The Key Parts,Important Growth Stages And Related Elements In Cd/As Accumulation Of Rice

Rice,a staple food in China,is known to accumulate heavy metals such as Cd/As,thereby adversely affecting food security and human health.It is then imperative to control Cd/As accumulation in cultivated rice crops.The mechanism of Cd/As accumulation in rice is still unclear and begs further research.Therefore,it is essential to investigate the distribution and absorption mechanisms of Cd/As in different parts and growth stages of rice,as well as the elements correlated with Cd/As during accumulation using transcriptomic,ionomic,and stable isotope tracing technologies.In the present study,16 elements,in 14 different parts of 21 rice genotypes grown in Cd/As compound contaminated soils,were investigated by inductively coupled plasma mass spectroscopy.Additionally,digital gene expression profiling was used in the comparison of different nodes.The results indicated that Cd/As content in the roots and nodes was significantly higher than in other parts.However,the distribution of Cd in different nodes differed from that of As.The Cd content in Node I was significantly higher than in the other nodes whereas As content in the nodes appreciably decreased from the bottom to the top.The number of different genes expressed in response to Cd across different nodes was found to be significant,and insignificant in the case of As.The functions of these genes were to induce the expression of molecules and enzymes involved in glycolytic reactions and Cd detoxification.Our results show that roots and nodes are the two key barriers for inhibiting Cd/As transport into brown rice,and the accumulation capacity for As gradually decreases from the bottom node to the top node,whereas the accumulation capacity for Cd in Node I is the highest.High Cd content in Node I induced an increase in gene expressions of molecules and enzymes involved in glycolytic reactions and Cd detoxification.To study Cd/As-correlated elements in the transportation of rice,accumulation of other mineral elements and their correlations with Cd/As in different parts along with their ionomic profiles were analyzed.The results showed that Cu/Zn/Co/Mg was closely correlated with Cd,and Fe with As,and these elements might be closely linked in uptake or translocation systems.Additionally,a pot experiment was carried out where two genotypes of rice?Teyou 524;Y Liangyou696?were grown in two different Cd-contaminated soils and the resulting rice seeds were sampled at the end of jointing-booting,heading,grain-filling,and maturing stages to estimate Cd concentrations per grain.Subsequently,a hydroponic experiment was carried out where solutions of two Cd isotopes(¹¹¹Cd and ¹¹⁴Cd)were alternately added at the different growth stages?tillering,elongation,booting,heading,grain-filling,ripening,and maturing stages?of each of the two rice genotypes.The results showed that heading and grain-filling were the primary stages in accumulation of Cd and the cumulative Cd percentages in the grains could reach up to 80%.The stable isotope tracer results showed that the Cd absorbed in the roots during booting,heading,and grain-filling stages,the contribution rate of which could reach up to 65-75%across all growth stages,was the source Cd in the grains.Thus,it is inferred that these growth stages could effectively control Cd entry into the grain.