Effects of short-term ozone fumigation on carbohydrates in darkened tobacco leaves

The effects of short-term ozone (150 ppb for 2 h) treatment on leaf carbohy drate mobilization was evaluated in the O-3-tolerant Havana and O-3-sensiti ve Bel W3 tobacco cultivars (cvs) in the dark. During the first 3 h in the dark, treatment caused a transient incapacity to degrade starch in the leav es of both cvs, while the content of other sugars decreased irrespective of treatment. Starch degradation then resumed and after 20 h in the dark almo st all starch was degraded in all plants of both cvs. Short-term ozone fumi gation inhibited starch degradation in tobacco leaves. The degradation was unrelated to long-lasting damage to plant metabolism, the amount of sugars in the leaves at the moment of treatment, the particular sensitivity to ozo ne or a decreased capacity to translocate photosynthetic products in the da rk. This transient inhibition of starch degradation could contribute to the frequently observed starch accumulation in plants exposed to ozone. (C) 20 01 Editions scientifiques et medicales Elsevier SAS.