Cadmium translocation and accumulation in developing barley grains.

Soil cadmium (Cd) contamination has posed a serious problem for safe food production and become a potential agricultural and environmental hazard worldwide. In order to study the transport of Cd into the developing grains, detached ears of two-rowed barley cv. ZAU 3 were cultured in Cd stressed nutrient solution containing the markers for phloem (rubidium) and xylem (strontium) transport. Cd concentration in each part of detached spikes increased with external Cd levels, and Cd concentration in various organs over the three Cd levels of 0.5, 2, 8 microM Cd on 15-day Cd exposure was in the order: awn > stem > grain > rachis > glume, while the majority of Cd was accumulated in grains with the proportion of 51.0% relative to the total Cd amount in the five parts of detached spikes. Cd accumulation in grains increased not only with external Cd levels but the time of exposure contrast to stem, awn, rachis and glume. Those four parts of detached spike showed increase Cd accumulation for 5 days, followed by sharp decrease till day 10 and increase again after 12.5 days. Awn-removal and stem-girdling markedly decreased Cd concentration in grains, and sucrose or zinc (Zn) addition to the medium and higher relative humidity (RH) also induced dramatic reduction in Cd transport to developing grains. The results indicated that awn, rachis and glume may involve in Cd transport into developing grains, and suggested that Cd redistribution in maturing cereals be considered as an important physiological process influencing the quality of harvested grains. Our results suggested that increasing RH to 90% and Zn addition in the medium at grain filling stage would be beneficial to decrease Cd accumulation in grains.