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 carbohydrate mobilization was evaluated in the O3-tolerant Havana and O3-sensitive 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 leaves of both cvs, while the content of other sugars decreased irrespective of treatment. Starch degradation then resumed and after 20 h in the dark almost all starch was degraded in all plants of both cvs. Short-term ozone fumigation 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 ozone or a decreased capacity to translocate photosynthetic products in the dark. This transient inhibition of starch degradation could contribute to the frequently observed starch accumulation in plants exposed to ozone.