DR.JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR.JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Transmission electron micrograph (TEM) of five nitrogen fixing bacteria Rhizobium leguminosarum, in tissue of a pea plant Pisum sativum. The bacteria are encased in a structure called an infection thread. The thread, made of host cellulose, is the route taken by the bacteria from the initial site of infection in the root hair, through the cortex of the plant, to the cell that initiates the growth of the root nodule. In the nodule the bacteria releases the enzyme nitrogenase, which converts atmospheric nitrogen into a form that the plant can take up. The plant repays the bacteria for this service by providing them with ample food. Magnification: x4620 at 35mm size.
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