Effects of cadmium exposures in different stages on plant growth ,cd uptake and cd concentrations in brown rice of a hybrid and conventional rice variety

A comparative study was conducted on the responses of hybrid rice “Weiyou 1126” and conventional rice “Zhefu 802” in plant growth, dry matter production, and cadmium (Cd) uptake, accumulation and distribution under Cd exposure in various growth stages through a water culture pot experiment with split addition of Cd reagent. Results showed that there were different responses of rice plants on Cd exposure in various growth stages. In the stage before spikelet initiation (the early stage), the major response of Cd toxicity was the reduction of photosynthetic potential. In the stage from spikelet initiation to flowering (the middle stage), Cd toxicity mainly reflected on inhibition of the process of spikelet initiation and development. In the stage after flowering (the later stage), Cd exposure mainly resulted in an obstacle in transfer, as well transformation of carbohydrates and NP nutrients from the straw to the ear. Considering the aspect of grain yield, the middle stage was the most sensitive one of the two types of rice to the Cd stress. The sequence of Cd uptake rate was the middle stage the later stage the early stage of both rice varieties. Concentrations of Cd in the brown rice was related to both, the amount of Cd uptake by rice plants as well the rate of Cd transfer from the straw to grains. There was a comparative potential of Cd uptake by the hybrid and the conventional rice. However, ratios of Cd in the upper ground parts to the total uptake by the hybrid rice was 4.9~21.8 % higher than that of the conventional rice, while the ratio of Cd accumulated in grains to that in straw of the hybrid rice was 49~95 % higher that that of the conventional rice. Finally, concentration of Cd in brown rice of the hybrid rice was 33~72 % higher than that of the conventional rice. From this experiment, it can be concluded that the hybrid rice is more sensitive to an environmental Cd pollution than the conventional rice in aspects of the reduction of yield and the damage effect on hygienic quality of rice grains.