Effects of sulfur nutrition on photosynthesis in cadmium-treated barley seedlings

The effects of sulfur (S) nutrition at 0.1 or 1 mM S on cadmium (Cd) toxicity measured by photosynthesis in barley (Hordeum vulgare L. cv. UC 476) seedlings were studied. Eight-day-old seedlings were treated with 25 mu M Cd by adding cadmium chloride (CdCl2) to the nutrient solution. Then photosynthetic carboxylation efficiency (ACi curve) and stomatal conductance of the primary and second leaves were measured at four and eight days after Cd treatment. Fluorescence parameters were measured every 24 h for eight days after two days of Cd treatment. At 20 days, plant growth parameters were measured and dry biomass determined. The results showed that ACi was significantly reduced by Cd, but more in the low (0.1 mM) S than in the high (1 mM) S-treated plants. Stomatal conductance of plants was also decreased by Cd, but more in the low S-treated giants. Low S-treated plants exposed to Cd showed an increase in Fo and Fq, and a decrease in Fv/Fm and T-1/2, indicating photoinhibitory damage to PSII. Analysis of the growth parameters showed that Cd decreased giant size and biomass, but the reduction was more severe in the low S-treated plants. These results support the hypothesis that S is a critical nutritional factor in plants which is important for the reduction of Cd toxicity.