Fig. 3. In situ RNA hybridization. For each row of three panels, the left panel is a bright-field image, the center one is a dark-field image and the right one a composite using Photoshop. (A,B) Wild-type floral sections hybridized with the ATK1 antisense RNA. (A) A stage 8 floral bud with ATK1 transcripts in young anthers before meiosis and the tip of a petal primordium (arrow). (B) A stage 9 floral bud with male meiocytes (arrows) in the anther and the developing pistil, both showing ATK1 expression. (C) An atk1-1 section of a stage 9 flower, showing background levels of silver grains.