Leaf reflectance and photo‐ and antioxidant protection in field‐grown summer‐stressed <i>Phillyrea angustifolia</i>. Optical signals of oxidative stress?

• Here we aimed to assess the photo and oxidative stress linked to the Mediterranean summer conditions characterized by drought, heat and high irradiance, and to find possible optical signals of such changes. • Foliar reflectance was measured in parallel to leaf water content, gas exchange, chlorophyll fluorescence, extent of oxidative stress, and mechanisms of photo- and antioxidative protection in leaves of the evergreen Phillyrea angustifolia (Oleaceae) plants exposed to Mediterranean field spring-summer conditions. • Relative leaf water content (RWC) of nonirrigated plants (WS) decreased from 82 to 50% after 48 d without rain, and net photosynthetic rates and stomatal conductances decreased c. 90%, but there was no photo- and oxidative damage. The amounts of the photoprotector zeaxanthin and of the antioxidant a-tocopherol increased up to threefold. The b-carotene concentration decreased to 50%. The reflectance indices WI (water index), PRI (photochemical reflectance index), and BPI (brown pigment index) followed the changes in water content, photosynthetic rates, and oxidant status, respectively. • These results show that severe drought leads to oxidative stress in field-grown P. angustifolia plants, highlights the significance of photo- and antioxidative protection for the survival of drought-stressed plants, and indicates that the changes in oxidant status may be assessed by leaf reflectance (brown pigment index, BPI).