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Role of phospho enol pyruvate carboxylase in anaplerosis in the green microalga Dunaliella salina cultured under different nitrogen regimes
Author(s) -
Norici Alessandra,
Dalsass Alessia,
Giordano Mario
Publication year - 2002
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2002.1160207.x
Subject(s) - phosphoenolpyruvate carboxylase , pyruvate carboxylase , biochemistry , biology , gene isoform , algae , cyanobacteria , rubisco , dunaliella salina , green algae , botany , photosynthesis , enzyme , gene , bacteria , genetics
Anaplerosis plays a very important role in providing C for N assimilation. In green algae and higher plants, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) is the main anaplerotic carboxylase. On this basis we hypothesize that N availability affects PEPC expression. In order to test this hypothesis, the model organism Dunaliella salina was cultured under a variety of N growth regimes. Our results show that the level of PEC activity was unaffected by the N form in which N was supplied to the cells, when N concentration was low (0.5–0.01 m M ). When cells were adapted to growth at 5 m M N, however, PEPC activity on a per cell basis was substantially higher in NH 4 + ‐adapted cells as compared to their NO 3 – ‐adapted counterparts; however, the same difference was not observed on a protein basis. This notwithstanding, even at low N, PEPC of cells cultured in the presence of either NH 4 + or NO 3 – appeared to differ in their molecular masses. These results suggest that cells adapted to different N‐form express distinct PEPC isoforms. In addition to this, we observed that, in algae adapted to high (5 m M ) NH 4 + concentration, a PEPC isoform was induced that differed from the isoforms observed in algae adapted to lower concentrations of the same N‐source. These findings lead us to conclude that the expression of PEPC isoforms in D. salina responds to the variation in the C‐skeleton demand deriving from changes in the chemical form and availability of N.