Study On The Physiological Mechanism Of Different Water Status Affecting The Cadmium Accumulation In Rice During Flowering Stage

Cadmium（Cd）as a non-essential element of plants has become a common pollutant in farmland soil.Excessive Cd in the rice seed would cause great harm to human health through the food chain.Therefore,under soil Cd pollution,reducing the accumulation of Cd in rice has become an urgent problem.To investigate the mechanism of Cd absorption and translocation under different water conditions,rice yield,Cd absorption and translocation,photosynthesis and other indicators were determined in pot experiment an d field experiment.ERECTA（er）is a gene that plays a coordination role in plant transpiration and photosynthesis.It affects transpiration efficiency by regulating epidermal and mesophyll development,changing stomatal density and leaf porosity.The japonica rice cultivar Nipponbare（Oryza sativa L.）,east japonica,er（er-deficient mutant constructed with east japonica as the background material）,ER-OE（over-expressed rice material constructed with japonica rice cultivar Nipponbare as background material）were selected as materials for pot experiment,were used to study the physiological mechanism of different water treatments（flooded treatment,one day after drought,three days after drought,five days after drought）on the accumulation and transportation of Cd during the flowering stage of rice.In field experiments,the plots with a soil Cd background value of 2.076 mg kg^-1and the rice variety（Tianyouhuazhan）were selected.The flooded treatment,intermittent flooding treatment,and drought treatment were carried out to explore the physiological mechanism of Cd accumulation and transportation in rice during the flowering stage.The main results are as follows:（1）Effects of different water conditions on rice growth status under Cd pollutionThere were significant differences in the growth status of rice under different water conditions in pot and field experiments（P<0.05）.Under the decreased soil moisture content,the rice biomass was decreased gradually,and Ca,Cu,Mg,Mn,Fe,and Zn content of rice in pot experiments also showed a reduction.In addition,a similar trend was found in the agronomic traits.The plant height,100-grain weight（thousand-grain weight）,grain length,ear weight per plant,and yield per mu was decreased when the soil moisture content was reduced.These results indicated that under the flooding treatment of potted and field,rice growth and yield is better than other treatment.In the pot experiment,the growt h status of ER-OE rice was significantly better than its background material,while er was lower than that of East japonica（P<0.05）.（2）Effects of different water conditions on Cd accumulation in riceThe promotion of soil moisture content in pot experiments and field experiments resulted in a significant reduction of Cd accumulation in rice（P<0.05）;The accumulation of Cd in rice was the lowest under the flooding treatment of pot and field experiments.The accumulation of Cd in different parts of rice was:root>stem>leaf>rice.In pot experiments,it was found that the accumulation of Cd accumulation of ER-OE was significantly lower than that of wild type,but er was significantly higher than that of wild type.（3）Effects of different water conditions on rice photosynthesisDifferent water conditions had significant effects on photosynthesis of rice under Cd pollution in pot and field experiments（P<0.05）.The net photosynthetic rate（P_n）of rice was increased,but the stomatal conductance（G_s）and intercellular CO₂ concentration（C_i）were decreased under the condition of decreased soil moisture content.When the soil moisture was increased the transpiration rate（T_r）and P_n was decreasd.It showed that the transpiration of rice was the weakest under flooding treatment in pot and field,and the transpiration of ER-OE were weaker than that of wild type,and er was significantly stronger than that of East japonica（P<0.05）.（4）Effects of different water conditions on Cd transport in riceDecreasing the soil water content resulted in a significant promotion in the Cd transport coefficient of rice.Under potted and field flooding treatments,the Cd transport coefficient of each part of rice was the lowest,and ER-OE was lower than wild type,er was significantly higher than that of wild type（P<0.05）.In addition,this study also measured the Cd content in the xylem sap of rice in pot experiments,and found that the Cd content in xylem was the lowest under flooding treatment.ER-OE rice was lower than that of wild type,and er rice was significantly higher than that of East japonica（P<0.05）.It showed that under the flooding treatment,the ability of rice to transport above ground was the lowest,and the content of Cd in the grain was the lowest.In summary,in the flooding treatment of pot experiment and field experiment,due to the weak transpiration of rice,the transfer of Cd to shoot is restricted,resulting in a decrease in the Cd content in the rice.The Cd content in rice was reduce d to 0.4 mg kg^-1under flooding treatment in the field experiment,which was 77%lower than that in the drought treatment.The Cd content was basically reduced to the internationally safe value,and the rice yield was the highest.This indicates that flooding treatment can effectively reduce the Cd content in rice while ensuring the yield of rice,and provide a reference for the safe production of rice in Cd-contaminated areas.