Gametophyte Development And Cytological Studies Of Oogenesis In The Fern Equisetum Arvense L.

Sexual reproduction is the most important aspect in the studies ofReproductive Biology. But the studies of sexual reproduction in fern arestill weak among the plants. The Equisetaceae is the important group inferns according to the classification system which was provided bySmith in2006. However, it’s still not well konwn about the studies ofgametogenesis and sexual reproduction in Equisetaceae. Up now,studies about the spermatogenesis are more known than other aspectsin sexual reproduction. But there is no research about oogenesis whichhas important scientific significance in clarify cytology process,mechanism and the evolution of oogenesis in Equisetum arvense. Wechoose E. arvense as the experimental material in present thesis andmade a research about gametophyte development and oogenesis inmany aspects using the methods of the microscopic observation,cytochemistry studies and transmission electron microscope. Thepresent studies have the significance in clarify the cytology mechanismof oogenesis and reveal the evolution of sexual reproduction in fern.The major contents and results of this study are as follows:1. The development of gametophyte of E. arvense undergoes thestages of the germination of spores, filament and plates. The branchesof male gametophyte are strong and antheridium is formed at the endof the branches. The female gametophytes are more fine than themale ones. The archegonium is produced in the base region whichbetween two thin plate-like branches about two months. The length ofthe archegonium is about0.2centimeter and the neck of thearchegonium is formed by four rows of cells and looks like the cylinder.2. The section observations show that the archegonium of E.arvense is derived from the initial cell. The division order of the cells ofarchegonium of E. arvense is different to the advanced leptosporangiate ferns. The initial cell divides into two cells by a celldivision. The top cell is the neck jacket mother cell, which will becomethe jacket cells of archegonium, the bottom cell is the primary cellwhich divide into the neck canal mother cell and central cell by aperclinal division. Then the neck canal mother cell produce two obliquearranged neck canal cell whose size are different The central cell divideinto a ventral canal cell and an egg which go through the stage of eggdevelopment. With development, the neck jacket mother cell divideinto four cells by twice anticlinal divisions, then the four cells becomefour or five layers of jacket cells by3-4periclinal divisions. When thearchegonium becomes matured, the four end cells elongate quicklywhich could play a part in preventing the fertiization.3. The ultrastructural observations of oogenesis of E. arvenseindicate that there are some plasmodesma conections between thecanal cells and the egg in the younger stages of egg. Then theplasmodesma conection disappeared and the cells go into theindependent development stage. The canal cells secrete lots ofmucilaginous materials when they are degenerating and there aremany of the Golgi bodies and vesicles produced in the cells. The starchgrains in the plastid disappeared gradually. The shape of the canal cellsbecome irregular and will completely disappear. The typicalcharacteristic of egg is that the starch grains in the plastid become welldeveloped gradually and finally to form amyloplasts. There are also welldeveloped mitochondria in the egg cyoplasm. Compared with theadvance ferns there is no separation cavity formed during thedevelopment of egg and no egg envelop formed in the upper surfaceof the egg. As well as no fertilization pore and nuclear evaginationproduced in the egg.4. The histochemistry of oogenesis of E. arvense indicates thatdegenerated 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 whichcontain some small starch grain exist both in the egg and canal cells.With development of egg, the volume of the starch grain is becomebigger and the number also increase somewhat. But the volume of thestarch grains in the amyloplast of the canal cells becomes smallgradually and finally disappear. The staining of Sudan Black B indicatesthat there are lipid materials existing in the egg, which are emerge inthe middle and later stages of the egg development and forms clusterswhen the egg is matured.In conclusion, our study fristly clarify the particular process of thedevelopment of archegonium and oogenesis. It reveals the cytologymechanism of oogenesis of E. arvense and made the foundation forthe fertilization and the cytology mechanism of sexual reproduction forE. arvense.