Abstract
Different wheat cultivars have their individual defense response to heavy metal stress, exploring which is beneficial to using targeted and effective agronomic practice to reduce cadmium (Cd) accumulation in plants. Our previous study shows Cd concentration is higher in the Cd-tolerant cultivar Bainong 160 than the sensitive one Pingan 8. In this experiment, Bainong 160 showed stronger Cd uptake capacity and lower Cd translocation than Pingan 8, leading to its higher Cd concentration in roots and shoots, as verified by both dose- and time-dependent experiments. This study aims at exploring the factors underpinning Cd resistance and accumulation in wheat, and whether there is an interaction between them. There was a positive correlation between Cd distribution in organelle and H2O2 concentration in both shoot (r = 0.7) and root (r = 0.94**), suggesting that the less Cd distribution in organelle of Bainong 160 contributes to its lower H2O2 concentration than Pingan 8. For Pingan 8, lower expression of TaNramp6 and Cd-induced programmed cell death in cortex lead to its weaker Cd uptake capacity; while for Bainong 160, there are stronger positive cellular responses to Cd stress, including severe lignification in cortex cell, casparian strip formation, increment of both GSH and phytochelatins, and significant increased expression of TaHMA3 and repressed expression of TaHMA2, which together result in its stronger Cd retention in root and so as to inhibit Cd root-to-shoot transfer. Correlation analysis shows most of these reactions are associated with H2O2 concentration. In conclusion, Cd stress induced higher H2O2 concentration in sensitive cultivar Pingan 8 than tolerant one Bainong 160. The excessive H2O2-associated passive reaction in sensitive cultivar caused its lower Cd uptake ability, and moderate H2O2-induced stronger active response in tolerant cultivar, promoting Cd retention in root.
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