Agriculture Reference
In-Depth Information
Figure 1.2
Major types of legume nodule.
A
, desmodioid nodule as found in the phaseoloid tribes (Table
1.15, and some members of tribe Loteae (Table 1.16). Lenticels are characteristic. Nodules vary from
2 to 5 mm in diameter and the infected tissue contains both infected and uninfected cells (Fig. 1.1C).
B
, symbiosomes; these membrane-bound structures may contain 1 to 8 bacteroids (the nitrogen-fixing
form of rhizobia).
C
, a much-branched indeterminate nodule, as found in many species from all three
subfamilies. Other indeterminate nodules may be much less branched or unbranched, and the infected
tissue may contain only infected cells or a mixture of infected and uninfected cells (Fig. 1.1A, B), a
taxonomic characteristic. Size varies from 3 mm to several cm in length.
D
, a broken modified infection
thread (IT), often called a fixation thread, showing bacteroids. This is considered a primitive state in
which bacteria are not released into symbiosomes and is found in caesalpinioid and some papilionoid
nodules.
E
, infected tissue containing a mixture of infected (darkly stained) and uninfected cells (see Fig.
1.1).
F
, infected tissue containing only infected cells. Infected cells in either
E
or
F
arrangements may be
highly vacuolate in some species. (From Sprent, 2007.)
