Chapter 5 Genetic Analysis of Apomixis - cimmyt

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(Figure 4.2a,b,c). Their cytoplasm containsnumerous plastids and mitochondria, andplasmodemata are scarce or appear to be filledwith a cellulose-like matrix. The degenerationof meiotically derived megaspores and earlystages of aposporous initiation has recentlybeen investigated in Brachiaria brizantha. In thisgrass, aposporous initials appear to containdedifferentiated organelles reminiscent oforganellar populations found in pre-meioticMMCs (A.c. Guerra de Araujo and V. Carneiro,personal communication).Aposporous MegagametogenesisSeveral aposporous embryo sacs can developin a single ovule (Figure 4.2d). Aposporousfemale gametophytes show a differentorientation with respect to the micropylarchalazalaxis, and usually differentiateheterochronically with respect to each other.The transition from aposporous initial to onenucleatedembryo sac is characterized by anincrease in cell size (Figure 4.3a). The first signsof cellular polarity are the consequence ofvesicular fusion; two large vacuoles are formedat opposite sides of a centrally located nucleus.Cell wall thickness also increases, and noplasmodesmata can be discerned (Figure4.2d,e). In Pennisetum ciliare, the nucleusmigrates to the periphery of the cell beforedividing (Figure 4.3b). The first mitotic divisionis perpendicular to the long axis of the cell andusually close to the micropylar region of theone-nucleated embryo sac (Figure 4.3c). Thesecond mitotic division is synchronous in bothsister nuclei, giving rise to a four-nucleatedtype of embryo sac that lacks antipodals at thechalazal pole (Figure 4.3c,d).The Cellularized AposporousMegagametophyteThe second mitotic division is followed by thecellularization of individual nuclei. Little isknown about the processes that regulatecelll;llarization and differentiation ofaposporous megagametophytes.ln Pennisetllnlciliare, as in most reported aposporous species,female gametophytes usually contain twosynergids, an egg cell, and a single polarnucleus in the central cell; however, a variablenumber of female gametophytes (up to 20%in certain genotypes) may be composed of asingle synergid, an egg cell, and two polarnuclei. On rare occasions, embryo sacscontaining three polar nuclei and no synergidshave been observed. This variable organizationappears to be associated with the localizationof nuclei prior to cellularization, and suggeststhat positional information plays a role ingametophytic cell specification.In all aposporous grasses ultrastructurallyexamined to date, the egg apparatusdifferentiates with morphologicalcharacteristics similar to those found insexually functional synergids and egg cells.These cells are attached at the micropylar apex,but the triangular organization of the eggapparatus is not necessarily conserved, as theunreduced egg cell may appear in a morelateral position with respect to one of thesynergids. Except for the presence of thefiliform apparatus, few differences are foundin the ultrastructural constitution of thesynergids and the egg cell in unpollinatedpistils of Panicum maximum. The three cellsappear vacuolated, with a centrally locatednucleus, and organelles preferentially locatedin the n:icropylar pole (Figure 4.2f,g,h).Naumov'a and Willemse (1995) characterize
Ultra.t..ct.raI baty.;. of Apamldk D...lop....' 49Figure 4.1 Integumentary embryony in Euonymus macroprera.(a) JunctiDn between meristematic integumentary tissue and endosperm, x5.000; (b) and (e) Micropylar region of ovules containingmeristematic integumentary tissue embryocytes and endosperm (bl, x570, and integumentary embryo (c), x850; (dl Seed with threeintegumentary embryos at different developmental stages, x 130; (e) Initial cells of integumentary embryo at micropylar region, x850; (f) Integumentary cell adjacent to the endosperm, x8.500; (g) Cell wall junction between an integumentary cell and endosperm,x42.500; (h) to (j) Cell walls tangenlialto the meristematic integumentary cells; (hl, x34.000; (il, x 10.200; li)' x42.500.Abbreviations on following page.
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(over illustration:Pictured is an i
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Institut de Recherche pour Ie Devel
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iv33 Outlook33 References35 Appendi
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vi131 Screening Procedures: Advanta
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VIIITables4 Table 1.15 Table 1.29 T
Page 12 and 13: xAcknowledgmentsWe are grateful to
Page 14 and 15: xiifood crops such as maize, wheat,
Page 16 and 17: 2 Gary H. T....i.....much food as i
Page 18 and 19: 4 Gary H. Toe"'...breeding: the evo
Page 20 and 21: 6 Gary H. T....it....The potential
Page 22 and 23: Chapter 2Apomixis and the Managemen
Page 24 and 25: 10M.. Be,th.dcategories n + nand 2n
Page 26 and 27: 12 J.&eo BertIoaodtwo tetraploid sp
Page 28 and 29: 14 JoG.. B.rth""dTable 2.8 Distribu
Page 30 and 31: 16 M......thodhexaploidy through 2n
Page 32 and 33: 18 JI&.. lertIoaodheterozygous cond
Page 34 and 35: 20 JM Iertltaodmarkers to retain th
Page 36 and 37: 22 JoA•• BerthudFurthermore, if
Page 38 and 39: Chapter 3Classification of Apomicti
Page 40 and 41: 26 (llarIesf.(r••3) The Ixeris-
Page 42 and 43: simultaneous division of the proxim
Page 44 and 45: 30 (\aries f. Crao.differentiating
Page 46 and 47: 32 CWIts F. C,..haploids from norma
Page 48 and 49: 34 cales F. (,...Campbell, C. S., C
Page 50 and 51: 36 GaOO F. er...media. There may al
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Page 54 and 55: 40 CWIes F.
Page 56 and 57: 42 C"Ie
Page 58 and 59: Chapter 4Ultrastructural Analysis o
Page 60 and 61: 46 T.""". N. Naomo•• ..dJ...·P
Page 64 and 65: 50 Tomaro N. Naurnovo ond Jeon-Phil
Page 66 and 67: Figure 4.2 (cont'd)
Page 68 and 69: 54 Tamara N. Nauma.a and J...-Phaip
Page 70 and 71: 56 Tamara H. Haumaya ...d J...-Phmp
Page 72 and 73: 58 Tamara N. N....... Old JOGO-PUIp
Page 74 and 75: 60 T.mar. N. N••may•••dJ
Page 76 and 77: 62 Tamara N. Nouma.o and Jeon-Phmpp
Page 78 and 79: Chapter 5Genetic Analysis of Apomix
Page 80 and 81: 66 Robe" T. SherwoodIn mitotic dipl
Page 82 and 83: 68 ••It T. Sllorwoodmegasporoge
Page 84 and 85: 70 Robert T. SherwoodIdentification
Page 86 and 87: 72 R....11 T. SlMrwoodwe postulate
Page 88 and 89: 74 Rob.rt T. Sherwoodin the gametop
Page 90 and 91: 76 Rokrt T. SHtwoodPerhaps the most
Page 92 and 93: 78 Robe" T. S~erwoodEnvironment pla
Page 94 and 95: 80 Robert T. SherwoodBanaglio, E. 1
Page 96 and 97: 82 Robe" 1. Sherwood---. 1989. Apom
Page 98 and 99: 84 Dcaitl ~11i-, lot To...., .od Di
Page 100 and 101: 86 Do.lel Griome/I-, Joe To~ ....,
Page 102 and 103: 88 Oaoitl G
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Page 106 and 107: and meiotic or developmental mutant
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Page 110 and 111: 96 10k. G.(o,.,..mechanisms (Figure
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98 Jolo.G.(_explain the existence o
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100 JolI.G.C....parameters affectin
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102 1010. G.(arma.was developed in
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104 J... G.(.....effects), which co
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106 J.hG.eforseveral thousand to a
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108 Jelo.G.(_large linkage group in
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11 0 Joh. G.(orma.---. 1997. Asynch
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112 a... A. 8icUeI1993). Before the
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114 ROil A. 8idlooll(Sherwood et al
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116 R... A. IkbeIlinduced mutation
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118 Ron A. Mlltllstudies of apomixi
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120 I... A. BkbollLeblanc, 0., M.D.
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122 Olivier L.bla.,.ncI A.d,ea M.nu
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124 Olivier lt~1ao< aod Aock.. Mau"
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126 OIlrier Ltblaooc ood AocI...Mo,
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128 or..Ie, leblal( allll Aodrea Ma
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130 Ofjyier LH......AodrH Mom","Mar
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132 Olivier leblaoc and Aldr.. Mall
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134 OIivie' I
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136 or..io. u.~100< awd Aod.... M.n
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138 udda lorge. do Val. aod Joh W.
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140 Ca
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142 C«ida Jorge. do Va" aod Jah W.
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144 (..iIda 80rges cit Va" DOd Ja~.
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146 Cacido ....... Vole..J.b W. MIe
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148 Ca
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150 (adlda Borge. da VaNe and Joh.
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152 Ccdda Borge. do v..... J.h W. M
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154 Yve< 5
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156 rn. s.mdaosearch for an opitimu
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158 Yv•• Savid..unreduced polar
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160 Yves SoviclaoBashawet al. (1970
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162 hOI Scrvidao211 = 56 chromosome
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164 r.., SaYid..Transfer of Gene(s)
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166 rves Sqyldaounanswered. However
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Chapter 12From Sexuality to Apomixi
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170 lie. Gros..iklalSgametes and em
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172 Uti Gro....1aosGunning 1990). T
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174 UeIGr.........embryogenesis, wh
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176 U.IGm..lln.apomictic pathway wi
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178 IJeIGr.........development with
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180 Ud Gr....lIoo,(Rhoades and Demp
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182 Ue5Gro........Meiosis is an alm
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184 Uel Gn...lIDo,To date, the phen
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186 Uei Gr....lIa..do not display p
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188 UtI GrOSllilaot.development of
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190 Ud e;,....1Ia..Arabidopsis, unp
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192 Ueli Gro".llae,system to identi
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194 UeI Gm..ikIonsystem developed b
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196 Ud Gro...ild...concentrate our
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198 lleIG
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200 UtlG09".ila,ndescribed that are
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202 UeIGfo...ll...Two additional po
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204 Uel G.....ilcmDiboll, A.G., and
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206 UeRG'....ild...--.1974. Reprodu
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208 Uel GtO,,"ikIa..MIodzik, M., Y.
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21 0 Ud Gromild.1S--.1982. Nature e
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Chapter 13Induction of Apomixis inS
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214 Uta Praebll aod Rod ScottCrosse
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216 Uta Praektlt.. Rod Scana minori
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21 8 Uta P...ke~ .d Rod S
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220 Ura P"",k.h .d Rod ScottStubby
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222 Uta Praekelt Old Rod S,ollelong
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224 Uta P...kek .d Rad Scaliresulti
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226 Uta P,..kelt ..dRod S
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228 Uta P..utt aod Rod 5
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230 1\omas Dresselhaus, Joh. G. (IJ
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progression or inhibition of develo
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234 T1lo.... Dr......... Jo~. G. (.
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236 TIoo.... D........., J.~. G. (a
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238 T1tonoas Dr......... Joino G. '
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240 no- P,ossdlaos, Jo. G.'-.... Y.
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242 1110""" 0,........, M. G. c,.._
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Chapter 5 Genetic Analysis of Apomixis - cimmyt

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