Effect of modified endogenous ethylene production on sex expression, bisexual flower development and fruit production in melon (Cucumis melo L.)

Members of the Cucurbitaceae family display a range of sexual phenotypes including various combinations of male, female, or bisexual flowers. Ethylene appears to be a key hormone regulating the sex determination process. Application of ethylene, or inhibition of ethylene action, increases or decreases the number of pistil-bearing buds, respectively. Elevated levels of ethylene production and expression of genes for ethylene biosynthesis, have been correlated with pistillate flower production. In this study, we sought to determine the effect of modified endogenous ethylene production on sex expression by constitutively expressing ACS (1-aminocyclopropane-1-carboxylate synthase), the first committed enzyme for ethylene biosynthesis, in transgenic melons (Cucumis melo L.). Most melon genotypes are andromonoecious, where an initial phase of male flowers is followed by a mixture of bisexual and male flowers. ACS melon plants showed increased ethylene production by leaves and flower buds, and increased femaleness as measured by earlier and increased number of bisexual buds. ACS melons also had earlier and increased number of bisexual buds that matured to anthesis, suggesting that ethylene is important not only for sex determination, but also for development of the bisexual bud to maturity. Field studies showed that ACS melons had earlier mature bisexual flowers, earlier fruit set, and increased number of fruit set on closely spaced nodes on the main stem. These results provide a direct demonstration of the importance of endogenous ethylene production for female reproductive processes in melon.     

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 determination in axillary buds of Nicotiana silvestris

At anthesis of the terminal flower the developmental fates of axillary buds of the long-day plant Nicotiana silvestris were assessed in situ and in isolation. The in situ developmental fate was assessed by decapitating the plant above the bud in question and letting the bud mature. The developmental fate of isolated buds was assessed by removing the bud from the main axis, rooting it, and letting it mature. The number of nodes below the terminal flower of the mature shoot was indicative of the developmental fate of the bud. Terminal meristems of rooted axillary buds exhibited two patterns of development: (1) Their developmental fate was the same as that of in situ buds at the same node or (2) their developmental fate was the same as that of seed-derived plants. For example, terminal meristems of rooted buds from the fourth node below the inflorescence produced either 15 to 19 nodes or 36 to 40 nodes. In situ fourth buds produced 12 to 14 nodes while seed-derived plants produced 33 to 39 nodes. Terminal meristems of rooted axillary buds that exhibited the same developmental fate as that of in situ buds were determined for floral development. Although determined buds produced a terminal flower, all but one had abnormal inflorescences. That is, in the place of floral branches determined buds produced vegetative branches. Four buds that were not determined for floral development had their shoot tips rooted each time the plant bolted. Only when the plants were allowed to grow without being rerooted did they flower. These results indicate that roots may prevent and/or destabilize floral determination in N. silvestris.     

Correlation between development of female flower buds and expression of the CS-ACS2 gene in cucumber plants

Ethylene plays a key role in sex determination of cucumber flowers. Gynoecious cucumber shoots produce more ethylene than monoecious shoots. Because monoecious cucumbers produce both male and female flower buds in the shoot apex and because the relative proportions of male and female flowers vary due to growing conditions, the question arises as to whether the regulation of ethylene biosynthesis in each flower bud determines the sex of the flower. Therefore, the expression of a 1-aminocyclopropane-1-carboxylic acid synthase gene, CS-ACS2, was examined in cucumber flower buds at different stages of development. The results revealed that CS-ACS2 mRNA began to accumulate just beneath the pistil primordia of flower buds at the bisexual stage, but was not detected prior to the formation of the pistil primordia. In buds determined to develop as female flowers, CS-ACS2 mRNA continued to accumulate in the central region of the developing ovary where ovules and placenta form. In gynoecious cucumber plants that produce only female flowers, accumulation of CS-ACS2 mRNA was detected in all flower buds at the bisexual stage and at later developmental stages. In monoecious cucumber, flower buds situated on some nodes accumulated CS-ACS2 mRNA, but others did not. The proportion of male and female flowers in monoecious cucumbers varied depending on the growth conditions, but was correlated with changes in accumulation of CS-ACS2 mRNA in flower buds. These results demonstrate that CS-ACS2-mediated biosynthesis of ethylene in individual flower buds is associated with the differentiation and development of female flowers.     

Osservazioni sul ciclo di sviluppo delle gemme di esemplari mascbili e femminili di Ginkyo biloba L.

Abstract

Observations on the development cycle of the buds of male and female specimens of Ginkyo biloba L. – A study of the buds of long shood and short shoot of male and female Ginkyo biloba L. individuals reveals the following: 1) All the buds of the male individuals are bigger and round in shape while those of the female individuals are smaller and conical. 2) Among individuals of the same sex there are no differences between the buds of long and short shoots except that the latter are always bigger. 3) All the buds, both male and female, show a constant number of buds scales (7–14), embryonic leaves (3–7) and leaf primordia (3–4). 4) The increase in diameters is greater in the male than in the female buds. 5) When opening, the buds of the male short shoots can get as big as 11,5 mm × 11,5 mm and those of the female short shoots 5 mmx4 mm. At this time, the long shoots of both sexes show a less marked differences in size (♂ 5 mm × 5 mm; 9 4 mm × 3,5 mm). 6) The male buds of both long and short shoots are always mixed, that is they are provided with a very small apex and pollen sacs. Only on exceptional cases has sterility been observed. On the other hand female buds are mixed, that is they are provided with a shoot apex and ovules, only in the long shoots of three or more years of age and not always; while the buds of the long shoots are always sterile. 7) Opening of the buds, which in both sexes occurs from the base upwards, takes place at the middle of March in the male and in the first decade of April in the female individuals. 8) The appearence of sex, starting from the base, takes place at an earlier time in male individuals. In fact in the buds of the male short shoots it appears as early as July. In the buds of the female short shoots it appears in October. 9) Pollen cones do not appear at the same time in all the buds of the two types of shoot. They are found in the buds of the short shoots in July, in October in the lateral buds of the long shoots and in November in the terminal buds of the same type of shoots. 10) Ovules appear only in some buds of short shoots three or more year old. They are never present in the long and short shoots one or two year old buds. 11) The dates of appearance of the pollen cones and ovules in our Florentine specimens are exactly the same as those reported by SPRECHER (1907) for the Ginkyo plants growing in Geneva.     

Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee

The effect of 100 mgl^–1 gibberellic acid (GA₃) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA₃ treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA₃ at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA₃ applications. Treatment with GA₃ did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.     

Behavior of current-year shoots as a mechanism to determine the floral sex allocation at the level of individual tree and population in Siberian alder (Alnus hirsuta var. sibirica)

Floral sex allocation (weight of male flower buds over weight of female flower buds) was examined at the levels of current-year shoot, individual tree and population, and the tree individual level and population level floral sex ratio was explained as a consequence of the behavior of current-year shoots in the shoot-level monoecious (flowering current-year shoots have both male and female flowers) species, Siberian alder (Alnus hirsuta var. sibirica). The current-year shoot level floral sex allocation was not size-dependent and not different over years. However, in the year when the reproductive intensity was high, individual tree level floral sex allocation was size-dependent and the population level floral sex allocation was relatively female-biased. The female-biased floral sex allocation at the population level resulted from many gynoecious shoots (current-year shoots which have only female flowers). These results suggest that the floral sex allocation of Siberian alder was controlled not by changing the floral sex allocation of each current-year shoot, but by shifting the sex expression of current-year shoots from shoot-level monoecy to shoot-level gynomonoecy.     

Studies on the Glasshouse Carnation: Effects of Light and Temperature on the Growth and Development of the Flower

Experiments were concerned with the growth and development offlowers of carnation (Dianthus) var. White Sim from the timethe flower buds became visible up to anthesis. Rates of growthin size of the flower were decreased by either low temperaturesor low light intensities but only low temperatures caused anappreciable delay in anthesis. Effects of low light intensitycould be simulated by partial defoliation and appeared to bemediated through effects on photosynthesis. Temperature, however,acted directly on processes occurring in the flower bud. The rate of development of the flower, in the sense of progresstowards anthesis, appeared to be independent of levels of assimilatesavailable for growth. It is suggested that processes controllingdevelopment in the flower regulate the partition of assimilatesbetween the flower and the remainder of the shoot system. Seasonal variations in rates of flower development under glasshouseconditions are considered to be largely attributable to variationsin the temperature of the flower buds.     

Effects of shoot bending on ACC content,ethylene production,growth and flowering of bougainvillea

Several factors, such as environmental conditions, pruning, and plant growth regulators, affect the flowering of bougainvillea. However, information on the effect of shoot bending on growth and flowering of bougainvillea is scarce. In the natural environment, most of the bougainvillea flowering shoots are inclining whereas vertical shoots are not flowering shoots. Bougainvillea shoots are artificially grown vertically, horizontally and at an inclined orientation, to investigate the effect of these orientations on plant growth and the development of flower buds. The results of this indicate an effect of shoot bending on the growth rate of bougainvillea and the rate of flower bud formation. Additionally, our results suggest that vertical shoots have a higher growth rate, more prolific vegetation growth, and longer plastochrons (which are the intervals between the initiations of successive leaves). In contrast, horizontal and inclined shoots exhibited slower growth, a shorter time to reach flowering, and more flower buds. Inclined shoots had a higher endogenous ACC (1-aminocyclopropene-1-carboxylate) content and produced more ethylene than either horizontal or vertical shoots, indicating that more ACC in the inclined shoot is converted into ethylene, and the higher ethylene concentration in the inclined shoot causes it to mature earlier and flower sooner.     

Expression of cucumber stress-related anionic peroxidases during flower development or a cryptic infective process

The striking diversity in the expression pattern of the stress-related anionic peroxidase was observed during development of female cucumber flower. While the isoenzyme Prx3 was accumulated constitutively in the course of flower development, the expression patterns of other two isoenzymes (Prx1 and Prx2) were restricted to the period after flower opening. The virus infection was simulated by careful opening of the intact female flower buds 3 d before anthesis followed by exposition to the glasshouse environment for 3 d. The results obtained in this experiment revealed a marked accumulation of the isoenzyme Prx1 and Prx2 at anthesis. Under normal flower development, the pistils did not accumulate these isoenzymes at this stage. In contrast, the pattern of expression of Prx3 as well as of the pistil-specific peroxidase isoenzyme remained unchanged, confirming a constitutive type of expression. Beside the pistil, a 3-d exposition of the stripped flowers resulted in a marked accumulation of Prx1 and Prx2 isoenzymes also in both adjacent flower organs - the ovary and the pedicel. At the same time of the normal development of female flower these organs did not accumulate these isoenzymes.     

Pollination Ecophysiology of Mercurialis annua L. (Euphorbiaceae), an Anemophilous Species Flowering all Year Round

Mercurialis annua L. is a dioecious anemophilous species thatflowers all year round in central and southern Italy. The flowersof both sexes are dimorphic: the female flower has a vestigialcalyx; the male flower consists only of a calyx that opens atanthesis. The anthers always dehisce after anthesis. The anthesisof male flowers seems to be temperature dependent, whereas antherdehiscence is related to relative humidity. The pollen grainsvary in volume according to the season: they are smaller whenrelative humidity is low and vice versa. They always decreasein volume after anther dehiscence and have the capacity to varyin volume and reach equilibrium with a changing environment.Viability is high, but may drop suddenly during heavy rain orhail that damage the exposed male flowers. The number of pollengrains per stigma varies from 0 to 300. The data is discussedin relation to the type of pollination and environmental characteristics.Copyright1994, 1999 Academic Press Mercurialis annua, dioecism, anthesis, anther dehiscence, pollen volume, pollen viability, anemophilous pollination, pollination ecology     

Primigenic and positional dominance among reproductive buds in shoots of two apple (Malus × domestica (Borkh.)) cultivars in a warmer and cooler site

Key message

In two apple cultivars, fruit set was due to primigenic dominance within the annual shoot in areas with insufficient winter chilling while positional dominance took precedence when chilling was sufficient.

Abstract

The purpose of our study was to use fruit set and inflorescence size to characterize the positional (position along the shoot) and/or temporal (relative time of budburst and flowering) influences on competition between reproductive laterals within an annual shoot. The relative time of budburst and flowering, and the relative position within the shoot of reproductive buds were recorded on 2-year-old shoots of ‘Granny Smith’ and ‘Golden Delicious’ apple (Malus × domestica (Borkh.)) trees. The trees were grown at two locations in South Africa, a cool area, Koue Bokkeveld, and a warm area, Warm Bokkeveld, with sufficient and insufficient winter chilling, respectively. Inflorescence size (leaf number, leaf area, and flower number) did not differ temporally or with position. For both cultivars, fruit set in the cool area was acrotonic and independent of relative flowering time, while it was more influenced by temporal (primigenic) dominance in the warm area. Therefore, there is a clear positional advantage within the shoot to fruit set in cool areas (i.e., better local climate conditions for the growing fruit), while there is a clear temporal advantage (first bud to burst sets a fruit), or a “first come, first serve” approach to fruit set, in warm areas, which have limited and delayed budbreak. Inflorescence size and fruit set indicate a separation of environmental (degree of winter chilling) and innate factors in competition among reproductive buds along the 2-year-old annual shoot.     

Topophysis affects the Potential of Axillary Bud Growth, Fresh Biomass Accumulation and Specific Fresh Weight in Single-stem Roses (Rosa hybrida L.)

Topophysis, the effect on growth and differentiation of positionof axillary buds along the shoot, was studied by propagatingfive-leaflet-leaf single-node cuttings which were excised fromseven stem positions and grown as single stemmed plants. InRosahybrida ‘Korokis’ Kiss®, ‘Tanettahn’Manhattan Blue®, and ‘Sweet Promise’ Sonia®,following release of the buds from apical dominance by excision,morphogenetic development was studied until anthesis. The timefrom excision/planting until onset of bud growth, visible flowerbud appearance, and anthesis was generally shorter in plantsoriginating from apical bud positions than from basipetal positions.Topophysis mainly affected the onset of axillary bud growth;the earliest growth and development was found in cuttings fromthe second uppermost node position. This node tended to havethe lowest plastochron value, which indicated the existenceof a transition between sylleptic and proleptic buds. Stem lengthat visible flower bud and at anthesis generally increased asthe cutting position changed basipetally until the second lowestposition, and the number of five-leaflet-leaves at anthesisand the total number of nodes generally increased basipetally.For internode length, growth rate, and fresh biomass efficiencythe cuttings taken from the uppermost and lowermost positionsgenerally had significantly lower values than cuttings fromall medial positions. At anthesis, plants originating from cuttingsexcised from lower medial positions generally had a higher freshweight, greater flower stem diameter, and a significantly higherspecific fresh weight than those plants originating from apicalor basal positions. Among the cultivars, Sonia was the mostefficient in increasing fresh biomass and had the highest growthrate, whereas Manhattan Blue possessed the highest specificfresh weight, indicating a higher plant quality. It is suggestedthat topophysis inRosa is an independent phenomenon intrinsicto the axillary bud. apical dominance; axillary bud growth; fresh biomass accumulation; cut rose; flowering; Rosaceae; Rosa hybrida L.; rose; shoot growth; single-stem roses; specific fresh weight; topophysis; quality     

Vascular development of the grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) inflorescence rachis in response to flower number,plant growth regulators and defoliation

The grapevine inflorescence is a determinate panicle and as buds emerge, shoot, flower and rachis development occur simultaneously. The growth and architecture of the rachis is determined by genetic and environmental factors but here we examined the role of flower and leaf number as well as hormones on its elongation and vascular development. The consequences of rachis morphology and vascular area on berry size and composition were also assessed. One week prior to anthesis, Merlot and Cabernet Sauvignon field vines were exposed to manual flower removal, exogenous plant growth regulators or pre-bloom leaf removal. Manual removal of half the flowers along the vertical axis of the inflorescence resulted in a shorter rachis in both cultivars. Conversely, inflorescences treated with gibberellic acid (GA₃) and the synthetic cytokinin, 6-benzylaminopurine (BAP) resulted in a longer rachis while pre-bloom removal of all leaves on the inflorescence-bearing shoot did not alter rachis length relative to untreated inflorescences. Across the treatments, the cross-sectional areas of the conducting xylem and phloem in the rachis were positively correlated to rachis girth, flower number at anthesis, bunch berry number, bunch berry fresh mass and bunch sugar content at harvest. Conversely, average berry size and sugar content were not linked to rachis vascular area. These data indicate that the morphological and vascular development of the rachis was more responsive to flower number and plant growth regulators than to leaf removal.     

THE EMERGENCE AND DEVELOPMENT OF BRANCHES IN CROTALARIA JUNCEA AND THEIR RELATIONSHIP TO FLOWERING

Nanda , K. K. (Forest Res. Inst., Dehra Dun, India.) The emergence and development of branches in Crotalaria juncea and their relationship to flowering. Amer. Jour. Bot. 49(4): 334–341. Illus. 1962.—Seeds of Crotalaria juncea L. were sown in pots on March 23, 1959, and records were kept of the dates of emergence of individual branches and the appearance of flower buds on them. Periodical observations were also made of the height of the main shoot as well as its branches and the number of nodes and leaves borne by them throughout the year. The main shoot elongates rapidly and terminates in an inflorescence. Development of lateral buds remains completely arrested during the period of rapid elongation and is initiated only after the appearance of the floral buds when it takes place in basipetal sequence. The flowering of the branches also takes place in a basipetal manner. This mode of emergence of branches and their flowering are exhibited even by secondary and tertiary branches. The length attained by these branches is very small as the flower buds appear soon after their emergence. In contrast, the branches formed towards the middle of May continue to elongate for a considerable period and become many times longer than the main shoot or the branches produced earlier in the season. The vegetative period of these branches is also very much prolonged. These differences in the height attained by branches produced at different times of the year and the basipetal sequence in the emergence of branches and their flowering appear to be under the control of some physio-chemical changes which cause the transformation of the growing apex from the vegetative to the reproductive state. This holds good irrespective of whether these changes are brought about as a result of a favorable environmental complex, as is the case with the main shoot and late-formed, much elongated branches, or are due to the favorable internal conditions produced within the plant as a result of the completion of the developmental process of the main shoot, as happens in the case of branches produced earlier in the season.     

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.     

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     

Involvement of Ethylene Biosynthesis and Signalling in the Transition from Male to Female Flowering in the Monoecious Cucurbita pepo

It is well established that ethylene is the main hormonal regulator of sexual expression in the Cucurbitaceae family, controlling not only the sexual fate of individual floral buds, but also the female flower transition, that is, the time at which the first female flower appears and therefore the number of female flowers per plant. Although sex determination of individual flower buds is known to be controlled by specific ethylene biosynthesis ACS genes in melon and cucumber, the role of ethylene genes in the control of the transition to female flowering is still unknown. We have identified two contrasting monoecious inbred lines of Cucurbita pepo, Bolognese (Bog) and Vegetable spaghetti (Veg), which differ in female flower transition but not in flower development. In Bog, which is very sensitive to ethylene, the transition to female flowering is very early, whereas in Veg, which is much less sensitive to ethylene, the transition occurs much later. In this article we compare the production of ethylene and the expression profiles of seven genes involved in the biosynthesis, perception, and signalling of ethylene in the two contrasting lines. Bog, with earlier female flower transition, showed higher ethylene production and CpACO1 expression in the apex at an earlier stage of plant development, when Bog is already producing female flowers, but Veg has not transitioned to female flowering yet. Moreover, the expression of the ethylene receptor and CTR-like genes in the apex of Veg and Bog plants indicates that these genes negatively regulate female flower transition during the earlier stages of plant development. The earlier transition to female flowering in Bog is not only associated with a higher production of ethylene in the apex but also with a premature decline of ethylene negative regulators (receptors and CTR-like) in the apex of the plant. These results provide the basis for a model that explains the regulation of female flowering transition in monoecious cucurbits.     

Floral structure and development of Ceratiosicyos laevis (Achariaceae) and its systematic position

The morphology and development of the flowers of Ceratiosicyos laevis (Achariaceae) were investigated. Plants are monoecious and the inflorescence is a thyrse composed of a single female flower and two male cymose partial inflorescences. The sympetalous flowers of both sexes have an unusual urceolate shape. In young buds the free parts of the petals are postgenitally united. Before anthesis the fusion is ruptured but the petals remain coherent due to marginal cilia. Nectary-like bodies situated at the floral base seem to stabilize the shape of the flower additionally. The anthers are coherent by interlocking epidermal cells and form a narrow tube. They lack an endothecium. In anthesis only the style and the anther tube respectively protrude out of the flower. The synorganization of the anthers, the powdery pollen and the lack of an endothecium are suggestive of a buzz pollination syndrome. Some characters point to an affinity of Achariaceae with Cucurbitaceae. However, the family seems to be more closely related to Passifloraceae.     

栝楼不同性别花芽分化形态解剖特征观察

采用体视显微镜、石蜡切片和树脂切片技术对栝楼(Trichosanthes kirilowii Maxim.)不同性别花芽分化发育时期的外部形态和内部解剖结构进行了观察。结果显示,栝楼花为雌雄异株,仅有雌花、雄花两种性别分化,且雄花的发育速度明显快于雌花的发育速度。栝楼雌雄花芽长0.2 mm左右已完成性别分化;栝楼雄花为单性花,分化过程可分为6个时期,整个发育过程仅见雄蕊原基的分化及生长。栝楼雌花为"两性花",分化过程可分为7个时期,存在雌蕊和雄蕊共同发育阶段,后期雄蕊发育败退。本研究明确了不同性别栝楼花芽发育发生的各个阶段、形态变化特点、外部形态变化特征以及雌雄花芽的分化差异,建立了雌雄花芽内部结构分化与外部形态之间相关性,为栝楼早期幼苗鉴定及性别分化研究提供了一定的参考。