Research Article Leaves of Field-Grown Mastic Trees Suffer Oxidative Stress at the Two Extremes of their Lifespan F Marta Juvany, Maren M ¨ uller and Sergi Munn ´ e-Bosch * Departament de Biologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal, 643, E-08028 Barcelona, Spain ∗ Corresponding author Tel. +34 9 3402 1463; Fax: +34 9 3411 2842; E-mail: smunne@ub.edu F Articles can be viewed online without a subscription. Available online on 5 July 2012 at www.jipb.net and www.wileyonlinelibrary.com/journal/jipb doi: 10.1111/j.1744-7909.2012.01141.x Abstract Leaf senescence is a complex phenomenon occurring in all plant species, but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions. To better understand the physiological processes underlying leaf senescence in mastic trees (Pistacia lentiscus L.), we evaluated leaf growth, water and N content, photosystem II (PSII) photochemistry, lipid peroxidation and levels of photosynthetic pigments, antioxidants, abscisic acid, and salicylic acid and jasmonic acid during the complete leaf lifespan, from early expansion to late senescence in relation to natural climatic conditions in the field. While mature leaves suffered from water and N deficit during late spring and summer, both young (emerging) and old (senescing) leaves were most sensitive to photo- oxidative stress, as indicated by reductions in the F v /F m ratio and enhanced lipid peroxidation during late autumn and winter. Reductions in the F v /F m ratio were associated with low α-tocopherol (vitamin E) levels, while very old, senescing leaves additionally showed severe anthocyanin losses. We have concluded that both young (emerging) and old (senescing) leaves suffer oxidative stress in mastic trees, which may be linked in part to suboptimal temperatures during late autumn and winter as well as to low vitamin E levels. Keywords: Leaf senescence; lentisc (Pistacea lentiscus L.); oxidative stress; phytohormones; seasonal effects. Juvany M, M ¨ uller M, Munn ´ e-Bosch S (2012) Leaves of field-grown mastic trees suffer oxidative stress at the two extremes of their lifespan. J. Integr. Plant Biol. doi: 10.1111/j.1744-7909.2012.01141.x Introduction Leaf development, from bud break to death, is a finely con- trolled process at the molecular, biochemical and physiological levels. The two extremes of leaf lifespan are characterized by rapidly growing, young emerging leaves on one hand, and very old, senescing leaves on the other. While studies of senescing leaves are common, their physiology is still poorly understood. Furthermore, there are few experiments to better understand the processes underlying what happens in emerging young leaves. Leaf senescence is characteristic of the latest stages of development and involves nutrient remobilization to other plant parts and some degenerative changes that lead these organs to death. It is usually characterized by three phases: (i) an initiation phase triggers the process in fully-expanded young leaves (also called mature, non-senescing leaves). This is followed by (ii) a remobilization phase, which is governed at the molecular level and allows nutrient remobilization accom- plishing one of the most important functions of the senescing process in leaves. Finally, (iii) a terminal phase occurs when nuclei and the nucleic acid-related machinery is destroyed and the leaf can no longer accomplish any physiological role (Munn ´ e-Bosch and Alegre 2004; Lim et al. 2007; van Doorn 2011; Fischer 2012). Reactive oxygen species (ROS) generation is common to all aerobic organisms including plants, and occurs in the plant’s response to various stresses, including water deficit, high light, low temperatures or salinity, etc., as well as during leaf senescence. The process of protein degradation during leaf senescence, which occurs to a high extent in chloro- plasts, is initiated by ROS and involves the action of prote- olytic enzymes (Bhattacharjee 2005; Khanna-Chopra 2011). C  2012 Institute of Botany, Chinese Academy of Sciences