Study Of Submicroscopic Generative Structure In Isoetes Sinansis And I. Orientalis

The origin of Isoetes is in Triassic, and Isoetes is the relict genus of Isoeta cea. Now, there are 250 species of Isoetes all over the world. Sporophyte is aki nd of perennialherbaceous plant with short corm where linear sporophylls spirally arrange on; and the sporangia develop on the base of sporophyll. There are 200 to 300 megaspores in megasporangia and several hundred thousand microspores in microsporangia. Root dichotomously branch. Heteromorphy gametophyte living within sporoderm all life.Only Isoetes sinensis, I. orientalis, I. yunguinensis, I. taiwanensis and I. hyp sophila produced in our country, they are all the national level to protact and cri tically endangered. Most studiesare about I. sinensis which distributein Anhui, Jia ngsu, Zhejiang, Guangxi et al, with 2n=44 pieces chromosome; I. orientalis only distribute in the area where I. sinensis inhabited, with 2n=66 chromosome.There are many accesses studies of ecological, physiological, palynological,an atomical about these two kind of Isoetes, but there are no reports about ultrastra cture including the ultrastracture of generation. This textresearch the generational structure and development of these two species of Isoetes with light microscopy,scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The submicroscopic character of these two species are basically the same: th e development of spores are beginning with the meiosis of spore mother cell,tetr ads form firstly, and then young megaspores form. In the peroid of sporegenesis,tapetum is the major nutritive tissue. Formation of exospore is earlier than peris pore, and perispore and endspore almost over formation at the same time. The whole megaspore wall are composed by perispore, exospore and endospore. Exos pore has two layers, there are some grains between the inner layerand outer laye r. The separablelayeris on the inner surface of exospore, and sometimes the inner separable are divide into two layers, with light inner and dark outer.The proteo micis completed and big in the early stage of the gametogenesis. Following the development, proteomic dissolve and smash at last. Cells whichnear the crack of spore wall are completed with observed developed organelle, the other cells kee p the primeval stage. There is noneckchannelcell or ventercell, but two venter ch annel cells in the archegonium. A spheriform structureis consist of two venter ch annel cells, one ovum and a thick wall. Ovum is ahemisphere, one venter chann el cell is a smaller hemisphere and the other is discshaped.Ovum is dense, with irregular structure and narrow amyloplast.Littlevesicles and lipidsare in venter cha nnal cell. Microgametophyte produce four sperm cells, which have filiform dense mass inside and reticular dense mass outside. Spermatozoid have 12 flagellums, s perm nucleus, microtubularribbon and accessory mitochondria, but no dorsal crest,apical ridge and multilayered structure.During the embryogenesis, every part have some difference on ultrastructurec haracter. First leaf primordium have dense cytoplasm, and plastid and nucleus ar e most developed. Protein body can be observed in the developing sieve cells.Leaf septal verrucous intercellular pectic protuberances(IPP) in the two speci es are both obvious, numerous IPP in Isoetes sinensis are more than it in I.orien talis.In corm, prismatic layer is a group of pluripotent cells, they can become tra cheid, sieve cell or sclereid. There are one kind gracile root thiner thannormal di chotomously branched, with normal structure withouttracheid or sieve cell. Ligule cell have numerous endoplasmic reticulum and golgi complex, with secretion fun ction, and there are some grains in secretion.There are difference between progress of megasporangium and microsporangi um. Tapetal cell of megasporangium are consist of several layer cells, and it can be divide into inner and outer two parts. The inner parts have trophic function,and the outer parts produce megaspore mother cells. Megaspore mother cells ha ve no obvious plasma concentrate. Microspore mother cells have tapetal cell with one or two layers cells. Microspore mother cells have obvious plasma concentra te.Reproductive process of Isoetes sinensis and I. orientalis is similarin ultrastruct ure level, but spore, ligule, leaf septal et al have lots of difference.