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     

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     

Floral induction by gibberellic acid in Impatiens balsamina,a qualitative short-day plant

Summary In the qualitative short-day plant Impatiens balsamina, gibberellic acid (GA₃) not only promoted the formation of floral buds in response to suboptimal photoinductive conditions and reduced the number of SD cycles that are required for their development into flowers, but also caused initiation of floral buds under non-inductive photoperiods. In plants treated with repeated applications of GA₃, the floral buds developed into flowers irrespective of whether the apex was left intact or was removed. In those that received a single application of GA₃ the floral buds developed into flowers only in decapitated plants.     

Photoperiodic Regulation of Flowering in Cowpeas (Vigna unguiculata (L.) Walp.)

To test the proposition that photoperiodic controls synchronizethe flowering of cowpeas, Vigna unguiculata (L.) Walp. [V. sinensis(L.) Savi], the day-length requirements for floral initiationand for flowering were investigated in several short-day accessions.No evidence was found of different critical photoperiods atdifferent stages of development, but exposure to only 2–4short days was required for floral initiation compared withabout 20 for development to open flowers. Pod setting was increasedafter exposure to even one short day more than the number requiredfor flower opening. Floral buds at higher nodes appeared to require fewer shortdays for development to flowering than buds at the lower nodes,and displayed faster rates of development. Inflorescence budsdid not resume development if they were exposed to 15 or morelong days following inflorescence initiation. Thus, any tendencytowards synchronous flowering in cowpeas is not due to the criticalday-length for flower development being shorter than that forflower initiation, but could be the result of cumulative photoperiodicinduction of plants and the more rapid development of later-formedflowers. Vigna unguiculata (L.) Walp., cowpeas, flower initiation, flower development, fruit set, photoperiodism     

Effect of Gibberellic Acid and Phosfon on the Critical Dark Period Reqnirement for Flowering of Impatiens balsamina cv. Rose

The critical dark period requirement for flowering of Impatiens balsamina L. cv. Rose, an obligate short day plant, is about 8.5 hours. While GA₃ completely substituted for the dark period requirement, Phosfon prolonged it to 9.5 hours. GA₃ hastened and Phosfon delayed the initiation of floral buds under all photoperiods. Floral buds opened into flowers only during 8 and 14 hour photoperiods in control and Phosfon-treated plants but during all photoperiods in GA₃-treated ones. The delay in floral bud initiation and flowering was correlated with shifting up of the node bearing the first floral bud and flower respectively. While GA₃ increased the numher of floral buds and flowers in all photoperiods except 8-hour, Phosfon increased their number in the 14-hour photoperiod only. The number of flowering plants decreased with increasing photoperiod regardless of GA₃ and Phosfon application. The effect of Phosfon was completely or partially overcome, depending upon the photoperiod, by simultaneous application of GA₃.     

Effect of Intercalated Long Days and Light Interruption of Dark Period on Flowering, Extension Growth and Senescence of impatiens balsamina

Plants of Impatiens balsamina L. grown under long days were divided into 5 lots to receive 1, 2, 4, 8 and 16 consecutive short day (SD) cycles respectively. Each lot was divided into 5 groups to receive 1, 2, 4, 8 and 16 long day (LD) cycles subsequent to SD regime and the cycles were repeated till the end. Observations on the number, position and time of emergence of floral buds, flowers and extension growth were recorded. The floral buds are initiated and these develop into flowers even when Individual SDs are intercalated with 16 LD cycles, showing that the sub-threshold stimulus is not wiped off but becomes effectively summated through a long non-inductive period. The floral bud initiation in lots receiving less than 4 and flowering in those receiving less than 8 consecutive SD cycles are delayed with decreasing number of consecutive SDs and increasing number of intercalating LDs. This progressive delay is probably due to the delay that is caused by these treatments in the completion of requisite number of SD cycles. The first node to show floral bud initiation is shifted up with increasing intercalated LDs only in plants receiving less than 4 SD cycles and not in those receiving more. Some of the lower floral buds in plants receiving less than 8 consecutive SD cycles either abort or revert to vegetative growth. The first node to flower is, therefore, shifted up. The number of such buds increases either with a decrease in the number of consecutive SDs or an increase in the number of intercalated LDs. The number of floral buds produced in plants receiving 2 or more and flowers in those receiving 4 or more consecutive SD cycles does not differ much with the number of intercalated LDs, but decreases in those receiving less number of SDs. Some nodes bear more than one floral bud and flower. Such nodes are observed in plants receiving individual SD cycles only when intercalated with individual LDs but in all groups in plants receiving 16 consecutive SD cycles. The rate of extension growth increases with an increase in the number of consecutive SDs. The rate in plants receiving individual SDs closely resembles that of plants grown under continuous LDs and that of consecutive 16 SDs with that of control SD plants. The attainment of maximum and the consequent steep fall preceding senescence is successively delayed with an increase in the number of intercalated LDs in plants receiving 16 consecutive SD cycles. Light interruption of the dark period inhibits both the initiation of floral buds and their development Into flowers. showing that in this plant. short days are necessary both for the initiation of floral buds and their development into flowers.     

Biosynthesis of Volatiles in Brown Boronia Flowers after Harvest: Effect of Harvest Time and Incubation Conditions

Brown boronia flowers (Boronia megastigma)were incubated at25 °C after harvest, increasing the concentration of a solventextracted product by up to 25% (d. wt basis) and floral volatilesby up to 300% (d. wt). Open flowers produced more volatilesduring post-harvest incubation than flower buds, whole flowersproduced more than flowers treated to simulate harvester damage,and fresh flowers produced more than frozen and thawed flowers.Flowers incubated in bags purged with air produced more extractand volatiles than those purged with nitrogen gas; ß-iononewas particularly depleted in nitrogen-purged flowers. Flowersand buds from three successive harvests (68, 82 and 90% openflowers) were incubated at several temperatures for up to 24h. The greatest increase in the concentration of floral extractoccurred in flowers harvested when 90% were open and incubatedfor 4 h at 12 °C, or 14 h at 23 °C. The largest increasein total volatiles occurred in material harvested at 82% openflowers and incubated for 25 h at 12 °C, or 13 h at 23 °C.The concentration of extract and volatiles declined after prolongedpost-harvest incubations. Brown boronia flowers produce volatilesand other components of the floral extract after harvest whenflowers with mature, intact enzyme systems are well suppliedwith oxygen, at temperatures at or below 25 °C. As flowersbecome visibly senescent, their ability to produce volatilesafter harvest declines.Copyright 1998 Annals of Botany Company Boronia megastigma(Nees); brown boronia; essential oils; floral volatiles; ß-ionone; phenology; post-harvest storage.     

Flower formation in vitro in a quantitative short-day tobacco: interrelation between photoperiod and infructescence development

The flowering response of thin layers excised from branch internodes of Nicotiana tabacum cv. Maryland Catterton (quantitative short-day plant for induction) was studied under three photoperiodic treatments. The explants were excised from inflorescences bearing flowers only, flowers and green fruits, or from infructescences with green fruits only. The aim of the study was to investigate the post-inductive photoperiodic effects on in vitro flower bud formation in a quantitative short-day tobacco and the relation with infructescence development. Short days quantitatively enhanced the flower bud regeneration capacities of explants in all stages of development, both as number of explants induced to produce flowers and as mean number of flowers per explant. There was no significant difference in flower bud formation on explants of the first two stages, which produced much more flowers than those of the third stage. Observations in planta showed that, during the 20 days separating the second stage from the first stage, there was no significant difference in the number of floral buds and flowers present on the inflorescence; however, the branch internodes lengthened, as did the floral buds and flowers. During the 10 days leading to the third stage, the number of capsules did not change significantly, but a high rate of floral abscission occurred. The present results show that in Nicotiana tabacum cv. Maryland Catterton short day quantitatively controls not only the inductive step of the flowering process, but also affects the capacity to regenerate flower buds during the late post-inductive phases. The responsiveness to the photoperiodic signal decreases only when the plant exhibits only fruits.     

Dwarfism Caused by Floral-Bud Removal in Petunia and its Reversal by Gibberellin

The effect of floral-bud removal at different stages of developmenton the plant height and on the total number of buds of Petuniawas studied. Continuous removal of all the floral buds 2 d beforeanthesis caused a marked decrease in plant height and also increasedthe total number of floral buds formed thereafter. At otherstages of floral bud development, bud removal had a lesser effecton both phenomena. Moreover, the plants did not respond to budremoval at anthesis. GA₃ at 25 ppm applied to plants from which the buds had beenremoved, promoted stem elongation. The most pronounced effectwas on plants from which the buds were removed 2 d before anthesis,but it had no effect on plants from which the buds were removedat anthesis stage. The possible involvement of endogenous growth hormones in theresponse of Petunia plants to floral-bud removal and to applicationof GA₃ is discussed. Bud removal, bud number, dwarfness, GA₃, Petunia, plant height     

Effects of Daylength on Floral Characteristics of Six White Clover (Trifolium repens) Varieties

The effect of daylength upon floral initiation, flower position,and associated features was measured in six white clover (Trifoliumrepens) varieties Most plants initiated flowers in the longest days (16 h). Thevarieties of more southerly origin and with large leaves hada greater spread of response to daylength. Increasing daylength increased the number of buds becoming inflorescencesin all varieties except Milkanova in which the reverse was true.Peduncle length and nectar production were both greatest inthe longest days. Trifolium repens, white clover, daylength, flower initiation, flower position     

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.     

Effects of culture conditions on development in continuous light of floral buds in Lemna perpusilla 6746

Effects of temperature on the subsequent development in continuouslight of floral buds formed after a single short-day cycle inLemna perpusilla 6746, a short-day plant, were studied usingfronds selected in relation to the order of emergence. The floralbuds developed to stage 1 regardless of the temperature duringthe following CL. The rate of development, however, was slowerat lower temperature. The minimum number of days in CL neededfor the abortion of once formed floral buds increased with adecrease in temperature, accompanied by an increase in the frondplastochron. Furthermore, when the frond plastochron was alteredby manipulation of the environmental conditions, i.e., lightintensity or medium strength, the minimum number of days inCL required for the abortion of the floral buds also changed.These results suggest that the development pattern of floralbuds in this plant is highly correlated with the frond plastochron. (Received September 20, 1977; )     

Interaction du photopériodisme et des effets de la zéatine, du saccharose et de ľeau dans la floraison du Chenopodium polyspermum

Interaction of photoperiodism and zeatin, sucrose and water effects on the flowering of Chenopodium polyspermum Root removal in Chenopodium polyspermum, a quatitative short-day plant, enhances flowering under non-inductive conditions. Presence of roots may be mimicked by zeatin applications on buds. Induction of flowering by short days may be counteracted by applications of zeatin, and appearance of flowers depends on the balance between number of inductive short days and zeatin quantity applied. Sucrose added in the culture medium or applied on buds acts as zeatin. Applications of water on buds may also delay flowering. These results show the plurifactorial regulation of the floral development of this plant. The relations between the non-specificity of the induction and the specificity of the morphogenetic response are discussed.     

LABILE SEX EXPRESSION IN ANDROMONOECIOUS SOLANUM HIRTUM: FLORAL DEVELOPMENT AND SEX DETERMINATION

Sex expression (the proportions of hermaphrodite and staminate flowers produced) of the andromonoecious species Solatium hirtum is labile, and this lability of whole plant sex expression is due to labile sex expression of individual floral buds. In this paper I examine the developmental processes that underlie the differences in floral sex expression of hermaphrodite and staminate flowers of Solarium hirtum, focusing particularly on the processes responsible for the observed lability of floral sex expression. Differences in bud growth rate and relative growth of floral organs in these buds are evident at about the time of megasporocyte meiosis (11–12 days before anthesis). However, gynoecial sterility in staminate buds does not occur until just 6–7 days before anthesis. At this time, abnormalities in ovule development occur in staminate buds: the ovules begin to appear necrotic, the integumentary tapetum collapses, and the megagametophytes of many ovules cease normal development. These observations are consistent with the predictions of labile floral development.     

Significance of timing and number of short-day cycles for initiation and subsequent development of floral buds in Lemna perpusilla 6746

Time courses of the flowering process in Lemna perpusilla 6746,a short-day plant, were studied using selected fronds in relationto the order of emergence. Various numbers of short-day cycleswere interposed during continuous light. The floral buds evokedby short-day cycles developed to a floral stage determined bythe number of short-day cycles 3 days after the transfer toconsecutive long-day cycles, but aborted on the next day, regardlessof the floral stages. At least 2 long-day cycles were requiredfor the abortion of the floral buds at any stage of development.These results suggest the importance of the number of short-daycycles not only for initiation but also for development of floralbuds. (Received February 4, 1977; )     

Effect of Gibberellic Acid and Monophenols on Flowering of lmpatiens balsamina in Relation to the Number of Inductive and Non-inductive Photoperiodic Cycles

A single treatment of plants with GA₃ (gibberellic acid) is not adequate to cause induction under LD (long day: 24-h photo-period) condition, but its effect is added to the sub-threshold induction caused by one SD (short day: 8-h photoperiod) cycle. Floral bud initiation is hastened, and the number of floral buds and flowers per flowering plant increases in plants receiving a single treatment with the combination GA₃+ SA (salicylic acid) accompanying a single SD cycle. However, the increase on 10 replicate basis is more marked in plants receiving three treatments with the combination GA₃+β-N (β-naphthol) and five treatments with the combination GA₃+ SA accompanying six and 10 SD cycles, respectively. The number of floral buds and flowers decreases with an increase hi the number of SD cycles, but it is higher in plants treated with GA₃, SA or GA₃+β-N than in the water-treated controls. — Under long days, treatment of plants with the combinations GA₃+ SA or GA₃+β-N accelerates the initiation as well as increases the number of floral buds. While a minimum of five treatments with GA₃ or of 25 with SA or β-N alone is needed for floral bud initiation under a 24-h photoperiod, three treatments are adequate to induce floral buds with the combination GA₃+ SA or GA₃+β-N under continuous illumination. Ten or more treatments with these combinations under a 24-h photoperiod produce more flowers than the same treatments under an 8-h photoperiod.     

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     

Floral activity in solutions of deoxyribonucleic Acid extracted from tobacco stems

For Nicotiana tabacum cv. Wis. 38 plants, the capabilities of solutions containing DNA, extracted from either homogenates of stems in a floral state or nuclei of stems in a vegetative state, to effect flowering of vegetative plants have been studied. Previous work indicates that the DNA from homogenates of stems in a floral state is mainly nuclear. If DNA solutions are supplied to axillary buds of vegetative plants and if the axillary buds are defoliated every 4th day for 12 days, the buds supplied a solution of DNA from stems in a floral state initiate flowers under noninductive conditions, and the buds supplied a solution of DNA from stems in a vegetative state remain vegetative. Heating and rapidly cooling a solution of DNA from stems in a floral state enhances its floral activity. Heating and cooling a DNA solution also results in novel flowers showing up in many treated plants. Novel flowers are more striking in the offspring than in the parents. The capabilities of heated-cooled DNA solution to initiate flowers in noninductive conditions and to cause novel flowers are eliminated completely by treating (before heating and cooling) the DNA solution with deoxyribonuclease. Heated-cooled solutions of DNA extracted from nuclei of either vegetative stems or vegetative leaves contain no floral activity.     

Disruption of an Ice-nucleation Barrier in Cold Hardy Azalea Buds by Sublethal Heat Stress

Ice nucleating barriers of undetermined composition are knownto occur in floral buds of several cold hardy species, includingAzalea. Fluorescence microscopy indicated the presence of phenolic-nchareas within hardy Azalea flower buds, which could be ice barriers.Hardy buds were subjected to a sublethal heat stress of 45 °Cfor 2 h to disrupt barrier integrity. Two hours after treatmentthe low temperature exotherms (LTEs) of flowers were observedusing differential thermal analysis (DTA). The LTEs of budsexposed to heat stress were either fewer in number and/or occurredat higher temperatures than in controls. Visual assay of theflowers following DTA confirmed that heat-stressed flowers werekilled at higher temperatures than control flowers. Heat-stressedbuds also have lower resultant hardiness compared to controlsas demonstrated by controlled freezing experiments. Acclimation, phenolics, resistance, stress     

Effects of gibberellic acid and cyclic 3',5'-adenosine monophosphate on the flowering of Eschscholtzia californica Cham., a qualitative long day plant.

GA₃ and cyclic AMP induce floral buds in Eschscholtzia californicaunder noninductive short days and hasten it under inductivelong day conditions. (Received June 8, 1976; )