黄花杓兰的花芽发育

对黄花杓兰（Cypripedium flavum P.F.Hunt et Summerh.）成年植株做了一个生长季的研究,提出了一年芽、二年芽和多年休眠芽的概念。指出由芽形成到植株开花需两年时间,其具体发育路线是：第一年6－7月份,根状茎顶端二年芽基部外侧有两个新的小芽产生,即“一年芽”,至9－10月份发育出7－9片幼叶,然后随气温下降停止生长;第2年4月份复苏,即为“二年芽”,二年芽在本生长季内发育成混合芽,但一般情况下只有一个充分发育,另一个未能充分发育并且一般将来也不再有发育的机会,被称为“多年休眠芽”;第3年5月份充分发育的二年芽长出地面,形成植株,迅速开花、结果,至9月底植株枯萎。本文还讨论了黄花杓兰发育过程与环境的关系。     

Ultrastructure of dormant buds of Salix sp. in early winter

In the apex of dormant buds of Salk a histological zonation comparable to that found in growing buds was observed. However, significant changes in relative volumes of cell components between dormant and growing buds were noted; the dormant buds had a lower volume density of vacuoles and higher relative volumes of mitochondria, plastids, lipid bodies, and starch grains than the growing buds. In the leaf primordia the relative volume of nuclei decreased with age, while the relative volume of plastids and mitochondria increased. The large central vacuole found in cells of e.g. the pro-cambium and rib meristem in growing buds is split into many smaller ones during the winter. A high content of tannin and calcium oxalate crystals was noted in dormant buds. They also accumulate lipids and starch. Phytoferritin may appear in plastids. Stacked ER and concentric sheaths of ER around lipid bodies appear, probably as a consequence of either anaerobic conditions or water stress. Several indications of metabolic activities in the seemingly dormant buds were found; plasmatubules at the plasmalemma particularly in the procambium, sheaths of smooth ER around the plastids, electron opaque globules (probably calcium-binding sites), and vacuoles that seemed to be autophagic.     

Expression of a ribosomal protein gene in axillary buds of pea seedlings

Axillary buds of intact pea seedlings (Pisum sativum L. cv Alaska) do not grow and are said to be dormant. Decapitation of the terminal bud promotes the growth of these axillary buds, which then develop in the same manner as terminal buds. We previously showed that unique sets of proteins are expressed in dormant and growing buds. Here we describe the cloning, sequencing, and expression of a cDNA clone (pGB8) that is homologous to ribosomal protein L27 from rat. RNA corresponding to this clone increases 13-fold 3 h after decapitation, reaches a maximum enhancement of about 35-fold after 12 h, and persists at slightly reduced levels at later times. Terminal buds, root apices, and elongating internodes also contain pGB8 mRNA but fully expanded leaflets and fully elongated internodes do not. In situ hybridization analysis demonstrates that pGB8 mRNA increases in all parts of the bud within 1 h of decapitation. Under appropriate conditions, growing buds can be made to stop growing and become dormant; these buds subsequently can grow again. Therefore, buds have the capacity to undergo multiple cycles of growth and dormancy. RNA gel blots show that pGB8 expression is reduced to dormancy levels as soon as buds stop growing. However, in situ hybridization experiments show that pGB8 expression continues at growing-bud levels in the apical meristem for 2 d after it is reduced in the rest of the bud. When cultured stems containing buds are treated with indoleacetic acid at concentrations ≥10 μm, bud growth and expression of pGB8 in the buds are inhibited.     

Uptake of (14C) leucine and protein synthesis in potato tuber buds and effect of abscisic acid on these processes]

The uptake of [14C] leucine and its incorporation into proteins of dormant and growing potato tuber buds were studied. It was found that the label uptake was increased at the beginning of the growth period, whereas the dynamics of this process were not changed in comparison with the dormant buds samples. The rate of [14C] leucine incorporation into proteins was increased in the growing buds; this increase was not, however, due to the increase in the uptake of the labelled precursor and was probably caused by activation of the protein synthesis. In contrast, the activation of protein synthesis was accompanied by changses is the dynamic incorporation of [14C] leucine into the protein at the end of dormancy. The effect of abscisic acid (10(-7) M) on the protein synthesis was not connected with its action of the uptake of labelled precursor and depended on the physiological state of buds and incubation time. A possible mechanism of regulatory effect of abscisic acid on protein synthesis in potato tuber buds is discussed.     

The Development and Emergence of Buds in Phragmites communis Trin.

Phragmites communis rhizomes grow during the autumn, but budsdevelop nearly all the year round. For much of the year thebuds remain dormant near the soil surface, and then in springthere is a period of rapid emergence which lasts from betweena few weeks to nearly 4 months. Apart from replacements of frost-killedshoots, few buds emerge during the rest of the year. Emergencestarts at the end of the period of internal dormancy if theweather is warm enough. In Britain it is not, and there is abouta month of temperature-controlled dormancy. Emergence can bedelayed further by unusually unfavourable conditions of temperatureor water-supply. Exposure to frost kills some shoots, but stimulates bud developmentand lengthens the emergence period. Burning and severence ofrhizomes break internal dormancy. Cutting does not, and so isvery damaging if carried out directly after the emergence period,since no replacement crop is then produced, and so that plantis unable to photosynthesize during half of the growing season.     

桃芽自然休眠与两条主要电子传递途径变化的关系

花芽和叶芽总呼吸速率最低点均与自然休眠进程有关,第一个与自然休眠的起始时间相对应,最后一个则与自然休眠解除期相对应;细胞色素途径抑制剂氰化钾（KCN）对休眠芽的呼吸起部分抑制作用;抗氰呼吸抑制剂水杨基氧肟酸（salicylhydroxamic acid,SHAM）对总呼吸速率的效应随休眠进程而变化,休眠前期起促进作用,随休眠进程其促进作用逐渐减弱,从可调控休眠期（对外源措施敏感期）起转入抑制效应;KCN＋SHAM混合剂对总呼吸速率的效应与SHAM单独使用的效果相似,但其时总呼吸速率促进作用的起始点和结束点均较SHAM单独使用旱7d左右。     

Properties of peach flower buds which facilitate supercooling

Water in dormant peach (Prunus persica [L.] Batsch. var. `Harbrite') flower buds deep supercooled. Both supercooling and the freezing of water within the bud axis and primordium as distinct components depended on the viability of the bud axis tissue. The viability of the primordium was not critical. Supercooling was prevented by wounding buds with a dissecting needle, indicating that bud structural features were important. Bud morphological features appeared to prevent the propagation of ice through the vascular tissue and into the primordium. In dormant buds, procambial cells had not yet differentiated into xylem vessel elements. Xylem continuity between the bud primordium and adjacent tissues did not appear to be established until buds had deacclimated. It was concluded that structural, morphological, and physiological features of the bud facilitated supercooling.     

三种白及属植物不同生长发育时期的菌根显微结构

采用石蜡切片技术对白及Bletilla striata、黄花白及B. ochracea和小白及B. formosana的栽培种在生长期、花期、果期和休眠期的菌根解剖结构特征、菌根真菌入侵方式和菌丝特征等进行观察研究,以进一步了解菌根真菌与白及属植物的共生关系。结果表明,3种白及属植物的菌根真菌均是通过通道细胞侵入根皮层薄壁细胞,侵入后菌丝靠近皮层细胞的细胞核分布,最终在皮层细胞形成菌丝团;真菌侵染率和菌丝形态随着植物生长发育变化而变化,3种白及属植物均表现为花期和生长期的真菌侵染率较高,以丝状菌丝团为主,而果期和休眠期较低,以团块状菌丝团居多;同一时期不同植物类型的菌根特征无显著差异。     

Branch construction and bud defence status at the canopy surface of a West African rainforest

Branch specimens were collected from the very tops of tropical tree crowns in southern Cameroon, West Africa. An analysis of branching patterns revealed a consistency of form across unrelated taxa. All specimens showed evidence of rhythmic growth cither due to the regular occurrence of dormant terminal buds or due to sympodial growth with loss or flowering of terminal buds. Study of bud anatomy revealed an extensive array of protective devices associated with drought tolerance and herbivore defence. Normally a considerable excess of dormant, well protected axillary buds were present which (almost without exception) existed in a viable state. In very many instances the large dormant bud population was due to the presence of accessory buds, i.e. > 1 bud in the axil of each leaf. The microclimate at the outer surface of a tropical rainforest may experience a daily increase in temperature and associated depression in humidity; the canopy surface characteristics are more akin to chaparral shrub vegetation than to familiar rainforest understorey vegetation.     

Changes in Protein Interactions of Cell Cycle-Related Genes during the Dormancy-to-Growth Transition in Pea Axillary Buds

Apical dominance is a phenomenon in which a terminal bud growspredominantly and the growth of the axillary buds is suppressed.Here, we investigated the molecular mechanisms associated withcell cycle control that occur in pea axillary buds as a resultof decapitation. Proliferating cell nuclear antigen (PCNA) proteinwas detected in both dormant and growing buds, while PCNA mRNAwas absent in dormant buds. Pissa;CycBl;2 and Cdc2 proteinswere undetectable during dormancy. To analyze an interactionbetween PCNA and Pissa;CycD3;l, we performed anti-PCNA immunoaffinitycolumn chromatography. Pissa;CycD3;l protein was detected inthe eluate prepared from the dormant buds, but not in the eluateprepared from the growing buds. Furthermore, we performed anti-Pissa;CycD3;limmunoaffinity column chromatography. PCNA protein was detectedin the eluate prepared from the dormant buds, but not in theeluate prepared from the growing buds. These results indicatedthat PCNA associated with Pissa;CycD3;l only during dormancy.In addition, the interaction between PCNA and Pissa;CycD3;lwas confirmed by a yeast two-hybrid system. (Received April 8, 1998; Accepted August 5, 1998)     

松嫩平原碱化草甸旱地生境芦苇种群的芽流和芽库动态

在松嫩平原碱化草甸,旱地生境芦苇种群的根茎分布在土层约1m的不同深度,一般可生活6个年度,个别根茎可存活7～9年,乃至更长的时间.通过芦苇根茎芽调查,创建了植物种群的芽流模型.提出了采用当年1龄级根茎芽的输入率与其它龄级休眠芽库存率之和估计芦苇种群芽库贮量动态的方法.结果表明,随着生长季的进程,芦苇种群芽库输入率呈不断增加趋势,而萌发输出率呈不断减少的趋势,死亡输出率则大体保持相同的较低水平.至休眠前期的9月底,芽库输入率已为输出率的2.04倍.在松嫩平原碱化草甸旱地生境,芦苇种群各龄级根茎的休眠芽有一个稳定的萌发输出过程.定量分析结果表明,芦苇种群不同龄级根茎的休眠芽每年都有11%的比率萌发形成1龄级新根茎.1龄级根茎顶端翌年发育为分蘖株后,可为直接相连接的老龄级根茎就近输送养分,从而实现老龄级根茎芽的活力.     

Dormancy in Peach (Prunus persica L.) Flower Buds : I. Floral Morphogenesis and Endogenous Gibberellins at the End of the Dormancy Period

Flower buds of peach (Prunus persica L.) trees, cv Novedad de Cordoba (Argentina), were collected near the end of the dormant period and immediately before anthesis. After removal of scale leaves, morphological observations of representative buds, made on transverse and longitudinal microtome sections, showed that all verticils making up the flower are present in an undifferentiated form during the dormant period (June). Flower buds collected at the end of dormant period (August) showed additional growth and differentiation, at which time formation of two ovules was beginning in the unicarpelar gynoecium. Dehiscence of anthers had not yet occurred 10 days before full bloom, and the ovules were still developing. Free endogenous gibberellin (GA)-like substances were quantified by bioassay (Tan-ginbozu dwarf rice microdrop) after SiO₂ partition column chromatography, reversed phase C18-high performance liquid chromatography, and finally Nucleosil [N(CH₃)₂]high performance liquid chromatography. Bioactive fractions were then subjected to capillary gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM). Gibberellins A₁, A₃, and A₈ were tentatively identified in peach flower buds using GC-SIM and Kovat's retention indices, and relative amounts approximated by GC-SIM (2:8:6 for GA₁, GA₃, and GA₈, respectively). The highest concentration (330 nanograms per gram dry weight) of free GA₁/GA₃ was found in dormant buds (June) and diminished thereafter. The concentration free of GA₁/GA₃ did not increase immediately prior to bud break. However, high GA₁/GA₃ concentrations occurred during stages where rate of growth and cellular differentiation of (mainly fertile) verticils can be influenced.     

The dormant buds of Rhabdopleura compacta (Hemichordata)

Rhabdopleura has an overwintering stage that consists of two layers of cells surrounding a central yolk mass. This cellular part is surrounded by a thick electron dense capsule which is secreted by the bud itself. The capsule is probably impervious and protective to its contents. Blood vessels join the buds to the zooids of the colony. They form the probable route of transfer of yolk from the zooids to the dormant bud. The capsule of the dormant bud has some structural features in common with the black stolon of the adult zooids. The black stolon is probably formed in a manner similar to that which made the fusellar fabric of the periderm of fossil graptolities.     

Dormancy-associated gene expression in pea axillary buds.

Pea (Pisum sativum L. cv. Alaska) axillary buds can be stimulated to cycle between dormant and growing states. Dormant buds synthesize unique proteins and are as metabolically active as growing buds. Two cDNAs, PsDRM1 and PsDRM2, were isolated from a dormant bud library. The deduced amino acid sequence of PsDRM1 (111 residues) is 75% identical to that of an auxin-repressed strawberry clone. PsDRM2 encodes a putative protein containing 129 residues, which includes 11 repeats of the sequence [G]-GGGY[H][N] (the bracketed residues may be absent). PsDRM2 is related to cold- and ABA-stimulated clones from alfalfa. Decapitating the terminal bud rapidly stimulates dormant axillary buds to begin growing. The abundance of PsDRM1 mRNA in axillary buds declines 20-fold within 6 h of decapitation; it quickly reaccumulates when buds become dormant again. The level of PsDRM2 mRNA is about three fold lower in growing buds than in dormant buds. Expression of PsDRM1 is enhanced in other non-growing organs (roots root apices; fully-elongated stems >elongating stems), and thus is an excellent “dormancy” marker. In contrast, PsDRM2 expression is not dormancy-associated in other organs. Received: 10 December 1997 / Accepted: 23 January 1998     

Modelling compensatory regrowth with bud dormancy and gradual activation of buds

Many plants show compensatory regrowth after herbivory and dormant buds often have an important role in compensatory responses. Theoretical models have shown that herbivore damage may select for a bud bank, i.e., a pool of dormant buds that are protected from herbivory and that are activated after herbivore damage. Earlier models assumed that undamaged plants cannot activate their dormant buds without damage, although they apparently have sufficient resources for successful seed production through the additional shoots dormant buds could produce. However, many plants are able to gradually activate buds over an extended period of time without any cue from damage. The aim of this study was to analyze how herbivory imposes selection for gradual mobilization of the bud bank. I assume that selection pressures that affect the fraction of buds active at each time point include damage by herbivores, time left to the end of season, and the opportunity costs of dormant buds. I modelled bud dynamics with gradual activation when there is a single damage event and (i) when the seed set of a shoot is not dependent on the time it is active, or (ii) when the seed set of a shoot diminishes with later activation. In addition, I analyzed how (iii) risk of repeated herbivory affects selection for gradual activation. Under these models, gradual activation is optimal over a wide range of herbivory pressures. Selection appears to favour activation of all buds at the beginning of the season only when herbivore pressure is weak and when early shoots have a higher seed set than late shoots. Alternatively, strong herbivore pressure and late damage may select for a large bud bank throughout the growing season, without gradual activation; the bud bank is only mobilized after damage. In this case, damaged plants can overcompensate, i.e. they have a higher seed set than undamaged plants with the same bud activation pattern. Selection for overcompensation demands a stronger herbivore pressure in this current model than in earlier bud bank models. The model never predicts selection for overcompensation when there is a risk of repeated herbivory. This revised version was published online in July 2006 with corrections to the Cover Date.     

A scanning electron microscope study of healthy pecan tissues showing the presence or absence of internal fungal contamination

Summary Healthy pecan, Caryaillinoensis (Wang) Koch, tissue was obtained from an 8-year-old grafted Cherokee tree. Dormant buds were gathered and stored until spring growth. After rigorous surface sterilization, halves of both stored and freshly harvested dormant buds and of actively growing shoots were plated onto sterile PDA. Corresponding halves wre fixed in FAA and processed for scanning electron microscopy (SEM). All plated dormant buds (both stored and freshly harvested) showed presence internally of a fungus, and SEM studies revealed hyphalike strands similar to those of the isolated fungi within cells of those buds. The spring flush was sterile in culture, and strands were absent in SEM studies.     

Seasonal culture of dormant reproductive buds ofSalix tetrasperma: Analysis of the flowering process

The flowering process in a female tree ofSalix tetrasperma was analysed by culturing its reproductive buds at different developmental stages during the dormant period on a chemically defined medium and examining the nature of sprouts produced by them. Buds at the upper eight nodes of the actively growing shoots developing in an acropetal sequence were cultured in separate lots. While all the buds collected from the 1st and 2nd nodes of the branches from the top downwards were vegetative and produced shoots, a considerable number of those collected from the 3rd and 4th nodes were reproductively determined and produced catkins. All the buds obtained from the 5th node and below were reproductive. Reproductive buds were cultured at regular time intervals during the dormant period. Freshly formed buds cultured in March during the spring growth flush produced catkins and were therefore reproductively determined. However, such a determination was not tantamount to flowering, as the floral meristems present in the axils of catkin bracts remained quiescent. Floral meristems of the buds cultured during April to August developed into small vegetative shoots. This was followed by the crucial period during September to December when the hitherto vegetative sprouts of the floral meristems showed a gradual transition into ovaries (female flowers) resulting in fertile catkins. Catkins produced from buds cultured in January and February produced well-developed ovaries.     

Cryo-scanning electron microscopic study on freezing behaviors of tissue cells in dormant buds of larch (Larix kaempferi)

The freezing behavior of dormant buds in larch, especially at the cellular level, was examined by a Cryo-SEM. The dormant buds exhibited typical extraorgan freezing. Extracellular ice crystals accumulated only in basal areas of scales and beneath crown tissues, areas in which only these living cells had thick walls unlike other tissue cells. By slow cooling (5 °C/day) of dormant buds to −50 °C, all living cells in bud tissues exhibited distinct shrinkage without intracellular ice formation detectable by Cryo-SEM. However, the recrystallization experiment of these slowly cooled tissue cells, which was done by further freezing of slowly cooled buds with LN and then rewarming to −20 °C, confirmed that some of the cells in the leaf primordia, shoot primordia and apical meristem, areas in which cells had thin walls and in which no extracellular ice accumulated, lost freezable water with slow cooling to −30 °C, indicating ability of these cells to adapt by extracellular freezing, whereas other cells in these tissues retained freezable water with slow cooling even to −50 °C, indicating adaptation of these cells by deep supercooling. On the other hand, all cells in crown tissues and in basal areas of scales, areas in which cells had thick walls and in which large masses of ice accumulated, had the ability to adapt by extracellular freezing. It is thought that the presence of two types of cells exhibiting different freezing adaptation abilities within a bud tissue is quite unique and may reflect sophisticated freezing adaptation mechanisms in dormant buds.     

MORPHOLOGICAL AND ULTRASTRUCTURAL DEVELOPMENT AND STARCH ACCUMULATION DURING CHILLING OF SOUR CHERRY FLOWER BUDS

Floral tissue of dormant sour cherry (Prunus cerasus L.) flower buds was examined by light and electron microscopy during field development and laboratory chilling. Differentiation of flower parts ceased by early November and there was no further morphological development until visible signs of budbreak occurred after the end of rest. Pollen meiosis occurred at the half green budbreak stage. No ultrastructural changes accompanied chilling accumulation except development of numerous starch grains in plastids. Buds on cut shoots held at the non-chilling temperature of 15 C developed more mitochondria but acquired no starch when compared with buds on cut shoots held at a 5 C chilling temperature. Nuclei and nucleoli enlarged with chilling in ovules and sporogenous cells but not in ovary parenchyma. Accumulation of starch with chilling in most bud tissues was demonstrated histochemically.     

Adaptive significance of sprouting ofEuptelea polyandra,a deciduous tree growing on steep slopes with shallow soil

We investigated growth characteristics ofEuptelea polyandra Sieb. et Zucc. (Eupteleaceae), a Japanese endemic deciduous tree species growing on unstable ground such as that of very steep slopes with thin soil.Euptelea polyandra began to sprout at the juvenile stage and had a multiple-stemmed tree form. There was a positive correlation between diameter of the maximumsized stem within a stool (DMS) and the number of stems within the stool. Many stools had suffered from disturbances as shown by the fact that uprooting scars were found on 31.4% and 42.4%, respectively, of the stools of the two populations studied. Sprouting played a significance role in repairing damaged stems and stools, and at least 15.5% and 18.2% of the stools of the two populations, respectively, had apparently avoided death by sprouting. Sprouted stems gradually inclined with the increase in their relative sizes within each stool, and this seemed to facilitate the establishment of younger sprouted stems. The small younger sprouted stems had their own roots. There were dormant buds on stems which originated from axillary buds, and secondary dormant buds occurred by branching. The total number of dormant buds in a stool increased with DMS. It is concluded thatE. polyandra accumulates dormant buds for sprouting in order to respond to disturbances quickly.