Limitations of monoterpene emissions and their antioxidant role in Cistus sp. under mild and severe treatments of drought and warming

Terpenes are involved in protection mechanisms against environmental-induced oxidative stresses. In this work we aimed to understand the potential role of terpenes in the response of Cistus monspeliensis to two abiotic stresses, typical of Mediterranean summers, such as drought and warming. Two different experimental setups were established: a long-term mild warming and drought treatment in the field and a more severe warming and drought treatment in laboratory conditions. Terpene emission strongly declined in plants under severe warming, as observed in the laboratory treatment. The decline in terpene emission was paralleled by an increase both in the concentration of the aqueous-phase antioxidant ascorbate and in the activity of ascorbate peroxidase (APX). Under severe drought, however, terpene emission was maintained even when assimilation and stomatal conductance were completely suppressed. In this case, ascorbate and ascorbate peroxidase activity were much lower than in warming treated plants all along the experiment. Data of our study reveals a possible shift from terpene-mediated to ascorbate-mediated ROS scavenging in plants under high temperature conditions in Cistus plants depending on stress severity. Our results also suggests a coordinated antioxidant response in Cistus under various environmental stress conditions.