PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Altered light acclimation in transgenic potato (Solanum tuberosum L. var. Desiree) plants with decreased leaf-ferredoxin content. Jan Backhausen^*,1, Simone Holtgrefe¹, Sabrina Jung¹, Renate Scheibe¹, ¹ Pflanzenphysiologie, Osnabrueck, Germany

ABSTRACT- The effect of increasing light intensity was analyzed in transgenic potato plants with reduced contents of leaf ferredoxin (Holtgrefe et al. (2003), Plant Physiol. 133: 1768-1778). After a transfer of low-light acclimated plants into high light, the Fd-underexpressing mutants rapidly developed an elevated PSII-redox pressure, but measurements of the CO₂-assimilation rate and of the activation state of NADP-malate dehydrogenase indicate that the stroma remains more oxidized. Compared to the wild-type plants, the amount of PSI proteins increased slightly, while the LHC-II amount decreased in the antisense plants. The relative amounts of chloroplast- and nuclear-encoded subunits of the thylakoid-membrane complexes changed in the same way between wild-type plants and mutants, indicating that chloroplast- and nuclear gene expression are still coordinated. The major differences between wildtype- and mutant thylakoids were the portion of ferredoxin-NADP⁺-oxidoreductase bound to the Cyt b/f complex, and the extent of PSII-subunit phosphorylation. Although the transgenic plants should potentially transfer a large portion of electrons towards O₂, we found no indications for an increased accumulation of reactive oxygen species. P700 measurements point to a non-covalent modification of PSI which can be interpreted as charge recombination within PSI, which may act to prevent oxidative damages. It is concluded that the decreased amount of ferredoxin in the antisense plants induces a pronounced light acclimation, although the redox pressure only of the PQ pool, but not of the stroma was increased, and no reactive oxygen species accumulated.

KEY WORDS: light acclimation, transgenic plants, redox regulation, oxidative stress