HAPPY LITTLE PLANT CELLS

Those grinning faces are actually veinlike structures in a piece of grass. Phil Gates of Durham University created the glowing smiles in this micrograph by adding two dyes to a thin slice of a marram grass (Ammophila arenaria) and then shining ultraviolet light on it. The first dye, calcofluor M2R, glows blue when bound to cellulose. The second, Auramine O, glows yellow when it binds to the plant polymers cutin and lignin. The blue smiles are made of phloem tissue, which carries nutrients around the plant and has pure cellulose cell walls. Chlorophyll-rich cells, which fluoresce brownish-red without any added dyes, can be exposed as the grooves in this sample open up in response to water in the air, uncurling the blades of grass and triggering photosynthesis.

Credit: Phil Gates

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