Cross Section Of A Pea Root Nodule #1
by Dr Jeremy Burgess/science Photo Library
Title
Cross Section Of A Pea Root Nodule #1
Artist
Dr Jeremy Burgess/science Photo Library
Medium
Photograph - Photograph
Description
Scanning electron micrograph of the cut surface of a root nodule of a garden pea, Pisum sativum. The picture shows a cross section of a small nitrogen-fixing nodule, 1mm in diameter. It is bounded by cortical cells (dull green) enclosing a mass of spongy cells with cross walls (green). Embedded within this tissue are (pink) cells containing a network of membranes filled with bacteroids of Rhizobium leguminosarum. Air from the surrounding soil reaches these cells via the sponge; the bacteroids, using a haem protein - leghaemoglobin - fix the atmospheric nitrogen to produce ammonium salts. This is an example of mutualism, or symbiosis. The bacterium gains a sequestered environment, and the plant uses the fixed nitrogen for its growth. Globally, nitrogen fixation by micro-organisms produces about three times more fertiliser" - 150-200m tonnes/yr - than the entire world chemical industry."
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May 9th, 2022
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