Cytological characteristics of nodules induced by NGR234 on roots of different plants

Root nodule symbiosis consists in an association with reciprocal goals between plants of leguminous family and bacteria belonging to the genus Rhizobium. It involves multiple interactions between the two partners and results in formation of a new organ called nodule on the roots of the plants. In these nodules bacteria differentiate in bacteroid able to fix nitrogen from atmosphere and to reduce this into a form directly available for the plant. One of the advantages for the leguminous plants is a better growth on soils low in nitrogen. The bacteria provide nitrogen sources for plant growth and in return plants provide photosynthates to the bacteria and a particular microenvironment required for nitrogen fixation. Two main types of nodules have been described: determinate and indeterminate (ID), the second ones being characterized by the persistance of a meristematic region.

The first example below illustrates the cytological characteristics of indeterminate (ID) nodules induced by NGR234 on roots of Leucaena leucocephela. The nodules show a typical zonation of ID nodules with an apical meristematic region.
The micrographs illustrate parts of Epon sections (80 nm thick) made in the two regions of the nodule and observed in a transmission electron microscope FEi – TECNAI G2 sphera. Above the apical region (meristem) and below the basal part with a bacteroid at higher magnification.

Cell in division in the apical part of an ID nodule.
n1 : nucleus cell 1; n2 : nucleus cell 2; hc: heterochromatin; re : reticulum endoplasmic

Site Nod1 -n28.jpg


Part of the section in the apical part of the ID nodule, the meristem (Scale : 5000 nm)
characteristics of this meristematic cell: polylobed nucleus and small vacuoles.
N: nucleus; nu : nucleolus; en: nuclear envelope; a: amyloplast

Nodule - partie apicale -NGR234 Leucaena l

Part of the section in the basal part of the nodule (Scale : 5000 nm)

Site Nod2-2 n2_001b.jpg

Appearance of a bacteroid at high magnification in the basal part of the nodule (Scale: 500 nm)

Site Detail Nod2-2 n12_001b.jpg