TENDRILS OF PASSIFLORA FOETIDA: HISTOGENESIS AND MORPHOLOGY

Passiflora foetida bears an unbranched tendril, one or two laterally situated flowers, and one accessory vegetative bud in the axil of each leaf. The vegetative shoot apex has a single-layered tunica and an inner corpus. The degree of stratification in the peripheral meristem, the discreteness of the central meristem, and its centric and acentric position in the shoot apex are important plastochronic features. The procambium of the lateral leaf trace is close to the site of stipule initiation. The main axillary bud differentiates at the second node below the shoot apex. Adaxial to the bud 1–3 layers of cells form a shell-zone delimiting the bud meristem from the surrounding cells. A group of cells of the bud meristem adjacent to the axis later differentiates as an accessory bud. A second accessory bud also develops from the main bud opposite the previous one. A bud complex then consists of two laterally placed accessory bud primordia and a centrally-situated tendril bud primordium. The two accessory bud primordia differentiate into floral branches. During this development the initiation of a third vegetative accessory bud occurs on the axis just above the insertion of the tendril. This accessory bud develops into a vegetative branch and does not arise from the tissue of the tendril and adjacent two floral buds. The trace of the tendril bud consists of two procambial strands. There is a single strand for the floral branch trace. The tendril primordium grows by marked meristematic activity of its apical region and general intercalary growth.     

Histochemical detection and image analysis of non-specific esterase activity and the amount of polyphenols during annual bud development in Norway spruce

The study focused on Norway spruce trees during their annual development and, specifically, on the histochemical analysis of the activity of the non-specific esterase and the amount of polyphenols in the vegetative buds. Azo-coupling reaction with naphthol-AS-acetate as a substrate and Fast Blue B Salt as a coupling reagent was applied to the longitudinal median cryo-sections of the formalin-fixed buds. A method of image analysis was developed to evaluate the intensity of the histochemical reaction quantitatively. High activity of non-specific esterase was detected in the cells of the collenchymatic plate, the youngest bud scales, the leaf primordia, in the zone of differentiation of vascular tissues and procambium of the dormant bud. The activity of non-specific esterase decreased in all tissues during bud break. During the growth of a new shoot enzyme activity was detected only in the vascular bundles of the shoot. Enzyme activity re-occurred at the beginning of the autumn in the cells of the collenchymatic plate of the newly establishing buds. Three different types of polyphenols at different intracellular localizations (as verified by scanning electron microscopy) were observed: granular, vacuolar and drop-like polyphenols. The amount and localization of those polyphenols changed during the bud growing cycle. The positive reaction of all three types of polyphenols are tannin in nature. These findings are discussed from the viewpoint of frost tolerance and tissue differentiation.     

Anatomy of shoots and tumors of in vitro habituated Rhododendron 'Montego' (Ericaceae) cultures with tissue proliferation

Tissue proliferation (TP) is characterized primarily by the formation of galls or tumors at the crown of container-grown rhododendrons that were initially propagated in vitro. In the cultivar 'Montego', TP-like symptoms are first observed in vitro as shoot clusters with small leaves and nodal tumors. In addition, unlike the normal in vitro non-TP (TP-) shoots, in vitro TP (TP+) shoots proliferate rapidly without the presence of the plant growth regulator cytokinin in the tissue culture medium. Comparisons of the anatomy of TP+ and TP- shoot tips showed that TP+ shoots had a less developed vascular system, longer cells in the pith and cortex, and altered internodal elongation at the shoot apex. In addition, TP+ axillary buds were abnormal in that they were displaced onto the stem above the leaf axil, and a small group of proliferating cells replaced the shell zone at the base of the bud. Initiation of tumor formation began with the expansion of this region of cell proliferation (RCP) and shoot growth from the abnormal axillary bud (tumor bud). Organization of the tumor bud and extension of the RCP characterized the further development of two types of tumors. In polar shoot tumors, shoot growth continued from the persistent tumor bud and the tumor at the base of the shoot remained small in size. The RCP extends downward to the vascular junction of the subtending leaf and the stem of the TP+ shoot. In nonpolar tumors, continuous de novo meristem formation led to the development of large tumors with or without shoots. The RCP is present throughout the tumor and is associated with de novo meristem formation. Comparisons to the anatomy of other tumor-like structures showed that TP tumors of Rhododendron 'Montego' are most similar to tobacco genetic tumors.     

Selective histochemical localization of alcohol dehydrogenase in bud primordia cells of wheat shoot apices

During the histochemical investigation of dehydrogenases in the developing shoot apex of wheat plants it was found that the morphologically similar cells of the peripheral meristem may be differentiated according to the differential activity of alcohol dehydrogenase. While the enzyme was not present or exhibited a very small activity only in the tissue of leaf primordia it was highly active in the cells of bud primordia irrespective of the degree of their development and their differential physiological determination.     

Development and Growth Potential of Axillary Buds in Roses as Affected by Bud Age

The effect of axillary bud age on the development and potentialfor growth of the bud into a shoot was studied in roses. Ageof the buds occupying a similar position on the plant variedfrom 'subtending leaf just unfolded' up to 1 year later. Withincreasing age of the axillary bud its dry mass, dry-matterpercentage and number of leaves, including leaf primordia, increased.The apical meristem of the axillary bud remained vegetativeas long as subjected to apical dominance, even for 1 year. The potential for growth of buds was studied either by pruningthe parent shoot above the bud, by grafting the bud or by culturingthe bud in vitro. When the correlative inhibition (i.e. dominationof the apical region over the axillary buds) was released, additionalleaves and eventually a flower formed. The number of additionalleaves decreased with increasing bud age and became more orless constant for axillary buds of shoots beyond the harvestablestage, while the total number of leaves preceding the flowerincreased. An increase in bud age was reflected in a greaternumber of scales, including transitional leaves, and in a greaternumber of non-elongated internodes of the subsequent shoot.Time until bud break slightly decreased with increasing budage; it was long, relatively, for 1 year old buds, when theysprouted attached to the parent shoot. Shoot length, mass andleaf area were not clearly affected by the age of the bud thatdeveloped into the shoot. With increasing bud age the numberof pith cells in the subsequent shoot increased, indicatinga greater potential diameter of the shoot. However, final diameterwas dependent on the assimilate supply after bud break. Axillarybuds obviously need a certain developmental stage to be ableto break. When released from correlative inhibition at an earlierstage, increased leaf initiation occurs before bud break.Copyright1994, 1999 Academic Press Age, axillary bud, cell number, cell size, pith, shoot growth, Rosa hybrida, rose     

Ontogeny of Axillary and Accessory Buds in Clerodendrum phlomidis L.

Plastochronic changes in the vegetative shoot apex and originand development of axillary and accessory buds are studied. The flat shoot apex shows structural and dimensional changesin a plastochron. They are described in three phases, the pre-leafinitiation, the leaf initiation, and the post-leaf initiation.The youngest axillary bud meristem is identified near the axilat the second node when the subtending leaf primordium is 200–12µ long. The corpus of the bud meristem has a more activerole in bud development than has the tunica layers. The shellzone associated with a young bud meristem persists until thebud has attained the structural and functional attributes ofthe main shoot apex. It loses its histological identity by producingderivatives which merge with the ground tissue and procambialcells of bud traces. In a developing bud the provascular systemof the bud appears as an arc, a loop, or as a ring in transversesections at different levels. These configurations are composedof anastomosing procambial strands of bud trace and residualmeristem, both being differentiated from developing bud meristem.     

Anatomical and Histochemical Changes of Norway Spruce Buds Induced by Simulated Acid Rain

The study was focused on changes of anatomical and histochemical parameters of buds of 4-year-old Norway spruce (Picea abies L. Karst) trees subjected to simulated acid rain (SAR). Solutions of pH 2.9 and 3.9 were applied by spraying on shoot and/or by watering for two years. No macroscopic changes of buds or needles were observed in connection with SAR application and the only induced change was 2-week earlier onset of bud break in all treated variants compared to the control. Two-year treatment caused decrease in number of leaf primordia and increase in number of living bud scales in treated dormant buds while these parameters remained unchanged in the control buds. Treatments with solution of pH 2.9 caused decrease of flatness of bud apical meristem during the vegetative season. Increased activity of non-specific esterase in treated buds occurred during dormancy and bud break and the enhanced accumulation of phenolic compounds was detected at the beginning of shoot growth. Changes in histochemical parameters of bud tissues were induced mainly by spraying of shoots and can thus be qualified as primary damage.     

Developmental study onHypolepis punctata (Thunb.) Mett.

The third petiolar bud ofHypolepis punctata appears on the basiscopic lateral side of the petiole above the fairly developed first petiolar bud. This investigation clarified the fact that the third bud is formed neither by the activity of the meristem of the first bud nor by the meristem directly detached from the shoot apical meristem, but is initiated in the cells involved in the abaxial basal part of the elevated portion of the leaf primordium. Thus the third bud is of phyllogenous origin. This investigation further revealed that the cells to initiate the third bud are originally located in the abaxial side of the leaf apical cell complex like the cells to initiate the first bud, but are not incorporated into the meristem of the first. After the first, second and third petiolar buds have been initiated, they are carried up into fairly high regions on the petiolar base by the intercalary growth which occurs in the leaf base below the insertion level of the first and the second buds.     

Histological analysis in shoot organogenesis from hypocotyl explants of<Emphasis Type="Italic"> Kandelia candel</Emphasis> (Rhizophoraceae)

In vitro culture of hypocotyl explants from Kandelia candel, a common mangrove species, on hormone-free Murashige and Skoog (MS) medium resulted in shoot formation. Since the hypocotyls showed good potential for in vitro shoot multiplication, the process of bud primordium formation was analyzed from a histological viewpoint. A wound periderm first appeared at the top, exposed cut surface of the explants. The wound-induced meristem continued to divide giving rise to suberized cells oriented towards the cut surface. After formation of the suberized cell layers, the meristem and its inner derivatives differentiated into multilayered, uniformly packed parenchyma cells. Bud primordia differentiated from the dense cytoplasmic cells of the wound-induced meristem just beneath the suberized layer near the severed vascular bundles. Each explant produced several visible shoot buds. Furthermore, histological sections revealed that additional bud primordia were present within the explant just underneath the suberized cells and that these bud primordia appeared to be arrested in their development. The fact that additional bud primordia were present within the explant suggests that further manipulation of the explant is helpful to maximize the potential of this system.     

THE SHELL ZONE: ITS DIFFERENTIATION AND PROBABLE FUNCTION IN SOME DICOTYLEDONS

Thirty-five species belonging to various dicotyledonous families were investigated to study the origin, development, and probable function of the shell zone, which is defined as an arcuate zone of cambiform cells delimiting the early axillary bud meristem. It is present in the majority of the investigated plants and five intergrading patterns of origin are described: (i) from the parenchymatized derivatives of the cells of the peripheral meristem of the shoot apex, adaxial to the bud meristem, (ii) from the peripheral meristem of the shoot apex along with the initiation of the early bud meristem, (iii) from the adaxial cells of the bud meristem, (iv) from the derivatives of the cells of the bud meristem at its base, and (v) partly from the parenchymatized cells of the peripheral meristem adaxial to the bud and partly from the adaxial derivatives of the bud meristem. The shell zone loses its identity at different stages of bud development in various species. Its cells ultimately contribute to the ground meristem, procambium, and pith cells of the axis. In Cuminum cyminum and lpomoea cairica the shell zone contributes in bringing about the axillary position of the bud from its early lateral position. In Solarium melongena, derivatives of the shell zone initiate the internodal elongation between the flower or inflorescence and the shoot apex, ultimately shifting the bud to an extra-axillary position on the internode.     

Seasonal variation of organogenetic activity and reserves allocation in the shoot apex of Pinus pinaster Ait

BACKGROUND AND AIMS: To understand better the basic growth characteristics of pines and the fundamental properties of the shoot apical meristem (SAM), variations within the shoot apex of buds were studied. METHODS: A detailed structural comparison of meristem dimensions, organogenetic activity, and the presence of lipids, starch grains and tannins was performed on shoot apices of juvenile, and male and female adult Pinus pinaster at five different times in the annual growth cycle. KEY RESULTS: There were significant correlations among traits and differences in the pattern for juvenile and adult shoots. In juvenile shoots, peaks of organogenesis were present in spring and autumn, but not in summer. In adult shoots, one peak, characterized by an increase in meristem dimensions, was present in summer. The accumulation of starch grains beneath the SAM and of tannin in sub-apical pith parenchyma were at their maximum when organogenetic activity was high in spring and autumn in juvenile plants, and in summer in adult plants. In juvenile and adult plants, lipids were stored within the SAM in autumn, filling a large part of the bud in winter, and were depleted in the cortical parenchyma and then in the pith during shoot elongation. CONCLUSIONS: Depending on the sites of accumulation within the SAM and on the stage of the annual growth cycle, lipids, starch and tannins may be involved in different processes. In spring, energy and structural materials released by lipid hydrolysis may contribute to stem elongation and/or cell-to-cell communication. During organogenesis, energy and structural materials released by starch hydrolysis may influence developmental programmes in the SAM and adjacent cells. Tannins may be involved in cellular detoxification. At the end of the growing season, accumulation of lipid and starch is positively correlated with the onset of dormancy.     

Cells within the nodal region of carnation shoots exhibit a high potential for adventitious shoot formation

Adventitious shoot formation was studied with leaf, stem and axillary bud explants of carnation (Dianthus caryophyllus L.). The shoot regeneration procedures were applicable for a wide range of cultivars and shoot regeneration percentages were high for all explant types. Using axillary bud explants, shoot regeneration efficiency was independent of the size of the bud and of its original position in the plant. In contrast, shoot regeneration from stem and leaf explants was strongly dependent on their original position on the plant. The most distal explants (just below the apex) showed the highest level of shoot regeneration. The adventitious shoot primordia developed at the periphery of the stem segment and at the base of leaf explants. In axillary bud, stem and leaf explants, shoot regeneration originated from node cells, located at the transition area between leaf and stem tissue. Moreover, a gradient in shoot regeneration response was observed, increasing towards the apical meristem.Abbreviations BA benzyladenine - NAA naphthaleneacetic acid     

THE DEVELOPMENTAL ANATOMY OF LONG-BRANCH TERMINAL BUDS OF PINUS BANKSIANA

A study of the composition of long-branch terminal buds (LBTB) of Pinus banksiana Lamb. and the yearly periodicity associated with their formation, development, and elongation was undertaken. Each LBTB has lateral bud zones and zones of cataphylls lacking axillary buds. When present, staminate cone primordia differentiate from the lowest lateral buds in the lowest lateral bud zone of the LBTB. Ovulate cone primordia and lateral long-branch buds can differentiate from the upper lateral buds in any lateral bud zone. When both types of buds are present, lateral long-branch buds are uppermost. Dwarf-branch buds occur in all lateral bud zones. During spring LBTB internodes elongate, new cataphylls are initiated, dwarf branches elongate, needles form and elongate, pollen forms and is released, and ovulate cones are pollinated. During summer buds form in the axils of the newly formed cataphylls. By early fall the new LBTB are in overwintering condition and the four types of lateral buds are discernable. The cytohistological zonation of the LBTB shoot apex is similar to that of more than 20 other conifer species. Cells in shoot apices of pine are usually arranged in distinct zones: apical initials, subapical initials, central meristem, and peripheral meristem. Periclinal divisions occur in the surface cells of the apex; therefore no tunica is present. At any given time, shoot apex volume and shape vary among LBTB in various positions on a tree. In any one LBTB on a tree, shoot apex shape changes from a low dome during spring to a high dome during summer to an intermediate shape through fall and winter.     

The blockage in the G 1 phase of the cell cycle in the dormant shoot apex of ash

The shoot apex of the terminal bud was studied in four successive physiological states: during dormancy, when dormancy breaks, during the third week after the break of dormancy, and during a later typical period of active growth. DNA content was measured in Feulgen-stained nuclei of the axial zone, of the lateral zone, and of the rib meristem. The mitotic index was established for each zone of the meristem. During the period of dormancy, all the nuclei of the meristem are in phase G ₁ of the cell cycle and are blocked at the same point common to all nuclei. When dormancy breaks, this blockage is removed simultaneously and all nuclei in the shoot apex resume their cell cycles starting at the same point. The cycles remain synchronized for awhile. In the axial zone they remain synchronized until the third week after resumption of active growth.     

Localization of cytokinins in somatic and zygotic embryos of Tilia cordata using immunocytochemistry

Immunofluorescent and immunogold labeling was used to study the localization of cytokinins in developing somatic and zygotic embryos of Tilia cordata Miller. Broad-specificity polyclonal antibodies active against dihydrozeatin riboside (DHZR)/zeatin riboside (ZR)-type and isopentenyladenosine (iPR)-type cytokinins were used for immunolabeling. Immunofluorescent microscopy showed that these cytokinins were concentrated in highly cytoplasmic cells showing meristematic character. Cotyledon initials and primary meristems of heart-stage somatic embryos, as well as heart-stage zygotic embryos, were labeled. During elongation of embryos, cytokinin immunoreactive material was concentrated to areas having meristematic character. Root apex, shoot meristem, and cotyledon cells of somatic and zygotic cotyledonary embryos, as well as epidermal and subepidermal cell layers of the hypocotyl, showed the strongest immunoreaction. The nucleoli, especially, had a very strong signal. Results at the ultrastructural level with gold-conjugated protein A supported these conclusions. Gold particles were distributed in the nuclei, especially in the nucleoli and throughout the ground cytoplasm. They were occasionally associated with plastids and mitochondria, but seldom with other organelles.     

HISTOCHEMICAL STUDY OF ENZYME ACTIVITY IN THE SHOOT APICAL MERISTEM OF BRASSICA CAMPESTRIS DURING TRANSITION TO FLOWERING. IV. GLUCOSE-6-PHOSPHATASE

Glucose-6-phosphatase (G6P) activity was determined in fresh-frozen, cryostat sections in the shoot apical meristem of Brassica campestris L. Enzymatic activity was differentially distributed in a zonate pattern in the vegetative meristem, but not in the transition and floral meristem. Vegetative apices showed a heterogenous localization with the highest activity in the central zone and the pith-rib meristem zone. At the early transition stage of development, G6P activity in the peripheral zone increased slightly. At the late transitional (prefloral) stage, G6P activity was not localized within the peripheral zone in island-like areas of activity. This is the first demonstration of G6P in shoot apical meristem at the vegetative, transition, and floral stage. The results indicate that G6P activity 1) is an accompanying event of evocation, but 2) does not mark incipient floral primordia. G6P may play an important role in the maintenance of glucose-6-phosphate homeostasis in an evoked shoot apical meristem.     

High frequency early in vitro flowering of <Emphasis Type="Italic">Dendrobium</Emphasis> Madame Thong-In (Orchidaceae)

We have successfully developed a method to induce early in vitro flowering of the self-pollinated seedlings of a tropical orchid hybrid, Dendrobium Madame Thong-In. Transition of vegetative shoot apical meristem to inflorescence meristem was observed when young protocorms were cultured in modified KC liquid medium. In contrast, protocorms cultured on Gelrite-solidified medium only produced axillary shoots and roots. CW was required to trigger the transitional shoot apical meristem and BA enhanced inflorescence stalk initiation and flower bud formation. However, normal flower development was deformed in liquid medium but developed fully upon transferring to two-layered (liquid over Gelrite-solidified) medium. Under optimal condition, in vitro flowering was observed about 5 months after seed sowing. Segregation of flower colours was observed in these seedlings and seedpods formed upon artificial pollination of the in vitro flowers.     

The shoot apical meristem restores its symplasmic organization during chilling-induced release from dormancy

The shoot apex of overwintering perennials ceases its morphogenetic activity at the end of the growing season and transforms into a bud which is dormant and freezing-tolerant. In birch (Betula pubescens) these events are triggered by short photoperiod, and involve the production of 1,3-beta-D-glucan containing sphincters on the plasmodesmata. As a result, all symplasmic pathways shut down. Here we show that breakage of bud dormancy by chilling involves restoration of the symplasmic organization of the meristem. This restoration is likely to be mediated by 1,3-beta-D-glucanase, which was present in small spherosome-like vacuoles that arose de novo during dormancy induction. During chilling these vacuoles were displaced from the bulk cytoplasm to the cortical cytoplasm where they became aligned with the plasma membrane, often associated with plasmodesmata. At this stage the enzyme also appeared outside the vacuoles. During chilling, 1,3-beta-D-glucan disappeared from the plasmodesmal channels and wall sleeves, and the plasmodesmata regained the capacity for cell-cell transport, as demonstrated by microinjection of Lucifer Yellow CH and Fluorescein-tagged gibberellic acid. Collectively, the present experiments demonstrate that restoration of the symplasmic organization of the meristem is indispensable for the release of buds from dormancy and the assumption of a proliferation-competent state, and implicate 1,3-beta-D-glucanase action at the plasmodesmata. Based on these findings we propose a model for 'dormancy cycling' which depicts the meristem as passing through three sequential states of cellular communication with characteristic sensitivities to distinct environmental cues.     

Cell lineage patterns in maize embryogenesis: A clonal analysis

The embryonic cell lineage of the shoot meristem in maize (Zea mays L.) has been characterized using clonal analysis. Although there is considerable variability in the size and distribution of somatic sectors induced at a given time in embryogenesis, the fate of meristematic initials is not entirely random. During embryogenesis the number of cells in the presumptive shoot meristem increases and their fate becomes progressively more restricted. Cells toward the periphery of the presumptive meristem give rise to the lower nodes of the plant, while central cells form more distal nodes. Cell lineages become restricted to single nodes starting at the base of the plant, indicating that restriction of cell fate progresses from the periphery towards the center of the meristem. The number of twin shoots produced by X irradiation declines dramatically between 8 and 10 days after pollination, and is preceded by an acropetal progression in the level at which twinning occurs. This phenomenon suggests that the shoot meristem becomes determined gradually and that this process is completed between 8 and 10 days after pollination; i.e., just prior to or during the transition stage of development. At this stage the shoot primordium consists of 100–200 cells encompassing two or more cell layers of the embryo. The orientation of sectors that saddle the shoot (extend from one side of the shoot to the other) demonstrates that the shoot meristem arises from a region of the embryo containing longitudinally oriented cell files and that this cell pattern is at least partially preserved during shoot initation.     

Ontogeny of proventitious epicormic buds in Quercus petraea. I. In the 5 years following initiation

 The persistence of large epicormic shoots is one of the main factors that reduces timber quality and value in Quercus petraea. The early phases of epicormic shoot formation, i.e. the initiation of the epicormic buds, their survival and their proliferation over the years, are not clearly understood. In the present work, we studied the initiation of the axillary buds giving rise to epicormic buds and shoots, and followed their behaviour during the first 5 years using both scanning electron microscopy and light microscopy. Two types of proventitious epicormic buds have been identified. The first type has small axillary buds associated with the rings of bud-scale scars which are found at the base and tip of each growth unit. These buds are made of a terminal meristem surrounded only by scales; no leaf primordium is detected. During the second and third years of epicormic life, meristematic areas appear in the scale axil. Progressively, the meristematic areas organize into secondary bud primordia composed solely of the terminal meristem surrounded by scales. The second type of epicormic bud has secondary buds produced by a large axillary bud when this large bud either developed into a shoot or partially abscised. The epicormic potential in Q. petraea is characterized by a balance between the epicormic buds in apparent rest, enclosing meristematic areas and secondary bud primordia, and their mortality over the years. Received: 22 January 1998 / Accepted: 8 May 1998