Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 8/2/1997
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: When subjected to phosphorus deficiency, white lupin (Lupinus albus L.) develop proteoid root segments that are composed of densely clustered lateral roots. Proteoid roots exude large quantities of organic acids, which mobilize P in the rhizosphere. A portion of the carbon used in the synthesis of the exuded organic acids is derived from non-photosynthetic C fixation in the roots, involving the enzyme phosphoenolpyruvate carboxylas (PEPC). It has been previously determined in our laboratory that PEPC enzyme levels are greater in proteoid root segments compared to normal root segments, beginning at approximately 10 days after emergence. To further understand the regulation of PEPC in this system, the enzyme was partially purified at 14 days after emergence from proteoid segments of lupin roots grown without P in sand culture. The purification scheme involved a 4-24% PEG cut, DEAE and hydroxyapatite columns, resulting in an approximately 80 fold purification. Native PAGE activity stains and SDS-PAGE indicate that lupin root PEPC is a 440 kD polypeptide. Inhibition studies demonstrated that lupin PEPC activity was reduced by the addition of malate and citrate, and activity was enhanced by the addition of Glu-6-P and Glu-1-P. Full length cDNA clones, encoding lupin PEPC, have been isolated by screening a cDNA library constructed from P-deficient lupin roots using alfalfa PEPC as a heterologous probe. Data on the characterization of these clones and the purified protein will be presented. This research was supported in part by the NRICGP grant USDA/93-371000-8941.