Gametophyte Development And Cytological Studies Of Oogenesis In The Fern Dryopteris Tsoongii Ching

Oogenesis is a key part of sexual reproduction in ferns.The developmental characteristics of oogenesis vary with their evolutionary status.Dryopteridaceae is a large family in ferns.In different classification systems,the species,genera and evolutionary status are different.The study of oogenesis is valuable for elucidating the mechanism of fertilization and revealing the evolutionary relationship of ferns.Therefore,Dryopteris tsoongii Ching was selected as materials to study its gametophyte development and oogenesis.The purpose of this study is to elucidate the cytological mechanism of oogenesis and fertilization of Dryopteris sightseeing,and to reveal the evolutionary status of dryopteridaceae.As can be seen above:1.The type of spore germination is Vittaria-type.The growth type of prothallium is Aspidium-type.The mature gametophytes are symmetrical or asymmetrical heart-shaped.After 45 days of spore inoculation,the archegoniums were observed under the growth point of gametophyte.In the lower part of the archegonium or in the base or middle part of the prothallus,the existence of Antheridium can also be found.2.The archegonium of Dryopteris tsoongii Ching was originated from the initial cell.After the division,the initial cell form a primary cell,a top cell and a basal cell.Then,the primary cell in the middle was divided into a central cell and a mononuclear neck canal cell.The trapezoidal central cell divided unequally into a young egg and a ventral canal cell.After that,the mononuclear neck canal cell becomes a binuclear neck canal cell.So far,the newly formed binuclear neck canal cell,a trapezoidal primary egg and a ventral canal cell are closely connected with each other.With the development of egg,separation cavity formed between the egg and the neck canal cell.After that,pore region,egg envelope and fertilization pore are gradually formed above the egg.After the egg is nearly mature,the two canal cells will begin to degenerate and formed amorphous flocculent substance.3.The cytological characteristics of oogenesis of Dryopteris tsoongii Ching are roughly the same as those of the subfamily of Eupolypods.With the accumulation of the endoplasmic reticulum layer to the plasma membrane,the continuous filling of osmiophilic vesicles,and the flocculent matter in the separation cavity gradually disappearing after approaching the egg,it is speculated that they stack together to form a "reticular" egg envelope.The fertilization spore is located off center.It is worth noting that the nuclear division of the mononuclear neck canal cell occurred after the central cell division,which is similar to most ferns in Pteridaceae,and different from Eupolypods,indicating that the phylogenetic position of Dryopteridaceae should be in the front of Eupolypods,belonging to the transitional group of Eupolypods and Polypods.4.The histochemistry of oogenesis showed that PAS reaction was positive in the two canal cells,which indicated that there were polysaccharide substance,but the PAS reaction of egg envelope not significant,which showed that the main component of egg membrane was not polysaccharides.During the whole process of sexual reproduction,the plastids and starch granules in the cells have gone through the process from less to more,from small to large,and finally to small or disappear.The changes of plastid and starch granule indicate the storage and consumption of energy in cells.The time and state of plastid and starch granule changes are different in different cells:Plastids can be observed throughout the development of egg cells.However,the plastids and starch grains of two canal cells and parietal cells are less disappeared after egg maturation.The whole process is similar to the energy utilization characteristics of ferns.As can be seen from the above,this study revealed the oogenesis and cytological changes of Dryopteris tsoongii Ching for the first time.The separation cavity and pore area appeared successively above the egg cell,followed by the formation of the egg envelope and fertilization pore,which indicated that Dryopteris tsoongii Ching belonged to the evolutionary fern.The disappearance of flocculent substance in the separation cavity,reticular egg envelope and off-central fertilization pore all indicate that Dryopteris tsoongii Ching belongs to Eupolypods.However,the division time of neck canal cell is different from the other species of Eupolypods.However,It is similar to some ferns in the Pteridaceae.It is inferred that Dryopteridaceae is a transitional group between them.