FUNCTIONAL-ANATOMY OF THE OVULE IN BROAD BEAN, VICIA-FABA L .2. ULTRASTRUCTURAL DEVELOPMENT UP TO EARLY EMBRYOGENESIS

Ovules of broad beans (Vicia faba) have been studied to analyze ultras tructural features for nutrient transport to the embryo sac at various ontogenetic stages up to 10 d after pollination. In unpollinated flow ers a notable homogeneous or fibrillar material is deposited in the en dostome, between the two integuments and on the nucellus. Osmiophilic globules accumulate at the plasmalemma and in the walls at the micropy lar end of the inner integument. These globules increase in number aft er fertilization and appear also in other cells near the embryo sac. T he central cell, which has some wall ingrowths typical for transfer ce lls, shows intrusive growth between cells of the nucellar cap. After f ertilization wall thickenings occur in cells close to the embryo sac. At 10 d after pollination the inner integument has degenerated entirel y. Also the nucellus, including the nucellar cap, is digested. In the endosperm free-nuclear divisions start and the cytoplasm increases in amount. Wall ingrowths are formed along the whole embryo sac boundary. The suspensor consists of two pairs of multinucleate cells: the pair adjacent to the embryo proper have rounded cells; the other pair have elongated ones. The suspensor cells that are attached to the embryo sa c boundary become transfer cells. Their plastids have prolamellar bodi es, and these structures are not seen anywhere else in the ovule. Our study confirms that transfer cells are common at junctions between the different generations in the ovules, that the transport to the embryo sac is apoplastic, and that symplastic transport is possible between endosperm and embryo and further between suspensor and embryo proper.