M. Takamiya et al., BIOSYSTEMATIC STUDIES ON THE GENUS ISOETES (ISOETACEAE) IN JAPAN .2. MEIOTIC BEHAVIOR AND REPRODUCTIVE MODE OF EACH CYTOTYPE, American journal of botany, 83(10), 1996, pp. 1309-1322
Meiotic behaviors and reproductive modes of Japanese Isoetes were stud
ied. The hexaploid (2n = 66) and the octaploid (2n = 88) of I. japonic
a consistently formed 33 and 44 bivalents, respectively, at diakinesis
and/or metaphase I in both micro- and megaspore mother cells. The tet
raploid (2n = 44) of L sinensis formed 22 bivalents and its hexaploid
made 33 bivalents in both types of spore mother cells. At diakinesis a
nd/or metaphase I of microspore mother cells in I. asiatica with 2n =
22, 11 bivalents were detected. Because behaviors of meiosis in all cy
totypes mentioned above were quite regular and plants yielded normal-a
ppearing spores, they should reproduce sexually. Aneuploids of I. japo
nica with 2n = 87 formed 43 bivalents and one univalent, and L sinensi
s with 2n = 65 formed 32 bivalents and one univalent in microspore mot
her cells. Meiosis of both cytotypes was almost regular and yielded mi
crospores of normal appearance. In the heptaploid (2n = 77) of I. japo
nica, a configuration of 22 bivalents and 33 univalents was detected i
n micro- and megaspore mother cells, and various irregularities were o
bserved throughout the meiotic divisions. Therefore, the genomic formu
la 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 r
egularly formed bivalents and odd-numbered ones displayed irregulariti
es, allopolyploidy should act as a significant speciation mechanism in
this genus.