Cross section of a pea root nodule
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.
Size: 4600px × 4100px
Location:
Photo credit: © DR JEREMY BURGESS/SCIENCE PHOTO LIBRARY / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ammonia, ammonium, bacterium, bacteroid, chemical, electron, fertiliser, fertilizer, fixation, garden, haem, industry, leghaemoglobin, leguminosarum, micrograph, mutualism, nitrogen, nodule, pea, pisum, protein, rhizobium, root, salts, sativum, scanning, sem, soil, symbiosis
