Ontogeny of the proventitious epicormic buds in Quercus petraea.

In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia. The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk, but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when epicormic buds develop into shoots. Received: 30 March 1999 / Accepted: 09 June 1999     

Plant regeneration via organogenesis from adventitious bud explants of a medicinal herb species, <Emphasis Type="Italic">Polygonatum cyrtonema</Emphasis>

Summary Explants derived from adventitious buds, rhizomes, stems, and leaves of a medicinal plant, Polygonatum cyrtonema, were studied for plantlet regeneration, and only adventitious bud explants were able to be regenerated into plantlets. Regeneration was also accompanied by the formation of rhizome-like tissue, the medicinal portion of the plant. The optimum hormone combination for plantlet regenertion was 4.44 μM benzyladenine plus 2.26 μM 2,4-dichlorophenoxyacetic acid, at which new adventitious buds were obtained from 96.6% of the adventitious bud explants, with an average of 5.2 buds per explant. The best medium for root induction was half-strength Murashige and Skoog medium with 4.57 μM α-naphthaleneacetic acid, as 92% of regenerated buds rooted. Regenerated plantlets were successfully transferred to a greenhouse with 86% survival. Histological observation indicated that new adventitious buds originated from the superficial meristematic cell cluster of the granular callus induced from adventitious bud explants via organogenesis.     

Rapid in vitro propagation of Aloe barbadensis Mill

Axillary bud development and adventitious bud formation was obtained with decapitated shoot explants of Aloe barbadensis Mill. Maximal bud growth and rooting of shoots was obtained on a modified medium of Murashige and Skoog supplemented with 5 M IBA. More adventitious and axillary buds developed on nutrient media supplemented with IBA than with NAA. Axillary buds but not adventitious buds developed with IAA in the medium. Morphogenesis was inhibited by 2,4-D. Kinetin, benzyladenine and thidiazuron were toxic to the explants and did not stimulate the development of axillary of adventitious buds. The optimal temperature for bud growth and development was 25°C. Axillary bud growth and the formation of adventitious buds was slowed down at 10°C and totally inhibited by 30°C. The optimal sucrose concentration was 3% with the inhibition of bud growth and development by higher sucrose levels.     

八角莲组织培养的器官发生途径研究

为探究小檗科植物八角莲组织培养的器官发生方式,该研究以八角莲离体叶片、叶柄在MS培养基上诱导产生的愈伤组织、不定芽、不定根为对象,用连续石蜡切片技术分析八角莲组织培养的器官发生途径。结果表明:八角莲愈伤组织形成的解剖学特征是靠近表皮的薄壁细胞经激素刺激恢复分裂能力,继续培养形成拟分生组织。拟分生组织可形成许多分化中心。通过对八角莲组织培养产生的不定芽细胞组织学观察发现芽原基起源于愈伤组织外侧的几层薄壁细胞,芽原基背离愈伤组织中央生长形成不定芽,故八角莲脱分化形成的芽起源方式为外起源。而八角莲的根原基起源于组织深处髓部薄壁细胞和部分维管形成层细胞,进而形成类似球形或楔形并朝韧皮部突起的根原基轮廓,根原基继续发育会突破表皮生成不定根,起源方式为内起源。八角莲离体再生途径为器官发生型,在组培苗生长过程中先诱导形成不定芽,再诱导形成不定根,在愈伤组织上形成维管组织将不定芽和不定根连接成完整植株。     

Dynamics of resprouting in the lignotuberous shrub Banksia oblongifolia

The resprouting response of different sized Banksia oblongifolia lignotubers (genets) was followed in two field experiments. In the first, the density and speed of resprouting, and the growth in length of the leading shoot from each lignotuber in response to fire and to the time elapsed since the last fire was monitored for 18 months after fire and clipping treatments. In the second, sizes of bud banks were estimated by repeatedly clipping new shoots from individual lignotubers. Density of resprouting (shoots dm^?2 lignotuber) decreased with increasing lignotuber size, and the length of the leading shoot increased. The direct effect of fire was to reduce shoot density by about 75%. The speed of resprouting (time taken by a cohort of shoots to reach 50% of their peak density) was similar after fire and clipping, but leading shoots grew significantly longer after fire. The elapsed time since lignotubers were last burnt did not influence their density of resprouting, but it did influence the speed of resprouting. Shoots from clipped lignotubers that had burnt 3 years earlier took about 90 days to each 50% of their peak density while shoots on lignotubers last burnt 5 and 17 years earlier took about 40 days. Death of shoots was unrelated to crowding in any stand. More lignotubers from the oldest unburnt stand were grazed by herbivores. The number of buds converted into shoots after successive clippings was surprisingly small; for most lignotubers this reserve was less than three times the size of their standing crop of shoots. In general, the smaller lignotubers carried a higher proportion of dormant buds in relation to their standing crop of shoots. About 30% of buds remained dormant after the first clipping and about 10% after the second and third clippings. Evidence suggests that buds are replaced within 6 months of fire. No lignotubers survived four clippings over 15 months.     

Root biomass,root distribution and the fine-root growth dynamics of Quercus coccifera L. in the garrigue of southern France

Quercus coccifera L., the characteristic scrub oak of the garrigue, covers more than 100,000 ha in southern France alone. Precipitation in this area averages 900 mm/year and summer rains are not rare. A total belowground biomass of 7.2 kg/m², including rhizomes and lignotubers, was harvested. Roots were concentrated in the uppermost 50 cm of the soil. It was hypothesized that low winter temperatures inhibit active fine-root growth. This hypothesis was tested by means of fine-root extractions of soil samples from 0–50 cm depth from November 1987 to June 1988. Although the fine-root analysis could not be extended into late summer and fall, the data supported the hypothesis. Ratios of live/dead fine roots reached their minimum at 0.2–0.3 from December to April. They increased to 1.0–1.2 during late spring and early summer. Initiation of fine-root growth in early April was synchronous with bud break. Starch contents of roots, rhizomes, and lignotubers fluctuated from 4.3% in January to 8.3% in April. The starch stored in belowground organs of Q. coccifera in a closed canopy stand amounted to about 500 g/m² in April. This amount declined to 400 g with bud burst and fine-root growth initiation.     

The Eucalypt Lignotuber: a Position-dependent Organ

Observational and experimental evidence is presented to showthat the capacity to form a lignotuber is not restricted tothe cotyledonary, and a few succeeding, nodes on the primaryseedling stems of certain eucalypts, but is also a propertyof shoots arising from their accessory buds. Erect secondaryshoots from the lignotuber, may bear lignotubers at a few nodes,rhizostolons at many nodes along their length, and, like stolons,rhizomes may give rise to leafy shoots bearing basal lignotubers.These facts describe a so-called position effect for the productionof lignotubers, in the sense that the term has been used forother position-dependent phenomena in plants. Seedlings of lignotuberousspecies remain competent to form lignotubers over a long periodof adversity during which lignotubers are not formed. Shootsof non-lignotuberous species do not inhibit lignotuber developmentwhen grafted to lignotuberous species. eucalypts, lignotubers, position effect, vegetative propagation, tissue culture, rhizostolons, rhizomes     

HISTOLOGICAL ANALYSIS OF ADVENTITIOUS BUD FORMATION IN CULTURED DOUGLAS FIR COTYLEDON

Initiation of adventitious bud formation in vitro from Douglas fir cotyledons required both cytokinin and auxin at concentrations of 5 μM BAP and 5 nM NAA. Histological observations showed that these adventitious buds arose de novo from cells residing in hypodermal layers. Development of adventitious buds in culture was characterized by the sequential appearance of four anatomically distinguishable structures: 1) meristemoid, 2) bud primordium, 3) shoot apex with needle primordia, and 4) adventitious bud. The anatomical structure of tissue culture-produced buds was similar to that of vegetative buds produced on intact plants. Cultured cotyledons capable of producing adventitious buds (bud culture) were compared with bud-callus and callus cultures initiated by 5 μM BAP plus 5 μM NAA and 5μM NAA alone without BAP, respectively. Results showed that, during early stages of the culture period (i.e., prior to the appearance of meristemoid structure), cell division of bud culture was mainly located in hypodermal layers, whereas for the other culture types, bud-callus and callus cultures, cell division occurred randomly in all tissues.     

Effect of Assimilate Supply on Development and Growth Potential of Axillary Buds in Roses

The effect of assimilate supply on axillary bud developmentand subsequent shoot growth was investigated in roses. Differencesin assimilate supply were imposed by differential defoliation.Fresh and dry mass of axillary buds increased with increasedassimilate supply. The growth potential of buds was studiedeither by pruning the parent shoot above the bud, by graftingthe bud or by culturing the bud in vitro. Time until bud breakwas not clearly affected by assimilate supply during bud development,Increase in assimilate supply slightly increased the numberof leaves and leaf primordia in the bud; the number of leavespreceding the flower on the shoot grown from the axillary budsubstantially increased. No difference was found in the numberof leaves preceding the flower on shoots grown from buds attachedto the parent shoot and those from buds grafted on a cutting,indicating that at the moment of release from inhibition thebud meristem became determined to produce a specific numberof leaves and to develop into a flower. Assimilate supply duringaxillary bud development increased the number of pith cells,but the final size of the pith in the subsequent shoot was largelydetermined by cell enlargement, which was dependent on assimilatesupply during shoot growth. Shoot growth after release frominhibition was affected by assimilate supply during axillarybud development only when buds sprouted attached to the parentshoot, indicating that shoot growth is, to a major extent, dependenton the assimilate supply available while growth is taking place.Copyright1994, 1999 Academic Press Assimilate supply, axillary bud, cell number, cell size, defoliation, development, growth potential, meristem programming, pith, Rosa hybrida, rose, shoot growth     

Morphogenesis in Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis> (Bong.) Carr.) bud cultures – tree maturation and explants from epicormic shoots

The adventitious bud forming ability of Sitka spruce (Picea sitchensis (Bong.) Carr.) buds in vitro was found to be dependent upon the age of tree from which the explants were taken. Bud formation declined exponentially with increasing tree age when 1.0 and 10 μM 6-benzylaminopurine (BA) were used to induce adventitious buds. When less BA was used (0.1 μM) bud production was much lower with all ages of tree and no mathematical relationship between declining bud production and tree age was found. By a tree age of 6 years bud-forming ability had declined severely. Even the few buds that developed on older tree tissues failed to elongate into shoots, became necrotic and eventually died, indicating that adventitious bud induction in this species is not a rejuvenative process. Callusing of bud explants also declined with increasing tree age when 0.1 μM BA was used whilst very little callusing occurred at the higher cytokinin concentrations (1.0 and 10 μM BA). Tissue necrosis in vitro increased with tree age, whilst the ability of BA to retard necrosis declined with increasing tree age. Buds from epicormic shoots, formed on the lower trunks of 20-year-old trees when these were exposed to light, were not significantly better at forming adventitious buds in vitro than buds taken from the lower branches of the crown.     

The influence of cytokinin pulse treatments on adventitious bud formation on vegetative buds of Picea abies

Resting vegetative buds of Picea abies collected from phytotron-grown rooted cuttings of 24-year-old trees or a 12-year-old hedge were tested for their capacity to form adventitious buds after various cytokinin treatments. The most effective method for obtaining a high yield of adventitious buds within 8 weeks was to pulse treat the buds in 250 M BA for 3 h and then culture them on medium containing 5 M each of BA and kinetin for 1 week. The developmental pattern for adventitious bud production, with the formation of 10 to 20 adventitious buds per bud, was similar for all tested genotypes, although the number of buds giving rise to adventitious buds varied significantly. The capability of some clones to form adventitious buds was correlated to endogenous cytokinin content. The clone which contained most endogenous cytokinin in its resting bud had the highest potential for adventitious bud formation.     

Shoot regeneration of dwarf dogwood (Cornus canadensis L.) and morphological characterization of the regenerated plants

Dwarf dogwoods (or the bunchberries) are the only suffrutex in Cornaceae. They are attractive ground cover ornamentals with clusters of small flowers surrounded by petaloid bracts. Little has been reported on plant regeneration of dogwoods. As a step toward unraveling the molecular basis of inflorescence evolution in Cornus, we report an efficient regeneration system for a dwarf dogwood species C. canadensis through organogenesis from rejuvenated leaves, and characterize the development of the plantlets. We used the nodal stem segments of vegetative branches as explants. Micropropogated shoots were quickly induced from axillary buds of nodes on an induction medium consisting of basal MS medium supplemented with 4.44 μM BAP and 0.54 μM NAA. The new leaves of adventitious shoots were used as explants to induce calli on the same induction medium. Nearly 65% of leaf explants produced calli, 80% of which formed adventitious buds. Gibberellic acid (1.45 μM) added to the same induction medium efficiently promoted quick elongation of most adventitious buds, and 0.49 μM IBA added to the basal MS medium promoted root formation from nearly 50% of the elongated shoots. The growth of plantlets in pot soil was characterized by the development of functional woody rhizomes, which continuously developed new aboveground vegetative branches, but not flowering branches, within the past 12 months. Potential reasons causing the delay of flowering of the regenerated plants are discussed. The establishment of this regeneration system facilitates developing a genetic transformation system to test candidate genes involved in the developmental divergence of inflorescences in Cornus. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

THE ORGANIZATION OF THE VASCULAR SYSTEM IN THE STEMS OF THE NYMPHAEACEAE. II. NYMPHAEA SUBGENERA ANECPHYA,LOTOS, AND BRACHYCERAS

The anatomy and organization of the stem vascular system was analyzed in representative taxa of Nymphaea (subgenera Anecphya, Lotos, and Brachyceras). The stem vascular system consists of a series of concentric axial stem bundles from which traces to lateral organs depart. At the node each leaf is supplied with a median and two lateral leaf traces. At the same level a root trace supplies vascular tissue to adventitious roots borne on the leaf base. Flowers and vegetative buds occupy leaf sites in the genetic spiral and in the parastichies seen on the stem exterior. Certain leaves have flowers related to them spatially and by vascular association. Flowers (and similarly vegetative buds) are vascularized by a peduncle trace that arises from a peduncle fusion bundle located in the pith. The peduncle fusion bundle is formed by the fusion of vascular tissue derived from axial stem bundles that supply traces to certain leaves. The organization of the vascular system in the investigated taxa of Nymphaea is unique to angiosperms but similar to other subgenera of Nymphaea.     

DEVELOPMENT AND PHYLLOTAXIS OF THE VEGETATIVE AXILLARY BUD OF MICHELIA FUSCATA

Tucker, Shirley C. (Northwestern U., Evanston, III.) Development and phyllotaxis of the vegetative axillary bud of Michelia fuscata . Amer. Jour. Bot. 50(7): 661–668. Illus. 1963.—The vegetative axillary buds of Michelia fuscala are dorsiventrally symmetrical with 2 ranks of alternately produced leaves. The direction of the ontogenetic spiral in each of these buds is related both to the symmetry of the supporting branch and to the position of the bud along the branch. On a radially symmetrical branch, all the axillary buds are alike—all clockwise, for example. But in a dorsiventrally organized branch the symmetry alternates from clockwise in 1 axillary bud to counterclockwise in the next bud along the axis. Leaf initiation and ontogeny of the axillary apical meristem conform with those of the terminal vegetative bud. The axillary bud arises as a shell zone in the second leaf axil from the terminal meristem. During this process the axillary apex develops a zonate appearance. The acropetally developing procambial supply of the axillary bud consists wholly of leaf traces. At the nodal level the bud traces diverge from the same gap as the median bundle trace of the subtending leaf. Only the basal 1–2 axillary buds which form immediately after the flowers elongate each year, while the majority remains dormant with 3 leaves or fewer.     

Induction of Adventitious Buds on Buds of Norway Spruce (Picea abies) Grown in vitro

Resting vegetative buds of Norway spruce, Picea abies (L.) Karst., were induced to form adventitious bud primordia when cultured on medium -containing cytokinin. After transfer of the induced buds to medium lacking cytokinin, adventitious buds developed. The adventitious buds arose from meristems formed de novo in the needle primordia. No differences were found in the ability to form adventitious buds among buds collected from trees ranging from 5–50 years old.     

Initial stages in the course of adventitious bud formation on embryos of Picea abies

Adventitious buds on embryos of Picea abies (L.) Karst. developed after a pulse treatment with 250 μ M benzyladenine (BA) of pH 5.5 for 2 h. Light and temperature regimes were not critical during the initial stages. Adventitious buds developed faster after a pulse treatment and the variation among different experiments was lower compared to when the embryos were cultured on media supplemented with BA. Various stages of the differentiation of adventitious buds were identified: stage 1 - appearance of meristematic centres (approximately the first two weeks); stage 2 - development of adventitious bud primordia (approximately the third week); stage 3 - adventitious bud development (from approximately the 4th to the 8th week). This system may be used for further studies on bud differentiation.     

AXILLARY BUD DEVELOPMENT IN POPULUS DELTOIDES. I. ORIGIN AND EARLY ONTOGENY

Origin and early development of axillary buds on the apical shoot of a young Populus deltoides plant were investigated. The ontogenetic sequence of axillary buds extended from LPI –1 (Leaf Plastochron Index) near the apical bud base to LPI –11, the fifth primordium below the bud apex. Two original bud traces diverged from the central (C) trace of the axillant leaf and developed acropetally. During their acropetal traverse the original bud traces gave rise to three pairs of scale traces. All subsequent scale traces, and later the foliar traces, were derived by divergencies from the first two pairs of scale traces. Just before the bud vascular system separated from that of the main axis, a third pair of traces diverged from the original bud traces to vascularize the adaxial scale. Concomitantly, the original bud traces were inflected toward the main vascular cylinder where they developed acropetally and eventually merged with the left lateral trace of the leaf primordium situated three nodes above the axillant leaf; they did not participate in further vascularization of the bud. During early ontogeny a shell zone formed concurrent with initiation of the original bud traces and lay interjacent to them. The shell zone defined the position of the cleavage plane that formed between the axillary bud and the main axis. The axillary bud apex first appeared in the region bounded laterally by the original bud traces and adaxially by the shell zone. Following divergence of the main prophyll traces from the original bud traces, the apex assumed a new position intermediate to the prophyll traces. Ontogenetic development suggested that the axillary bud apex may have been initiated by the acropetally developing original bud traces under the influence of stimuli arising in more mature vegetative organs below.     

黄连体内黄连素的组织器官定位和根尖屏障结构特征研究

黄连(Coptis chinensis)是毛茛科著名药材,该文研究了黄连体内黄连素在组织器官中的分布规律和根尖屏障结构特征。在白光和荧光显微镜下,组织器官中黄连素在蓝色激发光下自发黄色荧光,黄连素-苯胺兰对染研究细胞壁凯氏带和木质化,苏丹7B染色栓质层,间苯三酚-盐酸染色木质化。结果表明:黄连不定根初生结构为维管柱、内皮层、皮层、外皮层和表皮组成;次生结构以次生木质部为主、次生韧皮部和木栓层组成。黄连根茎初生结构由角质层,皮层和维管柱组成;次生结构由木栓层、皮层和维管柱组成,以皮层和维管柱为主。叶柄结构为髓、含维管束的厚壁组织层、皮层和角质层。黄连不定根的屏障结构初生结构时期由栓质化和木质化的内皮层、外皮层;次生结构时期为木栓层组成;根状茎的为角质层和木栓层。黄连素主要沉积分布在不定根和茎的木质部,叶柄的厚壁组织层,木质部和厚壁组织是鉴别黄连品质的重要部位。黄连根尖外皮层及早发育,同时初生木质部有黄连素沉积结合,可能造成水和矿质吸收和运输的阻碍,也是黄连适应阴生环境的重要原因。     

Dormant Buds and Adventitious Root Formation by Vitis and Other Woody Plants

Viticulture has historically depended upon clonal propagation of winegrape, tablegrape, and rootstock cultivars. Dependence on clonal propagation is perpetuated by consumer preference, legal regulations, a reproductive biology that is incompatible with sustaining genetic lines, and the fact that grapevine breeding is a slow process. Adventitious root formation is a key component to successful clonal propagation. In spite of this fact, grapevine has not been a centerpiece for adventitious root research. Dormant woody canes represent complex assemblages of tissues and organs. Factors that further contribute to such complexity include levels of endogenous plant growth regulators, the extent and duration of dormancy, carbohydrate storage, transport, the presence or absence of dormant buds or emergent shoots, and preconditioning treatments. For the above reasons, the mechanisms driving adventitious root formation by grapevine and other woody cuttings are poorly understood. We present results indicating that the dormant bud on cane cuttings from a non-recalcitrant to root Vitis vinifera cultivar, cv. Cabernet Sauvignon, slows or inhibits adventitious root emergence. In contrast to Cabernet Sauvignon, removal of the dormant bud from cane cuttings of a recalcitrant to root hybrid rootstock (V. berlandieri × V. riparia cv. 420A) and an intermediate to root hybrid rootstock (V. riparia × V. rupestris cv. 101-14) had no influence on adventitious root emergence. Reciprocal transplanting of nodes containing dormant buds among all three cultivars did not affect rooting behavior. Our results indicate that the commonly held belief that bud removal diminishes adventitious root emergence is not true.     

Plant regeneration via adventitious bud formation from cotyledon explants of Panax ginseng C. A. Meyer

Cotyledon explants of ginseng (Panax ginseng C. A. Meyer) produced somatic embryos directly on medium without growth regulators, with 89% of the explants forming somatic embryos. Cytokinin treatment greatly suppressed somatic embryo formation but stimulated the direct formation of adventitious buds. BAP treatment was more effective than the kinetin treatment for adventitious bud formation. Auxin (0.05 mg/l IBA) in combination with cytokinin enhanced adventitious bud formation, with the highest frequency, 40%, at 0.05 mg/l IBA and 5 mg/l BAP. Adventitious buds were mainly formed near the distal portion of the cotyledons, while somatic embryos were formed near the proximal excised margins. Shoots were developed from adventitious buds after transfer to MS medium with 10 mg/l GA₃. Root formation from the shoots was obtained after the shoots were transferred to half-strength MS medium with auxin (IAA). When the plants derived from adventitious buds were transferred to greenhouse soil, 36% were successfully acclimatized. Received: 7 November 1997 / Revision received: 12 January 1998 / Accepted: 7 February 1998