Leaf plasticity in peanut (Arachis hypogaea L.) in response to heavy metal stress

Phenotypic plasticity in morphological, anatomical and physiological traits of peanut (Arachis hypogaea L.) leaves was tested at four different concentrations of Cd, Cu and Zn under greenhouse conditions. Among 18 characteristics tested, nine were found to be the most sensitive and demonstrate the greatest phenotypic plasticity. These were: the leaf area (LA), the leaf mass per area (LMA), chlorophyll a concentration (Chl a), chlorophyll b concentration (Chl b), total chlorophyll concentration (Chl t), the effective quantum yield of photosystem II (ΦPS II), stomatal density of upper epidermis (SDU), palisade thickness (PT), and palisade to spongy thickness ratio (P/S). The plasticity of chlorophyll concentration and fluorescence parameters may be maladaptive and reflects metal toxicity to leaves, whereas the anatomical plasticity is adaptive, indicative of a tradeoff between the physiological and anatomic plasticity. The anatomical plasticity resulted in a xerophyte feature of leaves (i.e. small leaflets, thick lamina, upper epidermis, palisade mesophyll, as well as abundant and small stomata), which enhanced the capacity to resist drought caused by heavy metals via a decrease in root growth.