Postgerminative growth and lipid catabolism in oilseeds lacking the glyoxylate cycle.

The glyoxylate cycle is regarded as essential for postgerminative growth and seedling establishment in oilseed plants. We have identified two allelic Arabidopsis mutants, icl-1 and icl-2, which lack the glyoxylate cycle because of the absence of the key enzyme isocitrate lyase. These mutants demonstrate that the glyoxylate cycle is not essential for germination. Furthermore, photosynthesis can compensate for the absence of the glyoxylate cycle during postgerminative growth, and only when light intensity or day length is decreased does seedling establishment become compromised. The provision of exogenous sugars can overcome this growth deficiency. The icl mutants also demonstrate that the glyoxylate cycle is important for seedling survival and recovery after prolonged dark conditions that approximate growth in nature. Surprisingly, despite their inability to catalyze the net conversion of acetate to carbohydrate, mutant seedlings are able to break down storage lipids. Results suggest that lipids can be used as a source of carbon for respiration in germinating oilseeds and that products of fatty acid catabolism can pass from the peroxisome to the mitochondrion independently of the glyoxylate cycle. However, an additional anaplerotic source of carbon is required for lipid breakdown and seedling establishment. This source can be provided by the glyoxylate cycle or, in its absence, by exogenous sucrose or photosynthesis.

[1]  T. Thomas,et al.  Regulation of isocitrate lyase gene expression in sunflower. , 1988, Plant physiology.

[2]  T. Cooper,et al.  Mitochondria and glyoxysomes from castor bean endosperm. Enzyme constitutents and catalytic capacity. , 1969, The Journal of biological chemistry.

[3]  Kruger,et al.  Control of gluconeogenesis by isocitrate lyase in endosperm of germinating castor bean seedlings , 1999, The Plant journal : for cell and molecular biology.

[4]  M. Holdsworth,et al.  Molecular and genetic mechanisms regulating the transition from embryo development to germination , 1999 .

[5]  S. Smith,et al.  Glyoxysomal Malate Synthase of Cucumber: Molecular Cloning of a cDNA and Regulation of Enzyme Synthesis during Germination. , 1986, Plant physiology.

[6]  F. Culiáñez-macià,et al.  The dormancy-related peroxiredoxin anti-oxidant, PER1, is localized to the nucleus of barley embryo and aleurone cells. , 1999, The Plant journal : for cell and molecular biology.

[7]  F. Skoog,et al.  A revised medium for rapid growth and bio assays with tobacco tissue cultures , 1962 .

[8]  H. Tabak,et al.  The membrane of peroxisomes in Saccharomyces cerevisiae is impermeable to NAD(H) and acetyl‐CoA under in vivo conditions. , 1995, The EMBO journal.

[9]  A. Pradet,et al.  Quantification of carbon fluxes through the tricarboxylic acid cycle in early germinating lettuce embryos. , 1988, The Journal of biological chemistry.

[10]  H. Beevers,et al.  Oxidation of NADH in Glyoxysomes by a Malate-Aspartate Shuttle. , 1980, Plant physiology.

[11]  H. Krebs,et al.  Synthesis of Cell Constituents from C2-Units by a Modified Tricarboxylic Acid Cycle , 1957, Nature.

[12]  P. McCourt,et al.  Fatty acid composition of leaf lipids determined after combined digestion and fatty acid methyl ester formation from fresh tissue. , 1986, Analytical biochemistry.

[13]  J. Ohlrogge,et al.  Is Acetylcarnitine a Substrate for Fatty Acid Synthesis in Plants? , 1993, Plant physiology.

[14]  R. Dietrich,et al.  Coordinate expression of transcriptionally regulated isocitrate lyase and malate synthase genes in Brassica napus L. , 1989, The Plant cell.

[15]  K. Denby,et al.  Carbon Catabolite Repression Regulates Glyoxylate Cycle Gene Expression in Cucumber. , 1994, The Plant cell.

[16]  D. T. Canvin,et al.  Sucrose synthesis from acetate in the germinating castor bean: kinetics and pathway. , 1961, The Journal of biological chemistry.

[17]  Robert Kay,et al.  Duplication of CaMV 35S Promoter Sequences Creates a Strong Enhancer for Plant Genes , 1987, Science.

[18]  K. Thompson,et al.  Seeds: Physiology of Development and Germination , 1986 .

[19]  G. Heck,et al.  The Embryo MADS Domain Factor AGL15 Acts Postembryonically: Inhibition of Perianth Senescence and Abscission via Constitutive Expression , 2000, Plant Cell.

[20]  H. Saedler,et al.  Plant transposable elements generate the DNA sequence diversity needed in evolution , 1985, The EMBO journal.

[21]  H. Tabak,et al.  Molecular characterization of carnitine‐dependent transport of acetyl‐CoA from peroxisomes to mitochondria in Saccharomyces cerevisiae and identification of a plasma membrane carnitine transporter, Agp2p , 1999, The EMBO journal.

[22]  I. Graham,et al.  No Induction of β-oxidation in leaves of Arabidopsis that over-produce lauric acid , 1999, Planta.

[23]  J. F. Hogg,et al.  Chain length specificities of peroxisomal and mitochondrial beta-oxidation in rat liver. , 1979, Biochemical and biophysical research communications.

[24]  L. Comai,et al.  Isocitrate Lyase and Malate Synthase Genes from Brassica napus L. Are Active in Pollen , 1994, Plant physiology.

[25]  H. Kornberg,et al.  A Mechanism of Conversion of Fat to Carbohydrate in Castor Beans , 1957, Nature.

[26]  H. Saedler,et al.  Knock-out mutants from an En-1 mutagenized Arabidopsis thaliana population generate phenylpropanoid biosynthesis phenotypes. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[27]  M. M. Bradford.  A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. , 1976, Analytical biochemistry.

[28]  A. Pradet,et al.  Peroxisomal β-oxidation of fatty acids and citrate formation by a particulate fraction from early germinating sunflower seeds , 1992 .