore (Acer pseudoplatanusL.) and Cherry (Prunus aviumL.)

Flow cytometric analyses of nuclear DNA levels were carriedout during development, stratification and germination of dormantseeds from three tree species with contrasting characteristics.Norway maple (Acer platanoides) and sycamore (Acer pseudoplatanus)have orthodox (desiccation-tolerant) and recalcitrant (desiccation-sensitive)storage behaviours, respectively, and require only a periodof cold to break dormancy, whereas, orthodox cherry (Prunusavium) seeds require an initial warm period before cold stratificationto fully stimulate germination. Whole embryos and radicle tipsof both Norway maple and sycamore were found to have stablehigh levels of 4C DNA during the latter stages of developmentand both contained nuclei arrested at the 2C and 4C levels atmaturity. Mature cherry embryos had nuclei predominantly arrestedat the 2C level. This suggests that the acquisition of desiccationtolerance is not correlated with the arrest of the cell cycleat any particular nuclear DNA level. Neither DNA replicationin radicle cells nor germination occurred when seeds were maintainedmoist at a constant 20 °C. However, in the late stages ofcold treatment during stratification, nuclear DNA levels inradicle cells changed in advance of radicle emergence in theorthodox Norway maple and cherry, whereas in the recalcitrantsycamore, change was not recorded until after radicle emergence.These results show that DNA replication has potential use asan indicator of the progress of tree seeds through stratificationtreatments used to break some types of dormancy. The ways inwhich this indicator could be exploited for seed quality andperformance testing are discussed.Copyright 1998 Annals of BotanyCompany Norway maple,Acer platanoidesL., sycamore,Acer pseudoplatanusL., cherry,Prunus aviumL., DNA replication, flow cytometry, seed dormancy, stratification     

Phospholipid composition and fatty acid peroxidation during ageing of Acer platanoides seeds

Seeds of Norway maple ( Acer platanoides L.) differing in water content (10, 20 and 30%) were stored for 6 weeks at 20 to 30°C. During this period changes in phospholipids and fatty acids as well as in seed viability and germination capacity were studied. A considerable decrease in the phospholipid content was observed, which depended on the water content in the seeds and was related to the decrease of the seed germination capacity. The level of linoleic (18:2) and linolenic (18:3) acids in the phospholipid fraction decreased considerably in the course of the accelerated seed ageing. The results obtained suggest that phospholipid degradation and peroxidation of unsaturated fatty acids, followed by membrane destruction, play a considerable role in maple seed ageing.     

The Occurrence of Peroxiredoxins and Changes in Redox State in Acer platanoides and Acer pseudoplatanus During Seed Development

Journal of Plant Growth Regulation - Norway maple (Acer platanoides L.) and sycamore (A. pseudoplatanus L.) are genetically closely related species that produce desiccation-tolerant (orthodox) and...     

Association of Protective Proteins with Dehydration and Desiccation of Orthodox and Recalcitrant Category Seeds of Three Acer Genus Species

Mature and dried seeds from three species of the Acer genus, which differed in desiccation tolerance, were analyzed. The three species investigated were as follows: Acer platanoides L. (Norway maple, orthodox, A1 and A2 seedlots); Acer pseudoplatanus L. (sycamore, recalcitrant, B1 and B2 seedlots); and Acer saccharinum (silver maple, recalcitrant, C1 and C2 seedlots). We compared the appearance of dehydrins and small heat shock proteins in seedlots originating from cropping years that differed in weather conditions, which were monitored in detail during seed development. The experiments showed that three main dehydrins with approximate molecular weights of 46, 35, and 23?kDa were characteristic of all examined Acer species seeds. The three proteins were present in the A1 and A2 seedlots of the orthodox category Norway maple seeds and were noted either individually or together in the B1, B2, C1, and C2 seedlots of recalcitrant category seeds. It was found that one major small heat shock protein existed with a molecular mass of 22?kDa and was detectable at high concentrations in all seeds of the studied Acer species; after the seeds were dried, the content of this protein significantly increased. The potential modulation of dehydrin expression by environmental factors such as developmental heat sum and rainfall is discussed in the present work. The influence of water removal, which is caused by seed drying, in seeds of the same genus and belonging to the orthodox and recalcitrant categories is also explored.     

Adenine nucleotides and energy charge during dormancy breaking in embryo axes of <Emphasis Type="Italic">Acer platanoides</Emphasis> and <Emphasis Type="Italic">Fagus sylvatica</Emphasis> seeds

We analysed changes in AMP, ADP, and ATP concentrations and adenylate energy charge in Norway maple (Acer platanoides L.) and European beech (Fagus sylvatica L.) seeds during dormancy breaking (at 3 °C) and in the control variant at 15 °C. Values of the studied indicators in stratified beech seeds were generally higher at 15 °C, at least until germination (+3 °C). By contrast, in maple seeds, the values recorded during dormancy breaking by cold stratification were much higher than at 15 °C. Three peaks (usually in weeks 3, 6, and 8) were observed in maple seeds at 3 °C, but not at 15 °C. Among adenine nucleotides, AMP reached the highest levels in both species in both variants of the experiment.     

Norway Maple (Acer platanoides) Invasion of a Natural Forest Stand: Understory Consequence and Regeneration Pattern

Norway maple (Acer platanoidesis) is invasive in a natural stand in suburban Ithaca, NY. To determine the understory pattern and consequences of a Norway maple invasion, I compared density and species richness under Norway maples and sugar maples (Acer saccharum). Mean sapling density was significantly lower (P<0.0027) under Norway maples (3.64/100 m²±1.6 SE) than under sugar maples (19.4/100 m²±4.4 SE). Mean sapling species richness was significantly lower (P<0.0018) under Norway maples (0.7/32 m²±0.18 SE) than under sugar maples (2.6/32 m²±0.48 SE). Likewise, Norway maple regeneration is more frequent under sugar maples than sugar maple regeneration: 57% of sugar maple plots had Norway maple saplings while 0% of Norway maple plots had sugar maple saplings. Two significant plot effects were found for presence–absence: Norway maple saplings grow under Norway maples with a significantly lower frequency (P<0.03) than under sugar maples; sugar maple saplings grow under Norway maples with a significantly lower frequency (P<0.000) than under sugar maples. Across the site, Norway maple saplings were the most abundant (29 saplings for 480 m²). The success of Norway maple regeneration and the reductions in total stem density beneath Norway maples is most likely the result of its strong competitive abilities, notably its high shade tolerance and abundant seed crops.     

Spatial Characteristics of the Invasion of Acer platanoides on a Temperate Forested Island

We examined the spatial pattern of an introduced population of Norway maple (Acer platanoides L.) on a temperate forested island in order to quantify the influence of landscape context on invasion pattern. The spatial location of every Norway maple tree and sapling (≥0.5 m tall) that had invaded the island forest (n = 4496) was mapped using a global positioning system. The influence of landscape context was examined with the aid of a geographic information system and indices of spatial association. We found that the coniferous forest type was the most heavily invaded (71.9% of all Norway maple stems) when compared to either the hardwood or mixed conifer–hardwood forest types (5.4% and 19.3%, respectively). Across all forest types (excluding urban trees), the population was highly aggregated around roads and other Norway maple trees. For example, 90% of the population was within 40.8 m of a road with an average distance from road of 21.02 ± 0.40 m. This association around roads was significantly greater than would be predicted by chance alone (P < 0.001). Similarly, nearest neighbor distances averaged 4.5 ± 0.2 m with 90% of individuals within 8.3 m of another Norway maple. Measures of spatial association indicated that the invasion was significantly aggregated at both the stand and island scale. Nevertheless, a comparatively small but potentially influential set of individuals were observed at relatively long distances from the main invasion front. Ramifications of these disjunct establishments and other observed patterns are discussed in the context of current spread pattern theory, invasive species monitoring, and control efforts.     

Purification and characterization of an anionic peroxidase from sycamore maple (Acer pseudoplatanus) cell suspension cultures

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.     

The effect of the temperature of drying on viability and some factors affecting storability of <Emphasis Type="Italic">Fagus sylvatica</Emphasis> seeds

Beech (Fagus sylvatica L.) seeds, which are tolerant to desiccation, freshly harvested after shedding, were dried at 15 and 30 °C and at the similar rate, to 9% of water content. A slight decrease of germinability was observed in seeds dried at 30 °C. Moreover, there was a notably higher solute leakage and a higher level of lipid hydroperoxides. Seeds dried at 30 °C contained less PC and PE and a lower level of unsaturated fatty acids (18:2 and 18:3), sterols and α-tocopherol. These results as well as changes in ascorbate and glutathione contents provide conclusive evidence for the presence of oxidative stress in beech seeds desiccated at 30 °C, which damaged membranes due to increased lipid peroxidation and changed membrane structure leading to their enhanced sensibility to free radical attack during storage.     

Ascorbate and glutathione metabolism during development and desiccation of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) seeds

The ascorbate-glutathione system was studied during development and maturation of beech (Fagus sylvatica L.) seeds, the classification of which in the orthodox category is controversial. This study revealed an increase in glutathione content after acquisition of desiccation tolerance, which was more intensive in embryonic axes than in cotyledons. During seed maturation, the redox status of glutathione markedly changed toward the more reducing state, especially in cotyledons. Ascorbic acid content decreased during maturation, mostly in cotyledons. Activities of the enzymes of the ascorbate-glutathione cycle—ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2)—were markedly higher in embryonic axes than in cotyledons throughout the study period. In the course of seed maturation, the activities of these enzymes decreased. Importance of the ascorbate-glutathione cycle in desiccation tolerance of beech seeds was discussed in relation to results for typical orthodox and recalcitrant seeds of other broadleaved species.     

Extracellular laccases and peroxidases from sycamore maple (Acer pseudoplatanus) cell-suspension cultures

We have investigated the abilities of extracellular enzymes from dark-grown cell-suspension cultures of sycamore maple (Acer pseudoplatanus L.) to oxidize monolignols, the precursors for lignin biosynthesis in plants, as well as a variety of other lignin-related compounds. Laccase and peroxidase both exist as a multiplicity of isoenzymes in filtrates of spent culture medium, but their abilities to produce water-insoluble, dehydrogenation polymers (DHPs) from the monolignols (in the presence of hydrogen peroxide for the peroxidase reaction) appear identical whether or not the enzymes are purified from the concentrated filtrates or left in a crude mixture. The patterns of bonds formed in these DHPs are identical to those found in DHPs synthesized using horseradish peroxidase or fungal laccase, and many of these bonds are found in the natural lignins extracted from different plant sources. On the other hand, sycamore maple laccase is very much less active on phenolic substrates containing multiple aromatic rings than is sycamore maple peroxidase. We suggst that whereas laccase may function during the early stages of lignification to polymerize monolignols into oligo-lignols, cell-wall peroxidases may function when H₂O₂ is produced during the later stages of xylem cell development or in response to environmental stresses.Abbreviations DHP dehydrogenation polymer - IEF isoelectric focuring - NMR nuclear magnetic resonance - PAGE polyacrylamide gel electrophoresis The authors wish to thank Dr. Masahiro Samejima (University of Tokyo) for provision of lignin model compounds and Dr. Göran Gellerstadt (Royal Institute of Technology, Sweden) for helpful suggestions regarding stilbene formation and light spectroscopy. Monolignols were prepared by Mr. Nate Weymouth with help from Dr. Herb Morrison (USDA/ARS, Richard B. Russell Research Center, Athens, GA). Thanks also to Ms. Izabella Poppe of the Complex Carbohydrate Research Center (CCRC) for assistance with carbohydrate analyses, and Mr. Vincent Sorrentino for help with the growth of cell-suspension cultures.     

Grow slowly,persist, dominate—Explaining beech dominance in a primeval forest

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.     

Oxidative metabolism-related changes during germination of mono maple (<Emphasis Type="Italic">Acer mono</Emphasis> Maxim.) seeds under seasonal frozen soil

The influence of seasonal frozen soil and buried depth on germination of mono maple (Acer mono Maxim.) seeds was studied in field conditions in winter in a sub-alpine region. Mono maple seeds almost lost their ability to germinate in non-freezing soil, while seasonal frozen soil treatments facilitated the germination accompanied with a progressive accumulation of reactive oxygen species (ROS). The result indicates that ROS may act as a positive signal for seed dormancy. However, exceeding accumulation of ROS led to decrease in germination rate. We suggest that the shift from a signaling to a deleterious role may be related to the accumulation of these ROS above a threshold level that leads to various cellular alterations and damage. The enhanced activities of antioxidant enzymes appear to be more closely related to freezing tolerance, because of their ability to scavenge ROS to avoid deleterious events. Seasonal frozen soil was beneficial in accelerating the germination of mono maple seeds. However, a slight increase of freezing temperature may have also facilitated the germination of mono maple seeds by enhanced activities of antioxidant enzymes. Hence, moderate winter warming may be beneficial to mono maple regeneration due to the improvement of seed germination, but the disappearance of seasonal frozen soil may lead to germination failure of the mono maple seeds.     

Seed dormancy in Acer: Endogenous germination inhibitors and dormancy in Acer pseudoplatanus L.

Summary Dormant seeds of Acer pseudoplatanus L. contain two zones of inhibition on paper chromatograms in 10:1:1 as detected by the lettuce and cress seed germination, and the wheat coleoptile bioassays. One zone at R_f 0.6–0.8 was partitioned into ethyl acetate at acid pH and was shown to contain ABA by its behaviour on GLC and isomerization under ultra-violet light. The other zone at R_f 0.9 was detected only in the germination bioassays and was partitioned into ethyl acetate over a range of pH indicating the presence of one or more neutral compounds.The inhibitors present in the embryo of dormant sycamore seeds inhibited the germination of non-dormant sycamore seeds at relatively low concentrations. A comparison with the effects of application of exogenous ABA indicated that endogenous ABA could not solely account for the inhibitory activity of seed extracts, which appeared to be due partly to the presence of ABA and partly to that of neutral compounds present in the embryo. Leaching treatments that removed dormancy led to a decrease in the level of inhibitors present mainly in the basic fraction. The exogenous application of kinetin to dormant sycamore seeds increased germination whereas gibberellic acid had no effect. Similar responses were obtained with lettuce seeds inhibited by the basic fraction of dormant sycamore seeds.It is suggested that an inhibitor-cytokinin interaction may be involved in the dormancy of sycamore seeds.     

The effects of desiccation on seeds of Acer saccharinum and Aesculus pavia: recalcitrance in temperate tree seeds

This study was undertaken to determine how the results from lipid, moisture, and differential scanning calorimetry analyses conducted on silver maple (Aceraceae: Acer saccharinum L.) and red buckeye (Hippocastanaceae: Aesculus pavia L.) compared with those obtained from previous studies on white and water oaks (Fagaceae: Quercus alba and Q. nigra), and the tropical zone species American muskwood (Meliaceae: Guarea guidonia) and carapa (Meliaceae: Carapa guianensis). Seeds were air-dried at room temperature for 9-11 days. At intervals, germination was tested, moisture determined, and lipids extracted. It was found that, like the other recalcitrant seeds, (1) viability was greatly reduced or lost after 11 days of drying, (2) percentage changes in individual fatty acids were not related to seed viability, and (3) results from the differential scanning calorimetry studies revealed a strong relationship between enthalpy/onset data from the embryo and cotyledon tissues and loss of viability. Also, silver maple seeds experienced a 50% reduction in viability by day 5 of drying and retained an axis moisture content over 25% throughout the experiment. However, unlike the other recalcitrant seeds surveyed, both silver maple and red buckeye had a significant reduction in the total amount (mg/g) of cotyledon lipids as the experiment progressed. However, no decrease in the unsaturated/saturated fatty acid ratio was found, so we conclude that in these species lipid peroxidation is not a marker of declining seed viability. Also, red buckeye seeds did not lose 50% viability until after day 8 of the experiment, and axis moisture content fell well below 20% as the seeds dried.     

Biochemical characteristics of urban maple trees

The study, which covers the period between 2014 and 2018, was carried out in the city of Naberezhnye Chelny, Republic of Tatarstan, Russia. The aim of the study was to examine the biochemical response of maple trees growing in the anthropogenic environments. Leaf samples from 600 trees (Acer platanoides L. and Acer negundo L.) were collected at monthly intervals from June through August. Sampling was performed early in the morning (11 a.m.) in the middle of the month. The study offers statistical data on the tannin content, determined via permanganometry; the ascorbic acid concentration, found via titration with 2.6-dichlorophenolindophenol; the ascorbate oxidase activity determined by absorbance at 265 nm; and the polyphenol oxidase activity, found by the spectrophotometric method. Relatively higher ascorbate oxidase activity was detected in August among ash-leaved Acer platanoides L. and Acer negundo L. in areas with strong anthropogenic impact. Due to increased air pollution, maple trees were found to exhibit an increase of polyphenol oxidase activities. The condensed tannin content in Norway maple trees dropped over time: by 1.24 in July (avenue); by 0.94 (buffer area) and 0.76 (avenue) in August. The condensed tannin content in the ash-leaved maple trees also decreased: by 0.69 (buffer area) and 0.22 (avenue) in July; by 0.37 (buffer area) and 0.61(avenue) in August.     

Cell Cycle Activity and β-Tubulin Accumulation During Dormancy Breaking of Acer platanoides L. seeds

Cell cycle events in embryo axes of Norway maple (Acer platanoides L.) seeds were studied during dormancy breaking by flow cytometric analyses of the nuclear DNA content and by immunodetection of β-tubulin. Most embryonic nuclei of dry, fully matured seeds were arrested in the G₂ phase of the cell cycle. In addition, the lowest content of β-tubulin was detected in dry, mature seeds. Imbibition in water and cold stratification resulted in a decrease in the number of nuclei in G₂, and a simultaneous increase in β-tubulin content. In germinated seeds the content of β-tubulin was the highest and the number of cells in G₂ was the lowest. Both cell cycle events preceded cell expansion and division and subsequent growth of the radicle through the seed coat. The anatomical investigation has proved that the main reason for decrease in the number of nuclei in G₂ is mitosis, started with seeds germination (radicle protrusion). The activation of the cell cycle and the β-tubulin accumulation were associated with embryo dormancy breaking. This revised version was published online in July 2006 with corrections to the Cover Date.