Variations among rice cultivars in subcellular distribution of Cd: The relationship between translocation and grain accumulation

•Rice cultivars differed largely in Cd translocations from shoots to grains.•Grain Cd levels correlated with Cd translocation factors from shoots to grains.•Rice cultivars differed in Cd distributions in cell wall and soluble fractions.•Cell wall plays a main role in Cd deposition in rice shoot.•Soluble fraction is the main Cd pool in rice shoot for transport into the grain.

The variations of subcellular distribution of cadmium (Cd) among six rice (Oryza sativa L.) cultivars, and the relationships with Cd translocation in the plants and accumulation in the grain were studied. The results showed that the rice cultivars varied greatly in Cd translocation factors (TFs) from shoots to ears/grains and subcellular distribution ratios (SDRs) in cell wall fraction (F1) and soluble fraction (F4), particularly in Cd-contaminated soils. These variations resulted in different Cd levels in the rice grain. There were positive and highly significant (P < 0.01) correlations between grain Cd contents and the TF from shoots to ears/grains. The TF from shoots to ears/grains was negatively and significantly (P < 0.05, or 0.01) correlated with the SDR in F1 of shoots, but positively and significantly (P < 0.05, or 0.01) correlated with the SDR in F4 of shoots. These results indicate that the translocation of Cd from shoot to grain is a main factor responsible for Cd accumulation in the grain, and the soluble fraction of Cd in rice shoot is the main subcellular pool for transferring Cd into rice grain. The cell wall fraction plays a main role in Cd deposition in rice shoot, which restrains the translocation from shoot to the grain. So subcellular distribution of Cd in rice shoot is one of the main mechanisms that differentiate rice cultivars in governing the translocation and accumulation of Cd in rice grain.