Mild reductions in mitochondrial citrate synthase activity result in a compromised nitrate assimilation and reduced leaf pigmentation but have no effect on photosynthetic performance or growth.
Transgenic tomato (Solanum lycopersicum) plants, expressing a fragment of the mitochondrial citrate synthase gene in the antisense orientation and exhibiting mild reductions in the total cellular activity of this enzyme, displayed essentially no visible phenotypic alteration from the wild type. A more detailed physiological characterization, however, revealed that although these plants were characterized by relatively few changes in photosynthetic parameters they displayed a decreased relative flux through the tricarboxylic acid cycle and an increased rate of respiration. Furthermore, biochemical analyses revealed that the transformants exhibited considerably altered metabolism, being characterized by slight decreases in the levels of organic acids of the tricarboxylic acid cycle, photosynthetic pigments, and in a single line in protein content but increases in the levels of nitrate, several amino acids, and starch. We additionally determined the maximal catalytic activities of a wide range of enzymes of primary metabolism, performed targeted quantitative PCR analysis on all three isoforms of citrate synthase, and conducted a broader transcript profiling using the TOM1 microarray. Results from these studies confirmed that if the lines were somewhat impaired in nitrate assimilation, they were not severely affected by this, suggesting the presence of strategies by which metabolism is reprogrammed to compensate for this deficiency. The results are discussed in the context of carbon-nitrogen interaction and interorganellar coordination of metabolism.
Sienkiewicz-Porzucek
Agata
A
Max-Planck-Institut für Molekulare Pflanzenphysiologie, 14476 Golm, Germany.
Nunes-Nesi
Adriano
A
Sulpice
Ronan
R
Lisec
Jan
J
Centeno
Danilo C
DC
Carillo
Petronia
P
Leisse
Andrea
A
Urbanczyk-Wochniak
Ewa
E
Fernie
Alisdair R
AR
D000596:Amino Acids / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D019069:Cell Respiration / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D002950:Citrate (si)-Synthase / Q000378:metabolism*; D002952:Citric Acid Cycle; D003001:Cloning, Molecular; D018076:DNA, Complementary; D035264:Flowers / Q000502:physiology; D005638:Fruit / Q000502:physiology; D015870:Gene Expression; D007527:Isoenzymes / Q000378:metabolism; D008027:Light; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000254:growth & development / Q000502:physiology; D008928:Mitochondria / Q000201:enzymology; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000378:metabolism
D000596:Amino Acids; D018076:DNA, Complementary; D007527:Isoenzymes; D009566:Nitrates; D010860:Pigments, Biological; D002244:Carbon; D002950:Citrate (si)-Synthase; D009584:Nitrogen