The critical role of the shoot base in inhibiting cadmium transport from root to shoot in a cadmium-safe rice line (Oryza sativa L.)

Highlights: • Shoot base played an important role as switch in Cadmium (Cd)-safe rice line D62B. • Shoot base retained amounts of Cd, resulting in low Cd translocation to shoot. • Glutathione (GSH) and phytochelatins (PCs) biosynthesis was vital for Cd chelation. • Exogenous GSH further promoted Cd retention in shoot base. Cadmium (Cd) is harmful to rice and human, thus screening and understanding the mechanism of Cd-safe rice lines, which accumulate little Cd in brown rice, is necessary. D62B was screened as a Cd-safe rice line with low Cd translocation from roots to shoots, and there must be a switch restricting Cd transport from roots to shoots. Here we found that shoot base played the role as switch. Cd concentration in the shoot base of D62B was 1.57 times higher compared with a high Cd-accumulating rice line (Wujin4B) and lower Cd translocation under Cd stress. Glutathione (GSH) and phytochelatins (PCs) were important in this process. GSH and PCs concentrations in the shoot bases of D62B were 1.01– 1.83 times higher than Wujin4B as well as the glutathione S-transferase (GST) and phytochelatin synthase (PCS) concentrations, keeping in consistent with up-regulation of the genes OsGST and OsPCS1. PCs synthesis was further promoted by exogenous GSH. Our results prove the role of shoot bases as switch for restricting Cd transport in D62B due to its great potential for GSH and PCs biosynthesis, and thereby Cd chelation. This could be considered a key mechanism for low Cd accumulation in brown rice of the Cd-safe rice line.