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Images of Arabidopsis pollen grains from the early polarized microspore through the bicellular stages of development (see the pollen development overview for descriptions of the different stages). N = Nucleus, GN = Generative Nucleus, VN = Vegetative Nucleus, V = Vacuole. Scale bars = 1 µm. Lower panels are closeup views of the edge of the grain to show the development of the intine layer of the pollen coat, which is secreted by the pollen grain itself. The intine not only becomes thicker as the pollen develops, but also more convoluted, with cytoplasmic inclusions. Scale bars = 1μm in upper panels and 200 nm in lower panels.
These images are from the work that I did characterizing the drp2 mutants in Sebastian Bednarek's lab at UW Madison, and were used in Backues et al. 2010 Plant Cell 22:3218-31 They are from 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. I used toluidine blue staining of 1 µm thin sections to find the plane that I was interested in, then collected 90 nm sections for electron microscopy.
A pollen grain undergoing cytokinesis after pollen mitosis I.
Note the characteristic curved cell plate. This plate is relatively mature, although not yet fused with the plasma membrane. A convoluted sheet structure can be seen at the right end of the plate.
A closeup of the leading edge of a forming cell plate at pollen mitosis 1. Phragmoplast microtubules are visible extending out from the forming plate
During pollen mitosis I, the large central vacuole is divided into many smaller vacuoles. Here is an image of vacuole undergoing division.
Glancing section of a nucleus during pollen mitosis I.
The generative cell of a bicellular pollen grain is surrounded by lipid droplets (white blobs).
Closer view of the cell wall of the generative cell. The inner surface is lined with cortical microtubules that help to maintain the characteristic oval shape of the cell.
Plastids from a bicellular pollen grain containing plastics with prominent starch granules.
A section of the endoplasmic reticulum (ER) in a pollen grain just prior to pollen mitosis I. The curly lines of ribosomes are polysomes assembled on the surface of the ER.
A Golgi stack (top) and a multi-vesicular body (middle) near the edge of the pollen grain (lower left)
A Golgi stack with vesicles budding. The cis face of the Golgi is to the left, the trans face is to the right. At the far right a trans-Golgi network (TGN)/endosome can be seen.
An image of the cytoplasm of a pollen grain near pollen mitosis 1 showing the morphology of the mitochondria. Note the elongated mitochondrial crossection near the center of the image, hinting at the tubular nature of the mitochondrial network.
Another image at higher magnification of mitochondria in the cytoplasm of a pollen grain during pollen mitosis 1.
A glancing section of a pollen grain at high magnification, showing the highly convoluted nature of the intine and its warren-like network of interconnected cytoplasmic inclusions.
Three images of pollen grains at the late polarized microspore stage; magnification increases from left to right. All three of these are dramatic examples of the plasma membrane sheets that are associated with this stage of intine development. These sheets resemble structures described as "convoluted sheets" in an electron tomographic study of cell plate formation during microsporogenis (the meiotic event that generates pollen grains) (Otegui and Staehelin (2004) Planta 218:501). However, the sheets pictured here are not associated with a forming cell plate but instead the intine.
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