Following their survey of cytoplasmic male sterility Laser and Lersten (1972, Bot. Rev. 38:425) proposed a diagrammatic scheme of normal microsporogenesis (MSG) which included eight cytological stages beginning with the onset of the sporogenous cell division and ending in the trinucleate pollen stage. In our study the determination of cumulative frequency--an indicator of microspore stage development--begins with the leptotene stage instead of the sporogenous cell stage and ends in the trinucleate pollen stage when the pollen is shed.
The relative frequencies of each of the eight cytological stages were estimated from a total of 3,404 upper flowers and are listed in Table 1, column 4. Approximately one-fifth (19.83%) of the MSG period was spent in the process of meiosis and within this meiotic period 92.3% (18.30/19.83) occupied meiosis I. Meiosis II, on the other hand, occupied only 1.53% (19.83-18.30) of the total MSG period or 7.7% (1.53/19.83) of the meiosis period.
Approximately four-fifths (80.17%) of the whole MSG period is spent in the maturation of pollen grains. The tetrad stage consumes 6.64% of the MSG period where four newly formed young microspores are still held together by callose. The length of the other stages can be seen in Table 1.
Sun-Yuan Hsu and Peter A. Peterson
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