Photo- and antioxidative protection, and a role for XXXX during drought and recovery in field-grown Phillyrea angustifolia plants.

@entity3785 @entity2066 @entity7695 @entity1881 @entity1234 @entity1865
Mechanisms of photo- and antioxidative protection, the extent of oxidative stress, and @entity3785 accumulation in leaves of Phillyrea angustifolia L. (Oleaceae) plants exposed to drought and recovery in Mediterranean field conditions were studied. The amounts of @entity1881 increased up to 4-fold and those of @entity7695 increased up to 3-fold at relative leaf water contents (RWCs) of ca. 60%, which caused up to 70% increases in the de-epoxidation state of the xanthophyll cycle (DPS). While @entity1881 increased further in severe drought, @entity7695 levels and DPS remained constant, @entity2066 decreased and @entity1234 ( @entity1865 ) levels increased at RWCs below 50%. Though this was associated with significant decreases in the maximum efficiency of photosystem II photochemistry (F(v)/ F(m)), the same leaves that suffered from drought recovered after rainfalls, and similar @entity1865 levels and F(v)/ F(m) ratios to those observed before drought were attained. During recovery (i) the F(v)/ F(m) ratio and @entity2066 levels increased slowly, (ii) @entity1881 levels decreased sharply, to increase again, and (iii) @entity1865 levels in leaves increased to values 35% higher than those observed at maximum drought, and decreased later. @entity3785 (SA) levels showed a strong negative correlation (r(2)=0.857) with the RWC, and increased progressively up to 5-fold, during drought. During recovery, SA levels decreased, but remained slightly higher than those observed before drought. SA levels were positively correlated with those of @entity1881 during drought (r(2)=0.718), but not during recovery (r(2)=0.221). We conclude that (i) P. angustifolia plants activate several mechanisms of photo- and antioxidative protection to withstand drought stress during a Mediterranean summer, (ii) endogenous SA levels increase in leaves of drought-stressed plants, thus suggesting a role for SA in plant responses to drought, and (iii) plants suffer oxidative stress during recovery, and this stress is more severe as the previous drought is more intense.
