PARENT SESSION
Posters P2A Type I reaction centres. Abstracts (181-218)

Photosynthetic electron transport supported by methyl viologen in the obligate shade plants Panax ginseng and Panax quinquefolius. Matthew Woods^*,1, Graeme Parmenter², Julie-Ann Miskell¹, Julian Eaton-Rye¹, ¹ Biochemistry Department, Dunedin, New Zealand² New Zealand Institute for Crop and Food Research Ltd, Mosgeil, New Zealand.

ABSTRACT- Panax ginseng C. A. Meyer (Korean ginseng) and Panax quinquefolius L. (American ginseng) are obligate shade plants found in broadleaf forests of Eastern Asia and North America, respectively. Measurements of electron transport in isolated thylakoid membranes from these species have been performed using methyl viologen as an electron acceptor. In both species oxygen consumption rates for whole chain or photosystem I (PSI)-specific assays were found to be < 2% of similar rates in Pisum sativum L. (pea) or Spinacia oleracea L. (spinach) thylakoids (J.-A. Miskell, G. Parmenter and J.J. Eaton-Rye (2002) Planta 215, 969-979). Both ginseng species were found to have a Ser residue at position 68 whereas a Tyr was present at this position in an amino acid alignment of PsaC from 32 species. However, electron transport to methyl viologen was unaffected in a Synechocystis sp. PCC 6803 strain carrying a Tyr to Ser substitution at position 68 in PsaC. A further mutant Y68T was also examined and photoautotrophic growth and PSI electron transport to methyl viologen were similar to wild type in this strain. Steady-state electron transfer to methyl viologen was also investigated in thylakoid membranes from ginseng, pea, and Arabidopsis thaliana by measuring chlorophyll a fluorescence transients. These data have shown that rates of electron transfer to methyl viologen are affected by the age of the ginseng plant. We are investigating the mechanism of this age-dependent effect on oxygen consumption in the presence of methyl viologen.

KEY WORDS: electron transport, ginseng, methyl viologen, PsaC