In vitro regeneration of Norway maple (Acer platanoides L.)

Regenerants were produced from axillary buds, but not from petiole segments, greenwood cuttings and leaf discs. Petiole segments and greenwood cuttings responded by massive callus cell proliferation without adventitious shoot formation. The development of induced buds into shoots occurred on WPM medium containing kinetin. Vigorous shoots larger than 2.0 cm in length were successfully rooted in half strength WPM medium supplemented with 1.0 mg dm^-3 indole-3-butyric acid.     

The Role of Osmotic Potential in Spring Sap Flow of Mature Sugar Maple Trees (Acer saccharum Marsh)

Field measurements of xylem sap osmotic and pressure potentialwere made on sugar maple trecs (Acer saccharum Marsh) duringthe winter and spring of 3 years to determine whether the hydrostaticpressure was osmotically generated. Sap osmotic potential waslow enough to account for the hydrostatic pressure but the dynamicsof its diurnal behaviour indicated that osmotic potential wasnot directly responsible for hydrostatic pressure. The diurnalcourse of hydrostatic pressure showed definite peaks but osmoticpotential often did not. The magnitude of the diurnal changesin hydrostatic pressure was approximately 0·15 MPa whereasthe changes in osmotic potential were only 0·05 MPa.Because the sap osmoticum is primarily sucrose, and starch isstored in the xylem throughout the tree, the temperature dependenceof the sucrose-starch interconversion system was investigated.More active amylase was formed in maple twigs after incubationat 0°C and 4°C than at –3, 6 or 15°C. Therate of starch hydrolysis by maple amylase increased with temperature,reaching a maximum at approximately 45°C. There was somestarch hydrolysis at –3°C. The starch hydrolysis systemthus indicated no critical role for temperature fluctuationsabout 0°C. Starch was found to be densely stored in therays of the trunk and twigs and around the central pith in thetwigs. Key words: Acer succhmum Marsh, Osmotic potential, Xylem sap pressure     

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     

Effects of Elevated [CO2] and Low Soil Moisture on the Physiological Responses of Mountain Maple (Acer spicatum L.) Seedlings to Light

Global climate change is expected to affect how plants respond to their physical and biological environments. In this study, we examined the effects of elevated CO₂ ([CO₂]) and low soil moisture on the physiological responses of mountain maple (Acer spicatum L.) seedlings to light availability. The seedlings were grown at ambient (392 µmol mol⁻¹) and elevated (784 µmol mol⁻¹) [CO₂], low and high soil moisture (M) regimes, at high light (100%) and low light (30%) in the greenhouse for one growing season. We measured net photosynthesis (A), stomatal conductance (g_s), instantaneous water use efficiency (IWUE), maximum rate of carboxylation (V_cmax), rate of photosynthetic electron transport (J), triose phosphate utilization (TPU)), leaf respiration (R_d), light compensation point (LCP) and mid-day shoot water potential (Ψ_x). A and g_s did not show significant responses to light treatment in seedlings grown at low soil moisture treatment, but the high light significantly decreased the C_i/C_a in those seedlings. IWUE was significantly higher in the elevated compared with the ambient [CO₂], and the effect was greater at high than the low light treatment. LCP did not respond to the soil moisture treatments when seedlings were grown in high light under both [CO₂]. The low soil moisture significantly reduced Ψ_x but had no significant effect on the responses of other physiological traits to light or [CO₂]. These results suggest that as the atmospheric [CO₂] rises, the physiological performance of mountain maple seedlings in high light environments may be enhanced, particularly when soil moisture conditions are favourable.     

Hormonal regulation of germination and early seedling development in Acer pseudoplatanus (L.)

Summary Dormancy of intact sycamore (Acer pseudoplatanus) seeds was broken by chilling (5°C) for several weeks in moist conditions. Treatment of unchilled seeds with kinetin induced some germination, but gibberellin was ineffective. This stimulation by kinetin was not suppressed by the added presence of abscisic acid during incubation.The chilling requirement of intact seeds was eliminated by removal of the testa, and the naked embryos developed with no morphological abnormalities. During early growth of isolated embryos in the light, two distinct developmental processes were recognised. One involved initial elongation of the radicle accompanied by geotropic curvature and was stimulated by kinetin but not by gibberellin, while the other involved unrolling of the cotyledons, which was accelerated by gibberellin but much less by kinetin. Abscisic acid strongly suppressed both developmental processes when applied alone, inhibited cotyledon expansion in the presence of gibberellin, but failed to overcome the promotory effects of kinetin on radicle growth. Experiments with CCC indicated that under natural conditions the unrolling of the cotyledons is dependent upon endogenous gibberellin. Radicle growth of isolated embryos was unimpaired by incubation in the dark, but cotyledon expansion of water incubated embryos was poor, and although it was accelerated by gibberellin, the responses in all treatments were slower than in the corresponding light grown samples.It is suggested that endogenous cytokinins are primary factors in the initiation of radicle growth, while gibberellins are important in cotyledon expansion. Abscisic acid appears to have an inhibitory role in both processes, and the interactions of these regulators in the control of germination and development are discussed.     

Antioxidative response of ascorbate-glutathione pathway enzymes and metabolites to desiccation of recalcitrant Acer saccharinum seeds

Ascorbate–glutathione systems were studied during desiccation of recalcitrant seeds of the silver maple (Acer saccharinum L.). The desiccated seeds gradually lost their germination capacity and this was strongly correlated with an increase in electrolyte leakage from seeds. Simultaneously the increase of reactive oxygen species (ROS) (superoxide radical – O₂⁻ and hydrogen peroxide – H₂O₂) production was observed. The results indicate that remarkable changes in the concentrations and redox status of ascorbate and glutathione occur in embryo axes and cotyledons. After shedding, concentrations of ascorbic acid (ASA) and the reduced form of glutathione (GSH) are higher in embryo axes than in cotyledons and their redox status is high in both embryo parts. Cotyledons in freshly shed seeds are devoid of GSH. At the first stages of desiccation, up to a level of 43% of moisture content, ASA content in embryo axes and GSH content in cotyledons increased. Below this level of moisture content, the antioxidant contents as well as their redox status rapidly decreased. The enzymes of the ascorbate–glutathione pathway: 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) increased their activity during desiccation, but mainly in embryonic axes. The changes are probably required for counteracting the production of ROS during desiccation. The relationship between ascorbate and glutathione metabolism and their relevance during desiccation of recalcitrant Acer saccharinum seeds is discussed.     

Branch growth and leaf numbers of red maple (Acer rubrum L.) and red oak (Quercus rubra L.): response to defoliation

Summary Branch growth and leaf formation from terminal and from lateral buds of red maple (Acer rubrum L.) and red oak (Quercus rubra L.) were measured in response to simulated insect defoliation. A single large branch representative of the crown of each tree was used for enumeration of growth and of bud numbers throughout three successive years of 0, 50, 75, and 100% leaf removal for the entire tree. Leaf number per tree for both species after the last year of defoliation was reduced in direct proportion to the severity of defoliation, in comparison to the predefoliation status of the trees. Bud number per tree for red maple, but not for red oak, was also reduced in proportion to severity of defoliation.Averaged over all defoliation treatments, defoliation reduced branch growth more than leaf production. Furthermore, the reduction in branch growth and leaf production was greater in red oak than in red maple. Three years of successive defoliation reduced the mean lateral plus terminal branch growth by 40% in red oak and by 23% in red maple, while leaf number was reduced 22% in red oak and remained unchanged in red maple. In red maple, 100% defoliation caused greater branch death than the 50 or 75% defoliation treatments, and the amount of death was greater after each successive year of defoliation. In contrast to red maple, undefoliated red oak incurred a substantial amount of branch death throughout the study which was little affected by defoliation treatment.     

The impact of season of harvest and duration of pre-measurement storage impact hydraulic conductance of stem samples for Acer rubrum L. x saccharinum L. and Fraxinus americana L

The influence of pre-measurement storage length and season of harvest of stem segment samples on hydraulic conductance and percentage embolism was determined for two tree species because no published guidelines exist concerning storage. Stem sections from Fraxinus americana L. 'Autumn Applause' (white ash) and Acer rubrum L. x saccharinum L. 'Autumn Blaze' (hybrid red maple) were collected from well-established trees in fall 1995 (October), spring 1996 (April), and summer 1996 (July). Ends of stem sections collected in the fall were either covered with wax or left exposed. Entire sections from all dates were placed in closed plastic bags to prevent desiccation during transport and subsequent storage. Stem sections were either analyzed immediately (0 storage) or held at 2 degrees C for 2 or 4 days. Hydraulic conductance before embolisms were cleared with positive pressure (initial k(h)), hydraulic conductance after embolisms were cleared (maximum k(h)), and percentage embolism were similar for all pre-embolism measurement storage lengths within each of the three seasonal sampling periods for hybrid red maple and spring- and summer-collected white ash. Fall-collected white ash samples with 0 storage had higher initial k(h), and percentage embolism increased if samples were stored. Embolism was greatest for summer-collected samples and lowest for spring-collected samples for hybrid red maple, but values were similar for white ash. Stem covering did not influence measured parameters. Our data indicate that hybrid red maple stem segments can be stored without significant loss of hydraulic conductance for up to 4 days, but white ash should not be stored in the fall. Unless maximum levels of native embolism have been reached, as determined from laboratory analysis, stem segments of species on which storage data are not available should be processed as soon as possible.     

Isolation and Characterization of Golgi Membranes from Suspension-Cultured Cells of Sycamore (Acer pseudoplatanus L.)

A simple and rapid technique was developed for the isolationof the vesicular Golgi membranes from suspension-cultured cellsof sycamore (Acer pseudoplatanus L.). The procedure involvespreparation of protoplasts and differential centrifugation ofdisrupted protoplasts followed by the sucrose density gradientcentrifugation. Starting from broken protoplasts, sedimentableat two different centrifugal forces (10,000g and 100,000 g),two Golgi-enriched fractions of lower density, GF₁ and GF'₁,and higher density, GF₂ and GF'₂, were separated. Purity ofthe fraction was assessed by determining the marker enzyme activitiesas well as the electron microscopy of the specimens obtained. Inosine diphosphatase was enriched about 15- and 6-fold, respectively,in the GF₂ fraction from 10,000g and the GF'₂ one from 100,000gpellets, whereas the enrichment in GF₁ and GF'₁ was approximately6–7 fold. Galactosyl-transferase in GF₂ was enriched about25-fold. GF₁ and GF₂ account for 3–4% of the total proteinof 10,000g pellets, and GF'₁ and GF'₂ for about 6–7%of the total protein of 100,000g pellets. Electron microscopicobservations show that GF₂ and GF'₂ consisted principally ofvesicular Golgi membranes without an internal matrix althoughGF₁ and GF'₁ were contaminated with ER membranes and ribosomes. (Received March 11, 1985; Accepted June 17, 1985)     

Effect of Iron Deficiency on the Respiration of Sycamore (Acer pseudoplatanus L.) Cells

The effects of iron deficiency on cell culture growth, cell respiration, mitochondrial oxidative properties, and the electron transport chain were studied with suspension-cultured sycamore (Acer pseudoplatanus L.) cells. Iron deprivation considerably decreased the initial growth rates and limited the maximum density of the cells. Under these conditions, the cells remained swollen throughout their growth. The absence of iron led to a steady decline in the uncoupled rate of O2 consumption. When the uncoupled rate of O2 uptake closely approximated the respiratory rate, the cells began to collapse. At this stage, the level of all the cytochromes and electron paramagnetic resonance-detectable Fe-S clusters of the mitochondrial inner membrane were dramatically decreased. Nevertheless, it appeared from substrate oxidation measurements that this overall depletion in iron-containing components solely disturbed the functioning of complex II, whereas neither complexes I, III, or IV, nor the machinery involved in ATP synthesis, was apparently impaired in iron-deficient mitochondria. However, our results suggest that the impairment of complex II resulted in a strong reduction of the overall capacity of the mitochondrial electron transport chain, which was responsible for determining the rate of endogenous respiration in sycamore cells. Finally, this situation led to a depletion of various energy metabolites that could contribute to the premature cell death.     

Autumn leaf colours as indicators of decomposition rate in sycamore (Acer pseudoplatanus L.)

We tested the hypothesis that there is a causal connection between autumn colour, nutrient concentration and decomposibility of fresh leaf litter. Samples from patches of different autumn colours within the leaves of the deciduous tree sycamore (Acer pseudoplatanus) were sealed into litter bags and incubated for one winter in an outdoor leaf mould bed. Green leaf patches were decomposed faster than yellow or brown patches and this corresponded with the higher N and P concentrations in the former. Black patches, indicating colonisation by the tar spot fungus Rhytisma acerinum, were particularly high in P, but were decomposed very slowly, owing probably to resource immobilisation by the fungus. The results supported the hypothesis and were consistent with a previous study reporting an interspecific link between autumn coloration and decomposition rate. Autumn leaf colour of deciduous woody plants may serve as a useful predictor of litter decomposibility in ecosystem or biome scale studies where extensive direct measurements of litter chemistry and decomposition are not feasible. This revised version was published online in June 2006 with corrections to the Cover Date.     

Protein Phosphorylation in Amyloplasts Isolated from Suspension-Cultured Cells of Sycamore (Acer pseudoplatanus L.)

Highly purified amyloplasts were isolated from cultured cells of sycamore (Acer pseudoplatanus L.). Incubation of amyloplasts with [γ-³²P]-ATP resulted in the labeling of more than ten polypeptides. Pulsechase experiments showed the reversibility of the process with some but not all of the polypeptides. The phosphorylation reaction of one polypeptide, M_r 100, was shown to be calcium dependent. Although exogenously added pig brain calmodulin had no effect, the calmodulin antagonist W-7 strongly inhibited phosphorylation of the 100 kilodaltons polypeptide. The presence of endogenous calmodulin, about 1 to 3 micrograms per milligram protein, in the amyloplast preparation was estimated by activation of phosphodiesterase in vitro.     

Dynamic changes in petiole specific conductivity in red maple (Acer rubrum L.), tulip tree (Liriodendron tulipifera L.) and northern fox grape (Vitis labrusca L.)

Diurnal variation in petiole specific hydraulic conductivity and simultaneous measurements of leaf water potential were recorded in red maple, tulip tree and fox grape. Petiole specific conductivity was determined from in situ measurements of water flow into the distal (leaf‐bearing) end of an attached petiole as a function of applied hydrostatic pressure and petiole dimensions. The hydraulic properties of the petiole dominated the measurements, indicating that this technique can be used for rapid estimates of petiole hydraulic conductivity. There was a significant decrease in petiole specific conductivity associated with increasingly more negative leaf water potentials in maple and tulip tree, but not in grape. Petiole specific conductivity increased during the afternoon while the plant was actively transpiring and the xylem sap was under tension. The recovery of petiole conductivity during the afternoon suggests that hydraulic conductivity reflects a dynamic balance between a loss of hydraulic conductivity with increasing water stress, and its restoration as tension within the xylem decreases. Three experimental manipulations were applied to red maple and tulip tree to examine the sensitivity of diurnal changes in petiole conductivity to various physiological perturbations. Both phloem girdling and application of HgCl₂ to the transpiration stream resulted in a marked decrease in the degree to which petiole specific conductivity recovered as xylem tension relaxed during the afternoon. Delivery of a surfactant to the xylem, however, did not significantly alter the relation between leaf water potential and petiole hydraulic conductivity.