For plants, lots of pollen can be too much of a good thing. Once deposited on their flowers (perhaps after hitchhiking on bees), these sperm-containing packets dig down, tunneling in search of waiting eggs. If more than one pollen grain heads for the same reproductive cell, however, it could mean that others will go unfertilized. To figure out how plants avoid such wastefulness, researchers marked pollen belonging to rockcress, or Arabidopsis, with fluorescent dyes, giving the team the chance to observe the sperm's intrepid descent. As it turns out, once the sperm cells within one of those grains fertilizes an egg, other pollen grains stay away, perhaps because the plants turn off the signal attracting the packets to that cell. This rebuff, reported today in Current Biology, helps ensure that plants make the best use of the pollen that's been plopped onto their flowers. After all, bees don't grow on trees.
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