Irregular meiotic behavior in Isoetes sinensis (Isoetaceae), a rare and endangered fern in China

Chromosomal abnormalities including cytomixis occurred in meiotic process of pollen mother cells of many angiosperm species at high frequency, but similar phenomenon was rarely reported in low vascular plants. This study we investigated the microsporogenesis of Isoetes sinensis Palmer, a quillwort of ancient heterosporous lycopsids Isoetaceae plants. Irregular chromosomal behavior especially cytomixis was emphasized. It appeared in each stage of meiotic division from prophase I to telophase II. The cytoplasmic channels between microspore mother cells were narrow and stretched. The genetic material connection was maintained mainly by visible chromatin fiber. The cytomixis was just occurred between two adjacent microspore mother cells of same stages. A variety of other abnormal chromosomal behaviors including chromosomal stickiness, fragmentation, bridge, laggards, micronucleus, were observed, albeit with low frequency. All sorts of chromosomal abnormalities were counted at two stages, anaphase I and anaphase II. They were approximately 24.4% and 26.9% respectively. This number was slightly higher than that of microspore abortion which was about 14.8%. I. sinensis was listed as a critical endangered species due to habitat fragmentalization, water pollution and wetland degradation. Human being activities are without doubt the immediate forces resulting in the population decreasing of I. sinensis. Whether the individual numbers dropping or habitat withdraw has consequently caused the producing of the overall high abnormalities of chromosomal behaviours is not determined yet. However, cytomixis and other irregular chromosomal phenomenon seemed not to be a natural process.