The mechanism of enhanced lignin regulating foliar Cd absorption and yield in rice (Oryza sativa L.)

The impact of atmospheric deposition of cadmium (Cd) in cereal crops has become a global concern. Enhanced lignin content was expected to benefit the plant performance against Cd exposure. To date, however, the underlying mechanisms of lignin regulating foliar Cd absorption in rice (Oryza sativa L.) and its effect on grain yield remains unclear. In present study, the effect and mechanism of rice in response to leaf Cd exposure were investigated using ¹¹³Cd stable isotope and a lignin-increased rice mutant. The highest Cd uptake efficiency and uptake amount was observed in wild type (WT) plant grown in the maturity period, which were 3-fold higher than in mutant plant. Compared to WT, the mutant exhibited 14.75% and 25.43% higher contents in G- and S-unit of lignin monomers. Lignin biosynthesis and polymerization related genes (OsPAL/OsCOMT/Os4CL3/OsLAC5/OsLAC15) were significantly up-regulated in mutants. In addition, the enzyme activities involved in the above process were also significantly increased by 1.24-1.49-fold. The increased Cd retention in cell wall and decreased gene expression levels of OsNRAMP5, OsHMA3 and OsIRT1 in mutant indicated that lignin effectively inhibited Cd transportion in plant tissues. Moreover, the antioxidant capacity and photosynthesis efficiency in mutant plant were obviously improved, leading to higher Cd tolerance and increased grain yield. Our results revealed the molecular and physiological mechanisms of enhanced lignin regulating foliar Cd absorption and yield in rice, and provided the valuable rice genotype to ensure food safety.