POSSIBLE MECHANISMS FOR THE INHIBITION OF PHOTOSYNTHESIS BY OZONE

Tropospheric ozone produced by industrial civilization is widespread. Although the levels are not clearly life threatening, they do have the potential to inhibit normal plant productivity, thought to be by an i nhibition of photosynthesis. While the mechanism for this inhibition i s not yet clear, there are several hypotheses for its cause. It is unl ikely that ozone can penetrate the cell membrane unreacted, therefore, reactions at the plasma membrane either causing general ionic and met abolic disturbance within the cell or causing the production of uniden tified toxic products must ultimately produce the alterations within t he chloroplasts. While model systems, such as individual biochemicals, isolated chloroplasts, and algae, can give some understanding of poss ible reactions, they cannot provide the full story. One continuing con troversy revolves about the role of stomata in the inhibition process - they play an important role, but the full interaction between stomat al closure and inhibition of photosynthesis has not yet emerged. In or der to reach a political compromise on air quality standards, we need to have a good understanding of the fundamental mechanisms by which oz one causes any decline in plant productivity.