Why does phosphorus limitation increase wood density in Eucalyptus grandis seedlings?

Wood density influences both the physiological function and economic value of tree stems. We examined the relationship between phosphorus (P) supply and stem wood density of Eucalyptus grandis Hill ex Maiden seedlings grown with varying soil P additions and determined how changes in wood anatomy and biomass partitioning affect the relationship. Plant height, stem diameter and total biomass increased by 400-500% with increasing P supply. Stem wood density decreased sharply from 520 to 380 kg m(-3) as P supply increased to 70 mg P kg(soil) (-1). Further increases in P supply to 1000 mg P kg(soil) (-1) had no effect on wood density. The increase in wood density at low soil P supply arose principally from enhanced secondary wall thickening of stem fiber cells. Cell wall thickness increased from 3.6 to 4.5 microm as soil P supply decreased. Because fiber cell diameter was independent of soil P (12 microm +/- 0.3), the proportion of the stem occupied by cell wall material increased as P supply declined. The enhanced secondary wall thickening of stem fiber cells at low P supply was not associated with changes in whole-plant biomass partitioning. Instead, low P supply appeared to alter biomass partitioning within the stem in favor of secondary wall thickening. Thus, increased wood density in E. grandis seedlings grown at low P soil supply was associated with inhibited stem cambial activity, resulting in an increased proportion of photoassimilates available for secondary wall thickening of fiber cells.     

毛竹茎秆纤维发育过程中细胞壁的变化规律研究

利用多种方法和技术,从壁厚、腔径、壁腔比、结晶度和细胞壁层次等方面对毛竹茎秆纤维细胞壁的变化规律进行了研究.结果表明,一年之中纤维细胞壁的积累主要集中在3-6月份;随着年龄的增加,纤维细胞壁将逐渐加厚,在前3年其加厚趋势明显,以后细胞壁的厚度逐渐趋于稳定;纤维细胞壁多层结构的形成具有类似于树木年轮的生长规律;而结晶度的变化反映了纤维细胞次生壁形成过程中各种成分的沉积规律.     

银合欢根瘤细胞的超微结构

银合欢是热带豆科固氮树种,已引起世界各国的普遍重视。我国大陆沿海亚热带地区已有60—70年的引种史。在过去引种栽培的基础上,80年代由国际固氮树种协会(NFTA)和麦威夷大学提供我们一批新银合欢种籽。厦门引种栽培的银合欢,与在其它热带地区有同样表现,速生快长、结果荚早、种籽成熟弹出,就地萌发丛生,压倒附近的其它植物。它的根系生长十分发达。幼苗期就结瘤很多,根瘤直径2.5—15mm,呈现不同形状的复式分叉瘤。测出固氮活性8.069—12.207βmC_2H_4·g~(-1)鲜瘤·时~(-1)。另外植株各部分蛋白质含量丰富,其中还含有一种特殊的氨基酸,与其固氮细胞累积转运有着密切关系。本文仅介绍银合欢根瘤细胞结构变化特征,和与其它豆科根瘤的比较进行了讨论。     

Loblolly pine seed dormancy: constraints to germination.

Stratification by moist chilling is often used to break seed dormancy in loblolly pine (Pinus taeda L.). The role that moist chilling plays at the cellular level in preparing the embryo for germination and early seedling growth was investigated. Moist chilling did not affect the embryo's ability to mobilize seed storage proteins, which is a biochemical marker of early seedling growth. Analysis of in vivo protein synthesis profiles indicated that moist chilling has only a subtle effect on gene expression in the embryo or germinant. The means by which moist chilling affects interactions between the seed coat and the living tissues of the seed also was studied. Although the seed coat is mainly a mechanical barrier to germination, seed coat replacement studies showed that moist chilling alleviates some factor(s) in the seed coat that significantly inhibit germination.     

珙桐种子休眠的解剖学研究

对珙桐核果进行解剖观察研究表明,珙桐果核壁细胞高度木质化增厚和各组成成分在三维空间排列上的相互穿插、纵横交织、彼此嵌合的结构特点,是导致珙桐种子难于萌发,长期处于休眠状态的最主要原因。其胚胎发育上的不成熟性,加重了种子休眠的双重性。提出克服果核障碍,是克服种子休眠的关键。     

濒危树种羊角槭种子基本生物学特征

采用种皮透水性测定、生活力测定、种皮和种胚甲醇提取液测定等方法,对羊角槭基本生物学特征进行了研究。结果表明:羊角槭种子呈压扁状卵圆形,由外种皮、内种皮、种胚和子叶组成,无胚乳;种子千粒质量50.88g,其中种皮占完整种子质量的79.55%以上;种子中空籽和败育种子比例达63.81%,反映出较高的种子败育率;饱满的种子中有生活力者占56.67%;种皮具有一定的透水性,种皮和种胚甲醇提取液对白菜籽发芽有抑制作用,说明羊角槭种子自身含有发芽抑制物可能是导致种子深休眠的主因。     

Lignin deposition during earlywood and latewood formation in Scots pine stems

Lignin deposition at consecutive secondary wall thickening stages of early and late xylem cells during annual ring wood formation in Scots pine (Pinus sylvestris L.) stems was studied. Lignin patterns, isolated by thioglycolic acid method, consisted of alcohol-soluble (LTGA-I) and alkali-soluble (LTGA-II) fractions. The sum of two fractions, being the total lignin content, gradually increased in the course of lignification. However, the increments of lignin amount at each development stage of early and late tracheids were different. The intensity of lignin deposition increased in the course of earlywood tracheid maturation and decreased toward the end of latewood cell differentiation. The deposition of two lignin fractions in each layer of forming wood also occurred oppositely. The increment of LTGA-I descended, whereas that of LTGA-II increased from the beginning to the end of early xylem lignification. In contrast, LTGA-I increment dropped, whereas LTGA-II rose during late xylem lignification. Gel permeation chromatography showed that the lignins, formed at the beginning of lignification, were more homogeneous and had higher molecular weight compared with the lignins at the end of cell differentiation. Besides, the content of cellulose, estimated as the residue after lignin isolation, and of cell wall substances, presented as cell wall cross-section areas, at consecutive maturation stages of early and late xylem cells have been found to be different. The data show that lignin deposition occurred in different conditions and with opposite dynamics during early and late xylem formation.     

Effects of tallowtree seed coat on seed germination

We measured physiological parameters including water uptake, in-vitro embryo germination ratio, and seed coat structure observed by scanning electron microscopy (SEM) to explore the influence of seed coat on the germination of seeds of tallow tree (Sapium sebiferum (Linn) Roxb.). Tallow tree seeds had good water permeability. We found that germination of cabbage seeds was inhibited when cabbage seeds were soaked in extracted solutions from tallow tree seed coat. Seed coat structure at the side of the radicle appeared to be a barrier to seed germination. We tested methods to break tallow tree seed dormancy. Dormancy of tallow tree seeds was overcome by soaking the seeds in 500 mg·L-1 or 1000 mg·L-1 GA3, followed by 100 days of cold stratification.     

CELLULAR SUBSTANCE EXUDATION AND SEED VIGOUR

In this paper.seeds of pinus koraiensis which has a characteristic of deep dormancywere selected as an expriment material,and the relation of cellular substance exudation to seed vig-our is discussed based on the dormant state,the different measuring parts and the imbibed state ofseeds before testing,as well as on the respiration of embryo and endosperm.The major measured re-sults are as follows:(1)After soaking for 24h,the dry embryo conductivity of seedlot L is greaterthat than of seedlot H:(2)The substance exudation of dry embryo of seedlot H is less than that ofseedlot L;(3)After seeds imbibed,the substance exudation of dormant embryo of seedlot H is morethan that of seedlot L;(4)After germination hastening treatment,the substance exudation of H em-bryos is greater than that of L embryos;(5)After artificially accclcrated ageing treatment,the em-bryo conductivity of imbibed seeds has a positive correlation with seed vigour.     

Lignin distribution in birch (Betula verrucosa) as determined by mercurization with SEM- and TEM-EDXA

Summary A new technique suitable for determination of lignin distribution in hardwoods has been developed. The technique is based on the mercurization of the aromatic nucleus of the lignin and a concomitant determination of the mercury content by the SEM- or TEM-EDXA technique. An incorporation of one mole mercury per mole lignin (C₉-unit) was obtained for the birch lignin. The concentration of lignin was found to be about 3 times higher in the cell corners of the middle lamella than in the secondary wall of the birch fibers. The cell wall of the vessels and the ray cells were almost equal in lignin concentration and had about 1.5–1.6 times higher concentration than the secondary wall of the fibers. No specific mass loss of the organically bound mercury during the electron beam bombardment was found under the conditions used in this work.     

Temperature effects on wood anatomy, wood density, photosynthesis and biomass partitioning of Eucalyptus grandis seedlings

Wood density, a gross measure of wood mass relative to wood volume, is important in our understanding of stem volume growth, carbon sequestration and leaf water supply. Disproportionate changes in the ratio of wood mass to volume may occur at the level of the whole stem or the individual cell. In general, there is a positive relationship between temperature and wood density of eucalypts, although this relationship has broken down in recent years with wood density decreasing as global temperatures have risen. To determine the anatomical causes of the effects of temperature on wood density, Eucalyptus grandis W. Hill ex Maiden seedlings were grown in controlled-environment cabinets at constant temperatures from 10 to 35 degrees C. The 20% increase in wood density of E. grandis seedlings grown at the higher temperatures was variously related to a 40% reduction in lumen area of xylem vessels, a 10% reduction in the lumen area of fiber cells and a 10% increase in fiber cell wall thickness. The changes in cell wall characteristics could be considered analogous to changes in carbon supply. Lumen area of fiber cells declined because of reduced fiber cell expansion and increased fiber cell wall thickening. Fiber cell wall thickness was positively related to canopy CO2 assimilation rate (Ac), which increased 26-fold because of a 24-fold increase in leaf area and a doubling in leaf CO2 assimilation rate from minima at 10 and 35 degrees C to maxima at 25 and 30 degrees C. Increased Ac increased seedling volume, biomass and wood density; but increased wood density was also related to a shift in partitioning of seedling biomass from roots to stems as temperature increased.     

林木种子休眠研究评述

种子休眠,是指在充分满足各种发芽条件时,有生命力的种子一时不能发芽或发芽困难的自然现象。处于休眠的种子,种皮坚硬、含水量低,细胞内养分处于难溶态,代谢活动较低。一般将种子休眠划分为三个类型:即强迫休眠、生理休眠和综合休眠。种子生理休眠的机理包括:种果皮的抑制;植物激素的作用;种子的二次休眠;综合因素造成的休眠;分子变化等方面。     

Kinetics of cell formation and growth stresses in the secondary xylem of Swietenia mahagoni (L.) Jacq. and Khaya ivorensis A. Chev. (Meliaceae)

The kinetics of xylem formation in four-year-old plants of Swietenia mahagoni (L.) Jacq. and Khaya ivorensis A. Chev. were studied by means of high resolution laser measurements (accuracy: ±2 μm) in a spatial resolution of 18.7 to 94.1 μm and a temporal resolution of 1 to 60 s. The radial enlargement of the xylem cells was completed within 0.36 to 8.85 hours in Swietenia and within 0.52 to 12.03 hours in Khaya, while secondary wall formation and lignification lasted days to weeks. Cell enlargement of vessels and ray parenchyma was significantly faster than radial enlargement of fibres and axial parenchyma. The processes of formation of the secondary cell wall and the lignification were slower in fibres than in vessels and parenchyma cells. In Swietenia new secondary cell formation was induced in distinct growth periods almost simultaneously in the whole shoot, while in Khaya new cell formation was restricted to parts of the shoot. Growth stresses in the shoot were studied in terms of released strain. Higher growth stresses were observed in the shoot of Khaya compared to Swietenia. The results indicate that the higher growth stresses in the xylem of Khaya compared to Swietenia originate in the different kinetics of cell development of different cell types in combination with the heterogenous sequence of cell formation within the shoot. Dedicated to Prof. Dr. Dr. h.c. mult. W. Liese on the occasion of his 80th birthday.     

Variability in fibre and parenchyma cell walls of temperate and tropical bamboo culms of different ages

This study tries to clarify the conflicting results from previous studies on cell wall thickening in bamboo culms by applying light and transmission electron microscopy in combination with image analysis. It focused on both fibre and parenchyma wall thickness of both temperate (Phyllostachys spp.) and tropical (Gigantochloa levis and Dendrocalamus asper) bamboo species of different ages in the light of their suitability for the wood industry. The observations indicated a great heterogeneity in cell wall thickness and cell wall layering pattern of fibres within one culm. Nested design ANOVA’s revealed a rising trend in wall thickness of late maturing fibres and parenchyma cells during the first year but significant wall thickening during later years could not be demonstrated. The high variability within one culm and between culms of the same age from 1 year on is partly masking a clear increased cell wall thickening at higher age. Nevertheless, the highest mean values for fibre wall thickness were recorded in culms of 44 months old or older, suggesting that some kind of late cell wall maturing can take place within one culm.     

柳河兰山日本落叶松次生种源优树株间种实性状的研究

以柳河五道沟林木种子园生产区中选至兰山林场的优树为对象,采集球果和种子,对优树株间有关种实性状进行观测与分析。结果表明:选至相同次生种源的优树株间在球果长度与直径、出种率和千粒重性状表现上差异显著;方差分析和F检验证实株间种子重量差异极显著(P<0.01),遗传差异是主要因素。种子重量是辽宁次生种源的1.3倍,有随积温降低而增加的倾向。     

Immunolocalization of an anionic peroxidase in differentiating poplar xylem

Peroxidases are the major candidate enzymes involved in dehydrogenative polymerization of monolignols. Peroxidases have the signal sequence at their N-terminus and this suggests that they are transported to extracellular spaces or developing cell walls. In this study, we focused on an anionic peroxidase isozyme encoded by prxA3a, which seems to be related to lignification. To investigate the localization of peroxidase in differentiating xylem cells of poplar (Populus sieboldii × Populus grandidentata), anti-PRX3 antibody was raised against the anionic peroxidase. Western blotting and peroxidase activity inhibition assay showed specificity of the antibody. Labeling by anti-PRX3 antibody was localized in vessels and fibers during the secondary wall formation and was observed along the plasma membrane beside the microtubules. The labeling was not seen in the cell wall, where localization of peroxidases was expected during lignification. The peroxidase isozyme, which is suggested to be involved in monolignol polymerization, is localized on the plasma membrane and its localization might be regulated by microtubules.     

Tracheary elements that resemble secondary xylem in calli derived from the conifers, Torreya nucifera and Cryptomeria japonica

Differentiated cells were recognized in calli derived from needles of Torreya nucifera and in calli derived from immature zygotic embryos of Cryptomeria japonica. Some differentiated cells resembled tracheary elements of primary xylem with spiral or reticulate thickening of cell walls. Other cells resembled tracheary elements with thick cell walls and bordered pits, which are features of secondary xylem. These tracheary elements were formed in cell clusters. Tracheary elements in calli of T. nucifera formed more highly developed structures, such as bordered pits and spiral thickening, than those of C. japonica. Cultured cells derived from conifers might provide a good model for studies of the differentiation of secondary xylem in vitro.     

Etching of wood surfaces by glow discharge plasma

This research tests the hypothesis that plasma will cause differential etching of wood cell walls because of variation in the susceptibility of aromatic and aliphatic polymers to degradation by plasma. Wood was exposed to glow discharge plasma, and scanning electron microscopy and chromatic confocal profilometry were used to examine etching of cell walls. Plasma etched cell walls and made them thinner, but the middle lamella was more resistant to etching than the secondary wall. Plasma created small voids within the secondary wall, which were separated by thin lamellae connected to the middle lamella and tertiary wall layers. Larger voids were created in cell walls by the etching of bordered and half-bordered pits. Etching of the uppermost layer of cells at wood surfaces occurs first and when large voids are created in the walls of these cells then significant plasma etching of the underlying cells occurs. Etching of wood cell walls can be quantified using confocal profilometry, and using this technique a strong relationship between applied plasma energy and volume of cell wall etched by plasma was observed. It is concluded that all of wood’s polymers can be degraded by plasma even though cell wall layers that are rich in lignin are etched more slowly than other parts of the cell wall.     

复叶槭不同栽培群体性别分化与种实性状的研究

以长春市街路绿化树种复叶槭为调查对象,研究不同栽培群体的性别分化和有关种实性状,结果表明:在几乎相同的栽培环境中,不同群体雌雄株性别分化比例差异显著,雄株多于或显著多于雌株;株间种实的大小与翅果开张角度等形态性状存在差异或明显差异;株间的种子饱满度变动在33.8%～84 1%之间,差异极显著;株间种子的千粒重变化范围在...     

怀槐种子性状的测定

从桓仁县八里甸子镇国营林场采种基地的林分内采集怀槐种子,按国家标准进行种子有关性状的测定。结果表明,桓仁产地的怀槐种子的净度为95.0%、发芽率为86.3%、优良度为97%、千粒重为55.6g;与哈尔滨市栽培怀槐的种子相比,发芽率相近,千粒重和净度均高于哈尔滨市的次生种源。