THE USE OF PHOTOACOUSTIC-SPECTROSCOPY IN ASSESSING LEAF PHOTOSYNTHESIS UNDER COPPER STRESS - CORRELATION OF ENERGY-STORAGE TO PHOTOSYSTEM-II FLUORESCENCE PARAMETERS AND REDOX CHANGE OF P-700

The effects of Cu-ions on an in vivo Cu-treated leaf system of Thlaspi ochroleucum have been identified by using photoacoustic, modulated fl uorescence methods and leaf absorbance. The deficiency in light harves ting capacity of PSII caused by the Cu-induced chlorophyll loss may re sult in the energy distribution of the two photosystems being out of b alance. Copper decreased maximal fluorescence (F-m, F-m') and changes at the variable fluorescence were also observed. The reduction state o f the primary electron acceptor (Q(A)) of PSII in leaves resulted in c hanges due to the imbalance between the rate of Q(A) reduction by PSII activity and the rate of Q(A)(-) reoxidation by PSI activity. Copper treatment also resulted in a dramatic decrease of Rfd (vitality index) , a moderate decrease in PES (energy storage) and a marginal decrease in F-v'/F-m' values. High Cu concentrations inhibit O-2 evolution and the enhanced heat emission may be due to an inhibition of electron tra nsfer and consequently of photochemistry. Thlaspi leaves maintained an increased capacity for PSI-driven energy storing electron flow, since measurements of 820 nm absorbance changes in saturating far-red light indicated less pronounced changes in the reaction center of PSI (P-70 0) activity after Cu exposure compared with that of PSII.