全 文 ：文章编号:1001-8220(2000)04-0328-04
Cytomixis during Microsporogenesis
in einkorn wheat
①
PENG Zheng-song
(Department of Biology , Sichuan Teachers College , Nanchong , 637002 , China)
ABSTRACT:Occurrence of cytomixis was detected in normal einkorn wheat(Triticum monococum L.).Presence of cytomixis was
restricted only in the synizesis stage of meiotic division.Transfer of nuclear materials from one pollen mother cell(PMC)to adja-
cent PMCs take place through cytoplasmic connections , and it occurred spontaneously and in specific direction within the PMCs.
Pollen abortion was not observed in this investigation , and normal seed setting was not affected in the plants which were affected by
cytomixis.At metaphase I some PMCs carried varied chromosomes , which caused abnormal separations occur in some PMCs at an-
aphase I.Because the abnormal PMCs were very rare , the Mendel′s segregation rate was still fitted.This was considered as the
cause that the effect of cytomixis could not be identified in general genetic analysis.
KEY WORDS:Wheat , cytomixis , chromosome mutation , meiosis , microsporogenesis
1　Introduction
　　Cytomixis was defined by Gates[ 1] as “an extrusion of chromatin from the nucleus of one mother-cell through cyto-
plasmic connections into the cytoplasm of an adjacent mother -cell” .This phenomenon was firstly described by
Kornicke
[ 2]
in pollen mother cells(PMCs)of Crocus sativus.It has been reported more commonly during microsporgenesis
in a wide range of angiosperms which include geneticly unbalanced types such as hybrids
[ 5] , mutations[ 3 , 4] , triploids[ 5 , 6]
and also in normal diploid
[ 7] .Opinions about the cause and significance of cytomixis have been extremely varied and con-
flicting.Woodworth[ 8] claimed it was an artifact , but Cooper[ 9] interpreted cytomictic figures as part of a regular process
involving the transfer of DNA from the tapetum into pollen mother cells.Mendes and Rijo[ 10] attributed cytomixis to the
occurrence of sticky chromosomal bridges during the last premeiotic anaphase.Others[ 7 ,11] believed it to be a genuine mi-
gration of chromatin during meiosis.It has also been considered as a possible cause of aneuploidy and polyploidy[ 11 , 12] ,
and even as one of the modes of origin of B chromosomes
[ 13] .This article reports the occurrence of cytomixis in the dip-
loid einkorn wheat and attempts to explain its significance.
2　Material and methods
　　The material used for this study was normal einkorn wheat(Triticum monococum L.), which was provided by Trit-
iceae Research Institute , Sichuan Agricultural University.Seeds were sawed in experimental garden of Sichuan teachers
college.Yong spikes were fixed in carnoy′s fluid.Chromosome numbers were counted at metaphase I and anaphase I of
the PMCs.Microsporogenesis was studied on slides that prepared by standard acetocarmine squashing , and cells were
① Received date:2000-12-2.
Foundation item:Financially supported by the Postdoctoral Science Foundation of China(grant 1999)and the Science and Technology
Committee of Sichuan Province(grant 1998)
　第 21卷　第 4期　　 　　　　四 川 师 范 学 院 学 报 (自 然 科 学 版 )　　　 　　　2000年 12月
　Vol.21　 No.4　　　 　　Journal of Sichuan Teachers College (Natural Science)　　　　　　Dec.2000
DOI :10.16246/j.issn.1673-5072.2000.04.007
stained with 1%propionic carmine.All meiotic phases were analyzed for enough cells perplant.Paraffin sectioning was
used to avoid any physical changes of cell structure in squash preparations , and stained following the Feulgen procedure.
All the figures were photographed with Olympus Wx50 microscope.
3　Results and discussion
　　At early synizesis stage of meiosis , the nucleus moved to one side of the PMC until the nuclear membrane was in de-
rect contact with the cell wall(Fig.1a).
Fig.2　Normal(a)and abnormal(b)PMCs at Metaphase I
of meiosis of einkorn wheat.(×500)
Fig.1 　Longitudinal sections showing the PMCs from anthers of
einkorn wheat(×140).a)the nuclear menbrane of PMCs is in di-
rect contact with the cell wall;b)chromatin substance in various nu-
clei has begun to migrate through walls into adjacent PMC
Then cytomixis took place simulta-
neously in all or some cells of the pol-
len sac(Fig.1b), and so far as ob-
served always in the same direction in
all of the cells.As soon as a PMC had
discharged its chromatin into one or
more neighboring cells , and the whole
invading chromatin had formed several
small lumps(Fig.1b), a new nucleus
was subsequently reformed.It was fol-
lowed by return of the nucleus to a cen-
tral position , and the later stages of
meiosis were progressing immediately.
This phenomenon , intercellular chro-
matin migration , is cytomixis.Cyto-
mixis occurred spontaneously in PMCs
of T.monococum at the synizesis stage
of meiosis.Before and after this stage ,
cytomixis almost not occurred at all.
The procedure of cytomixis in T .
monococum is very seminal to that in
Lilium davidii reported by Cheng et
al
[ 14] .
The chromatin substance may mi-
grate from one nucleus into an adjacent
cell.This was the most often observed
type.Other cytomixis pattern were oc-
curred some times , such as chromatin
substance migrate from one nucleus into
two or more than two cells , and from
two or more nuclei into one cell.
All the chromosomes were pared
in metaphase I in this investigation , indicating that migration phenomenon has initiated after chromosome pairing in this
material.Most of the PMCs at metaphase I showed 7 bivalents(Fig.2a), which was not affected by cytomixis and could
329　第 21卷第 4期 彭正松:一粒小麦小孢子发生过程中的细胞合并
produce normal microspores.But some abnormal PMCs were also observed(Fig.2b).Some PMCs carried varied chro-
mosomes.At anaphase I , chromosomal pares separated each other and moved to two polar.Normal 7+7separation were
observed(Fig.3a)most frequently in this experoment.In some PMCs , abnormal separations were taken place (Fig.
3b , c).Records indicated that abnormal PMCs are much less than the normal ones(Table 1).The percentage of PMCs
carrying more than 14 chromosomes is 0.94 , lower than those carrying lower than 14(3.14).
Fig.3　PMCs at anaphase I of einkorn wheat.a)Normal 7+7 separation(×500);b)abnormal
7+6 separation(×500);c)with lagging chromosomes(×250)
Table 1　Chromosome number of pollen mother cells in einkorn wheat
Chromosome number 8 10 12 13 14 15 16 17 28
No.of cells 1 4 10 5 612 0 4 0 2
Percentage 0.16 0.63 1.57 0.78 95.92 0 0.63 0 0.31
Although cytomixis is a common phenomenon among plants , the number of cells affected is usually expected for Vig-
na glaberscens
[ 15]
and Prunus amygdalus
[ 16] , for which the percentage of cytomixis was 41.42 and 97.00 , respectively.
In T.monococum , the percentage of affected PMCs ranged from 12 to 76 depending on the division stage.In addition to
true cytomixis , cytoplasmic bridges joining adjacent cells are common in affected plants[ 17 , 18] .In T .monococum plants
the frequency of these connections was higher than the frequency of cytomixis.Once contact between adjacent cells is es-
tablished , cytomixis may occur.
Cytomixis has been observed in countless species , its causes are still unclear.Several suggestions have been made
to explain its probable origin.Among them are fixation effects[ 19 , 20] , pathological conditions[ 21] , altered physiological co-
ntrols
[ 12] , changes in gene control[ 7] , the action of herbicides[ 21] and changes in temperature[ 22] .The material T.mono-
cocum studied here , normally grown during the cultived session and herbicides were not used.All the spikes used in this
experiment were collected from vigorous plants that showed no pathological trait.So it could be concluded that the cyto-
mixis is spontaneous occurred in T .monococum.
In many species in which cytomixis was observed , the phenomenon was closely correlated with pollen fertility[ 23] .In
T.monococum , cytomixis could not result in pollen sterility , because FCR test showed that higher than 98%male ga-
metes were vigorous.Nevertheless , some abnormal PMCs were indeed observed at anaphase I in this investigation.This
could result in occurrence of abnormal male gametes.However , the percentage of abnormal gamete is very much lower
than the normal ones.Statistic analysis indicated that these low frequency abnormal gametes could affect the segregation
rate of Mendel.This may the cause that genetics had not identified the effect of cytomixis.
330　　　　　　　　　　　　　　　四川师范学院学报(自然科学版)　　　　　　　　　　　　 2000年
References:
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[ 2] Kornicke M.Uber Ortsveranderung von Zellkarnern[ J] .Naturu.Heikunde Bonn , 1901 , 1:14-25.
[ 3] Datta A K , Biswas A K.Cytomoxis and tri somic in Nigella sativa L.[ J] , Cytologia , 1984 , 49:437-445.
[ 4] Gottschalk W.Chromosome and nucleus migration during microsporogenesis of Pisum.sativum[ J] .The Nucleus , 1970 , 13(1):1-9.
[ 5] Salesses G.Sur Le phenomene de cytomixie chez des hybrids triploids de prunier.Consequences genetiques possibles[ J] .AnnAmelior Plant , 1970, 20:383-388.
[ 6] Semyarkhina S Y , Kuptsou M S.Cytomixis in various form of sugarbeet[ J] .Vests I AN BSSR.Ser.Biyal , 1974 , 4:43-47.
[ 7] Omara M K.Cytomixis in Lolium perenne[ J] .Chromosoma , 1976, 56:267-271.
[ 8] Woodworth R H.Cytomixis[ J] .J Arnold Arbor , Harvard Univ , 1931 , 12:23-25.
[ 9] Cooper D D.The transfer of desoxyribose nuclei s acid from the tapetum to the microsporocytes at the onset of meiosis[ J] .Am.Nat.1952, 86:219-229.
[ 10] Mender E J , Rijo L.A new interpretation for cytomixis[ J] .Port Acta Biol , Series A , 1951, 3:211-218.
[ 11] Sarvella P.Cytomixis and the loss of chromosomes in meiot ic and somatic cells of Gossypium[ J] .Cytologia , 1958 , 23:14-24.
[ 12] Bell C R.Cytomixis in Tauschia nudicaulis[ J] .Cytologia , 1964, 29:396-398.
[ 13] Cheng K C , Nieh H W , Yang C L.Light and electron microscopical observations on cytomixis and the study of its relation to variation and evolution[ J] .
Acta Bot Sin , 1975 , 17:60-69.
[ 14] Cheng K C.The relationship between cytomixis , chromosome mutation and karyotype evolution in Lily[ J] .Caryologia , 1987 , 40(3):243-259.
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[ 16] Soodan A S , Wafai BA.Spontaneous occurrence of cytomixis during microsporogenesi s inAlmond(Prunus amygdalus Batch)andPeach(P.persica Batsch)
[ J] .Cytologia , 1987 , 52:361-364.
[ 17] Cansolaro M E L , Pagliarini M S.Cytomixis in pollen mother cells of Centella asiatica(L.)Urban(Umbelliferae)[ J] .The Nucleus , 1995 , 21:22-26.
[ 18] Sarbhoy R K.Spontaneous occurrence of cytomixis and syndiploidy in Cyanopsis tetragonoloba(L.)Taub[ J] .Cytologia , 1980 , 45:375-379.
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一粒小麦小孢子发生过程中的细胞并合①
彭正松
(四川师范学院生物系 , 南充市 , 637002)
摘　要:经检测 , 在正常的一粒小麦(Triticum monococum L.)中有细胞并合发生.细胞并合仅存在于减数分裂的凝线期 , 核
物质从一个花粉母细胞到邻近花粉母细胞的转移是通过胞质通道进行的.细胞并合的发生是自发的 , 且在花粉母细胞中有方
向性.本次调查中未观察到花粉败育现象 , 具细胞并合的植株结实也未受影响.中期 I一些花粉母细胞的染色体数目有变化 ,
这造成一些花粉母细胞在后期 I时出现非正常分离.由于异常花粉母细胞很少 , 孟德尔分离比例仍然成立.这被认为是在常规
遗传分析中不能检测出细胞并合的效应的原因.
关键词:小麦;细胞并合;染色体畸变;减数分裂;小孢子发生
中图分类号:Q2.21　　　文献标识码:A
331
① 收稿日期:2000-12-02.
基金项目:中国博士后科学基金(1999)和四川省科委应用基础研究基金(1998)资助项目.
作者简介:彭正松(1964-),男 , 四川安岳人 , 四川师范学院生物学教授 , 博士 , 主要从事植物遗传学与细胞生物学研
究.
　第 21卷第 4期 彭正松:一粒小麦小孢子发生过程中的细胞合并