01570nas a2200217   4500008004100000245010000041210006900141260001200210300001400222490000800236520085800244653001201102653002101114653001201135653001701147653002201164653001701186100001601203700001701219856011601236       1989                        eng d00aMorphogenetic plastid migration and microtubule organization during megasporogenesis in Isoetes0 aMorphogenetic plastid migration and microtubule organization dur  c1989///  a136 - 1470 v1523 aThe large megasporocytes of Isoetes provide an exceptional system for studying microtubule dynamics in monoplastidic meiosis where plastid polarity assures coordination of plastid and nuclear division by the intimate association of MTOCs with plastids. Division and migration of the plastid in prophase establishes the tetrahedrally arranged cytoplasmic domains of the future spore tetrad and the four plastid-MTOCs serve as focal points of a unique quadripolar microtubule system (QMS). The QMS is a dynamic structure which functions in plastid deployment and contributes directly to development of both first and second division spindles. The nucleation of microtubules at discrete plastid-MTOCs is compared with centrosomal nucleation of microtubules in animal cells where growth of microtubules involves dynamic instability. © 1989 Springer-Verlag.10aIsoetes10amegasporogenesis10ameiosis10aMicrotubules10aMitotic apparatus10aMonoplastidy1 aBrown, R.C.1 aLemmon, B.E.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-0001447651&partnerID=40&md5=8b7012cd1332d93eee67552099d26e3802381nas a2200253   4500008004100000245013000041210006900171260001200240300001600252490000700268520155900275653001501834653001101849653001201860653002101872653001201893653002301905653001501928653002201943100001701965700001701982700001201999856011602011       1996                        eng d00aBiosystematic studies on the genus Isoetes (Isoetaceae) in Japan. II. Meiotic behavior and reproductive mode of each cytotype0 aBiosystematic studies on the genus Isoetes Isoetaceae in Japan I  c1996///  a1309 - 13220 v833 aMeiotic behaviors and reproductive modes of Japanese Isoetes were studied. The hexaploid (2n = 66) and the octaploid (2n = 88) of I. japonica consistently formed 33 and 44 bivalents, respectively, at diakinesis and/or metaphase I in both micro- and megaspore mother cells. The tetraploid (2n = 44) of I. sinensis formed 22 bivalents and its hexaploid made 33 bivalents in both types of spore mother cells. At diakinesis and/or metaphase I of microspore mother cells in I. asiatica with 2n = 22, 11 bivalents were detected. Because behaviors of meiosis in all cytotypes mentioned above were quite regular and plants yielded normal-appearing spores, they should reproduce sexually. Aneuploids of I. japonica with 2n = 87 formed 43 bivalents and one univalent, and I. sinensis with 2n = 65 formed 32 bivalents and one univalent in microspore mother cells. Meiosis of both cytotypes was almost regular and yielded microspores of normal appearance. In the heptaploid (2n = 77) of I. japonica, a configuration of 22 bivalents and 33 univalents was detected in micro- and megaspore mother cells, and various irregularities were observed throughout the meiotic divisions. Therefore, the genomic formula of the heptaploid is symbolized as AABBCDE, and the heptaploid is a sterile F 1 hybrid between the hexaploid (AABBCC) and the octaploid (AABBDDEE) of I. japonica. Since diploid and even-numbered polyploids regularly formed bivalents and odd-numbered ones displayed irregularities, allopolyploidy should act as a significant speciation mechanism in this genus.10aChromosome10aHybrid10aIsoetes10amegasporogenesis10ameiosis10amicrosporogene sis10apolyplo id10areproductive mode1 aTakamiya, M.1 aWatanabe, M.1 aOno, K.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-0030475989&partnerID=40&md5=996182a1723b75d447e3a2137006f7bd