The Rest Period of RhododendronFlower Buds I. EFFECT OF THE BUD SCALES ON THE ONSET AND DURATION OF REST

Shortly after flower differentiation, Rhododendron flower developmentis interrupted by a rest period. The results reported here showthat the onset and duration of rest depended upon the presenceof the flower bud scales. When the scales were removed beforethe onset of rest, the flowers continued to elongate and attainedanthesis. Intact buds stopped growing and remained in rest forat least four months. Scale removal after the onset of restterminated the rest period, though there was a lag phase beforethe flowers began to elongate. The duration of the lag phasewas related to the time of scale removal. The scales preventedflower development in situ, on detached stems and in vitro.Theresults further show that the rest period of each flower budwas independent of the rest period of adjacent flower buds andthat the resting terminal flower buds correlatively inhibitedthe growth of the lateral vegetative apices. The correlativeinhibition was eliminated by removing the terminal flower budor by breaking the rest period of the flower bud.     

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     

Epicormic Bud Development in Quercus robur L. Studies of Endogenous IAA, ABA, IAA Polar Transport and Water Potential in Cambial Tissues10

Seasonal measurements of IAA,³ made using GC-MS, ⁴ indicatedthat in Q. robur the spring initiation of cambial activity andonset of visible bud outgrowth in the canopy is preceded byan increase in cambial region IAA. The effects of notch-girdlescut into the bole indicated that IAA in the cambial region laterwas present in separate physiological pools, with only the polar-transportedfraction affecting epicormic bud outgrowth. The stage in thespring when the epicormic buds grew out coincided with an increaseboth in cambial region IAA and in the capacity of cambial explantsfor IAA polar transport. Thus the stimulus needed by the epicormicbuds to overcome inhibition by polar-transported IAA appearedto be self-generated. The observed effects of exogenous hormoneson epicormic bud outgrowth from stem explants indicated thatthis stimulus might be cytokinin. The seasonal changes detectedin cambial region ABA³ were consistent with a role for stress-inducedABA in the induction of epicormic bud dormancy after canopydevelopment during the summer. No consistent effects of standthinning on cambial region IAA, ABA, water potentials or watercontents were detected, although polar transport of exogenousIAA by cambial region explants removed in the spring was reducedby thinning. Key words: Epicormic buds, cambium, hormones     

The Influence of Ringing on Bud Development and Flowering in Satsuma Mandarin

Ringing of Satsuma mandarin (Citrus unshiu Marc.) trees showedincreased flowering in the following spring when performed duringSeptember and October, but not during November. Most of theeffect on flowering was due to an enhancement of both bud sproutingand the number of flowering shoots formed per node. In addition,a direct effect of ringing on flower initiation was demonstrated,since the number of vegetative shoots was reduced. The response of the buds to ringing was rapid as demonstratedby changes in bud weight, protein content, and electrophoreticpattern and behaviour when cultured in vitro. Buds from ringedtrees readily flowered in vitro when forced during the winterrest period and flower formation was enhanced by the additionof cytokinin. Buds from control trees formed a smaller numberof flowers in vitro, and flowering was much less enhanced bythe addition of cytokinin. It is concluded that ringing acceleratesflower initiation in the buds and this effect takes place beforethe winter rest period. Key words: Bud sprouting, Citrus unshiu Marc., flower initiation, flowering, in vitro flowering, Satsuma mandarin, ringing     

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     

Prognosis of iron chlorosis in pear (Pyrus communis L.) and peach (Prunus persica L. Batsch) trees using bud, flower and leaf mineral concentrations

Background and Aims

The possibility of using tree materials in early phenological stages, such as dormant buds and flowers, for the prognosis of Fe deficiency occurring later in the year has been studied in peach and pear trees.

Methods

Thirty-two peach trees and thirty pear trees with different Fe chlorosis degrees were sampled in different commercial orchards. In peach, samples included flower buds, vegetative buds, bud wood, flowers and leaves at 60 and 120?days after full bloom (DAFB). In pear, samples included buds, bud wood, flowers and leaves at 60 and 120?days DAFB. Leaf chlorophyll was assessed (SPAD) at 60 and 120 DAFB. Sampling was repeated for 3–5?years depending on the materials. Mineral nutrients measured were N, P, K, Ca, Mg, Fe, Mn, Zn and Cu.

Results

The relationships between the nutrient concentrations in the different materials and leaf SPAD were assessed using four different statistical approaches: i) comparison of means depending on the chlorosis level, ii) correlation analysis, iii) principal component analysis, and iv) stepwise multiple regression. In all cases, significant associations between nutrients and SPAD were found. The best-fit multiple regression curves obtained for the multi-year data set provided good prediction in individual years.

Conclusions

Results found indicate that it is possible to carry out the prognosis of Fe chlorosis using early materials such as buds and flowers. The relationships obtained were different from those obtained in previous studies using a single orchard. The different methods of analysis used provided complementary data.     

Genetic and Photoperiodic Control of the Relative Rates of Reproductive and Vegetative Development in Peas

The rates of leaf and flower production were determined in peas(Pisum sativum L.) of genotypes e sn hr (line 13), E Sn hr (line60), and E Sn Hr (line G2), to assess the role of the interactionof alleles Sn and Hr with photoperiod in development. The ratesat which flowers at successive nodes opened (AR) and leavesat successive nodes unfolded (PR) were constant. The AR wasfaster than the PR so that successive flowers opened at nodescloser to the apical bud. The rate at which this occurred wasindependent of photoperiod in line 13 but was slightly or markedlyslower in short days (SD) than long days (LD) in lines 60 andG2, respectively. The opening of flowers closer to the apicalbud of G2 peas in SD was so slow as to not be visually apparentduring the time of this study. The number of nodes between thefirst open flower and the apical bud was unaffected by photoperiodin line 13 but was greater in SD than LD in lines 60 and G2.The daylength effects are photoperiodic, since development ofG2 peas in LD with respect to the parameters measured was unaffectedby light intensity. It is concluded that photoperiod and theE Sn allele combination control the rate of reproductive developmentrelative to vegetative development in peas. The effects of ESn are magnified by the presence of the Hr allele. The constantrates of development measured are not consistent with declineof Sn allele expression with age. Delay of the rate of reproductivedevelopment relative to vegetative development correlated withdelay of apical senescence, suggesting that these processesare related. Pisum sativum, genotypes, photoperiod, flowering, reproductive development, vegetative development, senescence     

Studies of Growth and Flowering in Picea sitchensis (Bong.) Carr. 2. Initiation and Development of Male, Female and Vegetative Buds

Vegetative shoots from the base of the crown, and from partsof the tree likely to form male or female buds, were collectedfrom 40–years–old trees of Picea sitchensis (Bong.)Carr. throughout the 1973–4 annual growth cycle. The morphologyand growth rates of the terminal buds on these shoots were assessed. Bud scale primordia were formed most quickly in the female position,at an intermediate rate in the male position and most slowlyin the basal vegetative position during April, May and June.In July and early August the apical meristems swelled to formdomes and continued to grow at the same relative rates in themale, female and basal vegetative positions. Reproductive budswere first morphologically distinct in late August and sporangiaappeared in October. Dormancy, defined by the pause in apicalvolume increase, extended from mid-October to mid–March.Young strobili grew much faster than basal vegetative shootsof the same age between mid–March and bud burst in lateApril. Throughout the growth cycle, external changes in budsize reflected changes in size of the apical meristem, youngstrobihis or young vegetative shoot inside the bud. It is proposed that the rate of growth of an apical meristemmay be causally related to the type of bud which subsequentlydevelops from it. Sitka spruce, Picea sitchensis, bud development, morphology, growth of apical dome, flowering     

Floral bud reversion in Impatiens balsamina under non-inductive photoperiods

Summary All floral buds of Impatiens balsamina plants exposed to 4 short-day (SD) cycles and then returned to long days reverted to vegetative growth. The same happened with the upper buds of plants receiving a larger number of SDs, even as many as 90 cycles. The reversal proceeded in a basipetal order. The number of floral buds and flowers increased, and their reversion to vegetative growth was delayed with increasing numbers of SD cycles. Depending upon the stage attained by the floral bud before the transfer of the plant to noninductive photoperiods one or more inner whorls of the flower were replaced by a vegetative apex. The tip of the placenta was able to resume vegetative growth even after the formation of fertile anthers and an ovary with abortive ovules, showing that the potentiality for reversion is maintained till quite late stages in floral bud development. Continuous exposure to SD cycles is required not only for the continued production of floral buds, but also for their development to mature flowers, indicating that the floral stimulus in this plant is not self-perpetuating.     

In Vitro Plantlet Formation in Mangosteen (Garcinia mangostana L.)

Optimum conditions were determined for in vivo growth and multiplicationof Garcinia mangostana L. using explants from aseptically germinatedseedlings and field-grown plants. Proliferating shoots wereobtained from cotyledon segments cultured on modified Murashigeand Skoog's (1962) medium with 6-benzylaminopurine. Juvenileleaf segments produced adventitious buds on Woody Plant Medium(Lloyd and McCown, 1981). Root segments gave few buds. Shoottip, nodal, and internodal explants gave multiple axillary andadventitious buds. Shoots were multiplied by enhanced axillaryand adventitious bud formation. The shoots were rooted withindolebutyric acid treatment. Rooted shoots were readily establishedin vermiculite: sand (1:1) mixture. Garcinia mangostana L., Mangosteen, tissue culture, shoot regeneration, bud development     

The Control of Sex Expression in Cucurbits by Ethephon

Application of ethephon to field-grown plants of both bush andtrailing forms of Cucurbita maxima and C. pepo caused leaf epinasty,suppression of male flowers and earlier production and increasein numbers of female flowers. This gave rise to an increasein the ratio of female to male flowers per plant and a decreasein the total number of flowers. Observations of C. pepo showed that even at the two true leafstage there are several nodes present in the unexpanded shoot.Each node has one main and several secondary buds. The sex ofthe main bud at the first five to six nodes is usually determinedat this stage but the secondary buds still have bisexual potential.The change in sex expression was brought about by all male flowerbuds that had formed by the spraying time aborting, and allbuds that developed (both main and secondary) for at least 7days after spraying became female flowers. Thus, nodes fiveand six had male flowers in the controls, whereas in ethephon-sprayedplants the presumptive male flowers aborted at the bud stageat these nodes and secondary primordia developed into functionalfemale flowers. Cucurbita maxima, Cucurbita pepo, sex expression, ethephon, ethylene, flower abortion, flower differentiation     

Quantification of Trends in Wood Production Within Trees of Silver Birch (Betula pendula Roth.)

Trends in rate and duration of wood production are analysedalong and between branches, and along main stems of silver birch(Betula pendula Roth.) trees (at early canopy closure and closedcanopy stages of growth). These data are discussed in relationto the control of knot size, log diameter and taper. To providea field guide to cambial reactivation, progress of vessel productionhas been related to stages of leaf expansion.Copyright 1994,1999 Academic Press Betula pendula (Roth.), silver birch, cambial activity, wood production, wood quality, vessel production     

Further experiments on spermidine-mediated floral-bud formation in thin-layer explants of Wisconsin 38 tobacco

We studied the effects of various polyamines on bud regeneration in thin-layer tissue explants of vegetative and floweringNicotiana tabacum L. cv. Wisconsin 38, in which application of exogenous spermidine (Spd) to vegetative cultures causes the initiation and development of some flower buds (Kaur-Sawhney et al. 1988 Planta173, 282). We now show that this effect is dependent on the time and duration of application, Spd being required from the start of the cultures for about three weeks. Neither putrescine nor spermine is effective in the concentration range tested. Spermidine cannot replace kinetin (N⁶-furfurylaminopurine) in cultures at the time of floral bud formation, but once the buds are initiated in the presence of kinetin, addition of Spd to the medium greatly increases the number of floral buds that develop into normal flowers. Addition of Spd to similar cultures derived from young, non-flowering plants did not cause the appearance of floral buds but rather induced a profusion of vegetative buds. These results indicate a morphogenetic role of Spd in bud differentiation. Dedicated to Professor Hans Mohr on the occasion of his 60th birthday     

Periodicity of Wood Formation in Some Trees of Lowland Rainforest in Nigeria

Freshly prepared chlor-zinc-iodide was used to determine theperiodicity of wood formation at breast height (144 cm fromthe ground) in the trunks of some trees growing in the LowlandRainforest around Ibadan, Nigeria. Wood formation shows seasonal periodicity in the plants studied.The cambial derivates on the xylem side differentiate into woodcells, which at a certain stage of differentiation have abundantcellulose in their secondary walls. The cellulose stains deepblue in chlor-zinc-iodide. This has been used as a criterionfor deciding that wood formation has started. When no cellswith deep blue staining secondary walls are found the cambiumis known to be dormant or quiscent. The resumption of cambial activity is correlated positivelywith bud break and unfolding of new leaves. In Bombax buonopozenseP. Beauv. the relationship may be obscured by local cambialactivity induced by injury. Wood formation stops in the trunks either towards the end ofthe rainy season or at the early part of the dry season. Itstarts either during the dry season or at the beginning of therainy season; but the bulk of the wood is formed during therainy season. Cambial activity stops in most cases before leaffall. At the cessation of wood formation the fully lignifiedxylem elements abut on the xylem mother cells or on xylem cellswith incompletely thickened cell walls. Presence or absence of a starch-free-zone and the noding ofthe vascular rays also give indications of seasonal periodicityin wood formation. Growth rings are periodic and one growthring is generally formed each year.     

Flowering in Pisum: A Fifth Locus, Veg

In addition to the known loci, If, e, sn and hr, a fifth locus,veg, is shown to control flowering in peas. Regardless of thegenotype for the other flowering genes, plants homozygous forthe gene veg did not initiate flower buds under a wide rangeof photoperiod and temperature regimes, including those normallyhighly promotory in peas. Treatment with various plant growthsubstances and grafting to stocks known to promote floweringalso failed to cause initiation. Gene veg prevented expressionof allelic differences at the If locus but segregation for allelesat the sn and hr loci was clearly visible by examination ofseveral vegetative characteristics. For example, sn hr veg andSn hr veg plants showed an opening of the apical bud, productionof lateral branches, and a reduction in growth rate, leafletsize, internode length and stem thickness at approx the sametime as sn hr Veg and Sn hr Veg plants carrying the Lf allelecommenced fruit production, respectively. The graft-transmissibleinhibitor controlled by gene Sn is therefore not specific forthe transition from vegetative to reproductive growth. Geneveg allows the processes leading to apical and foliar senescenceto be examined independently of any effect of flowering andfruiting. We found that gene Sn influenced the total numberof leaves expanded in veg plants but not the time of shoot senescence,which, in plants without flowers and fruits appeared to resultfrom failure of the root system. Pisum sativum L., garden pea, flowering, senescence, genetics     

Regulation of Branching in Decussate Species with Unequal Lateral Buds

In the decussate plants Alternanthera philoxeroides and Hygrophilasp. the opposite axillary bud primordia are of unequal sizefrom the time of their inception; the larger or + buds lie alongone helix and the smaller or – buds along another (helicoidalsystem). In decapitated plants of Alternanthera both buds grewout, but unequally; if the node was vertically split growthof the two shoots was more equal, and if the + buds were excisedgrowth of the – shoots approximately equalled that ofcontrol + shoots. In decapitated shoots of Hygrophila grownin sterile culture only one bud, the + or larger one, grew outat each of the upper nodes. In excised cultured nodes, also,only the + bud grew out; but if the nodes were split longitudinallyboth buds grew out, initially rather unequally. These experimentssupport the view that the regulation of branching in these specieshas two components, apical dominance and the dominance of thelarger (+) bud over the smaller (–) bud at the same node.The restriction of growth potentiality imposed on the –bud is not permanent but can be modified. Further correlativeeffects on bud outgrowth include those of the subtending leavesand of buds at other nodes.     

Preformation of Node Number in Vegetative and Reproductive Proleptic Shoot Modules of Persea (Lauraceae)

The numbers of nodes on single flush terminal and axillary shootmodules were determined in a range of Persea species and cultivars.They were compared with node numbers in apical and axillarybuds to investigate whether preformation or neoformation ofnodes occurred. Mean number of nodes on terminal shoots was14 for vegetative shoot modules and 21 for reproductive shootmodules, and was similar across species, cultivars, rootstocks,locations and climates. In the cultivar 'Hass', numbers of nodeson axillary shoot modules were variable, and lower than thosefor primary shoot modules forming the dominant growth axis ofannual growth modules. There was a mean of 12 nodes for vegetativeproleptic shoot modules, 15 for reproductive proleptic shootmodules and six for sylleptic shoot modules, which were invariablyvegetative. All nodes were preformed within both apical andaxillary proleptic buds. This was not the case in syllepticbuds, which burst contemporaneously with extension of the parentaxis. The majority (63%) of reproductive buds formed indeterminatecompound inflorescences. They carried six basal bud scales,six axillary inflorescences and their subtending bracts, andup to nine true leaves.Copyright 1994, 1999 Academic Press Persea Clus., avocado, Persea americana Mill., bud morphology, shoot growth, preformation, prolepsis     

Morphogenic Potentialities of Flower Buds of Kalanchoe pinnata Pers. grown in vitro

Excised flower buds of Kalanchoe pinnata Pers. representingtwo early stages of development (designated sets I and II),were cultured on modified White's medium (WB). They failed toattain full development on WB or on WB containing any of thefollowing supplements: indole-3yl-acetic acid (IAA), 2,4-dichlorophenoxyaceticacid (2,4-D), naphthaleneacetic acid (NAA), kinetin, or coconutmilk (CM). A slight stimulation of the growth of corolla wascaused by kinetin (10 ppm). IAA (I ppm) and NAA (I ppm) inducedrooting from the cut end of the pedicel and from the proliferatedtorus tissue situated between the sepals and petals. 2,4-D (Ippm) either singly or in concert with CM (10 per cent) stimulatedthe formation of shoot buds and root growth. Addition of kinetin(I and 10 ppm) to WB favoured shoot formation, but suppressedrooting. Flower buds of set II developed shoot buds more readilythan those of set I. Thus, the primordia floral organs presentin the immature buds lose their ability for normal morphogenesisunder culture conditions. Buds destined to form flowers canbe made to revert to vegetative growth.     

Influence of Several Growth Regulators and Amino Acids on in vitro Organogenesis of Torenia fournieri Lind.

The effects of several growth regulators and amino acids onin vitro organogenesis of Torenia fournieri Lind. were determinedusing internodal segments. Treatment with 2,4-D¹ resulted innodular callus formation, while NAA and IAA induced roots constantlybut much less frequently shoot buds. Individually BA, zeatin,and 4-PU induced bud formation, but these shoot buds did notdevelop further. Formation of buds by cytokinin was influencedby a simultaneous application of NAA or 2,4-D, but not of IAA,its degree being reduced when BA was simultaneously appliedwith NAA or 2,4-D. When zeatin or kinetin was added with NAA,numerous roots were induced. The effects of various L-amino acids on in vitro organogenesiswere also investigated using the defined medium in which KNO₃was a principal source of nitrogen. The formation of buds wasconsiderably stimulated by alanine and asparagine, and slightlyby glutamic acid in the medium containing both NAA and BA, inwhich bud formation was easily induced. On the other hand, allamino acids except for glutamic acid and aspartic acid inhibitedroom formation in this medium. Root formation was greatly stimulated by proline, alanine, glutamine,glutamic acid, and aspartic acid, and slightly by arginine andtryptophan in the medium containing NAA but no BA. Glutamicacid and aspartic acid also enhanced bud formation in this medium.     

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