Open-air fumigation of winter barley with sulphur dioxide: effects on growth of the flag leaf and enzymes of photosynthetic carbon metabolism

The effects of sulphur dioxide (SO 2) on flag leaf growth and on a number of enzymes of photosynthetic carbon metabolism in leaves of winter barley ( Hordeum vulgare L. cv. Igri) were investigated. Plant material was obtained from an open-air fumigation experiment operated at Littlehampton, West Sussex, Gt. Britain throughout two growing seasons (1985–1986 and 1986–1987). In 1985–1986 samples were compared from an ambient plot (mean of 0.007 μl 1 −1 SO 2) and the highest SO 2 treatment plot (mean of 0.048 μl 1 −1). In 1986–1987 samples from the ambient SO 2 plot (mean of 0.005 μl 1 −1) and the two highest treatments (means of 0.028 and 0.038 μl 1 −1 SO 2) were sampled. The flag leaf was studied in particular because of its considerable contribution to grain filling. Significant reductions in flag leaf dry weight and flag leaf area were found in the highest SO 2 treatment in both seasons. In 1986–1987, delays in flag leaf emergence and senescence in both the 0.028 and 0.038 μl 1 −1 SO 2 treatments were observed. Leaf extracts were used to assay the following enzymes: stromal phosphoribulokinase and NADP-dependent glyceraldehyde-phosphate dehydrogenase, phosphoglycerate kinase (90% stromal) and cytosolic fructose-1,6-bisphosphatase. No effects of SO 2 were detected on the total activity of any of the stromal enzymes, or on the activation status of NADP-dependent glyceraldehyde-phosphate dehydrogenase. Significant reductions in the post-anthesis activity of cytosolic fructose-1,6-bisphosphatase were recorded for the highest SO 2 treatment (0.038 μl 1 −1) and provided a preliminary indication that these levels of SO 2 could affect the flow of fixed carbon in leaves and could thereby affect the availability of photoassimilate for export from source leaves. Both the reduction in size of the flag leaf and decreased levels of activity of cytosolic fructose-1,6-bisphosphatase may have important implications for the process of grain filling.