Male meiosis in onion

Just because people deserve microscopy! Here is illustrated a male meiosis, which produces the four pollen grains, in Allium senescens (Alliaceae, Asparagales). There is nothing like seeing chromosomes or cells dividing… (before I come back into writing stuff).

From left to right and top to bottom, you can see successively:

The first meiotic division with

-a prophase, the step where chromosomes are condensating from nucleic DNA;

-then a metaphase where these chromosomes unite and get paired on a metaphasic plate (it’s almost metaphysics here!);

-then an anaphase where two chromosomic sets migrate each to a single pole of the cell.

The second nuclear division follows (without telophase: DNA doesn’t turn back into the nucleus stage but immediately goes into the next steps), with

- prophase 2 (you can verify the two groups : one is above, and one slightly blurred is below);

-the end of metaphase 2 and the very beginning of anaphase 2, almost four sets of chromosomes are distinguished;

-and finally a tetrad of four microspores, which will mature into pollen grains. To date, they are still united within the callosic mother cell wall. Nuclei are easily observed in those cells…

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In the pictures illustrated here, cells were stained with Acetocarmine (colors are reversed so as to increase the contrast). Scales indicate 20 micrometers.