“…After the completion of meiosis and the initiation of microspore exine wall formation, the callose wall is broken down by callase, a tapetally secreted P-1,3-glucanase activity (Steiglitz, 1977), releasing free microspores into the locular space. In anthers of petunia and lily, callase activity follows a tight pattern of developmental regulation (Frankel et al, 1969;Steiglitz and Stern, 1973;Steiglitz, 1977). A relatively low leve1 of activity is present in anthers during the first meiotic division, but once the second meiotic division starts, this rapidly increases and peaks at the time of microspore release.…”