Infection and Nodule Development inAotus ericoides(Vent.) G. Don, A Woody Native Australian Legume

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Abstract
Infection and nodule development were studied by light and electron microscopy in Aotus ericoides, a woody native Australian legume, inoculated with a slow-growing field isolate of Rhizobium. Rhizobia bound to straight, but not deformed, root hairs, as detected by immunofluorescence. Neither markedly curled root hairs nor root hairs with infection threads were seen. Nodules were indeterminate (astragaloid), with a peripheral meristematic layer, few vascular traces and both infected and uninfected cells in the central infected zone. Infection threads containing contorted bacteria were present throughout the nodule. Swollen, rod-shaped bacteria in infected cells were in groups in vesicles bounded by plasmalemma-derived peribacteroid membranes. Senescence in infected cells was associated with accumulation of a fibrillar matrix inside peribacteroid membranes, distortion of bacteria and destruction of most cytoplasmic contents of the bacteria and host cells; however, most bacterial and plant membranes and plant cell walls remained intact. Ineffectiveness was associated with relatively little, short-lived infected tissue. Events in infection and nodule development were similar to those in most herbaceous legumes but showed characters of both determinate and indeterminate nodules.