Microsporocyte Growth and Meiosis in Phyllospadix torreyi, a Marine Monocotyledon

Abstract

In this paper we demonstrate spindle rotation during meiosis in filiform microsporocytes of a dioecious marine monocotyledon. Extensive populations of Phyllospadix torreyi, a seagrass, cover intertidal and shallow subtidal rocks in southern California. Flowering plants are unevenly distributed, being found only in patches within these beds, and apparently are disproportionally few relative to plants that do not produce flowers. Reduction division in male flowers occurs in an already elongate microsporocyte (pollen mother cell), where the chromosomes at metaphase lie in a plane across the narrow axis of the filamentous cell. However, the poles and spindles then rotate through 90° during anaphase of first and second meiotic divisions so that the cells divide longitudinally to produce tetrads which develop into filamentous pollen. Nine bivalents were counted in diakinesis figures. The presence of a heteropycnotic X-chromosome in male flowers is suggested by certain observations of prophase-anaphase figures.