Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract only
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: During phosphorus (P) deficiency white lupin (Lupinus albus) plants develop increased numbers of proteoid root segments, which can account for more than 50% of the dry root mass after 3 weeks of growth. These densely clustered lateral root segments secrete large amounts of organic acids, primarily citrate and malate, which assist in the mobilization of mineral bound P. Our previous research indicates that approximately one third of the carbon exuded as organic acids originates from carbon dioxide fixed in the root by the enzyme phosphoenolpyruvate carboxylase (PEPC). This work also showed increased activities of the enzymes PEPC, malate dehydrogenase (MDH), and citrate synthase (CS) in the roots of P-deficient white lupin. To further understand this altered carbon metabolism, cDNA clones for PEPC and MDH were isolated from a cDNA library made from P-deficient proteoid root segments. Transcript analysis indicated that both PEPC and MDH were significantly enhanced by P-stress in normal roots, proteoid roots, leaves, and nodules. Increased expression on both genes in proteoid and normal roots can be observed beginning 14 days after emergence. PEPC and cytosolic MDH were constitutively expressed in all tissues of P- sufficient plants, although reduced levels of the PEPC transcript were detected as compared to cytosolic MDH. An additional distinct PEPC cDNA was isolated, although the expression of this cDNA was not induced by P- deficiency. This research was supported in part by the NRICGP grant USDA/93-371000-8941.