Cadmium Accumulation Characteristic And Tolerance Mechanism In Leguminous Plants During Germination Period

In recent years, heavy metal pollution has received increasing attentions worldwide. Among all of the heavy metals, cadmium (Cd) is of the most concern due to its high mobility and toxicity in the environment. Phytoremediation, a low-cost and eco-friendly technology, has become an innovative way for eliminating Cd from contaminated environment. Currently, the application of documented Cd hyperaccumulators is limited due to their low biomass, long growth period, or environmental dependence. In the present study, Cd tolerance and accumulation characteristics in leguminous plants during germination period were investigated. In addition, the mechanisms of Cd tolerance in bean sprouts were discussed. The main results were summarized as follows:(1) The soybean sprout (SS) and ormosia sprout (OS) show great tolerance and accumulation characteristics in a hydroponic system. The SS and OS are able to tolerate (up to 20 mg L-1) and accumulate high concentration of Cd, and the absorbed Cd is mainly located in the roots. While the mung bean sprout (MS) exhibits poor tolerance and accumulation ability to Cd.(2) Cd accumulation in leguminous plants is a dynamic process, and presents apparent discrepancy with different species and growth period. In the initial stage, Cd are adsorbed firstly on the surface of seed husk, and then transported to the cotyledon. Afterwards, Cd are primarily accumulated in the roots of MS and SS, and then transported to the upper parts when Cd content in the roots reaches saturation. However, Cd accumulation in OS does not conform to the rule.(3) Cd uptake and accumulation by the bean sprouts are affected by cultural conditions. Altering media pH causes obvious variation of Cd translocation ability, but does not influence the growth and Cd uptake capacity of bean sprouts. The effect of illumination time on bean sprouts is just the opposite.(4) The sub-cellular localization of Cd in root cells of bean sprouts follows the order:soluble fraction> cell wall> organelle.(5) The chemical form of Cd in bean sprouts varies according to Cd accumulative area and initial Cd concentration in media. In the roots and stems, Cd exists mainly in the forms of organic acid salt and pectin acid salt. In the leaves, Cd exists mainly in the forms of heavy metal phosphate and oxalate, while in the cotyledons, water soluble organic acid salt is the dominating form.