The organization of the cytoskeleton during meiosis in eggplant (Solarium melongena (L)): microtubules and F–actin are both necessary for coordinated meiotic division

Abstract

Because two division planes form at right angles, male meiosis in higher plants provides striking examples of both division control and spatial programming. To investigate these processes we have stained microtubules and actin filaments during male meiosis in the eggplant. Our results indicate the following. (1) That microtubules and their nucleation sites are involved in the establishment of polarity; this is supported by our observation that the drug CIPC affects spindle polarity. (2) That actin microfilaments are involved in spindle formation and integrity, but not in the establishment of polarity: cytochalasin B and D affect the organization of the spindle microtubules, but not their polarized distribution. (3) That microtubules radiating from the daughter nuclei at the cell poles during interkinesis probably establish the future division plane by concentrating actin in that plane (cf. the proposed role of asters in positioning the contractile ring in animal cells). (4) That this concentration of F-actin in the division plane may be involved in preparing the cytoplasm for cytokinesis and in memorizing the division plane (much as the preprophase band observed in polarized tissues does). (5) That phragmoplast formation is a two-step process. No phragmoplast forms after metaphase I, but a four-way phragmoplast forms after metaphase U, indicating that mitosis and cytokinesis are not obligatorily coupled. These studies demonstrate that actin and microtubules are jointly involved in the spatial coordination of the division process.