Fig. 2. Defects in pollen development in msi1/+ mutants. Pollen development in meiotic tetrads from qrt1/qrt1 and qrt1/qrt1; msi1-1/+ Arabidopsis plants. At uni-nucleate stage (A) microspore tetrads of wild-type and mutant plants are indistinguishable. In contrast to wild-type tetrads (B), msi1/+ tetrads at the bicellular stage contain one arrested microspore (C, arrowhead). (D-F) At the tricellular stage, qrt1/qrt1; msi1-1/+ plants produce tetrads containing three wild-type pollen grains and an abnormal pollen grain (arrowhead). The abnormal pollen is either a dead microspore (D), an arrested microspore (E) or a bicellular pollen grain (F). Epifluorescence micrographs of DAPI-stained pollen. Scale bars: 10 µm.