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To determine the mechanism of male-sterility Cryptomeria japonica tree Shindai3, the process of microspore development was observed under light and fluorescence microscopy. Microspore development in the Shindai3 was normal until the tetrad stage, but separation of the microspores from the tetrads was not observed even after callose had been degraded. In contrast to the microspore stage in a male-fertile tree, amorphous substances were observed around tetrads in the Shindai3, and the amount of the amorphous substance increased from the middle of November to the middle of December. The substances are hypothesized to prevent the separation of individual microspores from tetrads by inducing adhesion between microspore cells within the tetrad or enclosing the tetrads. The form of the tetrads in the Shindai3 was maintained until just before the pollen dispersal season, but they ultimately degenerated. The results of this study indicate that the mechanism causing male sterility in Shindai3 differs from that previously reported for other male-sterile trees of C. japonica.

To determine a possible mechanism causing male and female sterility in Cryptomeria japonica male and female cones were collected from a C. japonica, tree, ShinDai2, that lacks pollen release and fertile seeds and specimens were processed to examine the development of pollen and female gametophytes using light microscopy and field emission scanning electron microscopy. Pre-meiotic development proceeded normally, but the formation of aberrant meiotic products was observed in cones of both sexes. In sterile microsporangia, heterogeneous microspore populations ranging from monads to polyads gave rise to mature pollen grains of non-uniform size. These pollen grains were covered with an amorphous layer and adhered to each other. In addition, they remained in the microsporangia and were not released even after the onset of pollen dissemination from fertile trees. In the ovules of sterile female cones, megaspores with abnormal shapes, numbers, and sizes formed, and the development of female gametophytes was arrested at the free nuclear or archegonium formation stages. These gametophytes collapsed, and no fertile embryo was generated. Results indicate that meiotic defects are important in the sterility mechanism.

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