Poster: Photosynthesis

Abs # 356: Short circuiting photorespiration

Presenter:	Parry, Martin AJ, martin.parry@bbsrc.ac.uk
Authors	Parry, Martin AJ (A)   Carvalho, Josirley FC (A)   Madgwick, Pippa J (A)   Keys, Alfred J (A)   Lea, Peter J (B)   Beale, Mike  (A)   Ward, Jane L (A)
Affiliations:	(A): Rothamsted Research, (B): Biological Sciences, Lancaster University

Transgenic tobacco (Nicotiana tabacum) plants have been generated in which the part of the photorespiratory cycle that converts glycine to serine has been bypassed. The plants have been transformed with the genes gcl and hyi encoding respectively two enzymes isolated from the bacterium Escherichia coli, glyoxylate carboligase (gcl; EC 4.1.1.47), which converts glyoxylate to tartronate semialdehyde and CO2, and hydroxypyruvate isomerase (hyi: EC 5.3.1.22), which converts tartronate semialdehyde to hydroxypyruvate. The two enzymes should short circuit photorespiratory metabolism and avoid the decarboxylation of glycine and the generation of ammonia. The new pathway should decrease the energy requirements of C3 photosynthesis, by avoiding the necessity of reassimilating the NH₃ released in the mitochondrial reactions. The transgenic lines 32, 33 and 37 expressing the E. coli gene for gcl modified by the addition of a peroxisome targeting sequence and the lines 79, 84 and 92 bearing both gcl and hyi transgenes appeared to grow normally under low light or elevated CO₂ concentrations. Under photorespiratory conditions, less ¹⁴C-glycolate was metabolised to glycine and serine and more to sucrose in the transgenic line than in the wild type plants. The amounts of glutathione in the leaves were variable in gcl and gcl-hyi lines but were always greater than the wild type. Amino acid quantification revealed that the glutamine:glutamate and the glycine:serine ratios were altered in the gcl and gcl-hyi lines. ¹H NMR has been used to further examine differences between null and gcl lines growing at high CO₂ and in the glasshouse.