Pollen peculiarities

In flowering plants, male meiosis occurs in the microsporocyte to produce four microspores, each of which develops into a pollen grain. The image at top left is a transmission electron micrograph of a wild-type microspore from Arabidopsis thaliana, showing the single, central nucleus. The tetraspore (tes) mutant of Arabidopsis fails to undergo cytokinesis at the end of male meiosis and all four meiotic products remain in a common cytoplasm. The image at lower left shows such a coenocytic microspore from a tes homozygote; three of the four nuclei are visible in this section. Despite the initial defect, most tes coenocytic microspores continue development to produce semi-fertile pollen. The mutant pollen grains, however, show a variety of abnormalities that are most likely indirect effects of the primary phenotype. A particularly striking effect is disruption to the patterning of apertures in the pollen wall. Wild-type Arabidopsis pollen grains have three longitudinal apertures, whereas tes grains (see the scanning electron micrograph at top right) show great variability in number, morphology, and placement of apertures. For more details, see Spielman et al.