|Litjens, Ralph - VENLO THE NETHERLANDS|
|Trepp, Gian - ETH ZURICH SWITZERLAND|
|Miller, Susan - UNIVERSITY OF MINNESOTA|
Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 1998
Publication Date: N/A
Technical Abstract: Malate dehydrogenase (MDH) catalyzes the reversible reaction of oxaloacetate into malate using either NADH or NADPH as a reductant. In plants the enzyme is important in providing malate for C4 metabolism, pH balance, stomatal and pulvinal movement, respiration, b-oxidation of fatty acids, and legume root nodule functioning. In root nodules malate serves as the primary carbon source to support the respiratory needs of the bacterial microsymbiont and the fixation of N2. In alfalfa, five MDH forms have been characterized, three of them, the cytosolic, the glyoxysomal, and the nodule-enhanced isoforms are expressed at high levels in root nodules. The mRNA expression of the cytosolic, glyoxysomal, and nodule-enhanced MDH mRNA's and the protein levels of the cytosolic and the nodule-enhanced forms were evaluated during nodule development. In situ hybridizations performed with 7, 9, and 12 day old alfalfa root nodules showed a differential expression of these three MDH isoforms. The hybridization signal for the cytosolic MDH was observed in the root nodule meristem, invasion zone, and the interzone. The nodule-enhanced form was expressed in the interzone and nitrogen-fixing zone. Whereas the hybridization signal for the glyoxysomal form of MDH was observed in the root nodule meristem, the invasion zone, the interzone, and the nitrogen- fixing zone. The differential expression pattern of the cytosolic, glyoxysomal, and nodule-enhanced MDH suggest different roles for these enzymes during nodule development.