Ultra-structural Studies on Root Nodules of Albizia Lebbeck (l.) Benth

Albizia lebbeck (L.) Benth., commonly known as Siris is a mimosoid tree legume widely distributed in Pakistani soils. The roots of A. lebbeck establish symbiosis with root nodule bacteria and form nodules which develop singly as well as in clusters on the primary and secondary roots. Mature nodules are oblate, elongate, branched and coralloid. Rhizobia in root nodules from naturally nodulated plants showed intercellular movement. Both determinate and indeterminate type of nodules were observed having similar structure. Anatomically nodules could be differentiated into a nodule meristem, nodule cortex, containing the vascular bundles surrounding the infected tissues. Nodule meristem was multilayered, comprising of thin walled, tightly packed and actively dividing cells. Nodule cortex was mainly composed of parenchymatous tissue. Distinct periderm was present. Amphicribal vascular bundles were arranged around the bacteroid region which showed both the infected and un-infected interstitial cells with starch grains in their cytoplasm. Infected cells were non-vacuolated. Studies was carried out to examine the initiation, early development and ultrastructure of root nodules of A. lebbeck.