|Samac, Deborah - Debby|
Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/1996
Publication Date: N/A
Technical Abstract: NADH-dependent glutamate synthase (NADH-GOGAT) is a key enzyme in primary nitrogen assimilation in root nodules of alfalfa and other legumes. The enzyme catalyzes the reductive transfer of the amido group of glutamine to the a-keto position of 2-oxoglutarate, yielding two glutamates. The amount of NADH-GOGAT enzyme activity in most alfalfa organs is low to non detectable. However, during root nodule development, activity of NADH GOGAT increases several-fold and is considered to be the major form of GOGAT in this tissue. Although we have reported on one NADH-GOGAT gene in alfalfa, we were concerned that there may be others. Based on sequences from PCR across introns and southern blots, we find NADH-GOGAT in alfalfa (cv. Saranac) is encoded by a single gene with multiple alleles. In situ hybridizations were performed to assess the location of NADH-GOGAT gene expression in alfalfa root nodules. In wild type Saranac nodules the NADH GOGAT gene is expressed in infected cells. The pattern of expression showed an interesting shift during nodule development. Until day 12, all infected cells appeared to express NADH-GOGAT. By day 19 there was a gradient of expression from high in the early symbiotic zone to relatively low in the late symbiotic zone. In day 33 nodules, expression was seen only in the early symbiotic zone. By comparison, ineffective nodules showed NADH-GOGAT gene expression in only a few cell layers of the early symbiotic zone after day 9. The promoter of NADH-GOGAT was evaluated in transgenic alfalfa carrying chimeric-GUS promoter fusions. Staining for GUS and assays of MUG suggest that there are at least two regulatory elements.