Effects Of Cadmium On Growth And Nutrient Uptake Of Rice And The Possible Role Of Apoplast In Tolerance To Cadmium

Cadmium is a heavy metal that is of wide spread in the environment. It can cause many toxic symptoms in plants. In the long-term of environmental option and evolutionary adaptation, plants have developed mechanisms to alleviate or avoid Cd toxicity.In this study, a hydroponic experiment was carried out to investigate the effects of Cd accumulation in vivo on rice growth and mineral nutrients uptake under different Cd treatment levels. The results showed that, as a nonessential element, Cd was very toxic to rice cultivars, and could counteract with the uptake of mineral elements. Cd accumulation in shoot/root decreased biomass accumulation and Ca, Mg uptake, but mcreased Fe uptake as compared to the control. The toxic effects of Cd on rice can be attributed to the interaction of essential mineral uptake, which disturbs the elements equilibrium in plants.In order to investigate the possible roles of apoplast in response to Cd stress, cell walls of rice root and iron oxides plaque deposited on root surface were studied. The results showed that Cd uptake in rice cultivars increased with the increase in amount of Cd absorbed on the cell walls, as well the amount being desorbed. This indicates that the ability of cell wall materials to adsorb/desorb Cd may influence the uptake of Cd through the plasma membrane: more exchangeable Cd ions on the cell walls, easier it can enter the root cell. Iron oxides plaque deposited on root surface may absorb Cd from the growth medium. The amount of Cd accumulated on rice root surface increased with the increase in amount of deposited iron oxides. Therefore, iron plaque can influence the Cd uptake in some extent too. All of these results suggest that the accumulation of Cd on the cell walls and iron plaque can influence the uptake of Cd by rice, thus to influence the ability of enduring the Cd stress. The studies on root cell wall and iron plaque provide some useful information for a deeper understanding of the role of apoplast in Cd stress.