PHOTOACOUSTIC MEASUREMENTS OF PHOTOSYNTHETIC ACTIVITIES IN INTACT LEAVES UNDER COPPER STRESS

Photoacoustic spectroscopy was used to monitor Cu damage to photosynth esis by measuring photochemical energy storage (PES) at high frequency of 600 Hz and yield of O2 evolution (Aox/Apt) at low frequency of 19 Hz in intact leaves of a Cu-tolerant (Silene compacta) and a non-Cu-to lerant (Alyssum montanum) species. The results indicated that Cu affec ted root growth (RRG), more severely than photoacoustic parameters in both species. Plants of S. compacta grown in lower Cu concentration re vealed an enhancement phenomenon on RRG, PES and Aox/Apt, in contrast, plants of A. montanum revealed a slight decrease in the above mention ed parameters. A remarkable decline of PES and Aox/Apt for both specie s, was observed, at higher Cu concentrations, a fact considered to ref lect inhibition of the photsynthetic e- flow in thylakoids. PES was le ss affected by Cu stress than O2 evolution showing a differential sens itivity of two photosystems in Cu. Photosystem II (PSII) seemed to be more sensitive because of degradation and leakage of chloroplasts memb ranes, inducing a decline in yield of O2 evolution. On the other hand, PES was appreciable because of cyclic e- transfer around the intact o r less inhibited photosystem I (PSI).