Figure 1. Close-up view of nodules of soybean (top) and alfalfa. The soybean
nodules on the right have been hand-sectioned to show the typical pink
appearance of the nodule interior which is due to leghemoglobin, an important
oxygen-binding protein present in nodules.
Figure 2. Crude extract from soybean nodules showing the red appearance due to
leghemoglobin. Nodules were ground in buffer, filtered through cheesecloth,
and centrifuged to remove cell debris. The sample shown is the supernatant
without any further purification. Leghemoglobin is about 50% of the total
soluble protein.
Figure 3. Electron micrograph of an infected cell from a cowpea (Vigna
unguiculata) nodule. Most of the figure consists of a single plant host
cell which is packed full of N-fixing bacteria - called bacteroids when in this
symbiotic form.
Figure 4. Alfalfa grown in the presence (right) or absence of molybdenum, an
element essential for N fixation due to its role in nitrogenase, the enzyme
that catalyzes nitrogen fixation.
Figure 5. Soybean grown in the presence (left) or absence of cobalt, an element
essential for N fixation due to requirements of the microbial symbiont
(Bradyrhizobium japonicum in this case).
Figure 6. Ion exchange column used for the purification of nitrogenase from
soybean nodules. Nitrogenase consists of two separate enzymes referred to as
the Fe protein (or dinitrogenase reductase, upper band) and the MoFe protein
(or dinitrogenase, lower band).
Figure 7. Cross section of nitrogen-fixing root nodule from alfalfa (Medicago sativa) with red Cy3 immunofluorescent probe indicating high concentrations of the antioxidant enzyme ascorbate peroxidase in the central infected region (INF) and in the endodermis (E). Other abbreviations: NC, nodule cortex; NP, nodule parenchyma.
Figure 8. Histochemical localization of ascorbate (an important antioxidant) in alfalfa nodules. Silver particles precipitated from AgNO3 indicating the presence of ascorbate in high levels in the endodermis region of the cortex. (INF: infected region, IC: inner cortex, OC: outer cortex)