Control of head morphogenesis in an invertebrate asexually produced larva-like bud (<Emphasis Type="Italic">Cassiopea andromeda</Emphasis>; Cnidaria: Scyphozoa)

Scyphopolyps of Cassiopea andromeda propagate asexually by forming larva-like buds which separate from the parent in a developmentally quiescent state. These buds metamorphose into sessile polyps when exposed to specific biogenic, chemical inducers. Morphogenesis of transversely dissected buds indicates the presence of pattern-determining signals; whereas the basal bud fragments may still form a complete scyphistoma the apical bud fragments develop spontaneously in the absence of an inducer into a polyp head without stalk and foot. Based on these findings Neumann (dissertation, Cologne University, 1980) postulated a head-inhibiting signal which is released at the basal pole and inhibits head formation at the apical end. Contrary to this hypothesis dissection itself might induce the development of head structures. The present study deals with the control of polyp head formation in C. andromeda. It concentrates on two points, namely the postulated head inhibitor and the involvement of compounds known to act during metamorphosis (the enzyme protein kinase C and the specific metamorphosis inducer Z-GPGGPA). We found that compared to intact buds and apical bud fragments transversely incised buds reached an intermediate stage of head development. This confirms Neumann's hypothesis. Consequently we focused on the mode of action and the chemical nature of the head-inhibiting signal in C. andromeda. Our results indicate that the head inhibitor may be included in one of six pooled fractions isolated from bud homogenate via gel filtration on a Sephadex G-50 column. The inhibitor is supposed to be water-soluble and to have a molecular weight of 850-1,500 Da. Furthermore we prove that head formation is not promoted by the metamorphosis-inducer Z-GPGGPA but is prevented by the inhibitors psychosine, chelerythrine and RO-32-0432 showing the involvement of protein kinase C in this process.     

The polarity of endogenous regulatory substances inBryophyllum crenatum leaves and stems

In isolated leaves ofBryophylluni crenatum the intensity of marginal bud formation decreases from the apex towards the blade base, which is associated with the decreasing content of enioganous gibberallins. As proved by Dostál (1930), the formation of marginal buds on transversely divided blade of the isolated leaf increases in comparison with the non-divided control leaf. The results of our experiments have revealed that the increase in the formation of marginal buds in the blade transversely divided into the apical, middle and basal parts is connected with the increasing level of endogenous gibberellins, especially in the apical part. This rising level appears as early as 7 days following blade division,i.e. at the time preceding the formation of marginal bud bases. InBryophyllum crenatum plants the level of endogenous cytokinins was estimated in apical, middle and basal leaves, as well as in adjacent internodia. Maximum content was found out in the leaves from the middle stem part, which is probably associated with the capacity of this part to form marginal buds spontaneously also in intact plants. However, prior to flowering the maximum of cytokinin activity is shifted to the apical stem part.     

Allocation of resources within mountain birch canopy after simulated winter browsing

As a response to browsing, birches are known to produce fewer but larger, more nutritious leaves, with enhanced palatability for herbivores. We simulated winter browsing in ramets of mountain birch ( Betula pubescens ssp. czerepanovii ) to find out whether it decreases subsequent foliage biomass and alters the number and type of shoots. After removal of a considerable proportion of buds (up to 35%) in late winter, the birches were able to compensate for the lost leaf biomass in the following summer; there were no differences in total leaf biomass between winter-clipped and control ramets. This indicates that foliage growth was limited by the total amount of stored resources, not by the number of buds. Depending on the position of the buds removed, different mechanisms were responsible for the compensation. After removal of apical buds, the number of leaves decreased significantly but leaves were larger than in control ramets. Removal of the same mass of basal buds – containing similar amount of carbohydrates and proteins as in the treatment removing apical buds – activated dormant buds, especially in apical locations, so that leaf number was similar as in the controls; consequently, size of individual leaves increased only slightly. Thus, while the total leaf biomass in a tree seems to be limited by resources from source organs, the distribution of resources among different canopy sections is controlled by their relative sink strengths. In terms of leaf biomass, apical parts are able to compensate for bud loss by increasing shoot number, basal parts only by increasing leaf size.     

The Effect of the Apical Bud on the Growth of Lateral Buds on Subterranean Shoots

The influence of the apical bud on the growth of the lateral buds on subterranean shoots was studied in Stachys sieboldiiMig. and Helianthus rigidus(Gass.) Desv. Removing and damaging the apical parts of subterranean shoots or their treatment with 2% chlorocholine chloride shoot enhanced shoot branching. The response to light of the apical bud was invariably negative: the stolons, which came out or were extracted from the soil, grew back into the ground (negative phototropism). The response to light of lateral buds was autonomous and depended on the conditions of their initiation. The lateral buds developed in darkness manifested negative phototropism when withdrawn from the soil and exposed to the light, whereas the buds developed in the light showed positive phototropism. The author concludes that the concept of apical dominance, thoroughly studied in aboveground shoots, is also valid for subterranean shoots. However, in contrast to the former, in the latter case, the apical bud does not control the growth orientation of the lateral buds.     

生长素极性运输抑制剂(TIBA)对烟草离体花柄花芽分化的影响

在只含6-BA(2mg/L)的MS培养基上,烟草花柄外植体形态学基端膨大,上着生再生花芽,而花柄中部大多都形成愈伤组织。添加IAA(2,10,20 mg/L)后,花柄基端膨大的现象依然存在,但再生花芽的分布并不限于基端,在花柄中部、顶端都可见再生花芽。花柄外植体中部愈伤组织的形成也随添加的IAA和IAA浓度升高而受到抑制。在上述培养基中添加生长素极性运输抑制剂TIBA后,无一花柄中部能形成愈伤组织,再生花芽的形态变化也很大,有具锥形花柄的花芽、喇叭叶和一些难于确定由何种器官衍生而来的喇叭状器官。这些异于正常形态的器官发生,显然与花柄外植体中生长素极性运输受抑制有关,本文对它们的形成机理作了一些推测。     

Burst Potential Characterisation by Capacity for Nucleotide Accumulation in Rhododendron Catawbiense Apical Buds

Rhododendron catawbiense cv. Album propagated in vitro were transferred ex vitro and grown in a greenhouse, under long or short days. Under long days, the rhythmic growth led to an acrotonous development. In contrast, under short days, the upper buds were unable to burst, allowing basitony. In both photoperiodic conditions, the apical buds were sampled at different stages of the experiment. Growth capacities of the isolated buds were estimated by measuring their abilities to increase and diversify their non-adenylic nucleotide pool (NTP) after supplying adenosine as a precursor. Under long days, during the growth pause, the apical buds were able to increase and diversify their NTP pool. Under short days, adenosine was used to produce important quantities of ATP, while NTP pool increase became weaker. Nevertheless, during this long growth pause, apical bud tissues retained capacities to increase their NTP pool until the basal shoots developed.     

Bud regeneration from inflorescence explants for rapid propagation of geophytes in vitro

Bulbs, corms and other subterranean storage organs are commonly used as explant source material for the establishment of geophytes in vitro. The inflorescence stalk was found to be a good alternative source of explants to overcome explant contamination originating from underground storage organs. Inflorescence explants of Allium, Dichelostemma, Eucrosia, Gladiolus, Haemanthus, Hyacinthus, Narcissus, Nerine and Ornithogalum were used to establish cultures in vitro. The regeneration potential of the inflorescence was compared with regeneration from bulb twin scales or from apical buds isolated from corms. Gladiolus (Iridaceae) explants isolated from the floral stem just below the expanding florets, still enclosed in the bracts, were highly regenerative in the presence of naphthalene acetic acid (NAA) and kinetin. In the presence of 2,4-dichlorophenoxyacetic acid and benzyl aminopurine (BA) in the medium, explants isolated from the tissue at the junction between the peduncle and the pedicels of a young Nerine (Amaryllidaceae) inflorescence regenerated several buds. The scapes of young unemerged inflorescences taken from sprouting bulbs of Narcissus (Amaryllidaceae), following a 15 °C storage treatment, regenerated buds in the presence of NAA, BA, elevated phosphate and adenine sulfate in the medium. The number of buds regenerated depended on the location on the scape from which the explant was isolated, and on the duration of the 15°C treatment. In Allium (Alliaceae), capitulum tissue between the flower pedicels regenerated buds. Explants excised from the peduncle, as well as the pedicel-peduncle junction of Dichelostemma (Alliaceae), Ornithogalum, Hyacinthus (Hyacinthaceae) and Eucrosia (Amaryllidaceae) regenerated several buds in each type of explant. In the case of Haemanthus (Amaryllidaceae), pedicel-peduncle junction explants regenerated buds only when excised from inner whorl florets. Propagation protocols and the potential use of expediently isolated inflorescence explants for efficient micropropagation of geophytes are discussed. Received: 1 September 1999 / Revision received: 13 December 1999 / Accepted: 13 December 1999     

Histogenesis of the taste buds of the vallate papilla in the in the rat in the postnatal stages of development

The developing taste buds of vallate papillae were studied with electron microscope in rats during the first 7 days after birth. Two types of cells--light and dark--are identified in the taste buds of a one day old animal. The apical parts of dark cells are characterized by numerous dark granules. A distinguishing feature of light cells is the presence of synaptic contacts with afferent intragemmal nerves. On the 4th day of development on the top of the apical parts of the cell, a microvillar apparatus is seen to form, which does not yet communicate with the oral cavity. On the 7th day, basal cells appear in the taste buds. Some of these cells are seen mitotically dividing. The differentiated microvillar apparatus now communicates with oral cavity. The structure of the taste buds is getting similar to that in the adults. The structural and functional peculiarities of the developing taste buds are discussed in association with the period of ontogenesis under consideration.     

Regeneration from rhizome fragments of Agropyron repens

Experiments were done with rhizome fragments of Agropyron repens with or without ‘late spring dormancy’. Increasing concentrations of KN0₃ from 1 to 210 ppm successively increased the percentage of buds released from dormancy, but the restriction of shoot extension was significantly lessened only when concentrations of nitrogen were 50 ppm or more. Solutions of sodium nitrite, ammonium chloride and glutamic acid with equal nitrogen contents were equally effective in releasing buds from dormancy. Larger amounts of nitrogen were required to stimulate growth in basal buds, than in apical buds. GA₃, and chilling at – 2 ^oC slightly increased the percentage of buds growing but did not significantly affect the amount of extension growth, while ethephon (2-chloroethylphosphonic acid) had no effect. The restoration of regenerative capacity was associated with increased utilization of rhizome sugars. In single-node rhizome fragments with ‘late spring dormancy’, chilling for 2 wk slightly increased the regenerative capacity but chilling for longer periods decreased it, possibly because respiration during the protracted period of chilling depleted rhizome reserves. Chilling also increased the utilization of rhizome carbohydrates during subsequent growth. Node position affected regenerative capacity: buds from the apical end of the rhizomes were found to have the highest regenerative capacity, this being associated with their greater nitrogen content. Because the name ‘late spring dormancy’ seems to be inappropriate for this phenomena, the term ‘Restricted Regenerative Capacity’ is proposed.     

Role of phytohormones in organogenic ability of elm multiplicated shoots

The study presents the comparative analyses of endogenous contents of auxin (IAA), cytokinins (CKs), polyamines (PAs), and phenolic acids (PhAs) in apical and basal parts of elm multiplicated shoots with regard to the organogenic potential. The shoot-forming capacity was higher in the apical part than in the basal part. However, the timing of root formation was in the apical type of explant significantly delayed (compared with the organogenic potential of basal part). Significantly higher contents of free bases, ribosides and ribotides of isopentenyl adenine, zeatin and dihydrozeatin that were found in the apical segments, might be considered as the most important factor affecting in vitro shoot formation. The content of endogenous free IAA was approximately three times higher in the basal shoot parts than in the apical parts. The amounts of putrescine and spermidine were higher in the apical part which generally contains less differentiated tissues than the basal part of shoot. The predominant PhA in both types of explants was caffeic acid, and concentrations of other PhAs decreased in the following order: p-coumaric, ferulic, sinapic, vanillic, chlorogenic, p-hydroxybenzoic and gallic acids. The contents of all determined PhAs in their free forms and higher contents of glycoside-bound p-coumaric, ferulic and sinapic acids, precursors for lignin biosynthesis, were found in the basal parts.     

Maintenance of MLOs (Mycoplasma-like Organisms) on Populus alba Micropropagation

Populus alba plantlet micropropagation has been used for maintaining MLOs more than three years in samples collected from infected trees in Paris. Symptoms were observed on plantlets obtained from subcultures of the apical, middle and basal parts of the stems, and from the roots. Fluorescent microscopy failed to detect MLOs in the apical part of the plantlets and showed that they increased near the roots. Electron microscopy confirmed their presence. Some root sieve tubes were completely packed with MLOs. The sensitivity of the two methods used, subculturing and microscopy, for detection of MLOs is discussed. The symptoms remained for one year in plants regenerated from diseased plantlets and grown in the greenhouse. Then they started to disappear.     

Relative importance of nodal roots and apical buds in the control of branching in Trifolium repens L.

Clonal species are characterised by having a growth form in which roots and shoots originate from the same meristem so that adventitious nodal roots form close to the terminal apical bud of stems. The nature of the relationship between nodal roots and axillary bud growth was investigated in three manipulative experiments on cuttings of a single genotype of Trifolium repens. In the absence of locally positioned nodal roots axillary bud development within the apical bud proceeded normally until it slowed once the subtending leaf had matured to be the second expanded leaf on the stem. Excision of apical tissues indicated that while there was no apical dominance apparent within fully rooted stems and very little in stems with 15 or more unrooted nodes, the outgrowth of the two most distal axillary buds was stimulated by decapitation in stems with intermediate numbers of unrooted nodes. Excision of the basal branches from stems growing without local nodal roots markedly increased the length and/or number of leaves on 14 distally positioned branches. The presence of basal branches therefore prevented the translocation of root-supplied resources (nutrients, water, phytohormones) to the more distally located nodes and this caused the retardation in the outgrowth of their axillary buds. Based on all three experiments we conclude that the primary control of bud outgrowth is exerted by roots via the acropetal transport of root-supplied resources necessary for axillary bud outgrowth and that apical dominance plays a very minor role in the regulation of axillary bud outgrowth in T. repens.     

Relationship of Apical Dominance to the Nutrient Accumulation Pattern in Pisum sativum var. Alaska

Decapitation of the pea plant resulted in the growth of all the lateral shoots. The initial growth of all lateral buds was somewhat similar. The differential growth rates developed later on. The pattern of growth of lateral shoots varied with the age of the plant when decapitation was performed. The basal shoots dominated when the plants were decapitated at the 2-leaf stage. At 3-leaf stage decapitation resulted in the dominance of shoot 5. Decapitation at 4-or-more-leaf stage resulted in the eventual dominance of the suhterminal lateral shoot. As a rule P-32 moved to the most actively growing part of the plant, i.e. apex in intact vegetative plant, the growing lateral shoots in a decapitated plant, the elongating subapical parts of the stem and the roots. The various metabolic sinks seemed to compete actively for this nutrient, therefore P-32 accumulation in any particular growing region of the plant was taken as an indicator of nutrient utilization potential of that part. The stem apex of an intact plant seemed to loose its dominance with the increasing age of the plant. The loss of apical dominance was almost complete during the reproductive phase of the plant, during which the upper lateral shoots initiated growth. Their growth, however, was inhibited soon because of competition with the other developing sinks, viz., the flower and the fruit. The amount of soluble carbohydrates in various parts of the pea plant followed essentially the same pattern as did P-32 accumulation. These distribution patterns were apparently correlated with the growth of the plant.     

Ciliated Receptors in the Pharyngeal Terminal Buds of Larval Lampetra planeri (Bloch) (Cyclostomata)

Terminal buds on the gill arches of larval Lampetra planeri have been investigated by scanning and transmission electron microscopy. Each terminal bud is composed of two types of elongated cells, which extend from an apical depression to the basal lamina; one type bears a pair of cilia and the other, microvilli. In addition there are peripheral and basal cells. Nerve-fibre profiles are lacking within the terminal bud epithelium and contacts between nerves and ciliated cells are established through holes in the basal lamina. The presence of ciliated receptor cells with such a mode of innervation presents a distinct contrast to the morphology of the taste buds of gnathostome vertebrates.     

Another evidence for inhibitory effect of auxin in adventitious bud formation of decapitated flax (Linum usitatissimum L.) seedlings

Adventitious buds were formed on the hypocotyls of decapitated flax seedlings. Scanning electron and light microscopic examinations of hypocotyls showed that epidermal cells divided to produce meristematic spots from which several leaf primordia were formed. Between leaf primordia and the original vascular tissues of hypocotyls, new xylem cells were formed which connected them. About 10, 30 and 60% of adventitious buds were formed on upper, middle and basal parts of hypocotyls of decapitated seedlings, respectively. Removal of apical meristem together with longer hypocotyl zero to four cm long below the apical meristem) induced higher percentage of adventitious bud formation in the remaining hypocotyl. When the entire hypocotyl was cut into 16 segments (0.25 cm each) and these segments were cultured on MS medium containing 3% sucrose and 0.8% agar, adventitious buds were mainly formed in the lowest five segments. These results suggested that there was a gradient of inhibitory factor(s) from apical to basal part of hypocotyl with respect to adventitious bud formation. Auxin transport inhibitors, morphactin and TIBA induced adventitious bud formation on intact seedlings by suppressing the basipetal movement of auxin.     

Endogenous levels of abscisic acid,indole-3-acetic acid and benzyladenine during in vitro bud growth induction of Wild cherry (Prunus avium L.)

Levels of endogenous growth substances (abscisic acid: ABA; indole-3-acetic acid: IAA) and applied benzyladenine (BA) were quantified during the eight first days of in vitro propagation of Wild Cherry (Prunus avium L.). Axillary buds from the middle part of the explants started to grow at day 2, thus were released from apical dominance. Hormone levels were measured in the apical, median and basal parts of the explants using an avidin-biotin based enzyme-linked immunosorbent assay (ELISA) after a purification of the extracts by high performance liquid chromatography (HPLC). All hormones showed rapid and considerable changes during the first eight days of growth. Exogenous IBA was probably transformed into IAA mainly in the basal part of the explant, and BA penetrated quickly. ABA levels were transiently enhanced in the apical part of the explants bearing young leaves. These phenomena are discussed in connection with the axillary bud reactivation.     

Development of the taste buds in rat embryogenesis

Electron microscopic studies have been made on the developing taste buds in fungiform and vallate papillae of prenatal rats. Three stages of differentiation of these buds are described. The first stage is characterized by presence of the nervous fibers in the connective tissue of the papillae and dense granules of various size, as well as dense-cored vesicles (500-700 A in diameter) in the basal parts of some epithelial cells at the top of the papillae (16-17th days of gestation). The second stage is characterized by nerve processes entering the epithelium and by formation of afferent synaptic contacts between the differentiating epithelial cells and the nervous fibers (19th day of gestation). At the third stage, the cluster of differentiating epithelial cells attains a form which is similar to mature taste buds (21-22nd days of gestation). Thus, to the birthday of rats, differentiation of the basal parts of the taste buds takes place, whereas the apical parts of the taste buds remain undeveloped and do not communicate with the oral cavity. Peculiarities of fine structure of differentiating epithelial cells at the three stages are discussed.     

Endogenous abscisic acid levels in stems and axillary buds of intact or decapitated broad-bean plants (Vicia faba L.)

Endogenous levels of abscisic acid (ABA) were measured by gas-liquid chromatography (electron capture) in stems and axillary buds of intact or decapitated broad-bean plants ( Vicia faba L. cv. Aguadulce). Endogenous ABA was distributed in the main axis according to a concentration gradient from the apical part of the stem towards the base. Axillary buds contained ABA levels which were from 4 to 9 times higher than those in the corresponding nodes and internodes. Decapitation of the plant was followed within 6 h by a large decrease of ABA levels in all the parts of the main axis. The diminution of ABA content was the most important in axillary buds released from apical dominance. Twenty-four hours after the decapitation, the ABA concentration further decreased in the upper parts of the stem, while no modification was observed in the basal parts of the stem containing the smallest levels of ABA.     

Developmental study onHypolepis punctata (Thunb.) Mett.

The origins of the first and second petiolar buds ofHypolepis punctata were clarified in relation to the early development of the leaf primordium, which arises from a group of superficial cells of the shoot apical meristem. One of these superficial cells produces a two-sided leaf apical cell which subsequently cuts off segments to make a well-defined cell group, called here the leaf apical cell complex, on the distal part of the leaf primordium. Meanwhile, cells surrounding the leaf apical cell complex also divide frequently to form the basal part of the leaf primordium. Two groups of basal cells of the leaf primordium located on the abaxial and the adaxial sides initiate the first and the second petiolar buds, respectively. The initial cells are usually contiguous to the leaf apical cell complex, constructing the abaxial and adaxial flanks of the very young leaf primordium. However, the first petiolar bud sometimes develops from cells located farther from the leaf apical cell complex. These cells are derived from those originally situated in the peripheral region of the shoot apical meristem. This study was supported by a Grant-in-Aid for Encouragement of Young Scientists by the Ministry of Education, Science and Culture, of Japan No. 474322 in 1979.     

伊乐藻和黑藻断枝根和芽的发生及生长研究

为了解外来种伊乐藻的无性繁殖力、评价其生态安全性,采用插植方式比较研究了伊乐藻(Elodea nuttallii)和本土种黑藻(Hydrilla verticillata)两种沉水植物不同节数(1至4节)和不同节位断枝的不定根和新芽的发生及生长情况。通过室内4周的3次平行实验,结果表明:两者顶芽段均有形成不定根继而形成新植株的能力,而顶芽以下茎段只有本身具有腋芽的断枝才有形成新芽和不定根的能力。两者具相同节数的断枝形成不定根的百分率及根、芽长度,以具顶芽断枝的均明显高于不具顶芽断枝的,具顶芽四节断枝的不定根生成率最高达到90%以上。不具顶芽断枝形成新芽和不定根的百分率及长度随着断枝节数的增加均呈显著递增趋势,每类断枝的发芽率显著大于其生根率;伊乐藻和黑藻枝条一般分别每7节和5节具有一个腋芽,只有具腋芽断枝才能存活,因此,对不具顶芽断枝,7节和5节分别是其形成新苗所需的最短断枝长度。根和芽的长度随节位的下降大致呈递增的趋势。但是节数对形成根、芽的影响显著大于节位的影响。具顶芽断枝的顶芽的增长量和具顶芽4节断枝的生物量增量伊乐藻的高于黑藻,其余指标伊乐藻均显著低于黑藻。伊乐藻断枝的繁殖力总体上低于黑藻。