Study On The Cytological Feature Of Spore Exospore Development And Tapetum Cell Apoptosis In The Fern Osmunda Japonica

Spore development is an important aspect of fern monogenesis research, In this process, Tapetum of the sporangium plays a very important role in the formation of the spore wall development. The structure and development of exospore and tapetum are important basises of fern evolution research.Osmunda japonica Thunb.is between the original and primitive in the system evolution.We used light microscope,scanning electron microscope, transmission electron microscope,histochemical staining methods,to study the exospore developmental process,the formation of spore ornamentation and the process of tapetum apoptosis in the different development stage.Observed the ultrastructure of tapetum sporangium and chemical properties of each part, Discussed the formation and sources of the exospore of spores as well as the role of the tapetum Our study can help with development mechanism of fern spores and the rule of the evolution of tapetum apoptosis process,Has a certain scientific significance of reproductive biology of ferns and system evolution research. The main research results and conclusions are as follows:(1)The spore morphology: O. japonica spores has tetrahedron form, and bulge outward ridge shaped trilete on the polar surface, The diameter of polar surface is about 50 ?m. Spore has a more developed exospore.The exospore is thick,Which is construct of inner exospore and outer exospore,the outer exospore can be distinguished into two layers inside and outside. In the forming process,verrucous, rod-shaped ornamentations appears on the spore surface in turn,Spinules formed on the top of the rods,Then merge with ornamentations. Spherical particles distribution in the surface of mature spores.Ornamentations are formed from the outer exospore. Perispore exists and only has one thin layer.(2)The characteristics of exospore development:The O. japonica exospore has a complicated forming process.Inner exospore is formed in early tetrad stage, for polysaccharide substance.The first layer of outer exospore is made of multiple layers, and some fibrous and granular material,also for polysaccharide substance.Then exospore forming material change into sporopollen mass wrapped in lipid.Then the second layer of outer exospore formed.The second layer of outer exospore and perispore of mature O. japonica spores belongs to the lipid compounds.The whole process of the formation of the exospore is as exospore material deposition and aggregation.(3) The characteristics and functions of tapetum apoptosis:O. japonica has two layers of tapetum.The outer secrytory tapetum and the inner plasmodium.In the progress of exospore formation,cytoplasm in outer tapetum go through degradation first,however the cell wall structure remain.Inner tapetum cell wall fusion into plasmodium, invasion to the sporangium cavity,surrounded the spore tetrads.The plasmodium joined in the whole process of the exospore formation.In the development process of O. japonica exospore, Plasmodium showed the typical morphological characteristics of plant cell apoptosis,including:(1)The concentration and vacuolization of the cytoplasm, plasmamembrane invagination,(2)the degradation of organelles,the changing process of mitochondria,endoplasmic reticulum,golgi apparatus,cavitation,is gradually hydrolysis inclusions.The changing process of plasmid is twisted, deformation,broken and release starch ornamentations.(3)Nucleus chromatin condensed and agglutination. nucleus forming a random pieces, strewn at random within the nucleus,nucleolus structure remains till the end.In apoptosis process, plasmodium will change polysaccharide material into different forms of lipid as exospore material, secrete to the lumen. Early is fibrous and granular sporopollen element,Later is sporopollen element mass, these substances deposition to the spore surface,forming the spore wall.(4) The development of exospore and the characteristics of tapetum apoptosis has certain instruction significance for evolution:O. japonica spore is tetrahedron form which has trilete.It has thicker exospore,and less developed perspore. Ornamentations are formed from the outer exospore.These are same primitive characters.O. japonica has hybrid form tapetum.In the development of exospore, inner tapetum plasma total integration into plasmodium,has a good contact with spores,ensures high efficiency of nutrient absorption, this is advanced in all types of tapetum.In the process of apoptosis,O. japonica tapetum cell go through organelle degradation,chromatin condensed and other characteristics which is consistent with the angiosperms.Therefore we can come to the conclusion that the O. japonica is between the original and primitive in the system evolution.