The Rest Period of Rhododendron Flower Buds: II. STUDIES ON THE REST PERIOD IN TISSUE 3IN SITU

Shortly after the onset of rest in Rhododendron flower buds,the buds were transferred to a tissue-culture medium. The resultsreported here show that the rest period in culture was identicalto the rest period of buds in situ. In both environments theduration of rest and the frequnency distribution of elongationof the buds were the same. Histograms of bud development againsttime were bimodal, with about 20 per cent of the buds elongatingduring the second peak. In culture, the rest period was notaffected by changes in pH, temperature, or the addition of nutrientsalts. The results further show that the duration of the rest periodof each bud was independent of the time of the onset of rest.Buds that were supplied with either indol-3yl-acetic acid orgibberellic acid in culture or in situ remained in rest. Onlya low temperature treatment had a rest-breaking influence.     

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     

THE FATE OF THE DWARF SHOOT APEX IN BRISTLECONE PINE (PINUS LONGAEVA)

The fate of the pine dwarf shoot (DS) apex after needle initiation has been controversial. Dwarf shoot primordia of Pinus longaeva were examined to determine the developmental basis for DS with and without interfoliar buds. Interfoliar buds are microscopic buds derived from the original terminal apex of the DS. In October, all the DS primordia are similar in size and appearance. However, as the needles elongate in the following June the apices of more proximal DS decrease in size, such that by July there is a clear diminishing size gradient of apical domes in going from the most distal to the most proximal positions. The distal DSs start to form bud scales in July and have fully formed interfoliar buds by mid-August. In contrast, those DS apices lacking protective bud scales at needle maturity become suberized and can never proliferate into long shoots. The distal placement of interfoliar buds may be due to a group effect, where each developing DS inhibits the more proximal DSs in the long shoot terminal bud.     

Flowering Habit and Vegetative Behaviour in Tea (Camellia sinensis L) Seed Trees in North-East India

Apical growth of a tea shoot occurs by a succession of flushesseparated by short periods of rest. This paper describes theexternal morphology of flowering, fruiting, and abscission ofleaves of the tea plant in north-east India in relation to thephasic activity of shoot apices. All shoots on a tree make leafy growth when a new cycle of growthbegins in the spring, but terminal buds apparently become dormantas the season advances. Apparently dormant terminal buds shedbud scales, leaving on the stem a considerable number of scars,representing leafless cataphyllary flushes. These cataphyllaryflushes are produced at the same time as the leafy flushes onother shoots. A flower is formed only in the axil of a bud scale. Flowerswhich appear to develop in leaf axils are in fact inserted inthe axils of bud scales of the axillary buds. A distal leafy flush is without flowers. Flowers appear in itsleaf axils only when the terminal bud starts growth for thenext higher flush. A distal floriferous cataphyllary flush appearsas a terminal cluster of flowers. Thus, there is an acropetalsuccession of flowers, flush by flush on a caulome, determinedby the phasic activity of the apical bud. The main crop of flowers exposes anthers from the end of thethird flush (late September to early October) until the endof the winter period of growth (late January to early February).In some plants a second, minor crop of flowers appears in thespring between the end of the first and beginning of the secondflushes. In spite of considerable time lag between anthesis,the fruits produced by these two crops of flowers mature anddehisce at the same time during October to November. Abscission of leaves is also dependent upon the phasic activityof the apical buds. Only the top two flushes of a shoot possessleaves. Resumption of apical growth for a third flush, leafyor cataphyllary, causes the abscission of leaves on the lowermostof the three flushes. Two cataphyllary flushes therefore resultin the loss of all leaves on a shoot.     

Floral determination in the terminal bud of the short-day plant Pharbitis nil

Temporal and spatial aspects of floral determination in seedling terminal buds of the qualitative short-day plant Pharbitis nil were examined using a grafting assay. Floral determination in the terminal buds of 6-day-old P. nil seedlings is rapid; by 9 hr after the end of a 14-hr inductive dark period more than 50% of the induced terminal buds grafted onto uninduced stock plants produced a full complement of flower buds. When grafted at early times after the end of the dark period the terminal buds of induced plants produced three discrete populations of plants: plants with no flowers, plants with two axillary flowers at nodes 3 and 4 and a vegetative terminal shoot apex, and plants with five to seven flowers including a terminal flower. The temporal relationship among these populations of plants produced by apices grafted at different times indicates that under our conditions, the region of the terminal bud that will form the axillary buds at nodes 3 and 4 becomes florally determined prior to floral determination of the region of the terminal bud giving rise to the nodes above node 4.     

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     

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.     

Supercooling Ability, Water Content and Hardiness of Rhododendron Flower Buds during Cold Acclimation and Deacclimation

The relationship between supercooling ability and water contentand killing temperature of flower buds during cold acclimationand deacclimation were studied using R. kiusianum and R. x akebono.The occurrence of multiple floret exotherms and their shiftto a narrow range at lower subzero temperatures, as well asthe marked decrease of florets water content, were observedas the symptoms of cold acclimation occuring in flower budsfrom fall to winter, and vice versa in spring buds during deacclimation.In R. kiusianum, the fully acclimated period was from Novemberto March and two months longer than that of R. x akebono. Thesupercooling ability of the former was about –25°Cand about –20°C in the latter. Although the watermigration within bud tissues during the freezing process wasdetermined in the acclimated and deacclimated buds for R. xakebono, no significant water changes could be observed, evenin the acclimated buds. Thus, it is conceivable that deep supercoolingin florets may result not necessarily from water migration fromflorets and bud axes to scales in response to freezing, butfrom low water content in situ of cold-acclimated or artificiallydehydrated flower buds. (Received July 29, 1981; Accepted October 12, 1981)     

Flower Formation from Citrus unshiu Buds Cultured In Vitro

Flowers were formed in vitro when buds of Satsuma mandarin (Citrusunshiu Mare) from the summer flush of growth harvested duringthe winter rest period before the onset of flower initiation,were grown on a solid Murashige and Skoog medium supplementedwith sucrose and a cytokinin. Flower development was dependentupon illumination, and was enhanced when a piece of stem wasattached to the bud. The percentage of flowering explants wasalways lower than the percentage of naturally flowering budsin spring, but treatments such as ringing which increase floweringin vitro, increased the number of explants flowering int vitroas well. Citrus unshiu Marc, ‘Satsuma’ mandarin, in vitro flowering, ringing     

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.     

Invertase Activity, Soluble Carbohydrates and Inflorescence Development in the Tomato (Lycopersicon esculentum Mill.)

The concentration of reducing sugars in the developing firstinflorescence of the tomato (Lycopersicon esculentum Mill.)increased steadily between the macroscopic appearance of theflower buds and the initial stages of fruit expansion. Overthis period sucrose concentrations remained relatively constant.The rise in reducing sugar concentration was accompanied byan increase in the activity of an acid invertase. In individualflower buds invertase activity rose to a maximum shortly beforeanthesis and declined sharply as the anthers dehisced. Increased planting densities and removal of source leaves reducedthe rate of dry matter accumulation by the first inflorescenceand increased the incidence of flower bud abortion. These changeswere correlated with reductions in reducing sugar concentrations,in reducing sugar/sucrose ratios and in acid invertase levels.Removal of young leaves at the shoot apex significantly increasedthe relative growth rate of the inflorescence and led to a substantialincrease in its invertase content. These treatments had relativelylittle effect on sucrose concentration in the inflorescence. The data are consistent with the operation of an invertase-mediatedunloading mechanism for transported sucrose at sinks in theflower buds. It is suggested that the retarded development ofthe first inflorescence and the high incidence of flower budabortion observed under conditions of reduced photoassimilateavailability are causally related to the decline in invertaseproduction in the flower buds. Possible mechanisms for the regulationof invertase synthesis in the flowers are discussed. Lycopersicon esculentum Mill, tomato, inflorescence development, invertase, sink activity     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17 °C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17 °C to27 °C strongly reduced pod production, mature pod size andseeds per pod, while an increase in day temperature from 22°C to 32 °C had smaller and less consistent effects.Pod production under high night temperature was not constrainedby flower production since 27 °C at night promoted branchingand flower bud appearance. Under 32/27 °C day/night temperaturethe large reduction in pod set was due to enhanced abscissionof flower buds, flowers and young pods (< 3 cm). Flowershad the highest relative abscission followed by young pods andflower buds. Therefore, the onset of anthesis and of pod developmentwere the plant stages most sensitive to night temperature. Podslarger than 3 cm did not abscise but usually aborted and shrivelledunder high night temperature. The effects of 32/27 °C werenot due to transient water stresses and were observed even undercontinuous irrigation and mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L., cv. Tenderette     

The Effect of Fruit Load, Defoliation and Night Temperature on the Morphology of Pepper Flowers and on Fruit Shape

The shape and regularity of bell pepper (Capsicum annuumL.)fruit are known to be determined at a very early stage of flowerdevelopment. Small, flattened fruit which are commonly parthenocarpicdevelop under low-temperatures (below 16 °C) from flowerswith enlarged ovaries. In such flowers self-pollination is notefficient because of the large distance between the stigma andstamens. Flower deformation of this kind is common during thewinter season. In the present study it was found that deformationsof flowers, similar to those found under low temperatures, wereinduced in 15 d by complete removal of fruit from plants growingunder night-time temperatures of 18 °C. Only flowers whichwere at the pre-anthesis stage at the time of fruit removalwere deformed by this treatment. Removal of leaves from thelower part of the plant (source leaves) partially reduced theeffect of fruit removal on the shape of the flowers and on subsequentfruit morphology. Fruit removal induced significant increasesin the concentrations of starch and reducing sugars, but notsucrose, in the flower buds. Likewise, flower buds of plantswhich grew under a night-time temperature of 12 °C containedmore carbohydrate than those which grew at 18 °C. Theseresults suggest that flower morphology in pepper is at leastpartly controlled by source-sink relationships. Assimilateswhich are normally transferred to developing fruit may be transported,upon fruit removal, to the flower buds which subsequently swell.A similar increase in assimilate translocation to flower budsmay occur under low temperatures, subsequently causing deformationof fruit.Copyright 1999 Annals of Botany Company Pepper, (Capsicum annuumL), flower shape, low temperatures, source-sink relationship, fruit shape, seeds, reducing sugars, sucrose, starch.     

The Effect of Flower Maturity and Harvest Timing on Floral Extract fromBoronia megastigma(Nees)

Development of floral organs during maturation of flower budsinto fully open boronia flowers is described. The petals andfunctional anthers attain their maximum size prior to the non-functionalanthers and the stigma. Organoleptic properties of the floralextract change with successive stages of bud development. Theconcentrations of extract and volatiles in the extract (% byf. wt) increase as buds mature, the extract concentration beinghighest in large buds and open flowers and the concentrationof volatile compounds being highest in open flowers. The rateof flower and extract development was measured. Yields of flowermaterial and floral extract per plant, and the concentrationof total volatiles including ß-ionone reach maximumlevels when 70% of flowers have reached anthesis. All measuredfactors decline after this point, except extract concentration(% of f. and d. wt) which is maintained up to 83% open flowers. Boronia megastigma(Nees); brown boronia; Rutaceae; flower development; floral extract; solvent extraction; ß-ionone; essential oils     

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     

NODE COUNTING IN AXILLARY BUDS OF NICOTIANA TABACUM CV. WISCONSIN 38, A DAY-NEUTRAL PLANT

A mature, quiescent, primary axillary bud on the main axis of a flowering Nicotiana tabacum cv. Wisconsin 38 plant, when released from apical dominance and before forming its terminal flower, produced a number of nodes which was dependent upon its position on the main axis. Each bud produced about one more node than the next bud above it. The total number of nodes produced by an axillary bud was about 6 to 8 greater than the number of nodes present above this bud on the main axis. At anthesis of the terminal flower on the main axis, mature, quiescent, primary axillary buds had initiated 7 to 9 leaf primordia while secondary axillary buds, sometimes present in addition to the primary ones, had initiated 4 to 5 leaf primordia. When permitted to grow out independently, primary and secondary axillary buds located at the same node on the main axis produced the same number of nodes before forming their terminal flowers. In contrast, immature primary axillary buds which had produced only 5 leaf primordia and which were released from apical dominance prior to the formation of flowers on the main axis produced only as many nodes as would be produced above them on the main axis by the terminal meristem, i.e., “extra” nodes were not produced. Therefore, it is the physiological status of the plant and not the number of nodes on the bud at the time of release from apical dominance that influenced the node-counting process of a bud. When two axillary buds were permitted to develop on the same main axis, each produced the same number of nodes as single axillary buds developing at these nodes. Thus, the counting process in an axillary bud of tobacco is independent of other buds. Axillary buds on main axes of plants that had been placed horizontally produced the same number of nodes as identically-positioned axillary buds on vertical plants, indicating that gravity does not play a major role in the counting, by an axillary bud, of the nodes on the main axis.     

THE DEVELOPMENTAL ANATOMY OF LONG-BRANCH TERMINAL BUDS OF PINUS BANKSIANA

A study of the composition of long-branch terminal buds (LBTB) of Pinus banksiana Lamb. and the yearly periodicity associated with their formation, development, and elongation was undertaken. Each LBTB has lateral bud zones and zones of cataphylls lacking axillary buds. When present, staminate cone primordia differentiate from the lowest lateral buds in the lowest lateral bud zone of the LBTB. Ovulate cone primordia and lateral long-branch buds can differentiate from the upper lateral buds in any lateral bud zone. When both types of buds are present, lateral long-branch buds are uppermost. Dwarf-branch buds occur in all lateral bud zones. During spring LBTB internodes elongate, new cataphylls are initiated, dwarf branches elongate, needles form and elongate, pollen forms and is released, and ovulate cones are pollinated. During summer buds form in the axils of the newly formed cataphylls. By early fall the new LBTB are in overwintering condition and the four types of lateral buds are discernable. The cytohistological zonation of the LBTB shoot apex is similar to that of more than 20 other conifer species. Cells in shoot apices of pine are usually arranged in distinct zones: apical initials, subapical initials, central meristem, and peripheral meristem. Periclinal divisions occur in the surface cells of the apex; therefore no tunica is present. At any given time, shoot apex volume and shape vary among LBTB in various positions on a tree. In any one LBTB on a tree, shoot apex shape changes from a low dome during spring to a high dome during summer to an intermediate shape through fall and winter.     

Exudation from Aphid Stylets during the Period from Dormancy to Bud break in Tilia americana (L.)

Aphid stylet exudation during the period from dormancy to budbreak was studied in Tilia americana by means of detached branchesbrought from the woods into conditions of warmth and extendedphotoperiod. During physiological dormancy little exudationwas obtained. Thereafter until mid-March exudation was morevariable, but its onset accelerated progressively until mid-March,after which persistent exudation could be obtained from allbranches within 2 days. When the buds were removed from onebranch at this time, exudation persisted for only 5 days comparedwith 14 to 21 days for branches with buds. To account for theseresults it is suggested that a hormonal factor is produced bythe buds which results in sieve-tube activation, that the factoris virtually absent during physiological dormancy, and thereafterrequires a few weeks to become fully active. Determinations of sugar concentration, level of exudation, andbud dry weight indicated that exudation was most intense beforethe bud sinks were active and then rapidly falls off. It issuggested that the stylet acts as a sink competing with thenatural sinks for solutes from a limited region of the stem.Other interpretations are also considered.     

Tissue 11In vitro Bud Formation on Explants from the Inflorescence of Nicotiana tabacum L.

Croes, A. F., Creemers-Molenaar, T., van den Ende, G., Kemp,A. and Barendse, G. W. M. 1985. Tissue age as an endogenousfactor controlling in vitro bud formation on explants from theinflorescence of Nicotiana tabacum L.—J. exp. Bot. 36:1771–1779. The in vitro formation of generative buds was studied on explantsfrom flower and fruit stalks and from internodes of the floralramifications of tobacco. A floral gradient was found to existalong the axis of the branch. The gradient concerns the numberof flower buds formed in vitro and is present in both typesof tissues. The number of flower buds is greater on tissuesfrom the apical than from the basal portion of the branch. Thecapacity to generate these buds is largely determined by tissueage at the moment of the excision. Consequently, the gradientmoves along the axis during the outgrowth of the inflorescence. The alternative possibility that some apex-derived stimuluspredetermines the morphogenetic capacity of the tissue priorto excision is excluded by the observation that the gradientremains virtually unaltered if the apex is removed one weekbefore the onset of culturing. Auxin affects the floral gradient Increasing the auxin concentrationin internode tissue culture causes a steeper gradient of flowerbud generation by almost completely abolishing bud formationon older tissues. Key words: Auxin, flower buds, gradient, tissue culture, tobacco     

Modelling Temperature Effects in Breaking Rest in Red-osier Dogwood (Cornus sericea L.)

Temperature requirements for bud development after a rest period(breaking rest) from maximum rest to end of rest were determinedto develop an empirical model for predicting rest developmentin terminal vegetative buds of red-osier dogwood (Cornus sericeaL.). One-year-old plants at maximum rest were exposed to temperaturesfrom 5 to 20 °C a 12 h photoperiod (SD) in growth chambers.Depth of rest was measured by days to bud break in either 16h photoperiod (LD) or natural daylength at 20/15 °C/nighttemperature. Developmental stages during rest development wereexpressed by degree growth stage (°GS). Chilling was effective breaking rest after plants attained maximumrest (270 °GS). Development during rest (breaking rest)increased with decreasing temperature. No significant developmentoccurred at 20 °C. Rate of rest development (°GS h^–1)at all temperatures varied during the breaking rest period anddepended on developmental stage (°GS). A °GS model describedand quantified rest development (°GS). Using temperatureand developmental stage, the model predicted end of rest (315°GS)within 3 days and daily rest development (°GS) in both years. Cornus sericea L, Cornus stolonifera Michx, dogwood, bud development, dormancy, temperature effects, chilling, degree growth stage