Histopathology of Seed-Borne Infections - Applied Research Center ...

Recommendations

Info

Reproductive Structures and Seed Formation 13homotypic division. The simultaneous type of wall formation is common in dicotyledonsand the successive type is common in monocotyledons.Recent studies using TEM and fluorescence microscopy have shown that duringearly stages of prophase of heterotypic division of meiosis, plasmodesmatal connectionsoccur between the tapetum and sporogenous cells as well as among thesporogenous cells, forming a syncytium. Subsequently, from pachytene I to telophaseI, the sporogenous cells gradually develop refractive walls of callose. The synthesisof callose is retarded during homotypic division. The callose isolates the microsporocytesand microspore tetrads from the tapetum and also from one another (Westerkeyn,1962). The autoradiographic study of Heslop-Harrison and Mackenzie (1967)has shown that the labeled thymidine derivatives do not penetrate microspore mothercells or microspores when they are surrounded by callose. Any irregularity in calloseformation results in male sterility (Frankel, Izhar, and Nitsen, 1969).2.3.1.2 Development and Structure of Male GametophyteWith the formation of microspore tetrads, the callose starts to dissolve due to theaction of b-1,3-glucanase (Stiegelitz and Stern, 1973). The microspores of a tetradusually separate, and the uninucleate microspores become more or less spherical(Figure 2.3G, H). Further development of uninucleate microspores follows a uniformpattern in angiosperms (Figure 2.4A to F). The microspore nucleus divides mitoticallyforming a generative cell close to the wall and the vegetative cell. Electronmicroscope studies have revealed that the formation of a wall around the generativecell corresponds to that in other cells (Karas and Cass, 1976). The generative cellacquires a spindle shape in the pollen grain. The generative cell divides in situ(Figure 2.4G, H) or after pollination in the pollen tube to form two sperms(Figure 2.4I, J).Mature pollen grains have a double wall, the exine and the intine (Figure 2.3I,J). The intine is thin and made up of pectocellulose while the principal componentof the exine is sporopollenin, derived from tapetum. The exine is thick andremarkably durable. The intine and the exine also contain enzymes (proteins) thatare released at the time of fertilization and degrade the cuticle of stigma papillae(Tsinger and Petrovskaya-Baranova, 1961). The intine proteins are the secretoryproducts of pollen protoplast whereas the proteins of the exine originate from thetapetum. The exine proteins are involved in the penetration of the pollen tube intothe stigma and also in pollen–stigma interaction that determines the incompatibilityrelationship (Heslop-Harrison, 1975).2.3.2 CARPELOne of the distinctive features of the angiosperms is the carpel, which bears theovules. A typical carpel consists of three parts, the basal fertile region — the ovary— and two sterile parts, the style and the stigma. The gynoecium is termedapocarpous when carpels in a flower are free, or syncarpous when carpels becomefused. In some angiosperms, the carpels are not completely closed, e.g., Degenaria,Drimys, and Reseda. Butomaceae, Hydrocharitaceae, and intraovarian pollen grainshave been reported in Butomopsis and Reseda.
14 Histopathology of Seed-Borne InfectionsvegetativecellABCDgenerativecellEFGHmale gametespollen tubeImale gametesJFIGURE 2.4 Development of male gametophyte. A, Newly formed microspore. B,Microspore showing vacuolation and wallward position of nucleus. C, Microspore nucleusdividing. D, Two-celled microspore. E, Generative cell losing contact with wall. F, Generativecell lying free in the cytoplasm of vegetative cell. G, H, Division of generative cell in pollengrain to form male gametes. I, J, Division of generative cell in pollen tube to form malegametes. (From Maheshwari, P. 1950. An Introduction to the Embryology of Angiosperms.McGraw-Hill, New York.)2.3.2.1 OvaryThe ovary bears ovules internally at distinctive sites called placentae. The ovary insyncarpous gynoecia is multilocular with axile placentation or unilocular havingparietal, superficial, and free central placentae. In the unilocular ovary, with one orseveral ovules, the placentation may be basal or pendulous. In the monocarpellaryovary, the placentation is marginal.As mentioned previously, the carpel is vascularized with a median (dorsal) andtwo lateral (ventral or marginal) traces. The ventral traces unite partially or completelyand give out the ovular supply. Before fertilization, the ovary wall comprisesparenchyma and vascular bundles. It may have secretory canals as in Apiaceae(coriander and cumin) and calcium oxalate crystals as in Asteraceae. The epidermisis cuticularized, and the stomata and hairs may occur (Figure 2.5A, B, D, E).
Page 2 and 3: Histopathology ofSeed-Borne Infecti
Page 4: PrefaceThe book deals with only one
Page 8 and 9: The AuthorsDalbir Singh, Ph.D., for
Page 10 and 11: ContentsChapter 1 Introduction ....
Page 12 and 13: 4.3.2 Routes for Infection from Ova
Page 14: 8.4 Survival in Seed ..............
Page 17 and 18: 2 Histopathology of Seed-Borne Infe
Page 19 and 20: 4 Histopathology of Seed-Borne Infe
Page 22 and 23: 2Reproductive Structuresand Seed Fo
Page 24 and 25: Reproductive Structures and Seed Fo
Page 26: Reproductive Structures and Seed Fo
Page 31 and 32: 16 Histopathology of Seed-Borne Inf
Page 62 and 63: 3Structure of SeedsThe seed habit i
Page 64 and 65: Structure of Seeds 49(1971) of usin
Page 66 and 67: Structure of Seeds 51is found in as
Page 68 and 69: Structure of Seeds 53dry seed of Ly
Page 70 and 71: Structure of Seeds 553.3.2 SEED COA
Page 72 and 73: Structure of Seeds 57Endosperm: One
Page 74 and 75: Structure of Seeds 59scendembepsmuA
Page 76 and 77: Structure of Seeds 61Endosperm: Sca
Page 78 and 79:
Structure of Seeds 63Chalaza simple
Page 80 and 81:
Structure of Seeds 65stystypmerA Bc
Page 82 and 83:
Structure of Seeds 67epsent endCADB
Page 84 and 85:
Structure of Seeds 69perhscendembpe
Page 86 and 87:
Structure of Seeds 71eposgepi′epo
Page 88 and 89:
Structure of Seeds 73(Zea and Sorgh
Page 90 and 91:
Structure of Seeds 75Baker, D.M. an
Page 92 and 93:
Structure of Seeds 77Maheshwari Dev
Page 94:
Structure of Seeds 79Vries, M.A. de
Page 97 and 98:
82 Histopathology of Seed-Borne Inf
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
100 Histopathology of Seed-Borne In
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
TABLE 5.6Location of Mycelium of St
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 214 and 215:
7Seed Infection by VirusesViruses a
Page 216 and 217:
Seed Infection by Viruses 201TABLE
Page 218 and 219:
Page 220 and 221:
Seed Infection by Viruses 205Unlike
Page 222 and 223:
Seed Infection by Viruses 2073. The
Page 224 and 225:
Seed Infection by Viruses 209Wilcox
Page 226 and 227:
Page 228 and 229:
Seed Infection by Viruses 213floret
Page 230 and 231:
Seed Infection by Viruses 215ptowvv
Page 232 and 233:
Seed Infection by Viruses 2177.4.2
Page 234 and 235:
Seed Infection by Viruses 219seed(s
Page 236 and 237:
Seed Infection by Viruses 221AMV fo
Page 238 and 239:
Seed Infection by Viruses 223REFERE
Page 240 and 241:
Seed Infection by Viruses 225Hunter
Page 242:
Seed Infection by Viruses 227Wolf,
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
Page 295 and 296:
Page 297:
show all

Histopathology of Seed-Borne Infections - Applied Research Center ...

Create successful ePaper yourself

Delete template?

Save as template?