The redox state of plastoquinone (PQ) pool is the incipient signal in the signal transduction pathway of state transition mechanism, shifting from state I to state II and vice versa. The redox state of the QA, the primary acceptor of photosystem II (PSII) and the PQ pool are easily monitored by the OJIP fast fluorescence transients. The OJIP fast Chl afluorescence transient studies revealed that in state II, there was reduction in maximal fluorescence which could be due to decreased antennae size of PSII. The same changes were not observed in Stn7 mutant lacking thylakoid kinase which phosphorylates light harvesting complex (LHC) II. The phosphorylated LHCII is associated with PSI under state II condition. The redox state of PQ pool is signal for the kinase to phosphorylate/dephosphorylate major LHCII of PSII. The 2-D electrophoresis results showed that LHCII is resolved into 3 spots in state I. However, in state II this has been resolved into 4 spots. However, Stn7 mutant there was no change of 2D spots in state II. The additional spot is yet to be investigated.