ULTRASTRUCTURE OF CHICKPEA NODULES

Developing and senescing chickpea (Cicer arietinum L.) nodules formed by Rhizobium sp. (Cicer) CC 1192 have been shown by light and electron microscopy to have general morphological and ultrastructural features that are characteristic of indeterminate nodules. These features incl uded the presence of persistent meristematic tissue at the distal ends of the multi-lobed nodules, and a gradient of cells at different stag es of development towards the proximal point of attachment of the nodu les to the parent root. The cytoplasm of infected cells in the nitroge n-fixing region of the nodules was densely packed with symbiosomes, mo st of which contained a single bacteroid. Infection threads containing bacteria were noted in invaded cells from the nitrogen-fixing region of the nodules. Other features that were observed in chickpea nodules included the presence of electron-dense occlusions in intercellular sp aces in the nitrogen-fixing region, and plasmodesmata that connected i nfected cells with other infected cells and with uninfected cells. No poly-beta-hydroxybutyrate granules were noted in the bacteroids. In la ter stages of development, infected cells became enlarged and highly v acuolated, and eventually lost their contents. Uninfected cells in the central region were smaller than infected cells and were also highly vacuolated. Some of the degenerative processes that take place in sene scing bacteroids were noted.