Dissection of Nodule Development by Supplementation of Rhizobium leguminosarum
biovar phaseoli Purine Auxotrophs with AICA Riboside.
Jeffrey D. Newman, Bruce W. Schultz, and K. Dale Noel
Department of Biology, Marquette University, Milwaukee, Wisconsin 53233
Plant Physiology. 99:401-408.
ABSTRACT
Purine auxotrophs of Rhizobium leguminosarum biovar phaseoli
CFN42 elicit uninfected pseudonodules on bean (Phaseolus vulgaris
L.). Addition of 5-aminoimidazole-4-carboxamide (AICA) riboside to the
root medium during incubation of the plant with these mutants leads to
enhanced nodule development, although nitrogenase activity is not detected.
Nodules elicited in this manner had infection threads and anatomical features
characteristic of normal nodules, such as peripheral vasculature rather
than the central vasculature of the pseudonodules which were elicited without
AICA riboside supplementation. Although 105 to 106 bacteria could be recovered
from these nodules after full development, bacteria were not observed in
the interior nodule cells. Instead, large cells with extensive internal
membranes were present. Approximately 5% of the normal amount of leghemoglobin
and 10% of the normal amount of uricase were detected in these nodules.
In order to promote the development of true nodules rather than pseudonodules,
AICA riboside was required no later than the second day through no more
than the sixth day following inoculation. After this period, removal of
AICA riboside from the root medium did not prevent the formation of true
nodules. This observation suggests that there is a critical stage of infection,
reached prior to nodule emergence, at which development becomes committed
to forming a true nodule rather than a pseudonodule.
Figure 4. Effect of delayed AICA riboside
addition on nodule distribution - diagram
Figure 5. Effect of delayed AICA riboside
addition on nodule distribution - graph
This page was created or last modified on 8/10/98 by Jeff
Newman .
© 1998 Jeffrey D. Newman
