Development of shoot inHydrangea macrophylla I. Terminal and axillary buds

The structure of shoots, in particular of winter buds, ofHydrangea macrophylla was examined. The non-flower-bearing shoot is usually composed of a lower and an upper part, between which a boundary is discernible by means of a distinctly short internode. This internode is the lowermost of the upper part, and it is usually shorter than the internodes immediately above and below, although the internodes tend to shorten successively from the proximal to the distal part of the shoot. Variations exist in the following characters among the terminal bud, the axillary bud on the lower part of the shoot and the axillary bud on the upper part: (1) length of bud; (2) character of the outermost pair of leaf primordia; (3) degree of development of secondary buds in the winter bud; and (4) the number of leaf primordia. Usually, the terminal bud contains several pairs of foliage leaf primordia with a primordial inflorescence at the terminal of the bud, but the axiallary bud contains only the primordia of foliage leaves in addition to a pair of bud scales.     

Development of Axillary and Leaf-opposed Buds in Rattan Palms

Axillary vegetative buds are present in Calamus, Ceratolobus,and Plectocomiopsis. Two species of Daemonorops Sect. Piptospathaalso have axillary vegetative buds. All species of Daemonoropshave only displaced adnate axillary inflorescence buds. A singlebud is initiated in the axil of the first or second leaf primordiumin a way similar to that for axillary inflorescence buds. Themeristem is displaced during development on to the internodeabove and sometimes on to the base of the leaf above. Leaf-opposedvegetative buds occur in five species of Daemonorops Sect. Cymbospathaand in one species of Daemonorops Sect. Piptospatha. This typeof bud is initiated 180° away from the axil of the firstor second leaf primordium. It is not a displaced axillary bud,but does become adnate to the internode above like the axillarybuds. One or more leaves, transitional between juvenile andadult, on a shoot often subtend both types of buds. Myrialepishas leaf-opposed vegetative buds, but their development wasnot observed. Korthalsia has buds that are displaced about 130°from the leaf axil and are intermediate between the axillaryand the leaf-opposed condition. Other forms of vegetative budsare described: multiple buds in Plectocomia, aerial forkingin Korthalsia, and suckering from inflorescences and from aerialstems in Calamus. bud development, rattan palms, palm taxonomy, branching     

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     

Shoot Axillary Bud Morphogenesis in Kiwifruit (Actinidia deliciosa)

The annual cycle of kiwifruit [Actinidia deliciosa(A. Chev.)C. F. Liang et A. R. Ferguson var.deliciosacv. Hayward] shootaxillary bud (first-order axillary bud, FOAB) morphogenesisis described. FOABs developed quickly with the majority of budscales and leaf primordia present approx. 125 d after budbreak(dab). Mature FOABs had, on average, 23.2 bud scales and leafprimordia. Most second-order axillary structures were also presentapprox. 125 dab. During the growing season, the second-orderstructures developed into second-order axillary buds (SOABs)or remained as simple, dome-shaped meristems (SDSMs). At maturity,nearly all FOABs had four SOABs and, on average, 12.4 SDSMs.Most SDSMs were fused to the subtending leaf primordia, butsome SDSMs developed so that they were ‘free’ fromthe subtending leaf primordia. Third-order axillary meristems(third-order SDSMs) were observed in the axils of most SOABs,and, on average, there were 20.6 per FOAB. Our observationson the development of second-order axillary structures are consistentwith evocation in kiwifruit occurring earlier than the generally-acceptedtime of late summer. Actinidia deliciosa; bud morphogenesis; development; flowering; evocation     

Growth and Histological Changes During Transition to Dormancy in the Regeneration Buds of Hordeum bulbosum L.

Growth and histological changes in a regeneration bud of Hordeumbulbosum during transition to dormancy were studied. Activeformation of new-leaf primordia on the elongating apex accompaniedby arrest of cell division in the lower leaf primordia characterizedthe first period. When activity subsequently in the distal partof the bud decreased, exillary buds and root primordia werestill actively being produced in its basal part.     

Effect of Light Quality (Red:Far-red Ratio) at the Apical Bud of the Main Stolon on Morphogenesis of Trifolium repens L.

A controlled environment experiment investigated whether thered:far-red (R:FR) ratio of light at the apical bud of the mainstolon could alter plant morphogenesis in clonal cuttings ofwhite clover (Trifolium repens L.) The apical bud included theapical meristem, five to six developing leaf primordia withassociated axillary bud primordia and stipules and the firstemerged folded leaf until development was greater than 0·3on the Carlson scale. Three light regimes were imposed on theapical bud by collimating light from R or FR light-emittingdiodes so that the R:FR ratio of light incident at the apicalbud was set at 0·25, 1·6 or 2·1, withoutsignificantly altering photosynthetically active radiation.The effect of these light regimes on white clover seedling growthwas also tested. At a low R:FR ratio seedling hypocotyl and cotyledon lengthswere significantly longer. However, with the cuttings, the lighttreatments did not alter node appearance rate or internode lengthof the main stolon, petiole length, area of leaves or totalshoot dry matter. There was one significant photomorphogeneticresponse in the cuttings, a delay of 0·5 of a phyllochronin the appearance of branches from axillary buds in the lowR:FR ratio treatment relative to the other treatments. Wherebranch appearance was delayed plants had fewer branches. Thisdifference could be ascribed solely to a delay in branch appearanceas there were no significant treatment effects on either theinitiation of axillary bud primordia within the apical bud,the probability of branching or on the rate of growth of branchesafter appearance. Because treatment of the apical bud inducedonly one of the many previously observed responses of whiteclover to a decrease in the R:FR ratio of light, we concludethat other plant organs must also sense the quality of incidentlight.Copyright 1994, 1999 Academic Press White clover, Trifolium repens, apical bud, light quality, red:far-red ratio, light-emitting diode, branching, axillary buds, photomorphogenesis     

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     

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.     

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     

Correlations between Growth and Flowering in Chenopodium amaranticolor: I. Initiation of Leaf and Bud Primordia

Vegetative plants of Chenopodium amaranticolor were inducedto flower by exposure to 2, 6 or continuous short days (SDs)and the effect of such treatments on organogenesis at the apexof the main stem followed by means of dissections. The mostoutstanding responses to SD treatment were (I) an immediateelongation of the apex, (2) a stimulation of the rate of initiationof leaf primordia, and (3) a promotion of the rate of initiationof axillary bud primordia. In response to as few as 2 SDs, therate of initiation of leaf primordia increased from 0.47 toa maximum of 3.70 per day and the rate of initiation of axillarybud primordia immediately increased from 0.47 to 1.35 per day. Precocious initiation of axillary bud primordia led to the formationof double ridges. The results indicate double ridges to be homologouswith vegetative axillary buds; although they normally developedinto reproductive tissues, they passed through a period of vegetativegrowth following minimal induction to flowering by exposureto 2 SDs. The rate and degree of flowering were highest in plants whichreceived the longest period of SDs, but the differences in finalflowering response were greater than the differences betweenthe initial responses at the apices. The effect of SDs was thusnot confined to an initial stimulation of organogenesis; a prolongedexposure to SDs must have enhanced the subsequent developmentof double ridges into flower primordia. The results are discussed in relation to previous findings andthe general conclusion drawn that the initiation of double ridgesis very widely accompanied by a stimulation of apical growth.It is suggested that inductive conditions remove a general growthinhibition and that the resultant stimulation of apical growthmight lead to the initiation of double ridges.     

Bud Content and its Relation to Shoot Size and Structure in Nothofagus pumilio(Poepp. et Endl.) Krasser (Nothofagaceae)

Buds of shoots from the trunk, main branches, secondary branchesand short branches of 10–21 year-old Nothofagus pumiliotrees were dissected and their contents recorded. The numberof differentiated nodes in buds was compared with the numberof nodes of sibling shoots developed at equivalent positionsduring the following growing season. Axillary buds generallyhad four cataphylls, irrespective of bud position in the tree,whereas terminal buds had up to two cataphylls. There were morenodes in terminal buds, and the most distal axillary buds, oftrunk shoots than in more proximal buds of trunk shoots, andin all buds of shoots at all other positions. The highest numberof nodes in the embryonic shoot of a bud varied between 15 and20. All shoots had proximal lateral buds containing an embryonicshoot with seven nodes, four with cataphylls and three withgreen leaf primordia. The largest trunk, and main branch, shootswere made up of a preformed portion and a neoformed portion;all other shoots were entirely preformed. In N. pumilio, theacropetally-increasing size of the sibling shoots derived froma particular parent shoot resulted from differences in: (1)the number of differentiated organs in the buds; (2) the probabilityof differentiation of additional organs during sibling shootextension; (3) sibling shoot length; (4) sibling shoot diameter;and (5) the death of the apex and the most distal leaves ofeach sibling shoot. Copyright 2000 Annals of Botany Company Axis differentiation, branching, bud structure, leaf primordia, neoformation, Nothofagus pumilio, preformation, size gradient     

Axillary Bud Development in White Clover in Relation to Defoliation and Shading Treatments

A period of growth under shade netting in the glasshouse allowedthe cultivation of white clover stolons with an accumulationof undeveloped axillary buds similar to that often found onstolons from grass/clover swards. The subsequent capacity ofthese nodes to develop branches under different circumstanceswas investigated in three experiments. Removal of the laminaeand petioles subtending sets of four buds along a stolon reducedthe rate at which branches were initiated from the buds. Treatmentsin which petioles, or petioles plus laminae, were retained initiatedbranches more quickly. Shading the stolons reduced both therate of initiation and the percentage of buds which developed,unless both petioles and laminae were retained. There was someevidence that conditions applied to individual buds may actin the same way as the same conditions applied to sets of fourbuds and that illuminated nodes may depress the performanceof neighbouring shaded notes. Fewer buds developed at older nodes than at younger nodes duringthe summer, but during the autumn younger buds initially developedmore slowly than older buds. This suggests that buds can developat a younger nodal age in summer than in winter. When leafless stolons were cut up into component internodesbuds developed faster than on intact stolons, provided the budwas located at the end of the internode nearest the main stolongrowing point. If the bud was at the other end, branch developmentwas slower than on intact stolons. The results are discussedin relation to clover growth in sward conditions. White clover, Trifolium repens, axillary bud development, branching, growing points, defoliation, shading     

Initiation of Procambial Strands in Axillary Buds of Dactylis glomerata L., Secale cereale L., and Lolium perenne L.

In axillary buds of Dactylis glomerata L., Secale cereale L.,and Lolium perenne L., the first two procambial strands of theprophyll and the median strand of the first normal leaf areinitiated in the bud in isolation from the vascular system ofthe parent axis. They rapidly form connections with the vascularsystem of the parent axis, presumably by downward extension,as is the case of the strands of leaf primordia on the mainaxis.     

Development of shoot inHydrangea macrophylla II. sequence and timing

The development of axillary buds, terminal buds, and the shoots extended from them was studied inHydrangea macrophylla. The upper and lower parts in a nonflower-bearing shoot are discernible; the preformed part of a shoot develops into the lower part and the neoformed part into the upper part (Zhou and Hare, 1988). These two part are formed by the different degrees of internode elongation at early and late phases during a growth season, respectively. Leaf pairs in the neoformed part of the shoot are initiated successively with a plastochron of 5–20 days after the bud burst in spring. The upper axillary buds are initiated at approximately the same intervals as those of leaf pairs, but 10–30 days later than their subtending leaves. Changes in numbers of leaf pairs and in lengths of successive axillary buds show a pattern similar to the changes in internode lengths of the shoot at the mature stage. The uppermost axillary buds of the flower-bearing shoot often begin extending into new lateral shoots when the flowering phase has ended. The secondary buds in terminal and lower axillary buds are initiated and developed in succession during the late phase of the growth season. Internode elongation seems to be important in determining the degrees of development of the axillary buds. Pattern of shoot elongation is suggested to be relatively primitive. Significances of apical dominance and environmental conditions to shoot development are discussed.     

The Initiation and Growth of Axillary Bud Primordia in Relation to Flowering in Trifolium repens L.

The initiation and growth of axillary bud primordia in relationto the growth of their subtending leaves was observed at theapices of three clones (A. B. and C) of white clover grown invarious combinations of photoperiod and temperature. ClonesA, B, and C flower in response to low temperatures, and clonesA and C, but not B, in response to a transfer from short tolong photoperiods at higher temperatures. The rate of growth of buds and leaves from node to node waslittle influenced by the various treatments imposed, but theinitiation of axillary bud primordia relative to the apicaldome was stimulated in conditions conducive to flowering. The number of budless leaf primordia at the apex ranged froma maximum average of 2.25 at 20° C. to approximately o.8oat 10° C. in all three clones. At the higher temperatures,runners possessed 2.06 budless nodes in short days but only1.12 in long days in clones A and C. In clone B, daylength didnot influence bud initiation at the higher temperature. The results provide evidence of the homology between vegetativeand repro-ductive axillary bud primordia. It is suggested thatflowering is brought about by the removal of an inhibition withinthe apex which leads to the precocious initiation of axillarybud primordia. Following the initiation of axillary bud primordia, the resultsshow their growth to be uninhibited for 6-7 plastochrons. Rapidinflorescence development occurs during this phase. Apical dominancehas no apparent influence on vegetative axillary buds untilthe onset of rapid petiole elongation in their subtending leaves.     

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     

Winter bud content according to position in 3-year-old branching systems of 'Granny Smith' apple

An investigation was made of the number of preformed organs in winter buds of 3-year-old reiterated complexes of the 'Granny Smith' cultivar. Winter bud content was studied with respect to bud position: terminal buds were compared on both long shoots and spurs according to branching order and shoot age, while axillary buds were compared between three zones (distal, median and proximal) along 1-year-old annual shoots in order 1. The percentage of winter buds that differentiated into inflorescences was determined and the flowers in each bud were counted for each bud category. The other organ categories considered were scales and leaf primordia. The results confirmed that a certain number of organs must be initiated before floral differentiation occurred. The minimum limit was estimated at about 15 organs on average, including scales. Total number of lateral organs formed was shown to vary with both bud position and meristem age, increasing from newly formed meristems to 1- and 2-year-old meristems on different shoot types. These differences in bud organogenesis depending on bud position, were consistent with the morphogenetic gradients observed in apple tree architecture. Axillary buds did not contain more than 15 organs on average and this low organogenetic activity of the meristems was related to a low number of flowers per bud. In contrast, the other bud categories contained more than 15 differentiated organs on average and a trade-off was observed between leaf and flower primordia. The ratio between the number of leaf and flower primordia per bud varied with shoot type. When the terminal buds on long shoots and spurs were compared, those on long shoots showed more flowers and a higher ratio of leaf to flower primordia.     

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.     

Tiller Bud Suppression in Reproductive Plants of Lolium multiflorum Lam. Cv. Westerwoldicum

The control of tiller bud growth during reproductive developmentwas investigated in experimental plants ofLolium multiflorumLam. cv. Westerwoldicum that were reduced to a main axis havinga developing but unemerged ear, elongating stem internodes,a series of expanded leaves, slow-growing tiller buds and aroot system. Isolation of the ear by excision of its base, ordecapitation so as to remove the ear together with the upperleaves, promoted the movement of ¹⁴C-assimilates to tiller buds,decapitation being the more effective treatment. Applicationof 0.1 per cent indol–3yl-acetic acid (IAA) to cut tissuesof decapitated plants diverted ¹⁴C-assimilates to upper internodesbut did not reduce import by buds, whereas application of 1.0per cent IAA both diverted labelled assimilates to upper internodesand reduced bud import. Radioactivity from [¹⁴C] IAA appliedto the upper leaves or to the ear base was recovered from budsin very small amounts; larger amounts were recovered from budsfollowing the application of labelled IAA to an elongating internode,especially from the bud at the base of the treated internode.It is suggested that tiller bud suppression may be influencedby the movement of inhibitory levels of auxin into buds fromnearby elongating stem internodes, whose activity in turn maybe controlled by the developing inflorescence and upper leaves.     

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