全 文 ：臭椿花器官分化的初步研究
?
王永周 , 古 松 ** , 任艳萍 , 许 珂 , 江 莎??
( 南开大学 生命科学学院 , 天津 300071 )
摘要 : 利用扫描电镜 (SEM) 和光镜 (LM) 对臭椿花序及花器官的分化和发育进行了初步研究 , 表明 : 1)
臭椿花器官分化于当年的 4 月初 , 为圆锥花序 ; 2) 分化顺序为花萼原基、花冠原基、雄蕊原基和雌蕊原
基。5 个萼片原基的发生不同步 , 并且呈螺旋状发生 ; 5 个花瓣原基几乎同步发生且其生长要比雄蕊原基
缓慢 ; 雄蕊 10 枚 , 两轮排列 , 每轮 5 个原基的分化基本是同步的 ; 雌蕊 5 , 其分化速度较快 ; 3) 在两性
花植株中 , 5 个心皮顶端粘合形成柱头和花柱 , 而在雄株中 , 5 个心皮退化 , 只有雄蕊原基分化出花药和
花丝。本研究着重观察了臭椿中雄花及两性花发育的过程中两性花向单性花的转变。结果表明 , 臭椿两性
花及单性花的形成在花器官的各原基上是一致的 (尽管时间上有差异 ) , 雌雄蕊原基同时出现在每一个花
器官分化过程中 , 但是 , 可育性结构部分的形成取决于其原基是否分化成所应有的结构 : 雄蕊原基分化形
成花药与花丝 , 雌蕊原基分化形成花柱、柱头和子房。臭椿单性花的形成是由于两性花中雌蕊原基的退化
所造成 , 其机理有待于进一步研究。
关键词 : 臭椿 ; 花原基 ; 花序 ; 性别分化
中图分类号 : Q 944 文献标识码 : A 文章编号 : 0253 - 2700 (2007) 06 - 639 - 09
Preliminary Study on Differentiation of Floral Organs of
Ailanthus altissima (Simaroubaceae)
WANG Yong-Zhou, GU Song
* *
, REN Yan-Ping, XU Ke, J IANG Sha
* *
( Nankai University, Collegeof Life Science, Tianjin 300071 , China)
Abstract: The investigation of the differentiation and development of inflorescences and flowers in Ailanthus altissima
(Mill .) Swingle (Simaroubaceae) using light microscopy (LM) and scanning electron microscopy (SEM) suggests: 1)
Flower bud differentiation of A. altissimaoccursinearlyApril on apaniclebearingmany flowers; 2) The sequenceof floral
development proceeds from calyx primordia to corolla primordia to stamen primordia and finally to carpel primordia . Five
sepal primordiaare initiated spirally and asynchronously . Fivepetal primordiaform nearlysimultaneously andgrowmoresl-
owly than the stamen primordia . The ten stamens are alternately arranged in two whorls; the two whorls develop simulta-
neously . The5-carpellategynoeciumgrows quickly . 3) In hermaphrodites, thefivecarpelsadhereto each other to formthe
styleand stigma; in staminateflowers, in latedevelopmental stages, thefivecarpels are sterileand fertilestamens differen-
tiate into anthers and filaments . In this paper, we focus on the morphological transition from bisexual to unisexual flower
development in A. altissima . We observedthat the primordiaof staminateflowersare initiated innearly the same way as in
hermaphrodite flowers ( although the timeof initiation of each organ is different) . The stamen and carpel primordia initiate
云 南 植 物 研 究 2007 , 29 (6) : 639～647
Acta Botanica Yunnanica

?
?? ?Author for correspondence; E-mail : songgu@ nankai . edu. cn; jiangsha@ nankai . edu. cn
Received date: 2007 - 03 - 19 , Accepted date: 2007 - 08 - 03
作者简介 : 王永周 (1982 - ) 男 , 在读硕士研究生 , 主要从事植物结构学研究。 ?
Foundation item: This research was supported by a Scholarship from the Scientific Research Foundation for Returned Overseas Chinese Scholars,
Scientific Research Foundation of Nankai University, Science and Technology of Maintain of Ecological SystemAnd AdaptabilityManagement on the
Interlaced Belt of Northern Grassland and Agriculture and Animal ( 2007CB106802 ) and Scientific Research Foundation of StateForestry Adminis-
trationof the P . R . China (“948”item) ,“Observation Technological Indraught of Characters of Soil Water and Heat in Arid Area” (2006 - 4 -
02) , Scientific Research Foundation of Tianjin (07JCYBJC12400 , 07JCYBJC12500)
simultaneously in both hermaphroditeand staminate flowers . Theformationof reproductive structures is dueto the differen-
tiation in the course of development of the floral primordia that form the anthers and filaments and?or styles, stigmas, and
ovaries . The formation of staminate flowers is dueto suppressionof the development of the gynoeciumin A. altissima . The
mechanismof transition from bisexual to unisexual flowerswill only be clarified by further study .
Key words: Ailanthus altissima; Floral primordia; Inflorescences; Sex differentiation
Ailanthus altissima (Mill ) Swing ( Ailanthus gla-
ndulosa Desf .; Simaroubaceae) , a deciduous tree
reaching about 20 m in height, occurs in north, east
and southwest China . It can withstand drought, toler-
ates saline and alkaline soils, is fast growing, and is
susceptible to few plant diseases and has insect pests .
Moreover, the plant is important in afforestation and
timber production . Until now, studies on A. altissima
havemainly focused on its physiological and biochemi-
cal properties (Cao, 2004; Gravano et al . 1999; Ha-
merlynck, 2001 ) , drug extraction and identification
(Lv and Xiong, 2002; Lv and Liu, 2003) and pollen
(Li , 2004 ) .
Here we wish to report on the development of
flowers in A. altissima . The differentiation of plant sex
is an interesting topic indevelopmental biology . Gener-
ally, there are three types of sex differentiation in flow-
ers: bisexual , unisexual ( staminate or pistillate) and
nonsexual . These types of flowers appear in many dif-
ferent plant groups and in diverse forms in plant popu-
lations . Wyatt ( 1983) reported that plant sex may be
divided into three levels: ( 1 ) single flower level ,
which include three types, hermaphroditic, staminate
and pistillate; ( 2 ) individual plant level , of which
there are seven types, hermaphroditic, monoecy, an-
droecy, gynoecy, andromonoecy, gynomonoecy and tri-
monoecy; and ( 3 ) population level , which includes
haploid and multitudinous groups . Dioecy, androdio-
ecy, gynodioecy and trioecy belong to the latter group .
Korpelainen (1998) reported that labile sex expression
in plants is seen as an ability to modulate sex expres-
sion is generally advantageous and can be viewed as
adaptation to unstable environments . How sex expres-
sion at three levels comes into being in nature is still
unclear .
There arevarious reportson sex expression inpla-
nts . For example, sex expression in the cucumber
( Cucumis sativus L .) is influenced by genotype and
plant hormones, such as ethylene ( Takahashi et al .
1983) . Sex differentiation in C . sativus appears to be
determined by the selective arresting of the stamen or
pistil primordia . When treated with an ethylene-releas-
ing agent or an inhibitor of ethylene biosynthesis at dif-
ferent developmental stages of the flower buds, sex de-
termination is influenced only at the stage of stamen
primordiadifferentiation in bothmonoecious andgynoe-
cious cucumbers ( Yamasaki et al . 2003 ) . In higher
plants that bear unisexual flowers, therefore, sex dif-
ferentiation occurs by the selective arresting of pre-
formed sexual organs in the flower buds during bisexual
development (Dellaporta and Calderon-Urrea, 1993 ) .
In most species, for examples in Silenelatifolia (Grant
et al . 1994 ) , asparagus ( Asparagus officinalis L .)
( Caporali et al . 1994 ) , Rumex acetosa L . (Ainsworth
et al . 1995) , Pistacia vera L . (Hormaza and Polito,
1996) , the flowers are morphologically bisexual during
the early stages of development, and ultimately unisex-
uality results from a secondary unbalanced growth in
the androecium and gynoecium . Additionally, sex ex-
pression insomeplants is related to resourceinvestment
(Doust et al . 1986 ) . In unisexual plants, cell death
in individual flower buds suppress oneor another organ
and lead to the abortion of organic primordia during an
early stage of sex determination . Cell death may take
placeduring the development of staminate and pistillate
organs, and during gamete formation ( Wu and
Cheung, 2000) .
Plants of Ailanthus are polygamous and dioecious
( Chen, 1997 ) . The transition from bisexual to unisex-
ual flowers is still unknown . Thegreatvariability in re-
productive systems in Ailanthus may offer clues in un-
derstanding the formation of sexual differentiation .
Consequently, wefocusedon themorphologyand struc-
tureof sexual transition . Detailed anatomical and mor-
phological observations on floral differentiation in A. -
altissima cansupply muchmoredataabout reproductive
biology, and provide information on the genetic control
of sexual determination for future molecular biological
studies in these plants .
046 云 南 植 物 研 究 29 卷
1 Materials and methods
Plants of Ailanthus altissima were grown in an openfield on
the campus of Nankai University, Tianjin City, China . Individu-
als of A. altissima (tree-of-heaven) with staminate and hermaph-
roditic flowerswas used for all analyses . Inflorescences and buds
at various developmental stages were obtained and fixed in FAA
(formalin: acetic acid: 50 % ethyl alcohol = 5∶6∶89 v?v) . Ma-
terial for scanning electron microscope (SEM) examination were
fixed in 4% ( v?v) glutaraldehyde in a phosphate buffer, fol-
lowed by dehydration through an ethyl alcohol series, sputtered
with gold and examined by SEM (S-3500N) and photographed .
2 Results
2 .1 ?Morphology and structure of the inflorescence
and flower
The inflorescenceof Ailanthus altissima is an api-
cal panicleon new branches . The flowers arepeagreen
and borne on a pedicel 1 - 2 .5 mm long . Five sepals
alternate with fivepetals, which have rigid hairs at the
bilateral base . The 10 stamens are arranged in two
whorls, the outer five stamens are opposite the petals
and the inner five are opposite the sepals . Rigid hairs
are at the base of linear filaments . The filaments are
longer than the petals in the staminate flowers, but
shorter in the hermaphroditic flowers . The anthers are
oblong . Five carpels are opposite the petals . In the
staminate flowers, the five carpels aredegeneratewhen
the flowers are mature, whereas in the hermaphroditic
flowers, they develop into an apocarpous gynoecium
with a fused style and 5-lobed stigma . The flowering
phase lasts fromearly April to late May .
2 . 2 ?Initiation and development of inflorescence
primordia
2 .2 .1 The transition of SAM from vegetative growth
to the reproductive growth Oblong axillary buds oc-
curs in the axils of newly formed branches in early May
of the first year . Threeor four primordiaof compound,
alternate leaves are revealed when 2 or 3 scales are re-
moved . Thevegetative apical meristem, in the shapeof
a dome (PlateⅠ : 1) , is slightly protuberant and lat-
erally elongated . It produces the primordia of com-
pound leaves . During the winter, that scales that cover
the apical meristem and young leaves become thicker
and harder . In early April of the secondyear the outer
scales become looser, the buds grow to about 1cm
long, and the leaves increase in length .The budsgrow
rapidly and form new branches . The apex of the new
branches elongates and continually produces leaf pri-
mordia . The main inflorescence axis arises in the axil
of compound leaves . The primordia of the main inflo-
rescence axis are flat ( Plate Ⅰ : 2) .
2 . 2 .2 Initiation of the primordia of main inflores-
cence axes Shoot apical meristem ( SAM ) produces
the primordia of the compound leaves and inflores-
cence, which are complex in Ailanthus altissima . The
primordiaof the main inflorescence axis are located in
the axils of the primordia of compound leaves and ap-
pear oblate . On the two sides of each main inflores-
cence axis, a pair of bract primordia forms ( PlateⅠ :
3) . In late April , differentiation of primordia of the
main inflorescence axes is completed and SAM differ-
entiates the bract primordia . Three to eight main inflo-
rescence axes are simultaneously arranged at the apex
of new branches . The primordia of the lateral inflores-
cenceoccur on eachmain inflorescenceaxis (PlateⅠ :
4) . With the development of inflorescence primordia,
the primordia of the compound leaves gradually degen-
erate .
2 . 2 .3 Initiation of primordia of lateral inflorescence
The primordiaof the lateral inflorescences formin
the axils of the developing bract primordia (Plate Ⅰ :
5) , which formthe first branches of thewhole inflores-
cence axes .Later, the primordiaof thelateral inflores-
cence axes develop further . New bracts and lateral in-
florescence primordia, which form the secondary
branches, are generated from the base of the first
branches (PlateⅠ : 6) . No additional branchesgener-
ate on the secondary branches . The floral primordia
form on the ends of each secondary branch . The
branches of the inflorescence appear as compound
raceme-like inflorescences .
Thelateral inflorescence areinoppositepairs, but
form asynchronously ( Plate Ⅰ : 7 ) . After the transi-
tion of the apical meristemfromvegetative to reproduc-
tive, there are about 15 layers of branches on each ma-
in inflorescenceaxis . The first branchesoccur from1 to
6 layers . The secondary branches only occur from 1 to
2 layers . Flowers, which are about6 to7 layersof near
the top of themain inflorescence axis, are 3 flowerlets
in a cluster and alternately arrange . The inflorescence,
which is a compound panicle of raceme-like branches
1466 期 WANG Yong-Zhou et al .: Preliminary Study on Differentiation of Floral Organs of . . .
Fig . 1 Diagram of inflorescence of Ailanthus altissima
(Mill .) Swingle plant
Prb . first branch; Seb . secondary branch
(Fig . 1) , and the flowers develop acropetally .
2 . 3 ?Differentiation and development of floral pri-
mordia
The floral organs begin to differentiate in late
April and finish in late May .Thesequenceof floral or-
gan differentiation is: calyx primordia, corolla primor-
dia, stamen primordia and pistil primordia .
2 . 3 .1 Differentiationof calyx primordia The apexof
the flower primordiumbecomes wider and flatter in late
April . The sepal primordia, which develop asynchro-
nously and spirally, initiate from the margin of the
flower primordium . The first initiated sepal is always
situated adaxially in the axil of a bract (Plate Ⅰ : 8) ,
the secondary sepal isopposite the first sepal and in an
abaxial position, the third is situated opposite thebract
(Plate Ⅰ : 9) , finally, the fourth and fifth primordia
differentiate between the first and second and first and
third sepal , respectively ( Plate Ⅰ : 10 ) . The apex of
the floral primordium further develops and expands to
become flatter due to the activity of the peripheral mer-
istem of the floral primordium (Plate Ⅰ : 11 ) .
2 . 3 .2 Differentiation of corolla primordia In early
May, with thedevelopment of sepal primordia, the flo-
ral primordia become wider and pentagonal in shape .
The petal primordia appear insideof and alternatewith
the sepals ( PlateⅠ : 11) . Thepetal primordia further
develop and become triangular, at which stage the sta-
men primordia appear ( Plate Ⅰ : 12) . The apparently
imbricate petals enclose the stamen primordia ( Plate
Ⅰ : 13) .
2 . 3 .3 Differentiation of stamen primordia The 10
stamens are arranged in 2 whorls of 5 (Plate Ⅰ : 13) .
In early May, five stamen primordia initiate simulta-
neously and alternate with the petals ( Plate Ⅰ : 12 )
followed by the remaining five stamenprimordia, which
are located between the stamens in the first row and
differentiate simultaneously and opposite the petals .
The stamen primordia rapidly develop into a globose
structure ( PlateⅠ : 14) . When the 10 stamenprimor-
diahavebecomeglobose, initiationof the pistil primor-
dia begins .
2 . 3 .4 Differentiation of carpel primordia In mid
May, the apex of the flower primordia changes from
dome shaped to flat . At the margin of the apex, five
hemispherical pistil primordia initiate opposite the pet-
als ( Plate Ⅰ : 14 ) . With the appearance of the pis-
tils, the stamen primordia differentiate into filament
and anther . The pistil primordia become conical and
the apex of thepistil primordia becomes concave ( Plate
Ⅰ : 15 ) . The five pistil primordia turn inward and
move closer to each other and toward the center ( Plate
Ⅰ : 16) . The development of the floral organs is iden-
tical in staminate and hermaphroditic flowers .
2 . 3 .5 Transition from hermaphroditic to unisexual
flowers In late May, the five carpels primordia of
hermaphroditic flowers turn inward ( Plate Ⅰ : 17 ) .
The apex of each carpel primordium bulges and the
bulges connect with each other ( Plate Ⅰ : 18 ) . The
bulges then expand laterally more than in other direc-
tions . Later, the styles and stigmas ( Plate Ⅰ : 20 )
differentiate from connected-bulges of a pentagonal
structure ( Plate Ⅰ : 19 ) . The styles, their base at-
tached to each of the five ovaries, quickly elongate
(Plate Ⅰ : 21 ) . With the initiation of the style and
stigma, the anthers and filaments become smaller and
shorter .
In staminate flowers, however, the differentiation
of floral organs differs from development in the her-
maphroditic flowers . The five carpels turn inward and
move close to each other, the same as inhermaphrodit-
ic flowers ( Plate Ⅰ : 22 ) , but then their development
stops at the stage when the five carpels are connivent
(PlateⅠ : 23) . Neither thestyle nor stigma arediffer-
entiated . At maturity of the anthers, the five carpels,
which are gradually surrounded by an external ridge
246 云 南 植 物 研 究 29 卷
(Plate Ⅰ : 24 ) , degenerate ( Plate Ⅰ : 25 , 26 ) . In
the staminate flowers, therefore, only stamens are ob-
served and the carpels are difficult to see . The differ-
entiationof thestyle and stigma in hermaphroditic flow-
ers and the degeneration of the carpels in staminate
flowers happens almost simultaneously .
In lateMay, most staminate flowers open, where-
as floweringis delayedby several days inhermaphrodit-
ic flowers . Additionally, some aberrant flowers in
which there are 6 petals, 12 stamens and 6 carpels in
one flower areobserved in both staminate and hermaph-
roditic flowers (PlateⅠ : 27 , 28) .
3 Discussion
3 .1 ?Differentiation of hermaphroditic and unisex-
ual flowers
Our study shows that A. altissima is an androdio-
ecious species with staminate and hermaphroditic indi-
viduals . The differentiationof floral organs in hermaph-
rodites is delayed about 4 or 5days in comparison with
staminate flowers . When petal primordia initiate in
hermaphroditic flowers, the carpel primordia begin to
differentiate in staminate flowers . Thedifferentiationof
floral organs is faster in staminate than in hermaphro-
ditic flowers . Most staminate and hermaphroditic flow-
ers open at the end of May . In hermaphroditic flowers,
when carpel primordia begin to differentiate the style
and stigma, the anthers are smaller and the erect fila-
ments areshorter than the petals . Instaminateflowers,
we noticed that the anthers are larger and that thebase
of the filaments bend so that the anthers and filaments
arewrapped by petals .
The development of the floral meristem in most
hermaphroditic, staminate and?or pistillate plants is
due to temporal and spatial regulation ( Ma, 1994 ) .
After floral primordia form, they are able to generate
sepal , petal , stamen and carpel primordia, respective-
ly . Our observations of A. altissima also confirmed
process . During floral development of A. altissima, the
processof floral organ development is identical in both
staminate andhermaphroditic flowersbeforeinitiationof
the style and stigma, but the timeof appearanceof the
floral organs differs . After initiation of the style and
stigma, essential differences appear between hermaph-
roditic and staminate flowers . In hermaphroditic flow-
ers, the stamens and carpels differentiate normally,
whereas in staminateflowers thereis normal stamendif-
ferentiation, and abnormal gynoecium initiation . This
phenomenon has also been observed in dioecious spe-
cies of wild grape ( Vitis vinifera ssp. sylvestris) (Cap-
orali et al . 2003 ) . The development of the floral or-
gans in wild grape is divided into eight stages: the de-
velopmental pathways of staminate and pistillate flowers
first begin to diverge at stage 6 . In pistillate plants,
the style and stigma differentiate normally, whereas
they do not differentiate in staminate flowers . In thedi-
oecious Asparagus officinalis sexual differentiation oc-
curs later in the initiation of flora organs: in pistillate
flowers, the stamens degenerate; whereas in staminate
flowers, theovary stopsgrowing, but does not degener-
ate ( Caporali et al . 1994) .
3 . 2 YFloral development and phylogenesis in an-
drodioecy
The characteristics of floral organogenesis may
play an important role indetermining theorigin and ev-
olutionof angiosperms and provide more important in-
formation about the relationship of plant species (Sun
et al . 1998) . Wolf (2001 ) indicates that androdioecy
is a rare andunusual breedingsystemin which popula-
tions contain both staminate and hermaphroditic indi-
viduals . Although androdioecy is rare, its maintenance
and evolution have broad implications for breeding sys-
tems .
Androdioecy is a rare phenomenon, but has been
proven in Datisca glomerata (Presl .) Baill . (Liston et
al . 1990 ) . Durand and Durand ( 1992 ) inaccurately
described sexual expression in Mercurialis ambigua L .
(Euphorbiaceae) as andromonoecy, whereas it should
have been referred to as hermaphroditic withboth stam-
inate and hermaphroditic flowers . Dioecywas suggested
to be the ancestral state, and both monoecy and andro-
dioecy were thought to be derived from dioecy in Mer-
curialis (Durand and Durand, 1992 ) . Current phylo-
genetic analysis shows that dioecy has evolved repeat-
edly from androdioecy in the genus Acer (Gleiser and
Verdú, 2005 ) . Although androdioecy either evolved
from hermaphroditism through the spread of a female-
sterility mutation, or a dioecious state through the evo-
lution of staminate function in females ( Pannell ,
2000) . All of the clearest examples of androdioecy in-
3466 期 WANG Yong-Zhou et al .: Preliminary Study on Differentiation of Floral Organs of . . .
dicate that it evolved fromdioecy, because related spe-
cies all have a dioecious sexual system ( Pannell ,
2002) . Schneider et al . ( 2006 ) analyzed the family
Quiinaceae using molecular phylogeny and found that
bisexual flowers ( Froesia) are ancestral in the family,
whereas androdioecy ( Quiina, Touroulia) and dioecy
( Lacunaria) are derived breeding systems . Although
there is no agreement on the evolution of androdioecy,
many studies indicate that it may arise fromdioecy and
not fromhermaphroditism .
3 . 3 ?Function of fertile structures in hermaphro-
ditic and unisexual flowers
Most studies that have looked at examples of an-
drodioecy have found evidence for cryptic dioecy in
which the morphologically perfect flowers are function-
ally pistillate ( Mayer and Charlesworth, 1991 ) . Cao
(2006) studied floral organogenesis and developmentof
Handeliodendronbodinieri (Lévl .) Rehd . (Sapindace-
ae) , the flowers of which are unisexual . In the pistil-
late flower, the ovary bulges and the stamens degener-
ate, whereas in the staminate flower, the stamens grow
normally but theovary degenerates .
In our observations, the A. altissima may be an
androdioecious species morphologically and structural-
ly, but it is difficult to explain the function of andro-
dioecious species . Because most studies of the mor-
phology of androdioecy have confirmed that androdioe-
cious species are actually functionally dioecious, al-
though pistillate plants are morphologically hermaphro-
ditic (Charlesworth, 1984) . Future studies may eluci-
date whether A. altissima is functionally androdioe-
cious .
3 . 4 ?The molecular mechanisms of floral organo-
genesis
During the last decade, after the ABC model of
genetic regulation of flower morphogenesis was put for-
ward, substantial work has been devoted to locating
and characterization genes controllingmeristemand flo-
ral organ identity . There is a great variety, however,
in floral architecture and organization within the plant
kingdomand it is critical toascertain thegenetic mech-
anisms responsible for this variability by investigating a
wider rangeof plant species ( Baum et al . 2002) . In
Atriplex halimus L ., day length and light intensity af-
fect sex ratio and flower distribution and flower position
on the reproductive axis, and thegeographical originof
the plant ( genotype) also affects sex and architecture
ratios (Talamali et al . 2003 ) . In Rumex acetosa L .,
a special stageof inappropriate arrested organ develop-
ment is correlated with the closed expression of the C
gene (Ainsworth et al . 1995) . In cucumber ( Cucumis
sativus) , sex is determined in unisexual flowers by the
selective repression of growth or the abortion of either
staminateor pistillate reproductiveorgans (Kater et al .
2001) . The changes in organ identity in the expression
patterns of B-function genes lead to sex determination
occurring in Asparagusofficinalis (Park et al . 2003) .
Interestingly, recently an AG-independent carpel de-
velopment pathway was found in Arabidopsis ( Pin-
yopich et al . 2003 ) .
Androdioecy ( mixtures of males and hermaphro-
dites) is a rarematingsystemin both theplant and an-
imal kingdoms . Specific mechanisms of androdioecy
have been most extensively examined in several species
(Weeks et al . 2005 ) . For example, in Eulimnadia
texana, maleness is determined by a recessive allele at
a single sex-determining locus (Sassaman and Weeks,
1993) . Vassiliadis et al . ( 2000 ) reports that a ga-
metophytic self-incompatibility systemwith links to nu-
clear sex determinismmay explain thehigh frequencyof
males by causing frequency-dependent selection . Wolf
( 2001 ) examined the sex-determining mechanisms in
the androdioecious species Datisca glomerata and its
dioecious sister species D. cannabina, using a combi-
nation of traditional genetic crosses and molecular
markers, and arrived at the following conclusions: (1)
sex in both dioecious and androdioecious species of
Datisca appears to be determined by a single nuclear
locus, at which the male-determining allele is domi-
nant; (2 ) the loci controlling sex determination in both
species may be homologous; ( 3 ) hermaphroditism is
recessive to femaleness and thus must have arisen as a
recessive mutation restoring staminate fertility in fe-
males . Our observations confirm that Ailanthus altissi-
ma is morphologically androdioecious, but the mecha-
nisms of formation of androdioecious plants need to be
clarified in further research . Molecular and genetic
studies of floral morphogenesis in species producing
unisexual flowers remain scarce . The above cited stud-
ies report exclusively on rudimentary and aborted or-
446 云 南 植 物 研 究 29 卷
gans . These studies clearly demonstrate, however, that
plants that produce diversified floral phenotypes offer a
uniqueopportunity for unraveling the genetic control of
flower development, which is complementary toworkson
classical hermaphroditic model species . Researchon the
developmental geneticsof floral organs and inflorescence
morphogenesis plays an important role in the molecular
mechanisms of the evolution of floral organs . Ailanthus
altissima obviously produces unisexual and hermaphro-
ditic flowers at inception . Its reproductive structures
arehighly plastic and amenable to environmental condi-
tions, makingit a unique and valuablesubject for clar-
ifying sex determination and development .
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Explanation of Plate
V . vegetative bud; L . compound leaf primordium; I . inflorescence pri-
mordium; B . bract primordium; a . apical meristem of shoot; LI . lateral
inflorescence primordium; F . floral primordium; Se . sepal primordium;
P . petal primordium; S . stamen primordium; C . carpel primordium
Plate Ⅰ : Floral organogenesis and development of Ailanthus altissima
(Mill .) Swingle under scanning electron microscope
1 - 16 Inflorescence and floral organogenesis in staminate and hermaphro-
dite 1 . Apical meristem of vegetative buds; 2 . Differentiation of pri-
mordiaof main inflorescence axes; 3 . Initiation of bract primordia; 4 .
Finishing of primordial differentiation of main inflorescence axes and shoot
apex; 5 . Initiation of lateral inflorescence axes primordia in axils of
bracts; 6 . Development of primordia of lateral inflorescence axes; 7 .
Mode of differentiation of primordiaof lateral inflorescence axes; 8 . Apex
of flower primordium and initiation of first sepal primordium; 9 . Initiation
of second and third sepal primordia; 10 . End of fifth sepal primordium
differentiation; 11 . Differentiation of petal primordia; 12 . Initiation of
stamen primordia; 13 . Tegular petals encasing stamen primordia; 14 .
Initiation of gynoecial primordia; 15 . Concave apex of gynoecial primor-
dia; 16 . Development of carpel primordia . 17 - 21 . Development of gy-
noecial primordia in hermaphrodites 17 . Five carpel primordia close to
each other; 18 . Initiation of stigma; 19 . Development of stigma; 20 .
Initiation of pentagonal stigma and style; 21 . Connected carpels at base
of style . 22 - 26 Development of gynoecial primordia in staminate flowers
22 - 23 . Five carpel primordia gradually becoming close to each other;
24 . Shrinking and diminishing five carpel primordia; 25 . Carpel primor-
dia further degenerated; 26 . Carpel primordia absent at anther matura-
tion; 27 . Six petals and twelve stamens in oneflower; 28 . Six gynoecial
primordia in one flower
646 云 南 植 物 研 究 29 卷
王永周等 : 图版Ⅰ WANG Yong-Zhou et al: PlateⅠ
7466 期 WANG Yong-Zhou et al .: Preliminary Study on Differentiation of Floral Organs of . . .