Species-Specific Relationship between Transpiration and Cadmium Translocation in Lettuce, Barley and Radish

Cadmium (Cd) may accumulate in plants to levels that are of concern in human diets. Our ability to predict the accumulation of Cd in plants is restricted by our poor understanding of the physiological processes that control Cd accumulation and translocation. A hydroponic experiment was carried out to test the hypothesis that the amount of Cd taken up and translocated to aboveground tissues is proportional to the volume of water transpired in lettuce (Lactuca sativa L.), barley (Hordeum vulgare L.) and radish (Raphanus sativus L.). Transpiration was measured as mass of water lost. Increased transpiration caused increased accumulation of Cd in plants; however, the proportion of total Cd translocated to the leaves ranged from 85% in lettuce to 66% in radish to only 21% in barley. Thus, factors controlling species-specific internal distribution of Cd are more important than transpiration in translocating Cd to aboveground tissues.