Growth and solute leakage in Hordeum vulgaris exposed to long‐term fumigation with low concentrations of SO2

Plants of three commercial cultivars of Hordeum vulgaris L. (Barberousse, Gerbel, Panda) were continuously exposed to two concentrations of SO2 (40±5 and 117±20 ppb) against a control (charcoal‐filtered air). Experiments were performed in fumigation chambers. Fumigation was started 9 days after seeding and plant material was harvested after 48 days. In none of the three cultivars did visible symptoms of injury appear on the leaves after exposure to SO2, while they all showed a reduction in plant height and dry matter of shoots and roots and a significant increase in the shoot/root dry weight ratios depending on the cultivars. The time course of conductivity, and K+ Ca2+ and sugar effluxes were determined for 24 h. Leaves from cvs Gerbel and Panda exposed to SO2 exhibited a progressive increase in conductivity, and in Ca2+ and sugar efflux (expressed as percentages of their total effluxes). Plusmn; efflux of the three cultivars and conductivity in cv. Barberousse increased only after 24 h incubation. A relative leakage ratio (RLR) was calculated from the UV absorption at 280 nm after 24 h incubation of the leaf strips and the total 280 nm UV absorption, obtained after liquid N2 killing of the tissues. The RLR was well correlated with the total amino acids and sugars found in the leachate and can be used as a test for determining the tissue response to SO2.