|Shi, Li Fang|
Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: Alfalfa root nodule development is the result of complex interactions between the soil bacteria Rhizobium meliloti and the plant. While numerous early nodulins have been localized by in situ hybridization, little attention has been given to the expression pattern of late nodule-enhanced genes encoding enzymes involved in nitrogen and carbon metabolism. The expression pattern of several plant and bacterial genes has been evaluated by in situ hybridization in 33-day-old alfalfa root nodules, using serial sections. This allows the direct comparison of the expression patterns of several genes within the same organ. The approach offers new insights into gene regulation during the late stages of root nodule development. In 33-day-old nodules, nodule-enhanced glutamine syntethase, NADH-dependent glutamate synthase, phosphoenolpyruvate carboxylase, alcohol dehydrogenase, and the bacterial encoded nitrogenase (nifH) were expressed predominantly in a 10 to 20 cell layer wide zone including the interzone and the early nitrogen-fixing zone. Asparagine syntethase was expressed in the nitrogen-fixing zone but not in the interzone, whereas aspartate aminotransferase hybridization signal was observed in the interzone and the nitrogen-fixing zone. By comparison leghemoglobin was expressed throughout the central zone of a nodule including the invasion zone, the interzone, and the nitrogen-fixing zone. Taken together these results suggest that in 33-day-old alfalfa root nodules nitrogen fixation is restricted to a 10- to 20-cell layer wide zone.