The maize mutant polymitotic affects cell cycle events during microspore development

The maize (Zea mays L.) male-sterile mutant polymitotic (po) was analyzed utilizing in-vitro cell culture and immunocytochemistry methods to better understand the relationship between the mutant phenotype and cell cycle events during microspore development. Using a live meiocyte culture system, initiation and progression through abnormal post-meiotic cell cycles at the end of meiosis II was documented in the po mutant with a CCD camera and a computer image analysis system. Our results showed that premature chromosomal condensation precedes abnormal post-meiotic cell cycle progression in the po mutant at the end of meiosis II. Temporal analysis of the po mutant in-vitro revealed that unsynchronized post-meiotic divisions occurred immediately following the end of meiosis II and did not require interaction with the surrounding somatic tissue. Furthermore, the altered distribution of p34^cdc2 protein kinase from a nuclear to a cytoplasmic location was identified in tetrads during onset of the unsynchronized divisions in the po mutant. In contrast, a predominantly nuclear location of p34^cdc2 was observed during interphase of the wild-type tetrads at the same stage. Received: 25 March 1999 / Accepted: 6 May 1999