Chlorophyll Fluorescence of Barley (h. Vulgare L.) Seedlings Grown in Excess of Cd*

The effect of excess of cadmium (Cd) on chlorophyll fluorescence of barley seedlings was studied. The leaves were dark-adapted and then illuminated at 10 different light intensities within the range of 70–1600 μmol.m–2.s–1 photosynthetically active radiation (PAR). It was found that Cd decreases the chlorophyll fluorescence parameters in dark-adapted leaves: ground (Fo), maximal (Fm) and variable (Fv) fluorescence. However the Fv/Fm ratio was slightly influenced. At light intensities below 400 μmol.m–2.s–1 PAR no significant differences between values of photochemical quenching (qP), non-photochemical quenching (qN) and yield of photochemical energy conversion (Y) of control and Cd-treated plants were found. At light intensities about 500 μmol.m–2.s–1 and higher significant decrease in qP, concomitant increase in qN as well as a reduction in Y were observed. In Cd-treated plants the maximum of apparent electron transport rate (ETR) were reached earlier than in control plants and under lower PAR intensities, indicating that the energy consumption by Calvin’s cycle reactions is reduced. It is speculated that excess of Cd in barley plants causes a down regulation of PSII to avoid over-reduction of primary electron acceptor QA and to reduce the load on the electron transport chain.