Untersuchung des Einflusses der Temperatur auf die Photosynthese-Induktion bei Chlorella vulgaris mit radioaktivem CO2

Summary The lateral bud of Solanum andigena has the potentiality to develop as a stolon or as a leafy, orthotropic shoot. Natural stolons are normally only produced from underground nodes, but aerial stolons can be induced to form by the application of a combination of indole-3-acetic acid and gibberellic acid (IAA/GA₃) paste to the cut surface; under some conditions both natural or induced stolons are converted to upright, leafy shoots. The presence of roots was found to be necessary for the conversion of a natural stolon to a leafy shoot, but this root effect could be replaced by the synthetic cytokinin, 6-benzylaminopurine (BAP). By using -¹⁴C-BAP it was demonstrated that cytokinin accumulates in the tip of an induced stolon, prior to its conversion to a leafy shoot caused by withdrawal of the IAA/GA₃ paste. The application of IAA/GA₃ to decapitated plants was shown to influence both the distribution and metabolism of the cytokinin. The possibility that the role of auxin in apical dominance, at least in part, is to control the distribution and metabolism of cytokinins is discussed.     

Anatomy and development of the fern sporophyte

Recent research on the developmental anatomy and morphology of the fern sporophyte is reviewed. Detailed histological and experimental studies of the organization of the fern shoot apical meristem have reconfirmed the recently controversial role of the shoot apical cell as the single apical initial of the meristem. The shoot apical meristem is nevertheless an anatomically and functionally complex structure with a strongly zoned cytohistological organization. Fern shoot apex organization can be compared with that of seed plants. The control of leaf initiation and phyllotaxy remains poorly understood. Studies differ as to whether leaf initiation in ferns involves one leaf mother cell or a multicellular region of the shoot apex. The concept of non-appendicular fronds is refuted for living ferns. The later developmental changes in the determinate leaf apical and marginal meristems of the leaf primordium form an area that is still largely unexplored but could be investigated by methods similar to those used to study shoot and root apices. Branching in ferns is morphologiclaly and developmentally diverse. There is apparently more than one developmental mode of dichotomous branching, and several modes of lateral bud formation have been described, including the phyllogenous initiation of branches at the base of leaf primordia. Developmental changes in bud meristems related to apical dominance, inhibition, and bud activation is another major area for continued study. The traditional concept of the role of the root apical cell has been reestablished by studies similar to those made of the shoot apex. Detailed ultrastructural investigations of the root ofAzolla have given a sophisticated new picture of developmental processes in that organ. Fern roots show remarkably precise patterns of histogenesis in relation to apical segmentation. The formation of secondary vascular tissue inBotrychium suggests that the Ophioglossales may be related to the seed plants. The causal relationship of leaf (and branch and root) formation and the initiation of vascular tissue in the shoot needs more study. Although still poorly understood, protoxylem systems in ferns are variable and may have morphological and systematic significance. Recent investigations of hydraulic conductance in fern stems have found possible correlations of conductance levels with growth forms. The anatomical diversity of ferns makes comparative functional anatomy a promising field for future study.     

Developmental anatomy of the shoot apical cell,rhizophore and root ofSelaginella uncinata

The developmental anatomy of the shoot apex, rhizophore and root ofSelaginella uncinata was examined by the semi-thin section method. The shoot apex has a single, lens-shaped apical cell with two cutting faces. Rhizophore primordia are initiated exogenously at the branching point of the second youngest lateral shoot. The rhizophore apex has a tetrahedral apical cell with three cutting faces. A pair of root primordia is initiated endogenously from inner cells of the rhizophore apex, after the rhizophore apical cell becomes unidentifiable losing its activity, and subsequently a root cap is formed from the distal face of the root apical cell. During the course of successive root branching the apical cell in an original root apical meristem becomes unidentifiable and then a new apical cell is initiated in each of the bifurcated root apical meristems. The root branching mode seems to be equivalent to the described dichotomous branching mode of fern shoots. Our results demonstrate a distinct morphogenetical difference between the rhizophore and the root, and confirm the exogenous origin of the rhizophore, as described for other species ofSelaginella. This evidence indicates that the rhizophore is not an aerial root but a leafless, root-producing axial organ.     

Cell Cycling and the Fate of Potato Buds

The cell cycling characteristics of the regions of the apicalmeristems of underground shoots and buds of Solanum tuberosumL. were investigated by stathmokinesis and labelling. The apicaldomes of orthotropic shoots produce cells at twice the elementalrate of those of stolons, and their youngest leaf primordiaat twelve times the rate. Changing the fate of stolons so thatthey will become orthotropic by decapitating the tuber sproutsthat bear them results within 24 h in a general increase incell production especially in the leaf primordia. Axillary buds on tuber sprouts induced to become precursorsof orthotropic shoots instead of stolons undergo a spectacularincrease in cell division within 24 h in all regions, especiallyin the primordia and bud anlagen where the rate increases 20-foldor more. The summit is slower to react than other regions, but,by 24 h, its rate of cell division increases 11-fold and itis contributing 14 cells per day to the flanks from its 80 cells. In all the axillary buds the rate of mitosis in the summit ishalf that of the flanks of the apical dome, but, in both stolonsand orthotropic underground shoots, the rate is higher in thesummit than in the flanks or rib meristem. The results are discussed in relation to what is known of cellcycling changes after floral evocation. Solanum tuberosum L., potato, fate, cell division, apical meristem, stathmokinesis     

Density and the commitment of apical meristems to clonal growth and reproduction in Hieracium pilosella

Summary We examined responses to population density in the commitment of apical meristems to reproduction and clonal growth in a rosette-forming, stoloniferous herb (Hieracium pilosella). Despite close physiological coupling between the evocation of the terminal inflorescence bud and the development of one or more axillary buds into stolons, the allocation of meristems was extremely plastic.Genets at the higher sowing densities showed density-dependent mortality consistent with self-thinning along a-3/2 trajectory. The probability of inflorescence evocation and associated stolon development was negatively dependent on surviving density. The proportinal distribution of primary stolons amongst genets became strikingly more unequal (expressed as the Gini coefficient) with increasing density. Clonal growth was resolved into the number of primary stolons per stoloniferous genet and the extent of stolon branching (i.e. number of apices per primary stolon); both showed strongly negative density-dependence. Reproduction, expressed as the mean number of flowering capitula per stoloniferous genet, declined 15-fold with increasing density; although theoretically expected to be unity, greater values resulted from capitulum production by attached secondary rosettes and lower values reflected the increasing abortion rate of inflorescence buds with increasing density.Both the total number of apices produced per unit area and the corresponding number of reproductive apices were maximal at intermediate surviving densities (700–1,000 m^-2). The balance between reproductive and clonal growth may be expressed as the probability of an apical meristem producing a capitulum, that also peaked sharply at intermediate density. This finding does not conform with linear models that predict a shift from vegetative growth to sexual reproduction with increasing population density.     

ORGANOGRAPHY,BRANCHING, AND THE PROBLEM OF LEAF VERSUS BUD DIFFERENTIATION IN THE VINING EPIPHYTIC FERN GENUS MICROGRAMMA

Investigation of the development and organography of the shoot systems of Microgramma vacciniifolia and M. squamulosa was undertaken for the purpose of determining: (1) the features of shoot growth that are responsible for the distinctive vining character of these epiphytic ferns; and (2) the mode of origin of branches and their contrast with leaf initiation. Shoots of both species are dorsiventral and plagiotropic (i.e., parallel to the substrate) in habit. Since the shoot apical meristem is radial in transectional symmetry, shoot dorsiventrality in Microgramma is a postgenital or secondary developmental event, and its inception is related to the initiation of lateral appendages. Leaves and buds arise in a distichous phyllotaxis and occupy opposite and alternating positions on the dorsal surfaces and flanks of the rhizome. Endogenous roots are initiated in two rows from the ventral surface of the stem, in the vicinity of the rhizome meristem; however, they do not emerge from the rhizome until some distance behind the tip and do not elongate until the region of substrate contact. We conclude that the vining nature of this fern rhizome is a result of precocious internodal elongation and the concomitant delay of leaf and bud expansion in the region of stem elongation. In addition, observation of branch origin confirms previous suggestions that branching in Microgramma is strictly lateral and extra-axillary and not a dichotomous derivative as proposed by some workers. Leaf and bud primordia differ not only in the nature of their respective vascular supplies but also in their actual course of initiation. In the case of the leaf, the primordium is precociously emergent and exhibits a lenticular apical cell at its summit when it is only one plastochron removed from the flanks of the apical meristem. By contrast, initials of the bud primordium divide less actively and remain in a sunken position for at least 5–6 plastochrons; only when the bud apex becomes expanded and emergent does a tetrahedral apical cell become recognizable at the tip of the bud promeristem. Because of the distinctive pattern of branch and leaf origin, as well as the lack of adventitious and phyllogenous origin of branch primordia, we suggest that the shoot of Microgramma is a useful test organism for the re-examination of the problem of leaf and bud determination in the ferns.     

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.     

DEVELOPMENTAL POTENTIAL OF AXILLARY BUDS OF WATER HYACINTH,EICHHORNIA CRASSIPES SOLMS. (PONTEDERIACEAE)

Buds axillary to foliage leaves of water hyacinth can elongate either as vegetative stolons or as renewal shoots produced in association with the terminal inflorescence. Stolons differ from renewal shoots in position within the shoot system, morphology, and function. Renewal shoot buds always expand, whereas stolon buds may or may not. A stolon bud develops in conjunction with the subtending leaf; as that leaf matures, the stolon bud reaches a critical period in development. At this point, the bud either continues to expand, producing a stolon, or it stops growth and matures. Maturation is not irreversible, but the probability of a bud expanding decreases as bud age increases. In the field, buds on plants at the water hyacinth mat edge frequently produce stolons, whereas buds on plants inside the mat rarely do so. Leaf morphology also varies between plants in these two regions of the mat. The particular association of leaf and branch type found in the field, however, can be reversed experimentally, indicating that although leaf and bud development are coordinated, the particular course of each is independent.     

SHOOT ORGANIZATION IN THE FILICALES: THE PROMERISTEM

The classical pteridophyte apical cell theory of meristem organization is not flexible or realistic enough to encompass the variation encountered in a comprehensive anatomical survey of fern meristems. The meristems of 28 taxa of ferns (both eu- and leptosporangiate) were studied. This analysis has led to the formulation of the concept of a promeristem composed of two zones: the surface and subsurface initials. This concept is flexible and sufficient to describe the variation encountered in the ferns as a group. No differences in promeristem organization were observed in plants with various rhizome morphology (e.g., upright and radial; prostrate and dorsiventral). Marking experiments, performed on living surface cells of fern promeristems, correlate with anatomical observations of division planes in the promeristem and indicate that the central, surface initials are not quiescent. Feulgen determinations indicate that Nephrolepis stolons have no endomitotically polyploid cells in the promeristem. Additional work is needed before a generalization can be made concerning ploidy levels in a more typical fern apex. Ferns, in general, have a zoned promeristem which is parallel to the zonation described for higher vascular plants.     

SYMMETRY AND DEVELOPMENT OF LIMNOBIUM SPONGIA (HYDROCHARITACEAE)

Limnobium spongia produces upright vegetative axes and prostrate stolons. The upright axes bear new stolons, whereas the stolons bear new upright axes and fertile and sterile branching systems. Upright axes and fertile and sterile branching systems are all interpreted to have sympodial growth. However, it was not determined whether growth of stolons is monopodial or sympodial. Both stolons and upright axes branch in alternate plastochrons, and branching is achieved solely by the bifurcation of apical meristems. Each meristematic bifurcation is interpreted to represent the formation of a precocious lateral bud. The upright axes develop from presumed precocious lateral buds on stolons, whereas such buds on upright axes produce renewal shoots. Limnobium spongia exhibits a marked degree of mirror-image symmetry.     

Formative and proliferative cell divisions,cell differentiation,and developmental changes in the meristem of Azolla roots

The root of the water fern Azolla is a compact higher-plant organ, advantageous for studies of cell division, cell differentiation, and morphogenesis. The cell complement of A. filiculoides Lam. and A. pinnata R.Br. roots is described, and the lineages of the cell types, all derived ultimately from a tetrahedral apical cell, are characterised in terms of sites and planes of cell division within the formative zone, where the initial cells of the cell files are generated. Subsequent proliferation of the initial cells is highly specific, each cell type having its own programme of divisions prior to terminal differentiation. Both formative and proliferative divisions (but especially the former) occur in regular sequences. Two enantiomorphic forms of root develop, with the dispositions of certain types of cell correlating with the direction, dextrorse or sinistrorse, of the cell-division sequence in the apical cells. Root growth is determinate, the apical cell dividing about 55 times, and its cell-cycle duration decreasing from an initial 10 h to about 4 h during the major phase of root development. Sites of proliferation progress acropetally during aging, but do not penetrate into the zone of formative divisions. The detailed portrait of root development that was obtained is discussed with respect to genetic and epigenetic influences; quantal and non-quantal cell cycles; variation in cell-cycle durations; relationships between cell expansion and cell division: the role of the apical cell; and the limitation of the total number of mitotic cycles during root formation.     

Shoot development and bud mite infestation in hazelnut (Corylus avellana)*

The interaction of environmental and genetic variation in hazelnut (Corylus avellana) shoot development and the behaviour, survival, and colonisation of eriophyid bud mites (Phytoptus avellanae and Cecidophyopsis vermiformis) were studied. The distribution of galled buds on shoots indicated that mites colonised only those buds formed during the mite migration period. The point of entry is probably the growing shoot tip. Once within this structure, as the shoot develops the mites have access to a succession of newly-formed, bud primordia that are unprotected by bud scales. The relative accessibility of the apical meristem and bud primordia may affect host susceptibility.     

A novel pathway for rapid shoot regeneration from the proximal zone of the inpocotyl of melon (Cucumis melo L.)

Summary Hypocotyl explants of melon (Cucumis melo L.) are capable of regenerating multiple shoots on Murashige and Skoog (1962) medium, augmented with 4.4 μM benzylademne. Regeneration from the hypocotyl is much more rapid than the more commonly reported regeneration from cotyledonary explants, producing shoots within 2 wk compared to more than a month required for cotyledon explants. The rapid regeneration response depends on the presence of a fragment of the cotyledon remaining attached to the hypocotyl. Controls were performed to ensure that the regeneration was not due to the presence of the shoot apical bud of the melon seedling after explant production. Scanning electron microscopy revealed that microsurgery to remove the apical bud left no excess bud material. Regeneration from the proximal part of the hypocotyl was due to production of a new shoot apical meristem, observed by histology. The apical meristem can be produced before leaf primordia in regeneration from the hypocotyl, in contrast to the regeneration process from the melon cotyledon.     

Effect of Main Root Decapitation on Root Branching in Flax Seedlings

Root branching patterns in intact and decapitated flax (Linum usitatissimumL.) roots were compared. The number of initiated primordia in the control and decapitated roots was similar, but decapitated roots produced an increased number of lateral roots owing to an increase in the number of primordia developed into the laterals. It is suggested that the apical meristem influences lateral root development only at the stage of root emergence from the parent root.     

Factors affecting the establishment and maintenance of ‘Titan’ red raspberry root organ cultures

Root organ cultures of red raspberry (Rubus ideaus cv. Titan) were established from two cm long terminal segments of adventitious roots induced in vitro on micropropagated shoot cultures. Growth of root organ cultures was almost entirely by initiation and elongation of lateral roots rather than by terminal elongation from the apical meristem of the original root explants. Indolebutyric acid (IBA) was required for lateral root initiation and elongation. The optimal IBA concentration for lateral root initiation decreased from 0.5 to 0.1 mg/L from the first to the fifth passage in culture. Two cm root explants initiated more lateral roots per unit length than four cm explants. Liquid Anderson's medium was superior to other basal nutrient and vitamin formulations tested. Root growth in liquid culture was stimulated by aeration. Root organ cultures also grew on media solidified with gelrite or agar. A rapid transfer technique was developed for subculturing these which involved cutting and transferring 1 cm discs of roots and underlying medium. Adventitious bud formation occurred spontaneously, but sporadically in liquid cultures, and was not influenced by cytokinin, auxin (spat) light, or chilling.     

Allelopathic effects of interrupted fern on northern red oak seedlings: Amelioration bySuillus luteus L.: Fr.

Summary The allelopathic effects of interrupted fern frond leachates on ectomycorrhizal (inoculated) and nonmycorrhizal (noninoculated) northern red oak (Quercus rubra L.) seedlings were investigated. Container-grown northern red oak was inoculated with vegetative mycelium ofSuillus luteus L. Fr. following acorn germination. Noninoculated control seedlings were also maintained. Seedlings were grown in a glasshouse under full sunlight or shaded (25% of full sunlight) conditions. Leachate or deionized water solutions were applied to seedlings eleven times over a 91-day period to simulate a rainfall induced transfer of allelopathic chemicals from fern fronds to the soil. Fern frond leachates significantly reduced seedling survival, however, inoculated seedlings showed less mortality. Chromium concentrations of pooled lateral root or leaf tissue were comparatively higher in tissues exhibiting greater mortality. Root biomass was reduced by fern fern frond leachate applications. Seedling biomass was not significantly affected by fungal inoculation. Our results confirm previous documentation of the allelopathic potential of ferns, and suggest that ectomycorrhizal fungi may ameliorate allelopathic effects of ferns on northern red oak seedling survival and growth.     

Effect of light quality (red: far-red ratio) and defoliation treatments applied at a single phytomer on axillary bud outgrowth in Trifolium repens L.

We studied the effects of light quality and defoliation on the rate of phytomer appearance and axillary bud outgrowth in white clover. The treatments were applied to one phytomer, a phytomer being defined as the structural unit comprising a node, internode, axillary bud, subtending leaf and two nodal root primordia. Light of a low red:far-red (R:FR) ratio (0.27) was applied to a target phytomer either (i) within the apical bud and then to the axillary bud after emergence of the phytomer from the apical bud, or (ii) to the axillary bud only after emergence. The light conditions were directed to these specific parts of the plant by collimating light from small FR light-emitting diodes; with this technique we were able to change the light quality without any change in the level of photosynthetically active radiation. The subtending leaf of the target phytomer was retained or defoliated when it had emerged from the apical bud. FR light applied from the time the phytomer was within the apical bud caused a delay in branch appearance at the target phytomer. In contrast, direct treatment of the axillary bud with FR light after it had emerged from the apical bud did not result in any delay in branch appearance. As the light treatment of the apical bud may have changed the light environment of any of the organs contained in the bud we were unable to ascribe the delay in branch appearance to light perception by any particular organ. However, indirect evidence leads to the conclusion that the likely site of light perception was the developing leaf subtending the axillary bud while it was the outermost phytomer within the apical bud. These results do not support the hypothesis that the R:FR ratio of light incident at an axillary bud site is the environmental factor that controls bud development. Defoliation of the unfolding leaf reduced the rate of phytomer appearance on the main stolon but had no immediate effect on branch appearance. As a consequence there was a reduction in the number of phytomers between the stolon apical meristem and the first phytomer with a branch. This is frequently taken to indicate a relaxation of apical dominance, but in this case was found not to involve a direct effect on bud activity. A current model of white clover growth suggests that there is integration of activity between apical meristems but independence of activity and response to the local micro-environment by axillary buds. In contrast, we found that (i) defoliation reduced phytomer appearance only at the main stolon apical meristem and not at all the meristems in the plant and (ii) that a change in the local light environment of an axillary bud had no discernible effect on bud activity once the bud had emerged from the apical bud but could delay branching if applied before emergence. These results are at variance with the predictions of the model.     

CYTOKININ- AND GIBBERELLIC ACID-INDUCED EFFECTS ON THE DETERMINATION AND MORPHOGENESIS OF LEAF PRIMORDIA IN OPUNTIA POLYACANTHA (CACTACEAE)

Cytokinins and gibberellins are able to strongly influence the development of “leaf” primordia in the cactus Opuntia polyacantha. Under the influence of cytokinin, the primordia produced by cultured axillary bud apical meristems develop as normal, photosynthetic leaves, being composed of regular epidermal cells, guard cells, mesophyll and mucilage cells as well as vascular tissue. Under the influence of gibberellic acid (GA), the primordia develop as cactus spines, composed of thick-walled epidermal and fiber cells. Guard cells, vascular tissue and parenchyma do not occur. Thus GA is able to redirect leaf morphogenesis in O. polyacantha far more completely than has been reported for other plants. The mitotic activity of the primordia that will develop into spines is significantly higher (at the 5 % level) than the mitotic activity of the primordia that will develop into leaves. This is interpreted to indicate that the primordia are either leaf primordia or spine primordia from a very early age, and possibly are never uncommitted or undetermined primordia, as has been suggested for fern leaf primordia.     

Induction of Adventitious Buds on Embryos of Norway Spruce Grown in vitro

Adventitious buds were induced when isolated embryos of Norway spruce (Picea abies L.) were cultured on a defined medium containing 2iP. Anatomically different bud primordia were formed at high and low cytoldnin concentrations. The highest percentage of embryos forming bud primordia was obtained after 4–5 weeks on 2iP medium. Buds developed after transfer of the induced embryos to medium without growth regulators. Many of the buds developed into elongated shoots. No root primordia were observed in any of the induced embryos.     

SEQUENCE AND PATTERN OF LATERAL ROOT FORMATION IN FIVE SELECTED SPECIES

The proximal-distal distribution of the lateral roots of five species was studied. A detailed investigation was carried out on two of the five species, Ceratopteris thalictroides and Cucurbita maxima. A definite pattern of lateral root arrangement, with a degree of variability related to the number of protoxylem poles, was found in all of the species studied. In the fern Ceratopteris, lateral root initiation was found to be related to the segmentation of the apical cell, which in turn determines the distribution of the laterals. In this species the lateral roots occur in a predictable sequence and they are grouped in pairs. In the angiosperms studied, the pattern of lateral root distribution seemed to depend primarily upon a rather strict longitudinal relationship between the lateral root primordia formed opposite any one protoxylem pole. In Cucurbita maxima, 93.7 ± 5.02% of the lateral root primordia observed were in a specific sequence. The laterals of this species are also arranged in groups. In the other plants studied, Arachis hypogaea, Victoria trickeri, and Eichhornia crassipes, the laterals were not as regularly arranged, but nevertheless they were found to be arranged in groups along the main root axis and not randomly dispersed. Factors controlling the spacing of lateral root primordia include their relationship with the developing vascular system, a direct effect of the parent root apex, and an effect of older lateral root primordia in the same sector of the root.