Development and structure of drought-tolerant leaves of the Mediterranean shrub Capparis spinosa L.

Capparis spinosa (caper), a winter-deciduous perennial shrub, is a consistent floristic element of Mediterranean ecosystems, growing from May to October, i.e. entirely during the prolonged summer drought. The internal architecture of young and fully expanded leaves was studied, along with certain physiological characteristics. Capparis spinosa possesses thick, amphistomatic and homobaric leaves with a multilayered mesophyll. The latter possesses an increased number of photosynthesizing cells per unit leaf surface, a large surface area of mesophyll cells facing intercellular spaces (Smes) and a low percentage of intercellular space per tissue volume. Smes and chlorophyll content attain their maximum values synchronously, slightly before full leaf expansion. Nitrogen investment is also completed before full leaf expansion. The structural features, in combination with the water status, could contribute to enhanced rates of transpiration and photosynthesis under field water shortage conditions.