Chemically Speaking - September 2006

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Plants Try to Shut the Door on Bacteria

Researchers at Michigan State are reporting on the description of a plant’s surface terrain and unveiling new knowledge of how bacterial pathogens invade plants and take hold.  The most recent paper, published in the September 8th edition of Cell, redefines the role of the plant’s stomates in defense against invading bacteria and how some bacteria can overpower plants.

Stomata are like tiny mouths that open and close during photosynthesis, exchanging gases.  In sunshine, the stomata open.  In darkness, they close to conserve water.  It has been assumed that these tiny ports were busy with their photosynthesis business and were merely unwitting doorways to invading bacteria on a plant’s surface.   MSU researchers have discovered that stomata are an intricate part of the plant’s immune system that can sense danger and respond by shutting down.  The research group performed experiments on Arabadopsis, a common laboratory plant, but the mechanisms could be universal across all land plants.

Some bacteria have gotten smarter. The group found that plants recognized human-infecting bacteria, such as E. coli, and kept the stomata closed to them.  But plant-infecting bacteria, like those most destructive to crops, have figured out a way to reopen the shut-down stomates.  It appears those plant-based bacteria produce a phytotoxin, a chemical called coronatine, to force the stomates back open.  For bacteria, plant entry is crucial to causing disease and probably survival. They could die if left lingering on the surface.  Interestingly, animal-based bacteria are not known to produce coronatine.  (MSU Today, 9/8/06).