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

Arabidopsis PSI-D and PSI-F mutants differ in gene regulation response to redox pertubation. Anna Haldrup^*,1, Dario Leister², Stefan Jansson³, Kasper Busk¹, Henrik Scheller¹, ¹ Plant Biochemistry Lab., Dept. Plant Biology, Frederiksberg C, Denmark² Abteilung für Pflanzensüchtung und Ertragsphysiologie, Köln, Germany³ Umeå Plant Science Center, Dept. Plant Physiology, Ümeå, Sweden

ABSTRACT- Arabidopsis plants down-regulated in PSI-F are affected in electron transport due to a weaker binding of plastocyanin (PC) (Haldrup et al. 2000) and in plants with low amounts of PSI-D no PSI complexes devoid of PSI-D are present, suggesting that PSI-D is important for assembly of PSI in plants (Haldrup et al. 2003) and has an essential function in PSI as earlier observed in cyanobacteria (Chitnis et al. 1989). Both mutants grow very slowly and become light-stressed even in low light at normal temperature. They both have an over-reduced plastoquinone pool, a less reduced stroma, and a high phosphorylation level of LHCII and both up-regulate the xanthophyll cycle in order to minimize the formation of dangerous oxygen radicals. Plants with reduced levels of PSI-F or PSI-D react like PSI photoinhibited plants as they all up-regulate VDE, PsbS, NDH-I, Fd, FNR and cytochrome f. In contrast, plants reduced in PSI-F up-regulate the amount of LHCII whereas plants reduced in PSI-D down-regulate the amount of LHCII. We therefore conclude that regulation of the expression of the antenna proteins in response to light stress follows a different signal transduction mechanism than the rest of the light stress responses. On the transcript level, plants with low amount of PSI-F up-regulate nuclear encoded PSI genes whereas plants low in PSI-D down-regulate the nuclear encoded PSI genes. We are currently investigating the levels of different ROS to determine whether they can be involved in signaling as suggested by Pfannschmidt et al. 2001. Thus transgenic plants reduced in PSI-F and PSI-D provides an excellent model system to study light-stress responses and redox regulation in plants both at protein and gene transcription level. Haldrup et al. (2000) J. Biol. Chem. 275, 31211-31218 Chitnis et al. (1989) J. Biol. Chem. 264, 18381-18385 Haldrup et al. (2003) J. Biol. Chem. 278, 33276-33283 Pfannscmidt et al. (2001) Physiol. Plant. 112, 1-9

KEY WORDS: PSI-D, photoinhibition, PSI-F, gene regulation