LEAF-OPPOSED BUDS IN MUSA: THEIR DEVELOPMENT AND A COMPARISON WITH ALLIED MONOCOTYLEDONS

A single, lateral, vegetative bud which is positioned 180° from the axil of a leaf is a generic feature of Musa (Musaceae). Such leaf-opposed buds occur in all ten species and five cultivars examined, representing all four sections of the genus and all groups of cultivated bananas and plantains. The bud arises relatively late and is first visible as a vascular-free “clear zone” in the axis directly below the future bud meristem site. It is first associated with the fifth or sixth leaf primordium from the apex. A defined superficial meristem develops on the stem directly above the insertion of the leaf margins one or more plastochrons later. Normal, basically axillary, vegetative buds occur in the closely related genera: Orchidantha (Lowiaceae), Heliconia (Heliconiaceae), Strelitzia, and Ravenala (Strelitziaceae). These buds arise in the axil of the first to the third leaf primordium in a manner similar to most other monocotyledons. Axillary vegetative buds also occur in the remaining families of the Zingiberales: Cannaceae, Costaceae, Marantaceae, and Zingiberaceae.     

Intrapetiolar inflorescence buds in Salacca (Palmae): development and significance

The inflorescence in all species of Salacca is enclosed in a chamber within the leaf base and is exserted through a slit on the abaxial surface of the leaf base. The inflorescence bud is interpreted ds an axillary meristem that becomes radially displaced by adaxial growth of the leaf primordium. A fine channel is produced from the leaf axil to the base of the inflorescence and persists at maturity. The channel and the bud chamber enlarge as the leaf elongates. They are lined by an epidermal layer. There is no cellular breakdown until the collapse and tearing of tissues of the leaf during inflorescence enlargement late in ontogeny. The vegetative bud is positioned about 130⁰ from the axil of its subtending leaf and lies directly below the abaxial inflorescence slit of the leaf above. Vegetative bud development was not observed, hut there is a suggestion of relatively late initiation. The separation of. Eleiodoxa from Salacca is supported by differences in the development of inflorescence and vegetative buds.     

AXILLARY AND DICHOTOMOUS BRANCHING IN THE PALM CHAMAEDOREA

In both Chamaedorea seifrizii Burret and C. cataractarum Martius each adult foliage leaf subtends one axillary bud. The proximal buds in C. seifrizii are always vegetative, producing branches (= new shoots or suckers); and the distal buds on a shoot are always reproductive, producing inflorescences. The prophyll and first few scale leaves of a vegetative branch lack buds. Transitional leaves subtend vegetative buds and adult leaves subtend reproductive buds. Both types of buds are first initiated in the axil of the second or third leaf primordia from the apex, P2 or P3. Later development of both types of bud tends to be more on the adaxial surface of the subtending leaf base than on the shoot axis. Axillary buds of C. cataractarum are similarly initiated in the axil of P2 or P3 and also have an insertion that is more foliar than cauline. However, all buds develop as inflorescences. Vegetative branches arise irregularly by a division of the apex within an enclosing leaf (= P1). A typical inflorescence bud is initiated in the axil of the enclosing leaf when it is in the position of P2 and when each new branch has initiated its own P1. No scale leaves are produced by either branch and the morphological relationship among branches and the enclosing leaf varies. Often the branches are unequal and the enclosing leaf is fasciated. The vegetative branching in C. cataractarum is considered to be developmentally a true dichotomy and is compared with other examples of dichotomous (= terminal) branching in the Angiospermae.     

Comparative morphology and development of inflorescence adnation in rattan palms

The morphology and development of inflorescences in 14 genera and 52 species of rattans and related genera of Lepidocaryoid palms were examined. Inflorescences are free (not adnate) in Ancistrophyllum, Eremospatha and Oncocalamus. Adnation between the inflorescence and internode above occurs in Korthalsia, Myrialepis, Plectocomia and Plectocomiopsis. Adnation between the inflorescence and both the internode and leaf sheath above occurs in Calamus, Calospatha, Ceratolobus and Daemonorops. This leaf-borne, but initially axillary, bud is displaced on to the base of the next younger leaf primordium by the second plastochrone. Later elongation of the internode further separates the inflorescence from its original node. Stages of initiation and early development of adnate buds are illustrated for ten species. Vegetative buds of some Calamus species develop like inflorescence buds. However, other species have unusual bud positions which cannot be interpreted at present. The degree of inflorescence adnation tends to be greater in presumably specialized species than in unspecialized ones.     

A COMPARATIVE DEVELOPMENTAL STUDY OF THE MUTANT SIDESHOOTLESS AND NORMAL TOMATO PLANTS

'Sideshootless,’ a mutant strain of tomato which does not produce axillary buds during vegetative growth, was compared with normally branching plants in order to study the nature of development particularly with regard to axillary buds. Sectioned material revealed no indication of axillary bud initiation in the sideshootless plant at any time during the vegetative phase of growth. In the normal plants, buds were noted to arise in the axil of the fifth youngest leaf. The buds take their origin in tissue which is in direct continuity with the apical meristem. The bud primordia later become set apart from the apex as vacuolation takes place in the surrounding tissue. At the time of floral initiation, the mutant and normal strains behave similarly. Axillary buds appear in the axils of the 2 leaves immediately below the floral apex. One of the buds elongates to overtop the existing plant axis; the other develops as a typical sidebranch. The inflorescence is pushed aside in the process. This pattern is repeated with each inflorescence; thus an axis composed of several superimposed laterals results.     

Determination for inflorescence development is a stable state,separable from determination for flower development in Pisum sativum L. buds

Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.     

DEVELOPMENT AND PHYLLOTAXIS OF THE VEGETATIVE AXILLARY BUD OF MICHELIA FUSCATA

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

MORPHO-HISTOGENIC STUDIES ON TENDRILS OF VITACEAE

The origin and development of the tendrils were studied in 16 species of the Vitaceae: Ampelopsis (7 sp.), Parthenocissus (4 sp.), Vitis (3 sp.), and Tetrastigma (1 sp.). Two types of arrangement of leaf and tendril occur: (a) two successive nodes have leaf-opposed tendrils alternating with each other, followed by a third node, with a leaf unopposed by the tendril; (b) all the nodes have leaf-opposed tendrils. The tendril, like a leaf, is a lateral product of the apical meristem of the shoot. A leaf opposite a tendril is initiated earlier than the tendril. Anticlinal and periclinal divisions in the second and/or third layer of the peripheral meristem of the shoot apex initiate the tendril. The procambium of the tendril first appears towards its abaxial side. Vascularization of the tendril is independent of the axillary bud of the next node below. The positional relationship of the nodal plate vis-à-vis the leaf-opposed tendril shows that the tendril and the leaf belong to the same node. Histological evidence does not show the uplifting of the tendril to the next node above during internodal differentiation. Ontogenetic and morphologic correlation and homology between the inflorescence and the tendril do not substantiate that the tendril in the Vitaceae is an organ sui generis. All available evidence indicates that the tendril is an extra-axillary lateral branch.     

A morphological study of the development of the second inflorescences in strawberry (Fragaria×ananassa Duch.)

To clarify the timing of the differentiation of the first and second inflorescences in strawberry (Fragaria × ananassa Duch.), morphological changes on shoot apices during short day and low night temperature treatments were observed by scanning electron microscopy (SEM) and optical microscopy. Axillary buds just below the first inflorescence (axillary bud 1) became visible when sepal primordia of the primary flower were differentiated. By this time, other axillary buds had already developed. Axillary bud 1 developed four leaf primordia, and then a differentiated inflorescence at its summit. The phase transition of shoot apices from the vegetative to the reproductive phase may therefore trigger the differentiation of axillary bud 1 which is destined to develop into extension crowns.     

Branching Principles Governing the Architecture of Cornus kousa (Cornaceae)

The complex structure of the crown of Cornus kousa, generallyfive-forked in vegetative branching and two-forked in reproductivebranching, is analysed quantitatively and described by two basicbranching principles: decussate phyllotaxy and the resettingrule for planes of branching. Most Cornus species have opposite,decussate phyllotaxis. The leaf pair (with axillary buds) definesthe branching plane of a node. Because of regular phyllotaxis,the fundamental branching pattern is that every branching planealong an axis is perpendicular to the preceding one. However,the first node of a lateral horizontal shoot always has a horizontalbranching plane; we term this the resetting rule. We observedthat resetting occurs when the first nodes initiated in thevertical plane are repositioned by a twisting of their firstinternodes. All later nodes alternate directions, i.e. showusual decussate alternation. Foliage leaf nodes usually producethree-forked branchings. When vegetative winter buds are formed,a foliar node and adjacent scale leaf node produce a five-forkedbranching. When reproductive winter buds with a terminal inflorescenceare formed, the last foliar node and two adjacent scale leafnodes can produce a variety of branchings but usually producean equal two-forked branching. To understand better the architecturein C. kousa, we contrast it with C. capitata which does notproduce buds with scale leaves and whose vegetative nodes areclearly separated. Copyright 1999 Annals of Botany Company Branching pattern, Cornaceae, Cornus kousa, decussate branching, dogwood, Japanese strawberry tree, tree architecture, tree geometry.     

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     

Auxin Depletion from the Leaf Axil Conditions Competence for Axillary Meristem Formation in Arabidopsis and Tomato

The enormous variation in architecture of flowering plants is based to a large extent on their ability to form new axes of growth throughout their life span. Secondary growth is initiated from groups of pluripotent cells, called meristems, which are established in the axils of leaves. Such meristems form lateral organs and develop into a side shoot or a flower, depending on the developmental status of the plant and environmental conditions. The phytohormone auxin is well known to play an important role in inhibiting the outgrowth of axillary buds, a phenomenon known as apical dominance. However, the role of auxin in the process of axillary meristem formation is largely unknown. In this study, we show in the model species Arabidopsis thaliana and tomato (Solanum lycopersicum) that auxin is depleted from leaf axils during vegetative development. Disruption of polar auxin transport compromises auxin depletion from the leaf axil and axillary meristem initiation. Ectopic auxin biosynthesis in leaf axils interferes with axillary meristem formation, whereas repression of auxin signaling in polar auxin transport mutants can largely rescue their branching defects. These results strongly suggest that depletion of auxin from leaf axils is a prerequisite for axillary meristem formation during vegetative development.     

Effect of Severity of Defoliation on the Viability of Reproductive and Vegetative Axillary Buds of Trifolium repens L.

This glasshouse experiment was performed to assess the effectsof a range of constant defoliation regimes applied to cuttingsof a single large-leaved genotype ofTrifolium repens L. on theviability of its axillary buds. Plants were established to comprisea single main stolon (axillary branches were removed) and defoliationtreatments were applied by removing the older (basal) leavesuntil leaf complements of 1·0, 1·5, 2·0,2·5, 3·0 or all leaves (control) remained. Basalleaves were subsequently removed as necessary to maintain thetarget leaf complements. Only severe defoliation (leaf complements of 1·0 and1·5) induced a loss of viability in axillary buds. Lossof viability was greatest in reproductive buds present withinthe apical bud when the treatments were first imposed. Althoughthe most severe treatment (leaf complement 1·0) resultedin death of half the plants, in plants surviving that treatment,death of vegetative axillary buds was restricted to 21% of thevegetative buds at the three youngest node positions withinthe apical bud at the time of treatment application. No othertreatment induced any loss of viability of vegetative buds.There was no loss of viability of axillary buds at nodes formedafter the treatments were imposed. The frequency of initiationof inflorescences at nodes formed after treatments were imposeddecreased as defoliation severity increased. Severe defoliation resulted in marked changes in plant morphologyindicative of a sharp decrease in availability of intraplantresources. It was concluded that under severe defoliation: (1)the potential for vegetative growth (as represented by viablevegetative axillary buds) was maintained at the expense of reproductivegrowth; and (2) that the loss of viability of axillary budswas associated with the sudden changes in physiological processesinduced by defoliation as there was no loss of viability inbuds formed after plants had adjusted their phenotype to oneof smaller size. Trifolium repens L.; white clover; defoliation; axillary buds; viability; inflorescences     

Unusual branch development in the palm, Chrysalidocarpus

Vegetative branch buds of C. lutescens are non-axillary and occur within an abaxial, tubular extension of the leaf sheath, either at the base of a shoot or aerially, a position unusual for palms. Buds are initiated on the abaxial surface of a leaf during its first plastochron (the youngest leaf primordium). The foliar origin of the vegetative bud appears to be unique for angiosperms. In contrast, inflorescence buds are axillary and are initiated as an adaxial ridge on the base of a leaf during its third plastochron (the third primordium from the apex). Aerial branches and basal suckers are developmentally identical and changes in their phyllotaxis are described. As far as can be established by comparative morphology, other species of Chrysalidocarpus have the same type of branch development as in C. lutescens. The development of branches is related to the morphogenetic characteristics of arborescent monocotyledons.     

Non-axillary branching in the palms Eugeissona and Oncosperma (Arecaceae)

FISHER, J. B., GOH, C. J. & RAO, A. N., 1989. Non-axillary branching in the palms Eugeissona and Oncosperma (Arecaceae). The south-east Asian palms, Eugeissona (Calamoideae) and Oncosperma (Arecoideae) are multiple-stemmed. The morphology and development of branching in two species of each genus were examined in Singapore, Borneo, and the Malay Peninsula. Cultivated seedling and adult plants of 0. tigillarium were also observed in Florida. A new shoot arises most often from a longitudinal abaxial groove at the base of an enclosing leaf sheath. In some instances, especially in E. tristis , the enclosing leaf has two equal, adjacent grooves such that any distinction between an original mother shoot and a lateral daughter shoot is impossible. No axillary buds occur in Eugeissona which is hapaxanthic. In Oncosperma , which is pleonanthic, axillary buds are absent from young pre-flowering stems, but an inflorescence bud occurs in the axil of each leaf in older aerial stems. Early ontogenetic stages of vegetative branching, as seen in sectioned apices, indicate that a new vegetative shoot is present on the abaxial base of the first (youngest) leaf primordium. There is no ontogenetic evidence for the displacement of an originally axillary meristem as previously described for the palm Salacca (Calamoideae). Shoot development in Eugeissona is interpreted as a putative dichotomy of the apical meristem in which the meristem centres commonly develop unequally. In Oncosperma the smaller sucker bud meristem may be described as an abaxial leaf base bud, but ontogenetic variations indicate this form of branching is close to dichotomous branching. These new examples of non-axillary branching are compared to similar cases previously reported for palms and other monocotyledons.     

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     

A Quantitative Study of Inflorescence Development in Phaseolus vulgaris

The paper describes the sequence and pattern of inflorescencedifferentiation in six determinate and three indeterminate varietiesof Phaseolus vulgaris. The terminal inflorescence of determinatevarieties is a compound raceme possessing a peduncle bearingtriads—branch inflorescences, each consisting of threeflower buds developed acropetally on a condensed axis. Irrespectiveof the number of leaves on the main stem the bud primordiumin the axil of the uppermost leaf differentiates into the firsttriad on the plant. In indeterminate varieties, the first formedtriad arises at the lowermost node of the first formed lateralinflorescence, the position of which on the main stem is a varietalcharacteristic.     

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

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

Development of Meristems of Weigela florida Variety 'Bristol Ruby' Following Reproductive Induction in Long Days

Weigela florida variety ‘Bristol Ruby’ has longday requirements for its growth and, in general, for its flowering.Vegetative development, floral initiation and floral organogenesisare described using scanning electron microscopy during photoperiodictreatment in long days, under controlled conditions. Flowering of axillary buds of cuttings has been studied. Theapex of Weigela at the vegetative phase is characterized bya very small hollow meristem. After 9 long days, the meristemenlarges and, after 12 long days, early axillary buds are initiatedin the axils of the leaves, which become bracts. When the numberof long days was increased, flowers were initiated in the budson the induced branches; first at the proximal part of the branchwhere development afterwards slowed down, then on the medianparts of the branch where development was accelerated. Two bracteoles are differentiated soon after floral initiation;first initiation of the calyx required 18 long days. Petals,stamens and ovary were rapidly initiated after that. Weigelaflowers are clustered; the inflorescence ceased growth by abortionof the terminal meristem or by formation of a terminal flower.In axillary buds of the fifth node the formation of the clusterwas completed about 20 days after the beginning of floral induction. Weigela florida ‘Bristol Ruby’, scanning electron microscopic analysis, vegetative meristem, floral development stages, long days induction