Submitted to: Molecular Plant Microbe International Symposium
Publication Type: Abstract only
Publication Acceptance Date: 7/23/2001
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The enzyme malate dehydrogenase (MDH), which catalyzes the reversible reaction of oxaloacetate to malate, is important in numerous processes including legume root nodule function. In root nodules, malate serves as the primary carbon source to support the energy needs of the microsymbiont and nitrogenase activity. Malate is also a pivotal compound in the synthesis of carbon backbones involved in nitrogen assimilation. Higher plants contain multiple forms of MDH that differ in co-enzyme specificity and subcellular localization. We report the cellular localization and the developmental expression of a nodule-enhanced (neMDH) and a cytosolic (cMDH) form of MDH in alfalfa root nodules. Transcript levels of neMDH progressively increased over a 19-day period. In contrast, cMDH transcripts show a constitutive background level at all time points with peak expression detected in 7 and 19 d nodules. Localization of mRNA transcript by in situ hybridization in 12 d nodules showed neMDH to be abundant throughout, whereas, cMDH was localized in the invasion and interzone. Protein immunoblots showed three different neMDH polypeptides over a 33 d period. One form progressively increased while another form simultaneously decreased. cMDH antiserum detected two constitutively expressed polypeptides. Immunocytochemical analysis of 19 d nodules showed neMDH localized in the periphery of infected cells near the intercellular spaces. cMDH was specifically located in uninfected cells and in cells of the inner cortex.