Water relations, gas exchange and amino acid content in Cd-treated lettuce

Water relations, gas exchange and amino acid contents in Lactuca sativa (L.) cv. Reine de Mai were studied at variable cadmium concentrations (0, 0.01, 0.1, 1, 100 μM) using axenic hydroponic culture. Ten-12-day-old seedlings were simultaneously placed in nutrient solution with or without Cd for 9 days and plants were labelled with 14 CO 2 24 h before amino acid quantification. Cadmium uptake by roots and shoots increased with Cd concentration in the medium. At low Cd concentrations (0.01, 0.1 μM) biomass production increased, while 100 μM Cd was toxic to both root and shoot growth. Water status and gas exchange also decreased at 100 μM Cd. These Cd effects seemed to involve stomatal closure, but low Cd concentrations enhanced stomatal conductance without any significant modification in net photosynthesis