PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Molecular dissection of LHCI in vivo : antenna sizes and pigment properties of Lhca-deficient A. thaliana mutants. Frank Klimmek^*,1, Ulrika Ganeteg¹, Poul Erik Jensen², Janne Ihalainen³, Stefan Jansson¹, ¹ Umeå Plant Science Centre, Umeå, Sweden² Department of Plant Biology, Copenhagen, Frederiksberg C, Denmark³ Free University Amsterdam, Amsterdam, De Boelelaan, Netherlands

ABSTRACT- In higher plants 4 different types of Lhca proteins (Lhca1-4) form the outer antenna of PSI (LHCI) and have been shown to associate with one copy/type at one side of the complex [1, 2]. A fifth antenna protein (Lhca5) associated with PSI in substoechiometric amounts has been described recently [3]. We isolated PSI particles from antisense (asLhca2-4) or knock-out (koLhca1) lines of A. thaliana each impaired in expression of one of the Lhca protein types. The lack of one Lhca protein affects the association of other LHCI proteins with the PSI core, resulting in a reduced fitness of the plants [4]. By measuring P700 oxidation kinetics we determined the functional antenna sizes of the different particles to be reduced with 20 % (for koLhca1 and asLhca3), 25 % (asLhca2) and 30% (asLhca4), respectively, when compared to the corresponding wildtype. HPLC analysis of pigment content of the different PSI particles was used to estimate the amount of pigments bound to each Lhca protein in vivo and chlorophyll fluorescence emission spectroscopy was employed to assign tentatively different chlorophyll spectral forms to the various Lhca proteins. Both, antenna size and pigment data, are modelled according to the recent structure of higher plant LHCI consisting of 4 Lhca proteins in vivo [2]. [1] Boekema EJ, Jensen PE, Schlodder E, van Bremen JFL, von Roon H, Scheller HV, Dekker, JP (2001) Biochemistry 40: 1029-1036; [2] Ben-Shem A, Frolow F, Nelson N (2003) Nature 426: 630-635; [3] Ganeteg U, Klimmek F, Jansson S (2004) Plant Molecular Biology, in press; [4] Ganeteg U, Kuelheim C, Andersson J, Jansson S (2004) Plant Physiology 134: 502-509

KEY WORDS: Lhca, LHCI, antenna, higher plant