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N Use By Plants
Nitrate Assimilation
Ammonia Assimilation
Glu, Gln, Asn, Gly, Ser
Asp, Ala, GABA
Val, Leu, Ileu, Thr, Lys
Pro, Arg, Orn
Non-protein AAs
Sulfate Assimilation
Cys, Met, AdoMet, ACC
His, Phe, Tyr, Tryp
Secondary Products
Onium Compounds
HORT640 - Metabolic Plant Physiology

Ammonia Assimilation and Recycling

Photorespiratory mutants of higher plants

Photorespiratory mutants of higher plants obtained by screening for normal growth at elevated CO2 or low O2 (non-photorespiratory conditions) and abnormal growth in air (Lea et al, 1989; Lam et al, 1995):

  • GS2 (barley).

  • Ferredoxin-GOGAT (barley, Arabidopsis and pea). Barley mutants still have a residual GOGAT activity of about 5% of wild-type, due to an NADH-dependent GOGAT, encoded by a separate gene. The rate of photosynthesis in the Fd-GOGAT mutants falls rapidly following transfer from low to high O2. Levels of glutamine increase, as other amino acid pools decline. Inhibition of photosynthesis may be due to accumulation of glyoxylate, due to lack of amino donors in the peroxisome. In Arabidopsis the gls1 locus (formerly called gluS) maps to the same chromosomal position as the GLU1 gene encoding the Fd-GOGAT that is expressed in leaves and induced by light and sucrose. However, Arabidopsis also has a second Fd-GOGAT gene (GLU2) that is preferentially expressed in roots (Coschigano et al, 1998).

  • Double mutants of barley have been obtained which are GS2- and Fd-GOGAT-deficient. The double mutants are just capable of growth in elevated levels of CO2, but show severe stress symptoms immediately following transfer to air. Double mutants show very low rates of CO2 fixation combined with very high levels of ammonia when exposed to air.

  • Mitochondrial serine hydroxymethyltransferase (SHMT) [serine transhydroxymethylase or glycine hydroxymethyltransferase] (Arabidopsis).

  • Chloroplast dicarboxylic acid transporter (Arabidopsis).

  • Catalase (barley)*.

  • Serine:glyoxylate aminotransferase (barley and Arabidopsis).

  • Glycine decarboxylase (barley and Arabidopsis).

    * Transgenic tobacco plants expressing sense and antisense cottonseed catalase and exhibiting a wide range of catalase levels (0.2 to >2.0 times wildtype levels), indicate that photorespiratory losses of CO2 were significantly reduced with increasing catalase at high temperatures (38oC) (Brisson et al, 1998). This suggests that the stoichiometry of photorespiratory CO2 formation per glycolate oxidized is modulated by catalase level.


    Brisson LF, Zelitch I, Havir EA 1998 Manipulation of catalase levels produces altered photosynthesis in transgenic tobacco plants. Plant Physiol. 116: 259-269.

    Coschigano KT, Melo-Oliveira R, Lim J, Coruzzi GM 1998 Arabidopsis gls mutants and distinct Fd-GOGAT genes: implications for photorespiration and primary nitrogen assimilation. Plant Cell 10: 741-752.

    Lam HM, Coschigano K, Schultz C, Melo-Oliveira R, Tjaden G, Oliveira I, Ngai N, Hsieh M-H, Coruzzi G 1995 Use of Arabidopsis mutants and genes to study amide amino acid biosynthesis. Plant Cell 7: 887-898.

    Lea PJ, Blackwell RD, Murray AJS, Joy KW 1989 The use of mutants lacking glutamine synthetase and glutamate synthase to study their role in plant nitrogen metabolism. In (JE Poulton, JT Romeo, EE Conn eds) "Plant Nitrogen Metabolism", Recent Advances in Phytochemistry Vol 23. Plenum Press, New York, pp 157-189.

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  • David Rhodes
    Department of Horticulture & Landscape Architecture
    Horticulture Building
    625 Agriculture Mall Drive
    Purdue University
    West Lafayette, IN 47907-2010
    Last Update: 10/01/09