Breakdown of division cycle and organisation of atypical spindles in fused pollen mother cells of Lolium

Abstract

1. Breakdown of meiotic division cycle in the plasmodial pollen mother cells of Lolium has been described. The plasmodia were formed in a clone following high temperature treatment of its plants. 2. Two characteristic features of meiotic sequence in the plasmodial masses are the organisation of giant metaphase plates and anaphase separation of divergent type. 3. The observations provide evidence which shows that the atypical spindles are organised exclusively through the activity of the centromeres. The lack of well defined poles in them is explained by the inactivity of centrosomes. It could be concluded that both metaphase arrangement of bivalents as well as their anaphase separation can occur independently of the polar or the centrosome forces. 4. It has been suggested that the temperature treatment affects one or more of the mechanisms responsible for carrying through of the division cycle.