Ethylene Evolution Changes in Tilted Fraxinus mandshurica Rupr. var. japonica Maxim. Seedlings in Relation to Tension Wood Formation

The effects of ethylene on tension wood formation were studied in 3-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings in two separate experiments. In experiment 1, ethylene evolution of buds and stems was measured using gas chromatography after 0, 2, 4, 7, 14, and 21 d of treatment; in experiment 2, both aminoethoxyvinylglycine （AVG） and AgNO3 were applied to the horizontally-placed stems, and the cell numbers on sites of applications were measured after 40 d. Ethylene evolution from buds was found to be much greater in tilted seedlings than in upright ones. The cell numbers of wood fibers in shoots and 1-year-old stems were reduced in treatments with 12.5×10^-7μmol/L AVG, 12.5×10^-8μmol/L AVG, and 11.8×10^-8μmol/Lmol/L AgNO3; whereas the horizontal and vertical diameters were reduced by treatment of 12.5×10^-7μmol/L AVG. Ethylene evolutions of shoots and 1-year-old stems were inhibited greatly in comparison with the control by applying 12.5×10^-7μmol/L AVG. The formation of a gelatinous layer of wood fibers was affected by neither AVG nor AgNO3 application. These results suggest that ethylene regulates the quantity of wood production, but does not affect G-layer formation in F. mandshurica Rupr. var.japonica Maxim. seedlings.     

Control of Negative Gravitropism and Tension Wood Formation by Gibberellic Acid and Indole Acetic Acid in Fraxinus mandshurica Rupr. var. japonica Maxim Seedlings

In the present study, we investigated the role of gibberellic acid (GA3) and indole acetic acid (IAA) in the gravity response of stems and tension wood formation using two-year-old stems of Fraxinus mandshurica Rupr. var.japonica Maxim seedlings. Forty-five seedlings were used and divided into nine groups that included five seedlings in each group. Seedlings were treated with applications of GA3 alone at concentrations of 2.89 × 10-8and 2.89 × 10-7 μmol/L, IAA alone at concentrations of 5.71×10-8 and 5.71 ×10-7 μmol/L, or their combination to the apical bud of the stem using a micropipette. Seedlings were positioned horizontally after the first treatment.The same treatments were repeated six times per week. At the end of the experiment, all seedlings were harvested. Then, stem segments were cut under a light microscope. Application of exogenous GA3 at the higher concentration stimulated the upward bending of stems, whereas exogenous IAA had no effect. A synergistic effect of GA3 and IAA on upward stem bending was observed following application of the two combinations of GA3 and IAA. Moreover, application of exogenous GA3 at the higher dose stimulated wood formation on both the upper and lower sides of the stems, whereas the mixture of GA3 and IAA had a synergistic effect on wood formation in horizontal stems. Application of exogenous IAA alone at the lower concentration (5.71×10-8 μ mol/L) or application of a mixture of the higher concentrations of GA3 (2.89 × 10-7 μmol/L) and IAA (5.71×10-7 μmol/L) inhibited the development of gelatinous fibers (the G-layer) of tension wood on the upper side of the horizontal stems. The differentiation of gelatinous fibers of tension wood was not inhibited by GA3when it was applied alone, whereas the development of the gelatinous fibers of tension wood was strongly affected by the application of IAA. The findings of the present study suggest that the development of the G-layer is not related to the dose of GA3, but needs a relatively lower concentration of IAA.     

Role of GA3, GA4 and Uniconazole-P in Controlling Gravitropism and Tension Wood Formation in Fraxinus mandshurica Rupr. var. japonica Maxim. Seedlings

GA3 and GA4 (gibberellins) play an important role in controlling gravitropism and tension wood formation in woody angiosperms. In order to improve our understanding of the role of GA3 and GA4 on xylem cell formation and the G-layer, we studied the effect of GA3 and GA4 and uniconazole-P, which is an inhibitor of GA biosynthesis, on tension wood formation by gravity in Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings. Forty seedlings were divided into two groups;one group was placed upright and the other tilted. Each group was further divided into four sub-groups subjected to the following treatments: 3.43 × 10-9 μmol acetone as control, 5.78 × 10-8 μmol gibberellic acid (GA3), 6.21 × 10-8 μmol GA4, and 6.86 × 10-8 μmol uniconazole-P. During the experimental period, GAs-treated seedlings exhibited negative gravitropism,whereas application of uniconazole-P inhibited negative gravitropic stem bending. GA3 and GA4 promoted wood fibers that possessed a gelatinous layer on the upper side, whereas uniconazole-P inhibited wood formation but did not inhibit the differentiation of the gelatinous layer in wood fibers on the upper side. These results suggest that: (i) both the formation of gelatinous fibers and the quantity of xylem production are important for the negative gravitropism in horizontally-positioned seedlings; (ii) GA3 and GA4 affect wood production more than differentiation of the gelatinous layer in wood fibers;G-layer development may be regulated by other hormones via the indirect-role of GA3 and GA4 in horizontally-positioned F. mandshurica seedlings rather than the direct effect of GAs; and (iii) the mechanism for upward wood stem bending is different to the newly developed shoot bending in reaction to gravity in this species.     

Ultrastructural Investigation of Tension Wood Fibre in Fraxinus mandshurica Rupr. var. japonica Maxim.

The ultrastructure of the fibre wall in Fraxinus mandshuricaRupr. var. japonica Maxim. was investigated by electron microscopy.The trees had been inclined artificially at an angle of 30°to the vertical at the beginning of the initiation of cambialgrowth in early spring. The secondary walls of tension woodfibres were of the outer (S₁) layer and gelatinous (G) layertype. The microfibrils in the gelatinous (G) layer were orientedas a steep Z-helix relative to the fibre axis with a deviationthat ranged from 0° to 25° but was mainly between 5°and 10°. The cross-sectional surface of tension wood fibresrevealed the relatively strong attachment of the G-layer tothe S₁ layer. The G-layer stained weakly with potassium permanganate.The S₁ layer of tension wood fibres stained less strongly thanthat of the normal and opposite wood fibres. These results indicatethat the tension wood in F. mandshurica var. japonica is nottypical and is somewhat anomalous. The secondary walls of normaland opposite wood fibres were composed of two layers, S₁ andS₂, and lacked an S₃ layer. Microfibrils in the S₃ layer ofjuvenile stems were extremely variable in orientation and weresparsely distributed without forming a layer. By contrast, avery thin S₃ layer was present in the wood fibres of maturestems. The variations in the formation of the S₃ layer in thefibre walls were probably due to the differences in the cambialage of the stems of F. mandshurica Rupr. var. japonica.Copyright1995, 1999 Academic Press Fraxinus mandshurica Rupr. var. japonica Maxim., Japanese ash, tension wood, fibre wall, G-layer, microfibrillar orientation, normal and opposite wood, juvenile stem, field-emission scanning electron microscopy, low accelerating voltage     

赤霉素对水平放置水曲柳幼苗的负向重性和木材形成的影响

对水平放置2年生水曲柳(Franxinus mandshurica)幼苗应用赤霉素(GAs)及其合成抑制剂烯効唑(Uni．-P)对幼苗的负向重性及木材形成中的生理作用进行了探讨。每种生长调节物质100μg溶于50％的丙酮中，每周1次处理于幼苗顶端，连续处理5周，并在第1次处理后24h，将幼苗水平放置。在实验期间，对照及GAs处理幼苗茎负向重性受到了促进，而Uni．-P处理则受到了抑制。GAs增加了茎上侧具有增厚细胞壁的胶质纤维细胞的数量。Uni．-P抑制了茎上侧的木材形成，但没有影响胶质纤维的分化。对照区木质部中纤维素与木质素的比值上侧大于下侧。该比值在上侧GA4处理区大于GA3处理区及对照区。该结果说明，胶质纤维的分化和木质部的增加对负向重性都是重要的；在该种中，赤霉素对于木质部细胞形成可能比对胶质纤维分化的影响更大。     

Phosphate Availability Alters Lateral Root Anatomy and Root Architecture of Fraxinus mandshurica Rupr. Seedlings

Plants have evolved some mechanisms to maximize the efficiency of phosphorus acquisition.Changes in root architecture are one such mechanism. When Fraxinus mandshurica Rupr. seedlings were grown under conditions of low phosphorus availability, the length of cells in the meristem zone of the lateral roots was longer, but the length of cells in the elongation and mature zones of the lateral roots was shorter,compared with seedlings grown under conditions of high phosphorus availability. The elongation rates of primary roots increased as phosphorus availability increased, but the elongation rates of the branched zones of the primary roots decreased. The number of lateral root primordia and the length of the lateral roots decreased as phosphorus availability increased. The topological index (altitude slope) decreased as phosphorus availability increased, suggesting that root architecture tended to be herringbone-like when seedlings were grown under conditions of low phosphate availability. Herringbone-like root systems exploit nutrients more efficiently, but they have higher construction costs than root systems with a branching pattern.     

Phosphate Availability Alters Lateral Root Anatomy and Root Architecture of Fraxinus mandshurica Rupr. Seedlings

Plants have evolved some mechanisms to maximize the efficiency of phosphorus acquisition. Changes in root architecture are one such mechanism. When Fraxinus mandshurica Rupr. seedlings were grown under conditions of low phosphorus availability, the length of cells in the meristem zone of the lateral roots was longer, but the length of cells in the elongation and mature zones of the lateral roots was shorter,compared with seedlings grown under conditions of high phosphorus availability. The elongation rates of primary roots increased as phosphorus availability increased, but the elongation rates of the branched zones of the primary roots decreased. The number of lateral root primordia and the length of the lateral roots decreased as phosphorus availability increased. The topological index (altitude slope) decreased as phosphorus availability increased, suggesting that root architecture tended to be herringbone-like when seedlings were grown under conditions of low phosphate availability. Herringbone-like root systems exploit nutrients more efficiently, but they have higher construction costs than root systems with a branching pattem.     

Fat-tailed gene flow in the dioecious canopy tree species Fraxinus mandshurica var. japonica revealed by microsatellites

Pollen flow, seed dispersal and individual reproductive success can be simultaneously estimated from the genotypes of adults and offspring using stochastic models. Using four polymorphic microsatellite loci, gene flow of the wind-pollinated and wind-seed-dispersed dioecious tree species, Fraxinus mandshurica var. japonica, was quantified in a riparian forest, in northern Japan. In a 10.5-ha plot, 74 female adults, 76 male adults and 292 current-year seedlings were mapped and genotyped, together with 200 seeds. To estimate dispersal kernels of pollen and seeds, we applied normal, exponential power, Weibull, bivariate t-distribution kernels, and two-component models consisting of two normal distribution functions, one with a small and one with a large variance. A two-component pollen flow model with a small contribution (26.1%) from short-distance dispersal (sigma = 7.2 m), and the rest from long-distance flow (sigma = 209.9 m), was chosen for the best-fitting model. The average distance that integrated pollen flows inside and outside the study plot was estimated to be 196.8 m. Tree size and flowering intensity affected reproduction, and there appeared to be critical values that distinguished reproductively successful and unsuccessful adults. In contrast, the gene flow model that estimated both pollen and seed dispersal from established seedlings resulted in extensive seed dispersal, and the expected spatial genetic structures did not satisfactorily fit with the observations, even for the selected model. Our results advanced small-scale individual-based parentage analysis for quantifying fat-tailed gene flow in wind-mediated species, but also clarified its limitations and suggested future possibilities for gene flow studies.     

Contrasting patterns of nuclear microsatellite genetic structure of Fraxinus mandshurica var. japonica between northern and southern populations in Japan

Aim The aim of this study is to detect extant patterns of population genetic structure of Fraxinus mandshurica var. japonica in Japan, and to provide insights into the post‐glacial history of this species during the Holocene. Location Hokkaido and Honshu islands, Japan (including the Oshima and Shimokita peninsulas). Methods We examined nine polymorphic nuclear microsatellite loci to assess genetic variation within and among 15 populations across almost the entire range of the species in Japan. Extant patterns of geographical structure were analysed using Bayesian clustering, Monmonier’s algorithm, analysis of molecular variance, Mantel tests and principal coordinates analysis. Recent bottlenecks within populations and regional genetic variation were also assessed. Results Northern populations (Hokkaido Island and the Shimokita Peninsula) formed a single homogeneous deme, maintaining the highest level of allelic diversity on the Oshima Peninsula. By contrast, southern populations (Honshu Island) demonstrated strong substructure on both coasts. Specifically, populations on the Pacific side of Honshu exhibited significant bottlenecks and erosion of allelic diversity but preserved distinct subclusters diverging from widespread subclusters on the Japan Sea side of this island. Main conclusions Genetic evidence and life history traits suggest that F. mandshurica occupied cryptic northern refugia on the Oshima Peninsula during the Last Glacial Maximum, which is reflected in the species’ extant northern distribution. Strong geographical structure in southern populations, in agreement with fossil pollen records, suggests geographical isolation by mountain ranges running north–south along Honshu. Given that this tree species is cold‐adapted and found in riparian habitats, populations on the Pacific side of Honshu probably contracted into higher‐elevation swamps during warm post‐glacial periods, leading to a reduction of effective population sizes and rare allelic richness.     

肥城佛桃果实软化过程中的超弱发光及其与乙烯释放的关系

无论在室温还是低温条件下,肥城佛桃(Prunus persica cv.Fei-Cheng)果实在衰老软化过程中超弱发光均有明显的高峰出现,其出现时间与乙烯释放速率峰值相一致。乙烯合成抑制剂2-氨基乙氧基乙烯甘氨酸(2-aminoethoxyvinylglycine,AVG)与乙烯利(ethrel,化学名称2-氯乙基膦酸)处理结果显示,果实超弱发光并不随乙烯释放速率的增减而定量变化,说明果实乙烯释放与超弱发光变化没有直接的因果关系,超弱发光高峰的出现可能是果实衰老软化过程中代谢活跃的反映。