The distribution of photosynthetic excitation energy in the psae1-1 mutant of Arabidopsis is arrested in state 2 due to constitutive association of LHCII with photosystem I

During photosynthetic state transitions, a fraction of the major light-
harvesting complex (LHCII) shuttles between photosystems II (PSII) and I
(PSI), depending on whether or not it is phosphorylated. Its
phosphorylation state in turn depends on the relative activity of the two
photosystems, which is a function of redox state and illumination
parameters. In the psae1-1 mutant of Arabidopsis thaliana (L.) Heynh.,
amounts of the PSI subunits E, C, D, H and L are decreased. A fraction of
LHCII is stably associated with PSI when plants are exposed to low light
conditions, giving rise to a high-molecular-mass protein-pigment complex
detectable in native protein gels. The formation of this abnormal LHCII-
PSI complex is associated with an almost complete suppression of state
transitions, a drastic increase in the levels of phosphorylated LHCII
under all light regimes tested, and a permanent reduction in PSII antenna
size. All these observations suggest that the altered polypeptide
composition of PSI perturbs the docking of phosphorylated LHCII, making
psae1-1 a unique mutant for the study of PSI-LHCII interactions and
additional effects of the mutation, such as a decrease in grana stacking
and increased adenylate kinase activity.