Diterpenes and antioxidative protection in drought-stressed Salvia officinalis plants

Previous studies have shown that diterpene carnosic acid plays a role as an antioxidant in rosemary, a drought-tolerant species. However, this mechani sm has not been tested so far in other species. The endogenous levels of di terpene carnosic acid and alpha -tocopherol, which are lipophilic antioxida nts found in chloroplasts, were measured in a drought-recovery cycle in lea ves of sage (Salvia officinalis L. subs. officinalis), a drought-susceptibl e species, growing in Mediterranean field conditions. The relative leaf wat er content of the sage plants fell markedly when exposed to drought during the summer. As the drought progressed, the carnosic acid amounts in the lea ves decreased, giving rise to increased levels of its oxidation products, r osmanol and isorosmanol, thereby revealing the antioxidant activity of carn osic acid in drought-stressed leaves. At the same time, alpha -tocopherol l evels decreased progressively with drought. Midday depression of carnosic a cid and alpha -tocopherol was observed throughout the study, and the highes t levels of carnosic acid oxidation products (i.e. rosmanol and isorosmanol ) were observed at midday when high light was simultaneous to water deficit . This report suggests that the same mechanism of antioxidative protection by carnosic acid applies in rosemary and sage, and shows that it is the com plete set of antioxidants (and not a single mechanism) that is responsible for avoiding drought-induced damage in plants.