Membranes in the spindle of Iris pollen mother cells during the second division of meiosis

Abstract

Spindle membrane in the second division of meiosis inIris comprises endoplasmic reticulum (ER) and small spherical vesicles (40–80 nm diameter). The vesicles are in all respects similar to those of dictyosomes and it is proposed that they originate in the Golgi system. ER on the other hand is generated from the nuclear envelope (NE). Invaginations and evaginations of the inner and outer membranes of the NE are present at interphase and they enlarge during prophase II and break to form spindle ER elements at the beginning of prometaphase II. The area enclosed by this ER continues to increase until the entire spindle is filled with irregular profiles at mid-prometaphase II. During late-prometaphase II the quantity of ER decreases and, concurrent with an increase in the number of microtubules (MTs), the cisternae align alongside MT bundles and accumulate at the poles. It is suggested that ER increases in quantity by growth of NE membranes. Furthermore, the alignment of ER along the interpolar axis and its transport polewardsprior to anaphase suggest the action of a force on each ER element.