Correlative Inhibition in the Shoot of Agropyron repens ( L.) Beauv

Correlative inhibition was investigated in plants of Agropyronrepens at two temperatures. Reciprocal inhibition ocrurred betweenthe main shoot apex and the outgrowing axillary shoots, withthe balance of inhibition varying with temperature. Apical dominancewas stronger at 10 °C than at 20 °C , but even at 10°C release of apical dominance by decapitation had onlyminor effects on the timing of outgrowth, growth pattern andrate of dry weight aocumulation of the axillary shoots. Dominanceof the main shoot apex by the axillary shoots was stronger at20 °C than at 10 °C. Removal of axillary buds preventeddecline in size and activity of the main shoot apex ard resultedin increased rates of primordium initiation, leaf emergenceand dry weight accumulation in the main shoot. It is suggestedthat a system of reciprocal dominance provides a mechanism formaintaining the characteristic habit of the grass plant andlimits growth in height of vegetative shoots. Agropyron repens (L.) Beauv, couch grass, correlative inhibition, apical dominance, shoot, apex     

Chimerism in grapevines: implications for cultivar identity,ancestry and genetic improvement

In the course of DNA profiling of grapevine cultivars using microsatellite loci we have occasionally observed more than two alleles at a locus in some individuals and have identified periclinal chimerism as the source of such anomalies. This phenomenon in long-lived clonally propagated crops, such as grapevine, which contains historically ancient cultivars, may have a role in clonal differences and affect cultivar identification and pedigree analysis. Here we show that when the two cell layers of a periclinal chimera, Pinot Meunier, are separated by passage through somatic embryogenesis the regenerated plants not only have distinct DNA profiles which are different from those of the parent plant but also have novel phenotypes. Recovery of these phenotypes indicates that additional genetic differences can exist between the two cell layers and that the Pinot Meunier phenotype is due to the interaction of genetically distinct cell layers. It appears that grapevine chimerism can not only modify phenotype but can also impact on grapevine improvement as both genetic transformation and conventional breeding strategies separate mutations in the L1 and L2 cell layers. Received: 14 March 2001 / Accepted: 22 May 2001     

EARLY HISTOGENESIS AND SEMIQUANTITATIVE HISTOCHEMISTRY OF LEAF INITIATION IN TRITICUM AESTIVUM

The shoot apex of Triticum aestivum cv. Ramona 50 was investigated histologically to describe cell lineages and events during leaf initiation. During histogenesis three periclinal divisions occurred in the first apical layer, with one or two divisions in the second apical layer. This sequence of cell divisions initially occurred in one region and spread laterally in both directions to encircle the meristem. Cells of the third apical layer were not involved in leaf histogenesis. Initially, young leaf primordia were produced from daughter cells of periclinal divisions in the two outer apical layers. Nuclear contents of protein, histone, and RNA in the shoot apex were evaluated as ratios to DNA by means of semiquantitative histochemistry. Daughter cells of periclinal divisions in the outer apical layer which produced the leaf primordia had higher histone/DNA ratios than cells of the remaining meristem. However, protein/DNA and RNA/DNA ratios were similar in both regions. Leaf initial cells had a higher ³H-thymidine labeling index, a higher RNA synthesis rate, and smaller nuclear volumes than cells of the residual apical meristem.     

Bud Structure in Relation to Shoot Morphology and Position on the Vegetative Annual Shoots of Juglans regia L. (Juglandaceae)

The length and basal diameter of all lateral and terminal budsof vegetative annual shoots of 7-year-oldJuglans regia treeswere measured. All buds were dissected and numbers of cataphylls,embryonic leaves and leaf primordia were recorded. Each axillarybud was ranked according to the position of its associated leaffrom the apex to the base of its parent shoot. Bud size andcontent were analysed in relation to bud position and were comparedwith the size and number of leaves of shoots in equivalent positionswhich extended during the following growing season. Length andbasal diameter of axillary buds varied according to their positionon the parent shoot. Terminal buds contained more embryonicleaves than any axillary bud. The number of leaves was smallerfor apical and basal axillary buds than for buds in intermediatepositions on the parent shoot only. All new extended shootswere entirely preformed in the buds that gave rise to them.Lateral shoots were formed in the median part of the parentshoot. These lateral shoots derived from buds which were largerthan both apical and basal ones. Copyright 2001 Annals of BotanyCompany Juglans regia L., Persian walnut tree, branching pattern, preformation, bud content, shoot morphology     

Chromosome Replacement and Deletion Lead to Clonal Polymorphism of Berry Color in Grapevine

Clonal polymorphism mainly results from somatic mutations that occur naturally during plant growth. In grapevine, arrays of clones have been selected within varieties as a valuable source of diversity, among them clones showing berry color polymorphism. To identify mutations responsible for this color polymorphism, we studied a collection of 33 clones of Pinot noir, Pinot gris, and Pinot blanc. Haplotypes of the L2 cell layer of nine clones were resolved by genotyping self-progenies with molecular markers along a 10.07 Mb region of chromosome 2, including the color locus. We demonstrated that at least six haplotypes could account for the loss of anthocyanin biosynthesis. Four of them resulted from the replacement of sections of the ‘colored’ haplotype, sized from 31 kb to 4.4 Mb, by the homologous sections of the ‘white’ haplotype mutated at the color locus. This transfer of information between the two homologous sequences resulted in the partial homozygosity of chromosome 2, associated in one case with a large deletion of 108 kb-long. Moreover, we showed that, in most cases, somatic mutations do not affect the whole plant; instead, they affect only one cell layer, leading to periclinal chimeras associating two genotypes. Analysis of bud sports of Pinot gris support the hypothesis that cell layer rearrangements in the chimera lead to the homogenization of the genotype in the whole plant. Our findings shed new light on the way molecular and cellular mechanisms shape the grapevine genotypes during vegetative propagation, and enable us to propose a scheme of evolutionary mechanism of the Pinot clones.     

Clonal Fidelity and Variation in Plantain (Musa AAB) Regenerated from Vegetative Stem and Floral Axis Tips in vitro

Recognition of a phenotypically distinct 'French-type' plantain(Musa AAB) designated 'Superplatano' (Superplantain) promptedevaluation of in vitro micropropagation as a means of generatingsufficient numbers of plants for field evaluation in three locationsin Puerto Rico. A multi-faceted study designed to evaluate relationshipsbetween different aseptic culture procedures and morphologicalorigins of primary explants was carried out. Vegetative budsfrom various positions relative to the mother corm (definedby cardinal points on the compass) and explants from the floralaxis of 'Maricongo' (the 'False-Horn', or florally determinatetype 'progenitor' of 'Superplatano'), and 'Superplatano' (a'French-type') were used as starting materials. Responses underfield conditions were studied using a number of parameters includingyield of commercially marketable fruits. We compared four populationsof shoots, each of which derived from at least three differentshoots from within one mat, shoots derived from vegetative andfloral material from the same mat for both 'Maricongo' and 'Superplatano',and shoots derived from a number of floral buds of the sameclone ('Maricongo') all of which were in culture for the samelength of time. 'Superplatano' was stable whether from vegetativecorm or floral bud apex. This shows conclusively that if thestarting point in the micropropagation process is a stable Musaclone, our tissue culture procedure is reliable. Considerablevariation in bunch phenotype was observed, however, in plantsregenerated from ten of 12 shoot and floral meristems startedfrom the 'False-Horn'-type 'Maricongo'. Change from 'False-Horn'-type(determinate) to 'French'-phenotype (indeterminate) was evidentin each of the three locations. Frequency of bunch reversionvaried from 0·4 to 100%, but was confined to individualoriginating stem tips rather than clones. The most dramaticbunch phenotypic change occurred in plants regenerated fromclone 3. All plants regenerated from shoot 3-North bore 100%'French-type' bunches. However, reversion in plants regeneratedfrom shoot 3-West was only 1·8%, and no bunch phenotypicchange was observed in plants from shoot 3-East. Plants regeneratedfrom both shoot and male floral axis tips in 'Maricongo' clone4 also bore 'French-type' bunches. Frequency of bunch reversionfrom shoot 4-East was 0·4% as compared to 2·6%from 4-floral. Bunch reversion occurred at the frequency of2·0% when plants were regenerated from clone 6-floral.No bunch reversion was observed in plants regenerated from asingle shoot tip in clones 1-West and 5-floral. No dwarfismwas encountered in any of the tissue culture-derived plants.We conclude that tissue culture per se plays a very small role,if any, in the direct induction of off-types. Pre-existing characteristicsof the primary explant determines whether products of a multiplicationshow fidelity or not. Our data suggest that 'Maricongo' is achimera and that 'Superplatano' is revertant off-type that resultswhen breakdown of the chimera occurs. Large numbers of stable'Superplatano' were produced from unstable 'Maricongo' and thisaffirms the value of micropropagation for generation of cloneswith desirable bunch phenotype.Copyright 1993, 1999 AcademicPress Musa, plantains, bananas, tissue culture, clonal multiplication, somaclonal variation, phenotype     

EVIDENCE FOR APICAL INITIAL CELLS IN THE VEGETATIVE SHOOT APEX OF HEDERA HELIX CV. GOLDHEART

We examined changes in the pattern of leaf variegation in a periclinal chloroplast chimera of Hedera helix L. cv. Goldheart to determine whether stable apical initials exist in the shoot apex. Additional data were obtained by histological analyses. All of the data indicate that four apical initials are present in the third layer of the apex, supporting the model of a structured apical meristem.     

Leaf Ontogeny in Digitaria eriantha

The shoot apex consists of two layers, the dermatogen and thehypodermis. The leaf primordia arise through periclinal divisionswithin these two layers on the side of the apex. Further divisionsof the dermatogen push the little protuberance upward and togetherwith divisions the hypodermis add internal tissues of the youngleaf. When the median and lateral bundles of the primordia arisein Digitaria eriantha they are isolated from the vascular supplyof the rest of the plant. The median strand, the first to form,and the first order laterals form at the disc of insertion ofthe primordium. The other laterals form higher up in the primordium.These strands extend both acropetally and basipetally to linkwith the vascular supply of the rest of the plant. Digitaria eriantha, apical meristem, leaf primordium, vascular bundle, orange G, tannic acid, iron alum     

ORIGIN OF ADVENTITIOUS SHOOTS REGENERATED FROM CULTURED TOBACCO LEAF TISSUE

Leaf discs from Nicotiana tabacum L., N. glauca Grahm., and a series of interspecific periclinal chimeras were cultured on Murashige and Skoog (MS) medium containing either 2.5 mg/1 6-benzylaminopurine(BA) or 3.0 mg/16-furfurylaminopurine (kinetin). Most shoots regenerated from chimeral leaf discs were non-chimeral but 51 of 658 shoots were chimeral. The histogenic composition of plants regenerated from leaf discs of periclinal chimeras indicated that any cell layer in a leaf can be the ultimate source of shoots, and that shoots can be multicellular in origin. Certain periclinal arrangements were recovered more frequently and their chimeral nature was more stable during subsequent shoot growth. While N. tabacum leaf discs regenerated shoots on MS medium supplemented with either BA or with kinetin, N. glauca leaf discs did not form shoots on the medium containing kinetin. However, chimeras which possessed cells of both species arose on medium containing BA or kinetin, indicating that the morphogenetically competent (i.e., able to produce shoots in culture), N. tabacum cells either interacted with N. glauca cells leading to their competence or incorporated non-competent N. glauca cells into nascent shoot apical meristems.     

Experimentally Synthesized Plant Chimeras 2. A Comparison of In vitro and In vivo Techniques for the Production of Interspecific Nicotiana Chimeras

In vitro and in vivo techniques were compared for synthesizingchimeras between Nicotiana glauca Grahm and N tabacum L Interspecificchimeral callus, produced from mixed callus cultures in vitro,was placed on media which favoured only N tabacum shoot formationNone of the 474 regenerated N tabacum shoots incorporated Nglauca cells into their meristems When chimeral callus was regeneratedunder hormonal conditions favouring simultaneous organogenesis,of 397 shoots, only non-chimeral shoots of both species aroseIn vivo, reciprocal splice grafts between species were decapitatedjust above the graft union and treated with or without auxin—lanolinpastes Auxin increased callus formation but inhibited adventitiousshoot formation Three of 209 adventitious shoots arising fromthe graft union were interspecific mericlinal chimeras whichwere later stabilized as periclinal chimeras All three chimerasformed when N glauca was the understock Two of the chimerasarose on untreated shoots which produced no visible callus,indicating that excessive callus formation may be unnecessaryfor multiple cell origin of adventitious shoots to occur Chimeras, tobacco, Nicotiana glauca, Nicotiana tabacum, tissue culture, graft chimeras, callus cultures     

Interspecific somatic hybrids between dihaploid Solanum tuberosum L. and the wild species, S. pinnatisectum Dun

Leaf-derived protoplasts of S. tuberosum and S. pinnatisectumwere electrofused. A culture medium-based procedure was usedto select heterok-aryon-derived tissues from which somatic hybridplants were regenerated. Somatic hybridity was confirmed bymorphological, isozyme and restriction fragment length polymorphism(RFLP) analyses. After 22 weeks, four somatic hybrid plantswere produced. These plants had phenotypically abnormal stolon-derivedshoots in which flow cytometry revealed a large degree of mixoploidy.Haploid nuclei were also present in these shoots. One shootexhibited a noticeably higher DNA content in comparison withother adventitious shoots. Key words: Potato, Solatium tuberosum, S. pinnatisectum, somatic hybridization, flow cytometry     

Growth of Carnation Meristems in vitro: Anatomical Structure of Abnormal Plantlets and the Effect of Agar Concentration in the Medium on their Formation

Carnation meristems cultured in vitro grow into shoots of threetypes: normal, translucent and succulent. The apical meristemof succulent shoots was of the mantle-core type and it lackedpro-vascular tissue. The leaf had large vacuolated mesophyllcells, fewer stomata (often plugged), and no plate meristem.A higher agar concentration in the medium increased the percentageof normal shoots developing. This supports other indicationsthat the water potential of the medium affects morphogenesis. carnation, Dianthus caryophyllus L, meristem culture, abnormal plantlets, shoot meristem     

The Relationship Between the Distribution of Periclinal Cell Divisions in the Shoot Apex and Leaf Initiation

Periclinal cell divisions in vegetative shoot apices of Pisumand Silene were recorded from serial thin sections by mappingall the periclinal cell walls formed less than one cell cyclepreviously. The distribution of periclinal divisions in theapical domes corresponded to the distributions subsequentlyoccurring in the apices when the young leaf primordia were forming.In Pisum, periclinal divisions were almost entirely absent fromthe I₁ region of the apical dome for half a plastochron justafter the formation of a leaf primordium and appeared, simultaneouslyover the whole of the next potential leaf site, about half aplastochron before the primordium formed. In Silene periclinaldivisions seemed to always present in the apical dome at thepotential leaf sites and also round the sides of the dome wherethe ensheathing leaf bases were to form. Periclinal divisionstherefore anticipated the formation of leaf primordia by occuring,in Pisum about one cell cycle and in Silene two or more cellcycles, before the change in the direction of growth or deformationof the surface associated with primordial initiation. Pisum, Silene, planes of cell division, orientation of cell walls, leaf primordia, shoot apical meristem, plastochron     

Chlorophyll fluorescence as a tool for evaluation of viability in freeze-stressed grapevine buds

This study examined the utility of the ratio of variable fluorescence to maximum fluorescence (F_v/F_m) to detect freezing injury on buds of two Vitis vinifera cultivars: Pinot noir and Pinot gris. Freezing treatments on buds caused a decrease both in F_v/F_m and percentage of budburst, more severely on Pinot gris than Pinot noir, specifically at the lower temperature (−20°C). F_v/F_m ratio showed a close correlation with percentage of budburst, and a threshold of the lethal F_v/F_m was proposed as an indicator of bud mortality.     

The development of the grape berry cuticle in relation to susceptibility to bunch rot disease

Some physical and morphological factors of grape berry cuticlewere investigated at different developmental stages of threeclones ofVitis vinifera cv. Pinot noir. The surface morphologyof grape berries was examined by scanning electron microscopyand cuticle anatomy was examined by light and transmission electronmicroscopy. During the period from flowering to maturity, thecomposition of the cuticular waxes changed, corresponding withan increase of waxy deposits and significant modifications ofthe wax surface morphology. The content in cutin per unit surfacedecreased more than 2.5-fold between berry set (16 d after anthesis)and veraison of the grape berries, and might predispose thegrape berry to fungal infection. This result was correlatedwith the differentiation of the cuticle layers and particularlywith a decrease in the thickness of the primary cuticle at harvest. Key words: Botrytis cinerea, cuticle, cutin, epicuticular waxes, Vitis vinifera L     

The Influence of Cotyledons in Axillary and Adventitious Shoot Production from Cotyledonary Nodes of Cucumis sativus L. (Cucumber)

Cucumber explants including at least part of the cotyledon,a short section of hypocotyl, and the apical bud, are capableof producing multiple axillary buds from the seedling apex andadventitious shoots from the hypocotyl base in a medium whichcontains 2·0 mg dm^–3 of kinetin. Removal of theapical bud triples the number of shoots produced from the apexof explants with two intact cotyledons but does not affect shootproduction from explants with some or all of their cotyledonsremoved. The area of intact cotyledon also influences morphogenesis,as explants with both cotyledons removed, failed to produceadventitious shoots from the hypocotyl base. Culture in continuousdarkness entirely prevents shoot development from the explantbase, but has little influence on shoot production from theapex. The influence of endogenous growth regulators and apicaldominance on the morphogenesis of shoots in cucumber seedlingsare discussed. Key words: Cucumber, cotyledons, apical dominance, morphogenesis, adventitious shoots, Cucumis sativus     

STABILITY OF LEAF VARIEGATION IN SAINTPAULIA IONANTHA DURING IN VITRO PROPAGATION AND DURING CHIMERAL SEPARATION OF A PINWHEEL FLOWERING FORM

Plants of the foliarly variegated cultivar Saintpaulia ionantha Tommie Lou and the florally variegated cultivar Candy Lou were regenerated through tissue culture from leaf sections, petal sections, and subepidermal tissue. This provided explants with derivatives of all histogen layers of the shoot apex, layers I and II only, and layers II and III only. Over 1,000 plants of Tommie Lou and Candy Lou were grown to flowering. A low level of phenotypic variation was observed, but in no case could this be attributed to the separation of genotypically distinct cell lines. The foliar variegation pattern of both cultivars was stable through in vitro propagation. In contrast, the chimeral components of the flower color pattern in Candy Lou separated during regeneration. These data demonstrate that Tommie Lou-type foliar variegation is not caused by periclinal chimerism and that all leaf cell layers possess the genetic information necessary to produce variegated foliage. The production of all green and all white plants from a radiation-induced periclinal chimera demonstrated that the system used could detect chimeral separation. These results support the contention that adventitious shoots in Saintpaulia almost always differentiate in vitro from a derivative(s) of a single histogen layer, and this layer is usually the LI.     

INFLORESCENCE AND FLOWER DEVELOPMENT IN THE PIPERACEAE. I. PEPEROMIA

Flowers of Peperomia species are the simplest structurally of any of the members of the Piperaceae. The spicate inflorescences form terminally and in axillary position; in each, the apex first is zonate in configuration with a two-layered tunica while 3-4 leaves are initiated. Later, when the inflorescence apical meristem begins bract initiation, the biseriate tunica persists, but zonal distinctions diminish and the apex can be described in terms of a simple tunicacorpus configuration. The inflorescence apex aborts after producing 30-40 bracts in acropetal succession an abscission layer forms across the base of the apex, and the meristem dries and drops off. Bracts are produced by periclinal divisions in T₂ (and occasionally also in the third layer as well); the later-formed floral apices arise by periclinal divisions in T₂ and the third layer. Each floral apex is at first a long transverse ridge in the axil, perpendicular to the long axis of the inflorescence. This establishes bilateral symmetry in the flower, which persists throughout subsequent growth. The floral meristem becomes saddle-shaped, and two stamen primordia are delimited, one at either end and lower than the central floral apex. A solitary carpel is initiated abaxially, and soon forms a circular rim which heightens as a tube with an apical pore. Within the open carpel, a solitary ovule is initiated from the entire remains of the floral apical meristem; it, hence, is terminal in the flower, and its placentation is basal. Carpellary closure in P. metallica results from accelerated growth of the abaxial lip, and the two margins become appressed. Species differ greatly as to whether the abaxial or the adaxial lobe predominates in late stages of carpel development. In P. metallica, the receptive portion of the stigma forms from the shorter lobe which is overtopped. Stigmatoid tissue forms internal to the receptive stigma. The prevailing bilateral floral symmetry, absence of a perianth, and the spicate inflorescence are features which distinguish Peperomia (and Piperaceae) from the magnolialian line of angiosperms.     

INFLORESCENCE AND FLOWER DEVELOPMENT IN THE PIPERACEAE. II. INFLORESCENCE DEVELOPMENT OF PIPER

The inflorescence development of three species of Piper (P. aduncum, P. amalago, and P. marginatum), representing Sections Artanthe and Ottonia, was studied. The spicate inflorescences contain hundreds or even thousands of flowers, depending on the species. Each flower has a tricarpellate syncarpous gynoecium and 4 to 6 free stamens, in the species studied. No sepals or petals are present. In P. marginatum the apical meristem of the inflorescence is zonate in configuration and is unusually elongate: up to 1,170 μm high and up to 480 μm wide during the most active period of organogenesis. Toward the time of apical cessation both height and diameter gradually diminish, leaving an apical residuum which may become an attenuate spine or may be cut off by an abscission zone just below the meristem. The active apex produces bract primordia; when each is 40–55 μm high, a floral apex is initiated in its axil. Both bract and floral apex are initiated by periclinal divisions in cells of the subsurface layer. The bracts undergo differentiation rather early, while the floral apices are still developing. The last-produced bracts near the tip of the inflorescence tend to be sterile.