Variation in Leaf Cutin Content and Chemical Composition along One Annual Cycle in the Mediterranean Cork Oak (Quercus suber L.)

Abstract

Cork oak (Quercus suber L.) has high economic value given by its sustainable production of cork, and ecological importance in the Mediterranean region. The species is well adapted to the dry climate, namely through the sclerophyllous nature of its leaves with a well-developed cuticle, including cutin and cuticular waxes that contribute to protection against drought. Leaves of cork oaks were collected along one annual cycle, starting from the young leaves in May to the one-year-old leaves in March. Leaf cutin content and chemical composition were determined by transesterification subsequently to the determination of cuticular waxes, and leaf features, and were analyzed along the leaf cycle. Cutin is a major component of the cuticle, representing on average 72.4% of the cutin and cuticular waxes. Cutin amounted to 71.0 g/1000 g of dry leaves, without significant seasonal mass proportion variation, while cutin coverage increased from May to December (429.7 μg/cm2 and 575.4 μg/cm2, respectively). In contrast, a clear seasonality was found in cuticular wax mass proportion and coverage (18.4 g/1000 g of dry leaves and 113.5 μg/cm2 in May, and 28.5 g/1000 g and 235.2 μg/cm2 in September). Cutin is a glyceridic polyester composed by long-chain acids, mainly ω-hydroxyacids, followed by fatty acids with a few ω-diacids and alcohols, and by a substantial proportion of aromatics. Cutin composition varied along time with a proportional increase in ω-hydroxyacids (45.8% in May; 50.8% in December), and a significant decrease in aromatics (24.2% in May and 8.5% in March). The cuticle seasonal development in the cork oak contributes to protect the leaves and the trees from the dry summer conditions.