Studies on pea and wheat showed that negative effects of enhanced UV-B radiation were alleviated by moderate drought, and resulted in increased dry mass production (Alexieva et al. 2001). It is quite well known that during drought, some plants promote the production of phenolic substances and wax that improves UV-B radiation screening and reflection, and thus reduces UV-B damaging effects (Kulandaivelu et al. 1997). Ameliorating effects of drought were ascribed to increased activity of antioxidative enzymes that protect plants against oxidative damages caused by UV-B radiation (Alexieva et al. 2001). On the other hand, Caldwell et al. (1998) suggested that drought masks UV-B effects on plants, because drought constitutes a stronger stress for plants than enhanced UV-B radiation.
In contrast, the earlier study of Runeckles and Krupa (1994) revealed that enhanced UV-B radiation increased the sensitivity of crops to drought. These UV-B effects were ascribed to altered stomatal function by UV-B radiation that additionally affects plant water status. Effect of combined effect of enhanced UV-B radiation coupled with drought on seed biomass has been shown in Fig. 12.1.
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