ACTION SPECTRA OF PHOTOSYSTEM-I AND PHOTOSYSTEM-II IN STATE-1 AND STATE-2 IN INTACT SUGAR MAPLE LEAVES

Photochemical activity, measured as energy storage of photosystems I ( PSI) and II (PSII) together and individually, is studied in sugar mapl e (Acer saccharum Marsh.) leaves in the spectral range between 400 and 700 nm in state 1 and state 2. Total photochemical activity remains t he same in both state 1 and state 2 between 580 and 700 nm, but it is lower in state 2 between 400 and 580 nm. Both PSI and PSII activities change significantly during the state transition due to the migration of light-harvesting chlorophyll a/b protein complex of PSII (LHCII). I n the action spectra of PSI and PSII, peak positions vary depending on the association or dissociation of LHCII, except for the peak at 470 nm in the PSII spectrum. PSII activity is about 3 times higher than or equal to PSI in state 1 or state 2, respectively, over most of the sp ectrum except in the blue and far-red regions. At 470 nm, PSII activit y is 8 or 1.6 times higher than PSI in state 1 or state 2, respectivel y. The amplitude of LHCII coupling-induced change is the same in both PSI and PSII between 580 and 700 nm, but it is less in PSI than in PSI I between 400 and 580 nm, which explains the lower photochemical activ ity of the leaf in state 2 than in state 1. This may be due to a decre ase in energy transfer efficiency of carotenoids to chlorophylls in LH CII when it is associated with PSI.