Summary: Photosynthesis Research 68: 7179, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Protein tyrosine phosphorylation in the transition to light state 2 of
Jens Forsberg & John F. Allen
Plant Biochemistry, Lund University, Box 117, SE-221 00 Lund, Sweden; Author for correspondence (e-mail:
firstname.lastname@example.org; fax: +46-46-222-4006)
Received 27 June 2000; accepted in revised form 11 January 2001
Key words: chloroplast, LHC II, photosynthesis, light state transitions, protein phosphorylation, thylakoid
Redox dependent protein phosphorylation in chloroplast thylakoids regulates distribution of excitation energy
between the two photosystems of photosynthesis, PS I and PS II. Several thylakoid phosphoproteins are known to
be phosphorylated on N-terminal threonine residues exposed to the chloroplast stroma. Phosphorylation of light
harvesting complex II (LHC II) on Thr-6 is thought to account for redistribution of light energy from PS II to PS
I during the transition to light state 2. Here, we present evidence that a protein tyrosine kinase activity is required
for the transition to light state 2. With an immunological approach using antibodies directed specifically towards
either phospho-tyrosine or phospho-threonine, we observed that LHC II became phosphorylated on both tyrosine
and threonine residues. The specific protein tyrosine kinase inhibitor genistein, at concentrations causing no direct