Gametophyte Development And Cytological Studies Of Oogenesis In The Fern Macrothelypteris Torresiana

The gametophyte development and oogenesis of ferns is an important part of the study of sexual reproduction.There are great differences in sexual reproduction of the ferns of different systems.In the Eupoolypods of Smith system,sexual reproduction of Eupoolypods II has not yet been reported.Therefore,this paper select Macrothelypteris torresiana as materials,which belongs to the Eupoolypods II Thelypteridaceae.The gametophyte development and oogenesis were studied through microscopic observation on and ultrastructural observation and histochemical method.It has important significance to improve reproductive biology and explore the evolution of ferns sexual reproduction.The main results of this paper are as follows:1.Gametophyte debelopments underwent spore germination,filamentous,flaky,prothallus stages.Spore germination is Vittaria-type,prothallial plate is spade-shaped.The gametophytes are heart-shaped,it has single cell rod like hairy body.The archegonia occur after 35 d of sowing in beneath the growth point.The archegonia show a cylindrical shape and consist of four tiers of cells.Gametophyte development type is Drynaria-type.2.The light microscope observations show that the archegonium of Macrothelypteris torresiana is derived from the initial cell.The initial cell divides into three cells by twice cell divisions,top cell,primary cell and basal cell.Then the primary cell divides into an egg,a ventral canal cell and a neck canal mother cell.The three cells are closely connected in the younger stages of egg.With development,the ventral canal cell and neck canal cell gradually degradated.Separation cavity formed around the eggs.3.The ultrastructural observations of oogenesis of Macrothelypteris torresiana indicate that the egg,the ventral canal cell and the neck canal cell are connected by some plasmodesma in the young egg stage.The mitochondria,Golgi bodies and plastids in the egg cytoplasm are well developed.And the starch grains in the plastid are also well developed.The separation cavity formed during the early development of egg,but a connection area between the center of the upper surface of the egg and the ventral canal cell is still connected.It is called pore region.With the development,the separation cavity filled with a lot of uncertainty substances and the starch grains in the plastid are decreased gradually.The shape of nuclear change from circular to bowl.In the mid stage of maturing egg,a large number of vesicles are formed in the upper part of the cytoplasm of the egg.And many nuclear evaginations occurred in the surface of the egg cell nuclears.Despite there are mucilaginous materials deposited in the upper surface of the egg,but no egg envelop formed in the upper surface of the egg.When the egg nearly mature,the separation cavity still filled with a lot of uncertainty substances,but these substances do not deposite on the surface of the egg.However,the connection area between the egg and the ventral canal cell has been separated at this time.When the egg completely matured,the mitochondria is well developed and a lot of endoplasmic reticulum occurred in the cell.The color of egg plasma membrane deepened,a layer of uncertainty materials deposited on the outside of plasma membrane.This structure is different from the membrane structure of typical leptosporangiopsida.In the stage of maturing egg,the ventral canal cell and the neck canal cell secrete lots of mucilaginous materials when they are degenerating and there are many of the golgi bodies and vesicles produced in the cells.The starch grains in the plastid disappeared gradually.The shape of the two cells become irregular and will completely disappear.4.The histochemistry of oogenesis of Macrothelypteris torresiana indicates that degenerated materials that the canal cells produced is PAS reaction positive which could prove that these material are the polysaccharide.In the early stage of the development of egg,the amyloplasts which contain some small starch grain exist both in the egg and canal cells.With development of egg,the volume of the starch grain becomes small gradually and finally disappear.In this study,the detailed process and cytochemical changes of the oocyte and oocyte in Macrothelypteris torresiana were clarified for the first time.These studies indicate that the occurrence of oocytes in Macrothelypteris torresiana has undergone new eggs and developmental eggs,including the separation cavity,pore area,fertilized pores,exellus and organelles,and mature eggs.These characteristics have laid a foundation for revealing the mechanism of fertilization and sexual reproduction and the evolution of the Pteridophyte reproduction.