Histological aspects of microsporogenesis in fertile, cytoplasmic male sterile and restored fertilePetunia hybrida.

A comparative histological study is made of microsporogenesis in fertile, cytoplasmic male sterile and restored fertilePetunia. Microsporogenesis in sterile anthers proceeds normally until leptotene. The development of the restored fertile type at 25°C is normal until the tetrad stage. In both types sporogenesis arrests and the meiocytes, c.q. microspores ultimately degenerate. The first phenomena of deviation are found in the tapetum. The effects of degeneration on cellular structure, vacuolation and cytoplasmic organization of the tapetal and sporogenous cells are variable. The deposition of callose around the meiocytes appears independent of the process of degeneration. The absence of an increase in callase activity possibly explains the remnants of callose found at late stages of development. The failure of callose wall dissolution appears to be the result of metabolic abnormalities in the tapetum and is regarded as an indirect effect of sterility.