Anatomy and Development of One-Seeded Fruits in Lespedeza buergeri (Leguminosae), with Emphasis on the Joint Structure

2008·4.4 MB·English

by  Tomoyuki Nemoto

植物研究雑誌
J.Jpn.Bot.
Originals
83:203–212(2008)
Anatomy and Development of One-Seeded Fruits in Lespedeza buergeri
(Leguminosae), with Emphasis on the Joint Structure
Tomoyuki NEMOTO and Wataru AIDA＊
DepartmentofBasicSciences,FacultyofScienceandEngineering,IshinomakiSenshuUniversity,
Ishinomaki-shi,Miyagi,986-8580JAPAN
E-mail:[email protected]
＊Presentaddress: Nagaoka-shi,Niigata,940- JAPAN
(ReceivedonMarch1,2008)
Fruit development in Lespedeza buergeri were anatomically studied. The one-
seeded fruits of the species have a structure of joint which separates the fruit into two
segments: the distal part including the seed and the proximal one including the stipe of
the fruit. The pericarp basically consists of outer epidermis, hypodermis, parenchyma,
sclerenchyma and inner epidermis. The sclerenchyma in the distal part is composed of
fibres, while that in the joint region is composed of non-fibrous and lignified
brachysclereids.Aparenchymatoustissueisinsertedintothesesclereidsatthejoint,giv-
ingrisetoaseparationtissue.Theinnerepidermiscellsonbothsidesofthepericarpwall
adhere to each other and participate in formation of the joint region. In addition, the
sclerenchymas,orphloemfibresborneexternallytothreemainvascularbundlesthrough-
out the length of the fruit, are not formed at the joint region. The absence of phloem
fibresalsoappearstocontributetothestructuralweaknessofthejointaswellasthesepa-
rationtissue.Althoughthesclerenchymaofsclereidsatthejointregionandthatoffibers
of the rest of the fruit are continuously distributed beneath the inner epidermis, develop-
mental processes revealed that these two kinds of sclerenchyma have different origins
andarenothomologous:theformersclerenchymaisoriginatedfromtheparenchymatous
groundtissue,i.e.,mesophyll,oftheovarywall,whereasthelatterfromtheinnerepider-
mis. The wall thickening of the former sclerenchyma, moreover, begins earlier than the
latter and also the phloem fibres in the course of fruit development.
Key words: Anatomy, development, fruit, joint, Lespedeza buergeri, loment.
The genus Lespedeza is composed of fruit.Inmostgeneraonefruitconsistsoftwo
about 35 species, most of which are distrib- or more articles and a joint transversely
uted in temperate Asia and eastern North separates each of these articles. The genera
America (Ohashi 2005). The genus is attrib- attributed to the subtribe Lespedezinae, how-
uted to subtribe Lespedezinae of tribe ever, have 1-ovulate ovaries which give rise
Desmodieae (Ohashi et al. 1981, Polhill to 1-seeded fruits. These fruits have been re-
1994, Ohashi 2005). One of the characteris- garded as to consist of only one 1-seeded ar-
tics of the tribe is the fruit which normally ticle(Ohashietal.1981).However,presence
consistsofindehiscentjointedarticles,called of the joint structure had not been investi-
the loment (Ohashi et al. 1981). There are gated in the 1-seeded fruit of the subtribe
variations among genera in shape of fruits Lespedezinae of tribe Desmodieae.
and articles and in number of articles per Nemoto and Ohashi (2003) studied ana-
—203—
204 植物研究雑誌 第83巻 第4号 平成20年8月
tomical structure of loments throughout the Results
tribe Desmodieae and showed the presence External features of fruit
of a joint structure only in Lespedeza among The fruit of Lespedeza buergeri is nar-
four genera examined in subtribe Lespede- rowly and obliquely elliptic, bilaterally flat-
zinae: Campylotropis, Kummerowia, Lespe- tened, acuminate at the apex and cuneate at
deza and Phylacium. However, the features the base, 10–12 mm long, 4–4.5 mm wide
of the joint structure need to be clarified and stipitate (Fig. 1). Because of the 1-
moreindetailforfurtherconfirmation.Inthe ovulate ovary, only one seed is included in
presentpaper,therefore,theauthorsintended the chamber of the fruit. At the basal part of
to provide anatomical structure and develop- the fruit just above the stipe there is a small
mental origin and stages of the joint region area of less than 1 mm long (jr in Fig. 1),
in the fruit of Lespedeza buergeri Miq. in both margins of which appear to be slightly
detail, which is the same species examined constricted at the distal end of the area.
by Nemoto and Ohashi (2003). When it is dried, the mature fruit is usually
broken easily at the centre of the small area
Materials and Methods and divides into two parts: the larger distal
The pericarp was examined externally and part containing the seed and the smaller
anatomically in Lespedeza buergeri Miq. proximal one including the stipe. The distal
Such materials as flower buds, flowers, and part therefore falls down from the plant,
young to mature fruits were collected from while the proximal one usually remains on
natural population in Ishinomaki-shi, Miyagi the plant. The easily broken plane function-
Pref., Japan in 1992 and preserved in FAA. ally corresponds to the “joint” of loment.
The voucher specimen (Nemoto 8643) was By staining with phloroglucinol-HCl after
kept in TUS. removing half of the pericarp, the tissues in
For morphological observations, mature the basal area of the fruit were stained red
fruits were dissected and half of the pericarp except for the centre that makes the fragile
was removed and stained with 1(cid:1) phloro- line of the joint (Figs. 1, 2). The phloro-
glucinol in 95(cid:1)ethyl alcohol acidified with glucinol-HCl staining indicates that the cells
HCl to detect liginified tissues and their constructing the joint region except for the
distribution. For anatomical observations, centre corresponding to the joint are
flower buds, flowers and young to almost lignified.
mature fruits were dehydrated through a
t-butyl alcohol series and embedded in Anatomical features of fruit
paraffin (mp. 58–60°C), and serially cross In the larger distal part of the fruit five
and longitudinally sectioned to 10 µm thick- layers of tissues are recognized in the
ness. Sections were stained with safranin O pericarp: outer epidermis, hypodermis, pa-
and fast green FCF, and mounted with renchyma,sclerenchymaandinnerepidermis
Entellan. (Fig. 3). The outer and inner epidermides are
Observations were performed with a bi- outer- and innermost tissues of the pericarp,
nocular microscope and a light microscope. respectively, and they are one cell thick. The
To detect sclerenchymatous tissues we also hypodermis is located beneath the outer epi-
used the light microscope under polarized dermis and is one or two cells thick. The
light transmitted by crossed two polarizing parenchyma is three to five cells thick and
filters. Photographs were taken by Leica DC contains vascular bundles. The sclerenchyma
200 digital camera, and printed by Olympus is located beneath the inner epidermis and is
Camedia P-400 printer. composed of elongated fibres of two to three
August2008 JournalofJapaneseBotanyVol.83No.4 205
Figs.1–4. MorphologicalandanatomicalfeaturesofmaturefruitsinLespedezabuergeri.Leftistheproximalside
of the fruit and right is the distal side. 1, 2. Fruit stained with phloroglucinol-HCl after removing the half of
the pericarp, showing lignified joint region (jr, sc) stained with phloroglucinol-HCl. 1. Lateral view of the
wholefruit,showingthepositionsofjointregionandjoint.2.Jointregionenlarged,showinglignifiedtissues
(sc)surroundingnon-lignifiedtissues(p).3,4.Longitudinalsectionsofpericarp,stainedwithsafraninOand
fast green FCF. 3. Pericarp in the area facing the seed, showing stratification of the tissue: outer epidermis,
hypodermis, parenchyma, sclerenchyma and inner epidermis. The sclerenchyma (sf) is composed of
circumferentiallyarrangedandnon-lignifiedfibres.4.Pericarpinjointregion,showingthickersclerenchyma
(sc) composed of lignified sclereids stained with safranin O than that (sf) composed of non-lignified fibres.
Parenchymatous tissues (p) are inserted into the sclerenchyma (sc). Some cells of inner epidermis (black ar-
rowhead)onoppositesidesofthepericarpadheretoeachother.Abrokenlineshowstheeasilybrokenplane
atthejoint.h.hypodermis.ie.innerepidermis.j.joint.jr.jointregion.oe.outerepidermis.p.parenchyma.s.
seed. sc. sclerenchyma composed of non-fibrous and lignified sclereids. sf. sclerenchyma composed of non-
lignifiedfibres.v.vascularbundle.Scalebars:1mm(1,2),100µm(3,4).
206 植物研究雑誌 第83巻 第4号 平成20年8月
cells thickness that are arranged circum- tains undeveloped vascular tissues. The
ferentially and not lignified. The cells of the thickness of the parenchyma is different be-
innermost cell layer of the parenchyma are tween those two parts: three to four cells
obviously smaller than other cells and often thick in the distal part of the ovary, while
contain crystals (Fig. 23). four to six cells thick in the proximal part.
In the joint region the pericarp is basically At anthesis (Figs. 8–10) the inner epider-
composedoffivelayersoftissueslikethatin mis of the ovary in the distal part thoroughly
the distal part (Fig. 4). However, the becomes two cells thick and the cells
sclerenchyma, although it is also located be- become longer in circumferential direction
neath the inner epidermis, is significantly (Fig. 9), which indicates that the inner epi-
different from that in the distal part in the dermal cells have simultaneously undergone
following features: the sclerenchyma of the periclinal division as well as slight elonga-
joint region is obviously thicker, two to five tion in a circumferential direction. However,
cells thick, and the component cells are non- neither such simultaneous periclinal division
fibrous sclereids, i.e., brachysclereids, with nor elongation is found in the inner epider-
lignified walls. The inner epidermis is one to mis in the proximal part of the ovary (Fig.
two(–three) cells thick and the cells are 10).
enlarged or elongated to adhere to those of Immediately after anthesis (Figs. 11–13),
the inner epidermis on the opposite side of the cells constituting the two-seriate inner
the pericarp (arrowhead in Fig. 4). The epidermis of the ovary, or young fruit, be-
parenchyma is three to five cells thick and come more elongated in the distal part (Fig.
located between the hypodermis and the 12). In the proximal part of the ovary, on the
sclerenchyma.Crystalliferouscellsarenotso other hand, neither periclinal division nor
much frequently found in the innermost cell circumferential elongation has occurred in
layer of the parenchyma. At the joint, more- the inner epidermis cells (Fig. 13). But the
over, there are parenchymatous cells inserted parenchymatous cells of three to four cells
into the sclerenchyma (p in Fig. 4), which thickness beneath the inner epidermis be-
give rise to the fragility of the joint. come slightly larger and their nuclei become
conspicuous.
Development of pericarp stratification In subsequent development of fruits (Figs.
The pericarp development was compared 14, 16), the inner stratum of the two-seriate
between the distal part and the proximal part inner epidermis becomes the inner epidermis
expected to be the joint region immediately and the outer one has undergone successive
before anthesis to almost fruit maturity. At periclinal division, resulting in a two-cell
the stage of flower bud immediately before thick layer whose cells become more slender
anthesis (Figs. 5–7), the ovary wall is distin- than those of the inner epidermis (Figs. 15,
guished into four layers of tissues in both 17). In almost mature fruits (Figs. 18–23),
parts: outer epidermis, hypodermis, paren- sclerenchymatous fibres, or phloem fibres,
chyma and inner epidermis (Fig. 6). The are observed externally to the main vascular
outer and inner epidermides are one cell bundles supplied along the adaxial and
thick. The hypodermis located beneath the abaxial sutures (pf in Figs. 18–21). At this
outer epidermis is one or two cells thick, and stage the two-cell thick layer beneath the
the cells contain some substances stained red inner epidermis has already changed to
with safranin O. The parenchyma, or the sclerenchymatous tissues composed of fibres
mesophyll of the carpel, lies between the which are detected by their thickened walls
hypodermis and inner epidermis and con- under polarized light (Figs. 22, 23).
August2008 JournalofJapaneseBotanyVol.83No.4 207
5
Figs.5–13. Transversesectionsofovariesimmediatelybeforeanthesis(5–7),atanthesis(8–10)andimmediately
afteranthesis(11–13).Topistheadaxialsideofovaryandbottomistheabaxialside.5,8,11.Sectionsmade
attheplaneincludingovule.6,9,12.Ovarywallsenlargedatthepositionfacingovulein5,8and11,respec-
tively,showingpericlinaldivisionssimultaneouslyoccurredintheinnerepidermiscells(blackarrowhead)ap-
proximatelyatanthesis.7,10,13.Sectionsmadeatthebasalpartofovary,showingthatthereisnoevidence
of periclinal divisions simultaneously occurring in the inner epidermis. Mesophyll cells (m) located between
vascularbundles(whitearrowhead)andinnerepidermisbecomestaineddarkerin13.h.hypodermis.ie.inner
epidermis.m.mesophyll.o.ovule.oe.outerepidermis.v.undevelopedvascularbundle.Scalebars:50µm.
208 植物研究雑誌 第83巻 第4号 平成20年8月
Figs.14–23. Transversesectionsofpericarpsmadeattheplaneincludingseedinthreedevelopmentalstagesfrom
immature(14–15and16–17)toalmostmaturefruits(18–23).Topistheadaxialsideoffruitandbottomisthe
abaxialside.19,21,23.Thesamephotographsas18,20and22,respectively,takenunderpolarizedlightto
showthepresenceofsclerenchymacellswiththickenedwalls.14,16.Sectionsincludingyoungseed,showing
twomainvascularbundles(whitearrowhead)alongadaxialsuture.15,17.Pericarpsenlargedatthepartfacing
seedin14and16,respectively,showingtheouterstratumoftwo-cellthicklayerthatwasoriginatedfromthe
innerepidermisbypericlinaldivision(cf.Figs.6,9and12),givingrisetotwo-cellthicklayer(blackarrow-
head) by further periclinal division. These cells are elongated circumferentially and become obviously more
slenderthanthoseoftheinnerepidermis.18–21.Pericarpsatupper(18,19)andlowersutures(20,21)offruit,
showing sclerenchyma cells (pf), or phloem fibres, located externally to vascular bundles (white arrowhead).
22, 23. Pericarp enlarged at the lateral side of fruit, showing sclerenchyma cells (sf) lying beneath the inner
epidermis.Thecrystalliferouscells(*)areformedexternallytothesclerenchyma(sf).h.hypodermis.ie.inner
epidermis.oe,outerepidermis.p.parenchyma.pf.phloemfibres(sclerenchymalocatedexternallytovascular
bundle).s.youngseed.sf.sclerenchymacomposedofnon-lignifiedfibresandlyingbeneathinnerepidermis.
v.vascularbundle.Scalebars:50µm.
August2008 JournalofJapaneseBotanyVol.83No.4 209
Figs.24–29. Transversesectionsofthreepericarps(24–25,26–27and28–29)madeatthejointinthesamefruits
asFigs.14–15,16–17and18–23,respectively.Topistheadaxialsideoffruitandbottomistheabaxialside.
24, 26, 28. Developmental changes and distribution of lignified sclerenchyma (sc) stained with safranin O,
showingparenchymatoustissues(p)insertedintothesclerenchyma.Someinnerepidermiscells(blackarrow-
head)ontheoppositesideofpericarpareelongatedtowardtheinsideandadheretoeachother.25,27,29.The
samephotographsas24,26and28,respectively,takenunderpolarizedlight,showingdevelopmentalchanges
of wall thickening in sclerenchyma cells (sc), inserted parenchymatous cells (p) without wall thickening and
theabsenceofsclerenchymacells(cf.pfinFigs.18–21)ontheoutsideofvascularbundles(whitearrowhead).
p.parenchyma.sc.sclerenchymacomposedofnon-fibrousandlignifiedsclereids.Scalebars:50µm.
Crystalliferous cells in a single cell layer are bundles, on the other hand, represent wall
also detected under polarized light between thickening in part (Fig. 25). As the fruit de-
the sclerenchyma and the parenchyma (Fig. velops, almost all of these parenchymatous
23). cells represent wall thickening and deposit-
During these later stages of fruit develop- ing lignin in their walls, resulting in the
ment, the proximal part has not represented sclereids for constructing the joint region
such successive periclinal division in cells (Figs. 26–29). Some cells, however, remain
beneath the inner epidermis (Figs. 24, 26, in parenchymatous state on both lateral sides
28). The parenchymatous cells that lie be- without wall thickening and depositing
tween the inner epidermis and vascular lignin (p in Figs. 26–29). These parts cor-
210 植物研究雑誌 第83巻 第4号 平成20年8月
respond to the parenchymas that participate basically similar to those of loments in
in formation of the fragile line of the joint Ornithopus of tribe Loteae (Kaniewski and
(Figs. 2, 4). During differentiation of the Waz·yn´ska 1968) and Hedysarum of tribe
sclereids some inner epidermis cells are Hedysareae (Mironov and Sokoloff 2000) in
elongated toward the inside and adhere with papilionoid legumes.
those of the opposite side (Figs. 4, 24). In The fruit of L. buergeri is supplied three
contrast with the distal part of the fruit, there main vascular bundles, two of them run
are no sclerenchymas formed on the outside along the ventral suture and the other along
of the main three vascular bundles in the the dorsal one. In mature fruits the
joint region (Figs. 25, 27, 29). sclerenchyma composed of fibres, termed as
phloem fibres, are externally associated with
Discussion these vascular bundles throughout the fruit
The morphological and anatomical evi- except for the joint region. The absence of
dence confirms the one-articulated nature of the sclerenchyma is also responsible for the
the one-seeded fruit in Lespedeza buergeri. weakness of the joint as well as the separa-
Developmental evidence, moreover, clarifies tion tissue.
the histological origin of the joint structure.
Developmental origin of sclerenchyma in
Characteristic structure of joint region joint region
The joint is formed at the base of seed In previous anatomical descriptions on
chamber of the fruit in L. buergeri. The tis- pericarps of legumes, three distinct layers
sue of the joint and its vicinity, or joint re- have been recognized, and they are referred
gion, consists of sclerenchymatous tissues to as exocarp, mesocarp and endocarp (Pate
composed of non-fibrous and lignified and Kuo 1981, Fahn 1982). The exocarp
sclereids and parenchymatous tissues. This usually consists only of an epidermis, but
parenchymatous tissue is inserted into the sometimes includes a hypodermis. The
sclerenchyma and facilitates separation of mesocarp consists of relatively thick paren-
the one-seeded article at the joint like the chyma, and the endocarp consists of
“separation tissue” (Fucskó 1914, Roth sclerenchyma and a thin-walled epidermis or
1977) of the loment. Moreover, adhesion a few parenchyma layers and an epidermis
between the inner epidermis cells on the op- on the inside. These three terms are, how-
posite sides of the pericarp wall also appears ever, used for purpose of description without
to contribute to the joint structure in L. relation to the ontogenetic origin of the lay-
buergeri. These anatomical features, referred ers (Esau 1960).
to as “Type C” by Nemoto and Ohashi In the pericarp of Lespedeza buergeri, the
(2003), are similar to the joints found in outer epidermis and hypodermis can be re-
some loments of such genera in tribe ferred to as the exocarp, the inner epidermis
Desmodieae as Eleiotis, which has one- andsclerenchymabeneathitastheendocarp,
seeded fruit like Lespedeza, and Alysicarpus andtheparenchymabetweenthehypodermis
(species attributed to Desmodiastrum), and sclerenchyma as the mesocarp. The en-
Desmodium (in part) and Trifidacanthus, docarp consists of two types of scleren-
these with two- or more-seeded fruit chyma: one is composed of non-lignified
(Nemoto and Ohashi 2003). In addition to fibres and the other composed of lignified
these genera of Desmodieae, the joint struc- sclereids, and both sclerenchymas appear to
ture composed of the sclerenchyma of be continuously distributed in the pericarp
sclereids and the inserted parenchyma is also (Fig. 4). The developmental evidence of the
August2008 JournalofJapaneseBotanyVol.83No.4 211
present study, however, clarified that these nor inner epidermis system was observed
two sclerenchymas have different origins. during development of the fruit in L.
The former is originated from the inner epi- buergeri, but the mesophyll of ovary wall
dermis of the ovary wall, whereas the latter mainly takes part in the making of joint
comes from the mesophyll lying between the structure.
outer and inner epidermis of the ovary wall.
Therefore, both sclerenchymas are not ho- This study was partly supported by a
mologous. The present observations, more- Grant-in-Aid for Scientific Research (C)
over, show that histological differentiation, from the Japan Society for the Promotion of
especially wall thickening, begins earlier in Science(09640821toTN).Wewouldliketo
the lignified sclerenchyma at the joint region thank Emeritus Professor H. Ohashi for his
than in the former one and also in another valuable comments on the manuscript.
sclerenchyma, or phloem fibres, on the out-
side of the main vascular bundles. References
Esau K. 1960. Anatomy of Seed Plants, 2nd ed. 550
Developmentaloriginofparenchymaatjoint pp.JohnWileyandSons,NewYork.
The parenchyma participating in the joint Fahn A. 1982. Plant Anatomy, 4th ed. 588 pp.
PergamonPress,Oxford.
structure is also originated from the
FucskóM.1914.StudienüberdenBauderFruchtwand
mesophyll of the ovary wall, and it is, there-
der Papilionaceen und die hygroskopische
fore, homologous to the characteristic Bewegung der Hülsenklappen. Flora 106: 160–
sclereidsinthejointregion.Theparenchyma 215.
canberegardedasanundifferentiatedpartof KaniewskiK.andWaz·yn´skaZ.1968.Developmentof
pericarp in Ornithopus sativus L. Bull. Acad.
the mesophyll. In tribe Desmodieae some
Polon.Sci.Cl.V.,Sér.sci.biol. 16:303–306.
loments possess joint regions composed only
Mironov E. M. and Sokoloff D. D. 2000. A
of sclereids, others possess those composed
carpological study of Eversmannia subspinosa
of sclereids more or less including paren- (Fisch. ex. DC.) B. Fedtsch. (Leguminosae,
chymatous tissues inserted into the centre as Hedysareae).FeddesRepert. 111:1–8.
a separation tissue (Nemoto and Ohashi Nemoto T. and Ohashi H. 2003. Diversity and evolu-
tion of anatomical structure of loments in tribe
2003). Thus, the structural diversity of the
Desmodieae(Papilionoideae).In:KlitgaardB.and
joint region in loments may be related with
BruneauA.(eds.),AdvancesinLegumeSystemat-
somemechanismscontrollingthedifferentia- ics10.pp.395–412.RoyalBotanicGardens,Kew.
tion or suppression of sclereids from the Ohashi H. 2005. Tribe Desmodieae. In: Lewis G.,
mesophyll. Schrire B., Mackinder B. and Lock M. (eds.),
Legumes of the World. pp. 433–445. Royal
Fucskó (1914) mentioned that the paren-
BotanicGardens,Kew.
chymatous tissue, called “seed-cushion”
Ohashi H., Polhill R. M. and Schubert B. G. 1981.
(translated from “Samenpolster” by Roth
Tribe Desmodieae. In: Polhill R. M. and Raven P.
(1977)), is originated from the inner epider- H. (eds.), Advances in Legume Systematics 1. pp.
misoftheovarywallandparticipatesinjoint 292–300.RoyalBotanicGardens,Kew.
formation for the loments of Coronilla, Pate J. S. and Kuo J. 1981. Anatomical studies of
legumepods–apossibletoolintaxonomicresearch.
Hippocrepis and Ornithopus. Kaniewski and
In:PolhillR.M.andRavenP.H.(eds.),Advances
Waz·yn´ska (1968) also mentioned that the
in Legume Systematics 2. pp. 903–912. Royal
inner epidermis cells give rise to a tissue BotanicGardens,Kew.
called “the inner epidermis system” by PolhillR.M.1994.ClassificationoftheLeguminosae
periclinal division and participate in the andcompletesynopsisoflegumegenera.In:Bisby
F. A., Buckingham J. and Harborne J. B. (eds.),
making of joint structure in Ornithopus
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1: Plants and their constituents. pp. xxxv–lvii. Handbuch der Pflanzenanatomie, Encyclopedia of
Chapman&Hall,London. PlantAnatomy,Spez.Teil.,Bd.X,Teil1.675pp.
Roth I. 1977. Fruits of angiosperms. In: Zimmermann GebrüderBorntraeger,Berlin.
W.,CarlquistS.,OzendaP.andWulffH.D.(eds.),
根本智行, 相田 渉＊：キハギ (マメ科) の1種
子果実の節構造
ハギ属はマメ科マメ亜科ヌスビトハギ連に分類 ンOで赤色に染まり, したがって, リグニンが沈
されている. ヌスビトハギ連の特徴の1つは, 種 着した厚い細胞壁をもつ短形厚壁異型細胞から構
子と種子の間に折れやすい節構造をもつ節果 成される. また, 節では厚壁組織に柔組織の貫入
lomentとよばれる果実をもつことである. 節果の がみられ, これが節の分離組織 (separationtissue)
節で折れて生じる種子1個を含む断片は小節果 として機能している. 節周辺部では向かいあった
articleとよばれている. ハギ属では子房に胚珠が 果皮の内表皮どうしで接着がおこり, これも節構
1個しかできないため, 1種子からなる果実とな 造の形成に関与している. さらに, 果実では腹側
り, これが1小節果からなる節果とみなされてき (向軸側) 縫合線に沿って2本および背側 (背軸
た. しかし, 節構造の存在を示す証拠は長らく実 側) 縫合線に沿って1本の計3本の主要な維管束
証されなかった. Nemoto and Ohashi (2003) はヌ が走行しており, 維管束のすぐ外側には維管束と
スビトハギ連全体について節果の解剖学的研究を 平行する果実長軸方向に伸長した繊維細胞からな
行い, ハギ属の果実にも節構造が存在することを る厚壁組織 (師部繊維) がみられるが, 節周辺部
報告した. 本論文ではハギ属キハギの果実におけ ではこの厚壁組織が発達せず, このことも節の折
る節構造の解剖学的特徴とその発生過程を報告す れやすさに寄与していると思われる.
る. 節周辺部を形成する短形厚壁異型細胞からなる
キハギでは節構造が子房の基部に形成される. 厚壁組織とそれ以外の部分で内表皮のすぐ外側に
成熟した果実は, 節構造により, 種子を含む果実 形成される繊維細胞からなる厚壁組織は, 連続的
先端側断片と果実の柄を含む基部側の断片とに分 に分布するようにみえる. しかし, 発生過程の観
離する. 果皮には, 外側から内側に向かって外表 察から, 前者は子房壁の葉肉から, 一方後者は子
皮, 下皮, 柔組織, 厚壁組織, 内表皮の5つの組 房壁の内表皮から由来することが判明し, 両者は
織層がみられる. しかし, 先端側断片では, 基部 相同ではないことがわかった. さらに, 前者の厚
の節周辺部を除いて, 厚壁組織は果実の横断方向 壁組織の厚壁化は, 後者の厚壁組織や師部繊維の
に伸長した繊維細胞から構成され, この繊維細胞 形成より早期に開始され, 形成時期も異なること
はフロログルシノール塩酸あるいはサフラニンO がわかった.
では染まらない. 一方, 節をはさんで2つの断片 (石巻専修大学理工学部基礎理学科
にまたがる節周辺部の厚壁組織は, 繊維状になら ＊現住所：新潟県長岡市 )
ず, フロログルシノール塩酸あるいはサフラニ