Embedded Files
Shown are 1 µm thick sections of embedded Arabidopsis anthers stained with toluidine blue (scale bars = 20 µm), showing pollen grains at different stages of development (see the pollen development overview for a description of the different stages). The dark shell around each pollen grain is the exine of the pollen coat, which is secreted by the surrounding tapetal cells of the anther and forms a protective meshwork over each grain. Within the pollen grain we can distinguish the dark-staining nucleolus (black arrows) within the homogeneously lighter-staining nucleus. These images are reprinted from Backues et al. (2010) Plant Cell 22:3218-3231.
The polarized microspore stage is characterized by the large vacuole (v) present in each grain, which disappears during and after pollen mitosis I. The curved cell plate (white arrows) stains dark purple.
After pollen mitosis 1 the generative cell detaches from the pollen cell wall and floats free in the cytoplasm of the larger vegetative cell. It can be recognized by its dark staining cell wall cell (black arrowhead, bicellular). The generative cell divides during pollen mitosis II to give rise to the two smaller, highly elongaged sperm cells (black arrowhead, tricellular).
Here is a close-up view of a toluidine blue-stained pollen grain late in pollen mitosis I. Note the curved cell plate separating the vegetative nucleus from the generative nucleus.
This is an electron micrograph of the curved cell plate forming in another pollen grain in pollen mitosis 1.
N = generative nucleus.
Follow this link to see more electron micrographs of developing pollen.
All of these images are of Arabidopsis anthers that were high pressure frozen, freeze substituted with 2% osmium tetraoxide in acetone and then embedded in epon resin as described in Otegui et al. 2001 Plant Cell 13: 2033–2051. 1 µm thin sections were cut with a microtome and stained in toluidine blue to visualize the different stages of pollen development and as a prelude to cutting 90 nm ultrathin sections for electron microscopy. I did this work in the lab of Sebastian Bednarek in the Department of Biochemistry at the University of Wisconsin, Madison while I was a graduate student there.
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