RESPONSE OF SO2‐SENSITIVE AND RESISTANT GENOTYPES OF RYEGRASS (LOLIUM PERENNE L.) TO PROLONGED EXPOSURE TO SO2

Abstract

SUMMARYTwo genotypes of perennial ryegrass (Loliutn perenne L.), one (S23) sensitive to SO2 and the other (BR) reported to be resistant, were exposed to 0, 50 or 150 ni SO2 1−1 (0, 133 or 398 μg SO2 m−3 at STP) for four weeks under conditions that gave ‘slow’, ‘medium’ or ‘fast’ rates of growth. These treatments allowed comparisons of the responses between genotypes over a range of conditions within which plants could be expected to exhibit maximum and minimum sensitivities to SO2. Significant effects on growth from exposure to SO2 were observed primarily when growth was slow, when the plants were expected to be most sensitive. Although exposure to 150 nl SO2 1−1 significantly increased stomatal resistance two‐fold in both genotypes during slow growth, there was no accompanying diminution in leaf sulphur content, implying that a two‐fold increase in stomatal resistance is not sufficient to be considered an avoidance mechanism to SO2.Compared with the sensitive S23 gentoype under control (SO2‐free conditions, the resistant BR genotype shows slightly greater stomatal resistance, reduced absorption of sulphate through the roots, and reduced dry matter production. Reduced dry matter production in BR may be attributed to its peculiar isoenzyme of ribulose‐1,5‐bisphosphate carboxylase, which shows a greater resistance to inhibition by sulphite but lower carboxylation rates than ribulose‐1,5‐bisphosphate carboxylase from S23.