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.     

Emission of Volatiles From Brown Boronia Flowers: Some Comparative Observations

Extensive research has focused on the concentration of aglyconeswithin brown boronia (Boronia megastigma) flowers, however emissionof volatiles into the headspace above these flowers is not welldocumented. Using solid-phase microextraction (SPME) to trapvolatiles and GCMS analysis, we observed 23 volatiles in theheadspace above buds and flowers throughout flower maturation,above dissected floral organs and above whole plants held for36 h under either continuous light, continuous dark or 12 hlight:12 h dark:12 h light treatments. Fully-opened flowersemitted the most complex mixture of volatiles and in the greatestquantity, with a rapid decline in senescent flowers. Caryophyllene,humulene and bicyclogermacrene declined as flower buds matured;ß-ionone increased. From the individual floral organs,emission from the petaline anthers comprised 38% of total emissionsfrom the (calculated) ‘whole flower’, with 27% contributedby the petals and 10.5% by the stigma. Monoterpenes dominatedthe headspace from the calyx; dodecyl acetate, methyl jasmonateand (Z)-n-heptadec-8-ene were relatively predominant in emissionsfrom the androecium. ß-Ionone, the major floral volatilein brown boronia, dominated volatiles emitted from the stigma(87%). However, the relatively tiny petaline anthers, activein pollen production and high in carotenoids, contributed thegreatest overall amount of ß-ionone to emission fromthe whole flower. There were three different patterns in emissionof volatiles from plants in response to different light conditions:(1) emission patterns identical irrespective of light environment,with maximum emission in the ‘endogenous’ dark period,i.e. when the plant would normally have been in the dark (-pinene);(2) similar emission in all treatments, with an increase anddecline over a period of 26 h (5-acetoxy linalool, cyclic ß-ionone,dodecyl acetate and (Z)-n-heptadec-8-ene); and (3) emissionin all treatments but enhanced in the dark, with a 27.5 h periodin some cases (cyclic ß-ionone endoperoxide, dihydroß-ionone, ß-ionone, and ‘total volatiles’).Preliminary evidence is presented for endogenous control ofemission of a number of volatiles such as -pinene, with perhapsdiurnal control of others such as ß-ionone. Copyright2000 Annals of Botany Company Boronia megastigma, brown boronia, SPME, headspace, floral volatiles, ß-ionone     

Volatiles in Different Floral Organs, and Effect of Floral Characteristics on Yield of Extract fromBoronia megastigma(Nees)

The relative amounts of volatile compounds in the extract andheadspace from each floral organ were assessed in order to identifythe main organs for accumulation and emission. The mass of flowers/organs,the number/density of oil glands and yield of volatiles wereexamined for their relationship with extract yield, in clonaland non-clonal plants. Boronia flowers were divided into componentorgans and the solvent extractable product and headspace aboveeach organ type was quantified. The petals comprised 50% ofthe weight of the flowers, and the stigma 20%; however, thestigma contributed 70% of the total volatile compounds to extractfrom the whole flower. Proportionately more ß-iononeand dodecyl acetate were emitted from the stigma and anthersthan were contained in the extract, compared with other volatiles.The sexual organs are morphologically equipped for emissionof volatiles to attract pollinators. Between non-clonal plants, there was a lower coefficient ofvariation for extract yield than for values relating to extractcomposition, indicating that the former is more heritable thanthe latter. Variation between clonal plants was reduced comparedwith variation between non-clonal plants. The environment modifiesyield and quality of extract in clonal plants, indicating thatboth have relatively low heritability. No significant relationshipsbetween any floral characteristics and extract yield were found.Biosynthetic potential to accumulate extract is therefore ofprime importance, and the effect of environment on this potentialshould be the subject of future work. Boronia megastigma; brown boronia; Rutaceae; essential oils; flower; stigma; oil gland; ß-ionone     

Intraspecific Variation in Oil Components ofBoronia megastigmaNees. (Rutaceae) Flowers

Intraspecific variation in the oil composition ofBoronia megastigmaNees.(Rutaceae) was examined. Boronia absolute is extracted fromblossom primarily for use as a food additive. A major componentis ß-ionone andB. megastigmais one of the commercial,natural sources of this compound. Genotypes superior in productionof ß-ionone and low in monoterpene hydrocarbons weresought from natural populations in the south west of WesternAustralia as part of a breeding programme. Flowers were collectedfrom 25 plants in each of 29 different populations. Blossomwas extracted with ethanol and analysed using a gas liquid chromatographfitted with ionisation detectors. The contents of ß-ionone,dodecyl acetate, -pinene, ß-pinene and limonene inthe oil extract were compared. Intra-population variation wasas great as inter-population variation and no distinct chemotypeswere found. Considerable variation existed in the content ofcomponents. The highest ß-ionone content was 1787mg g^-1f. wt. Some genotypes contained all five components analysed,others lacked one or more of the monoterpenes: -pinene, ß-pineneor limonene. Principle components analysis indicated that contentsof ß-ionone and dodecyl acetate were associated andthat they were distinct from the content of the monoterpenes,which were associated with each other. Natural shading was associatedwith lower levels of monoterpenes but other oils were unaffected.Young plants contained less pinenes than older plants and oldplants contained the most dodecyl acetate. Vigorous plants producedmore pinenes. Red flowers contained the least ß-iononeand dodecyl acetate.Copyright 1999 Annals of Botany Company Boronia megastigma,boronia, Rutaceae, oil, -pinene, ß-pinene, limonene, ß-ionone, dodecyl acetate, monoterpenes, chemotypes.     

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     

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     

Flower Colour Changes in Lantana camara

Lantana camara flowers undergo colour change subsequent to anthesis.In the colour variant selected for the present study, pink buds,yellow newly-opened flowers and ageing orange, scarlet and magentaflowers are found in the same inflorescence. The flower pigmentswere chemically analysed and identified as delphinidin monoglucosideand ß-carotene. Thrips are regular pollinators of Lantana under Delhi conditions.Pollination was identified as the trigger for rapid anthocyaninsynthesis. Even the presence of one pollen grain on the stigmaof a yellow flower was sufficient to cause colour change. Injectionof a suspension of pollen into flowers opened in vitro causedpigment changes. An extract of Lantana pollen was also ableto simulate the effect of pollination, suggesting the involvementof a pollen factor. The post-pollination shift in petal colourationis caused by the masking of carotenoids by differential amountsof anthocyanin. As thrips are attracted to only yellow flowers,chromatic changes play a role in conserving pollinator energy. Key words: Anthecology, Floral pigments, Lantana camara, Pollination     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18 °C). With a temperatureregime of 35 °C day, 25 °C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35 °C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.     

Injury-induced Cyanogenesis in Vegetative and Reproductive Parts of Two Grevillea Species and their F1 Hybrid

When leaves of three Grevillea species were macerated, hydrogencyanide was only released from the soft, immature ones. Thebark but not wood of young stems was weakly cyanogenic. Thegreatest concentration of cyanoglucosides occurred in peduncles,flower buds, open flowers, immature seeds and germinants. Nocyanide was released from nectar, pedicels, dry fruit, elaiosomesand dry walls mature seeds. Addition of ß-glucosidase,and sometimes water only, increased cyanogenesis in young leaves,bark, some seed and fruit walls, and embryos of mature seeds.The endogenous levels of ß-glucosidase were sufficientto release all the cyanide present in at least 80% of cases. Young leaves and germinants of G. bipinnatifida (resprouter)released more cyanide than those of G. banksii, while flowerbuds, stigmatic region, styles, perianths and ovaries of G.banksii (non-sprouter) released far more cyanide than thoseof G. bipinnatifida. The interspecific and intraplant distributionof cyanoglucosides is consistent with the expected impact ofbeneficial and herbivorous animals on long term fitness of thesespecies. The F1 hybrid (G. 'Robyn Gordon') tended to have intermediatecyanoglucoside levels between the two putative parents.Copyright1993, 1999 Academic Press Grevillea bipinnatifida, G. banksii, G. 'Robyn Gordon', cyanide, herbivory, ß-glucosidase, cyanogenesis     

Effect of decapitation, phosfon D and cycocel on the flowering of Impatiens balsamina exposed to varying numbers of short days

Impatiens balsamina L., a qualitative short day plant, requiresmore short days for the development of floral buds into flowersthan for their initiation. Phosfon D and cycocel reduce thenumber of short days required for flowering, increase the numberof floral buds and flowers and delay their reversion to vegetativegrowth when transferred to noninductive conditions. The effectof decapitation of the main shoot subsequent to the emergenceof floral buds resembles that of retardants indicating thatthe effect of the latter in flower promotion in this plant maybe by virtue of their effect on cessation of apical dominanceas a consequence of which reserve food materials may be channeledto axillary floral buds enabling them to develop into flowers. (Received January 9, 1969; )     

Effects of Gibberellic Acid on Floral Development in vivo and in vitro in the Cleistogamous Species, Lamium amplexicaule L.

Using established developmental markers in the corolla and androeciumof Lamium amplexicaule L., we investigated the apparent inductionof open (chasmogamous — CH) from closed (cleistogamous— CL) flowers after application of GA₃ (0.1 mM). In vivotreatment of potentially CL flower primordia caused cell expansionbut not the increased cell division in anthers and corolla necessaryto convert a CL into a CH flower. Floral primordia that appearedto be of undetermined floral type were grown in vitro on a basalmedium supplemented with kinetin (0.1 p.p.m.) and grew to maturityas CL flowers. On media additionally supplemented with GA₃,flowers underwent anthesis, but no true CH flower was produced.Gibberellins appear to be directly responsible for anthesisin the CH flower; but additional, as yet unknown growth factorsare involved in the switch from CL to CH floral form in a developinginflorescence. floral morphogenesis, Lamium amplexicaule L, henbit, cleistogamy, gibberellin, kinetin, anthesis     

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     

Flower and Volatile Oil Ontogeny in Boronia megastigma

The volatile oils of flowers of Boronia megastigma Nees. areimportant commercially but little has been published regardingtheir localization or the dynamics of their synthesis. In thisstudy we examined the histochemistry, anatomy and volatile oilcomposition of the floral organs of plants from a native populationby SEM. Lysigenous glands occurred in all organs except the stigma andandroecium and were associated with the presence of - and ß-pineneand limonene in tissue extracts. These compounds increased inconcentration throughout fruit development. Petals, stamens,staminodes and stigmas were glandular and contained phenolicdeposits, a dense cytoplasm and prominent intercellular spaces.Extracts of these tissues contained dodecanol, ß-iononeand dodecyl acetate, the concentrations of which were greatestat the time of stigma receptivity. The location and timing oftheir synthesis together with their biological activity suggeststhat these volatile oils may have a role in pollination.Copyright1995, 1999 Academic Press Boronia megastigma Nees., Rutaceae, essential oils, volatile oils, reproductive biology, -pinene, ß-pinene, limonene, ß-ionone, dodecyl acetate, heptadecene     

Some Effects of Indol-3-ylacetic Acid on the Rates of Initiation and Development of Flower Buds of Chrysanthemum morifolium

Frequent applications of a solution containing 50 p.p.m. IAAto the upper leaves of Chrysanthemum plants reduced the numbersof open and opening flowers and delayed harvesting. The ratesof initiation and development of flower buds were studied bydissection in relation to the concentrations of indol-3-yl-aceticacid (IAA) (20–200 p.p.m.) applied to the tops of theplants. Inereasing the concentrations of IAA resulted in a progressivedelay in bud initiation (P<0•001), but had little effecton their subsequent rates of development. The results differedfrom those previously obtained with copper deficient plantsin that the latter deficiency affected both initiation and developmentof the buds.     

Endogenous Cytokinins in Flower Bud Forming Explants of Tobacco

The accumulation of endogenous cytokinins was studied in pedicelexplants of tobacco (Nicotiana tabacumL.) during regenerationof flower buds in vitro. Maximal bud formation was induced onmedia containing 1.0 mmol m^–3 of benzyladenine or dihydrozeatin.No buds were formed in the absence of cytokinin. The levelsof dihydrozeatin, zeatin, and the corresponding ribosides weredetermined in explants cultured in the presence or absence ofcytokinin by means of a competitive ELISA technique. In explantsincubated without a cytokinin, only the dihydrozeatin concentrationincreased significantly during the first day of incubation anddecreased during the second day. No increase was observed inexplants incubated in the presence of benzyladenine. The concentrationof dihydrozeatin in these bud-forming explants was only 10 to15% of the concentration built up in explants cultured on dihydrozeatininstead of benzyladenine. This suggests that the endogenouscytokinins only play a minor role in the regeneration of flowerbuds in vitro. Key words: cytokinin, flower bud development, tissue culture, tobacco     

Flower Opening in Asiatic Lily is a Rapid Process Controlled by Dark-light Cycling

In commerce, Asiatic lilies are picked in bud, each stem holdingseveral buds. We found flower opening was rapid, taking lessthan 4 h both on the stem and for excised buds. Opening wasalso strongly synchronous. For a 12 h day-night cycle, openingbegan late in the dark period, reaching a mid-point after 11h of darkness. This was equally true of buds that were excisedwhen nearly ready to open, and those with 3–4 d of developmentto complete. Reversing day and night reversed the time of opening,and red light was as effective as white light in providing ‘day’conditions. A 15 min light break during the night did not affectthe opening. Lengthening the night (8, 12, 16 h) and shorteningthe day delayed opening from 9, to 11, to 13 h after the startof darkness, respectively. In continuous light and continuousdark, synchronicity was lost. If opening flowers were held inextended darkness, two phases of opening could be discriminated.In a ‘dark phase’, petals opened to approx. 40°,and anthers remained intact. When such flowers were returnedto light, there was a ‘light phase’, where petalsopened further, became more pigmented and began to recurve,and the anthers dehisced, these events taking only 2–3h. The net result was that flowers became fully open and anthersdehisced approx. 2 h after dawn, regardless of daylength. Copyright2000 Annals of Botany Company Asiatic lily, Lilium hybrid, flower opening, timing, endogenous rhythm, synchronicity     

Threatened pollination systems in native flora of the Ogasawara (Bonin) Islands

• Background and Aims Various alien species have been introducedto the Ogasawara Islands (Japan). A survey was made investigatingwhether the native pollination systems fit an ‘islandsyndrome’ (biasing the flora to dioecy, with subdued,inconspicuous flowers) and whether alien species have disruptedthe native pollination network. • Methods Flower visitors and floral traits were determinedin the field (12 islands) and from the literature. Associationsamong floral traits such as sexual expression, flower colourand flower shape were tested. • Key Results Among the 269 native flowering plants, 74·7% are hermaphroditic, 13·0 % are dioecious and 7·1% are monoecious. Classification by flower colour revealed that36·0 % were white, 21·6 % green and 13·8% yellow. Woody species (trees and shrubs) comprised 36·5% of the flora and were associated with dioecy and white flowers.Solitary, endemic small bees were the dominant flower visitorsand visited 66·7 % of the observed species on satelliteislands where the native pollination networks are preserved.In contrast to the situation on the satellite islands, introducedhoneybees were the most dominant pollinator (visiting 60·1% of observed species) on the two main islands, Chichi-jimaand Haha-jima, and had spread to satellite islands near Chichi-jimaIsland. • Conclusions The island syndrome for pollination systemsin the Ogasawara Islands was evident in a high percentage ofdioecious species, the subdued colour of the native flora andsolitary flower visitors on satellite islands. The shape andcolour adaptations of several flowers suggested native pollinationniches for long-proboscis moths and carpenter bees. However,the domination and expansion of introduced honeybees have thepotential for disruption of the native pollination network inthe two main, and several satellite, islands of the OgasawaraIslands.     

Quantitative developmental analysis of homeotic changes in the inflorescence of Philodendron (Araceae)

Background and Aims: The inflorescence of Philodendron constitutes an interestingmorphological model to analyse the phenomenon of homeosis quantitativelyat the floral level. The specific goals of this study were (1)to characterize and quantify the range of homeotic transformationin Philodendron billietiae, and (2) to test the hypothesis thatthe nature of flowers surrounding atypical bisexual flowers(ABFs) channel the morphological potentialities of atypicalbisexual flowers. Methods: Inflorescences of P. billietiae at different stages of developmentwere observed using SEM. The number of appendices in male, femaleand sterile flowers were counted on 11 young inflorescences(5–6 flowers per inflorescence). The number of staminodesand carpels on ABFs were counted on 19 inflorescences (n = 143).These data were used for regression and ANOVA analyses. Results: There was an average of 4·1 stamens per male flower,9·8 carpels per female flower and 6·8 staminodesper sterile male flower. There was an average of 7·3floral appendices per atypical flower. Staminodes and carpelsare inserted on the same whorl in ABFs. A negative exponentialrelationship was found between the average number of staminodesand the number of carpels in ABFs. If only the ABFs consistingof less than six carpels are considered, there is a linear relationshipbetween the number of carpels and the average number of staminodes.The value of the slope of the regression equation indicatesthat on average, in P. billietiae, 1·36 carpels are replacedby one staminode. Conclusions: In P. billietiae, the number of appendages in female flowersimposes a constraint on the maximum total number of appendages(carpels and staminodes) that can develop on ABFs. The quantitativeanalyses indicate that the average number of different typesof floral appendages on an ABF and the number of organs involvedin a homeotic transformation are two independent phenomena.     

Effects of IAA, Zeatin, Ammonium Nitrate and Sucrose on the Initiation and Development of Floral Buds in Torenia Stem Segments Cultured In Vitro

In Torenia stem segments cultured on a defined medium from whichammonium nitrate and growth regulators were omitted, adventitiousbuds were readily formed from epidermal tissue, with subsequentdifferentiation of floral buds. Using this plant material, thecorrelation between the time of application of various chemicalsand the time-course of floral bud differentiation was investigated.Histological examination showed that adventitious buds werevegetative during the first two weeks of the culture, and floralprimordia appeared after about three to four weeks of culture.We divided the flowering process in Torenia stem segments intothe following 3 phases: the first phase (first 2 weeks) duringwhich adventitious buds are formed, the second phase (3rd and4th weeks) during which floral buds are initiated and the thirdphase (5th to 12th weeks) during which floral buds develop.Then we added IAA, zeatin, ammonium nitrate or a high concentrationof sucrose to the medium during one, two or three of these phases.Ammonium nitrate added during the third phase suppressed floralbud development, but the high concentration of sucrose givenduring this phase stimulated it. These two chemicals influencedonly the development of floral buds previously initiated. Theapplication of IAA during the first phase promoted both theinitiation and development of floral buds. However, its applicationafter 2 weeks of culture failed to promote floral bud formation.Zeatin inhibited floral bud formation in a manner similar toammonium nitrate, but if it was added to the medium only duringthe first phase, it slightly promoted the initiation and developmentof floral buds. (Received July 7, 1981; Accepted October 12, 1981)