|Samac, Deborah - Debby|
Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2002
Publication Date: 11/1/2002
Citation: Schulze, J., Tesfaye, M., Litjens, R.H.M.G., Bucciarelli, B., Trepp, G., Miller, S., Samac, D., Allan, D., Vance, C.P. 2002. Malate plays a central role in plant nutrition. Plant and Soil Journal. 247:133-139. Interpretive Summary: Plant functions ranging from leaf movement and the opening/closing of stomates to the acquisition of nutrients from the soil and symbiotic nitrogen fixation are closely related to an organic compound called malate. Malate is a common constituent of all plants, and its formation is controlled by an enzyme (protein catalyst) called malate dehydrogenase (MDH). In order to understand how crop plants control malate formation, we isolated several alfalfa genes that make various kinds of MDH. We characterized the genes, evaluated where in the plant each is expressed, and also studied the enzymatic properties of the MDH proteins. We found that alfalfa contains a unique MDH gene, previously undiscovered, that was crucial for acquiring nutrients. This gene was highly expressed in symbiotic nitrogen-fixing root nodules and in root tips. This novel form of MDH appears to help plants obtain the nutrients nitrogen (N) and phosphorus (P). This research is important because it documents a new type of MDH that may be a useful target for plant breeders and biotechnologiests to improve in efforts to make plants more efficient in acquiring nutrients. Plants more efficient in acquiring and using N and P would reduce the need for these expensive inputs.
Technical Abstract: Malate occupies a central role in plant metabolism. Its importance in plant mineral nutrition is reflected by the role it plays in symbiotic nitrogen fixation, phosphorus acquisition, and aluminum tolerance. In nitrogen-fixing root nodules, malate is the primary substrate for bacteroid respiration, thus fueling nitrogenase. Malate also provides the carbon skeletons for assimilation of fixed nitrogen into amino acids. During phosphorus deficiency, malate is frequently secreted from roots to release unavailable forms of phosphorus. Malate is also involved with plant adaptation to aluminum toxicity. To define the genetic and biochemical regulation of malate formation in plant nutrition we have isolated and characterized genes involved in malate metabolism from nitrogen-fixing root nodules of alfalfa and those involved in organic acid excretion from phosphorus-deficient proteoid roots of white lupin. Moreover, we have overexpressed malate dehydrogenase in alfalfa in attempts to improve nutrient acquisition. This report is an overview of our efforts to understand and modify malate metabolism, particularly in the legumes alfalfa and white lupin.