Studies On Cytology Of Six Speceis In Subtribe Chrysantheminae And Reproductive Biology On O.taihangensis

The Compositae family(subtribe Chrysantheminae) comprises 27 genera in China(Ling and Shih 1983),including Dendranthema sensu stricto and its closely related genera Argyranthemum,Tanacetum,Pyrethrum,Opisthopappus and Crossostephium.These genera which have many excellent genes lacking in cultivars of Dendranthema are important parents of creation of chrysanthemum germplasm and renovation of cultivars.Karyotype and meiotic analyses of six species in the subtribe Chrysantheminae are studied by conventional pressed slice method,we also study Megasporogenesis,microsporogenesis,development of gametophyte and embryogenesis in O.taihangensis using paraffin wax of Hemerocallis citrine Baroni., which can provide the oretical clues for use of these promising germplasm.The results show that:(1) Pyrethrum coccineum(Willd.) Worosch.is tetraploid and the other five species are diploids.Chromosome modality is diverse.Karyotypes in most species consist of median centromere,submedian centromere besides Crossostephium chinense(L.) Makino with two terminal centromeres,Pyrethrum.parthenium(L.) Sm with two subterminal centromeres.We observe no satelalites in the six species.The classification of the karyotype in Pyrethrum coccineum(Willd.) Worosch.Shows 3A, whereas,the remaining genera are characterized as 2A.(2) Meiosis process of pollen mother cell(PMC) in six species are overall normal and simultaneous cytokinesis.The chromosome commonest configurations at metaphaseâ… of meiosis in diploid species are mainly 9â…¡,while Pyrethrum coccineum(Willd) Worosch.is 18â…¡,The chromosome pairing configurations at meiotic metaphaseâ… per PMC in Argyranthemum frutescens(L.) Sch.-Bip., Crossostephium chinense(L.) Makino,Opisthopappus taihangensis(Ling) shih, Pyrethrum coccineum(Willd.) Worosch,Pyrethrum parthenium(L.) Sm.and Tanacetum vulgare L.are 0.08â… +8.86â…¡+0.01â…¢+0.04â…£,0.04â… +8.61â…¡+0.02â…¢+0.17â…£,0.05â… +8.92â…¡+0.03â…£,0.15â… +16.39â…¡+0.01â…¢+1.25â…£,0.07â… +8.86â…¡+0.02â…¢+0.04â…£,0.21â… +8.82â…¡+0.04â…£,respectively.A few of chromosome bridges,laggard chromosomes micronucleus and nonsynchronous division are found in some PMCs at anaphaseâ… andâ…¡,telophaseâ… andâ…¡.It suggests that chromosome translocation or inversion has occurred.(3) The anther is tetrasporangiate,the development of antherwall follows dicotyledonous type.The anther wall includes 4 layers:epidermis,endothecium,middle Layer and tapetum.The middle layer vanishes when microspore tetrads appear;the tapetum is glandular and its peak of growth comes at the time of the meiosis of the microspore mother cells and then as being in degeneration;the tapetum vanishes at the time of 3-uncleates pollen grain.The microspore tetrads are tetrahedral,the mature pollen grain is of the 3-nucleates type,and has 3 germinal apertures.(4) The pistil has an ovary that contains one anatropous ovule,dual-integument, tenuinucellatae,the development of embryo follows the oenothera type.The archesporial cell below nucellus epiderm functions directly as the megaspore mother cell,and the megasporocyte undergoes two successive divisions to form a linear tetrad with four haploid megaspores,the megaspore at the micropylar end continues to develop into a functional megaspore whereas the others gradually degenerate;The embryo undergoes the stages of globular embryo,heart embryo,and torpedo embryo to develop into mature cotyledon embryo.Many pollen grains can germinate on the stigmas and come into embryo sac.