Effects of SO 2 on sulphur and nitrogen fractions and on free amino acids in perennial ryegrass

An investigation was made of the S and N fractions and of the free amino acids in the shoots of perennial ryegrass (Lolium perenne L.) cv S23 grown in soil with and without added sulphate and in filtered air containing 0 and 400 μg SO 2 m −3 . Exposure to SO 2 of potentially S‐deficient plants alleviated the signs of deficiency; compared to deficient plants, the content of total and sulphate S was increased and the ratio N:S, as well as content of free amino acids, including asparagine and glutamine, was decreased. Similar exposure of plants grown with an adequate supply of S through the soil increased the content of sulphate but resulted in no significant alteration of the content of free amino acids.