Sulphur dioxide effects on cell structure and photosynthetic performance in the liverwort Frullania dilatata

The effects of SO2 exposure, carried out in controlled-environment cuvettes , on the photosynthetic performance of the liverwort Frullania dilatata (L. ) Dum. were investigated by means of chorophyll a fluorescence induction ki netics and gas-exchange measurements. Additionally, visible-injury symptoms developing in leaves as a result of exposure to the pollutant were quantif ied and described. The adverse effects of SO2 on photosynthesis could be se en as (i) a decreased electron flow through photosystem II (PSII), (ii) an increased degree of closure of PSII centres, (iii) a lowered capacity for d issipative processes, and (iv) reduced net CO2 assimilation rates. Addition ally, SO2 induced severe cell injury that ranged from cells without oil bod ies to cells with collapsed plasma membrane and disorganized organelles. Th e distribution pattern of injuries in the shoots of F. dilatata suggests th at SO2-induced damage is related to the degree of direct exposure to the po llutant. It is possible that, because this liverwort grows in dense patches with overlapping branches, some protection is conferred to basal leaves.