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. 2009 Apr 9;106(17):7257–7262. doi: 10.1073/pnas.0810992106

Fig. 1.

Fig. 1.

Cell over-proliferation during pollen development in rbr/+ mutants. (A–C) WT pollen development. (A) The microspore with the undetermined cell fate undergoes an asymmetrical mitosis, leading to bicellular pollen (B). At that stage the pollen grain composes a large vegetative cell containing a small germ cell with a nucleus showing relatively higher chromatin compaction. The germ cell divides into 2 sperm cells with highly condensed chromatin, leading to the tricellular pollen grain (C). (D–I) rbr pollen development. Cell fates are determined on the basis of nuclear morphology. (D) At the microspore stage, rbr pollen grain with 2 undetermined cell nuclei. (E) Bi-cellular-stage rbr pollen grain with 2 vegetative cell nuclei and 1 germ cell nucleus. (F) Tri-cellular-stage rbr pollen with 2 vegetative cell nuclei and 2 sperm cell nuclei. (G) Tri-cellular-stage rbr pollen with 4 vegetative cell nuclei and 1 germ cell nucleus. (H) Tri cellular-stage rbr pollen with 1 vegetative cell nucleus and 4 germ cell nuclei. (I) Tri-cellular-stage rbr pollen with 2 vegetative cell nuclei and 4 germ cell nuclei. Nuclei are stained with DAPI. (Scale bars, 10 μm.) (J) Bi-cellular-stage WT pollen. The cell wall (arrows) is asymmetrically placed between the vegetative nucleus and the generative nucleus. (K) Bi-cellular-stage rbr pollen. The cell wall (arrows) is symmetrically placed between the 2 vegetative nuclei. Nuclei are stained with DAPI, and the cell walls are stained with aniline blue. (L and M) Transmission electron micrographs of bi-cellular-stage WT pollen (L) and rbr pollen (M). Note the internal wall indicated by arrows in rbr pollen. (Scale bars, 10 μm in J and K; 5 μm in L; 2 μm in M.) (N) Bar chart showing percentage of the pollen contains 2 vegetative cells in rbr-2/+ mutants at microspore, early bi-cellular, mid-bi-cellular, and late bi-cellular stages. At late bi-cellular stage, the over-proliferation in pollen from rbr-2/+;cdka-1/+ plants was reduced to one seventh of the over-proliferation in pollen from rbr-2/+ plants. Error bars correspond to SEs calculated on the basis of several samples of 100 pollen grains, and the size of total population analyzed (n) is indicated above each column. m, microspore nucleus; g, germ cell nucleus; v, vegetative cell nucleus; s, sperm cell nucleus.