Lignin side chain region participates in Cd detoxification related to the cultivar-dependent Cd accumulation in Brassica chinensis L

Abstract To investigate the effect of lignin in the cultivar-dependent Cd detoxification of Brassica chinensis L., Cd and lignin contents, lignin composition and laccase genes expressions in low-Cd-accumulating (LAJK) and high-Cd-accumulating (HAJS) cultivars grown under control (CK) and 25 μM Cd-treatment were determined. The results showed that lignin combined about 14% of total Cd in both LAJK and HAJS. LAC genes were more up-regulated in HAJS than in LAJK, indicating that the LAC genes were involved in the cultivar-dependent lignin functions. Higher β-aryl ether (A) proportion in the lignin side chain region in LAJK than in HAJS were observed, whereas resinol (B) and phenylcoumaran (C) constitute much higher proportions in HAJS than in LAJK. Chemical calculation to estimate Cd affinity associating with lignin side chain region displayed that i) β-aryl ether (A) exhibited major coupling with lignin aromatic region; ii) resinol (B) and phenylcoumaran (C) displayed major participation in complexation with Cd. We therefore conclude that Cd compartmentalization in the secondary cell wall (SCW) by coupling with lignin side chain region is responsible for Cd detoxification related to cultivar-dependent Cd accumulation of Brassica chinensis. This is the first study on lignin composition in relation to Cd retention mechanisms in SCW.