Root Cell Wall and Phytochelatins in Low-Cadmium Cultivar of Brassica parachinensis

Abstract ‘Lvbao-701’ is a Brassica parachinensis cultivar that exhibits low accumulation of cadmium (Cd) and high Cd tolerance. This cultivar was compared with a high-Cd accumulating cultivar, ‘Chixin-4’, to characterize the mechanisms influencing Cd accumulation in B. parachinensis . Root cell walls were isolated by dissolving the cytoplasm with organic solvent, and the root Cd and phytochelatin (PC) contents were subsequently analyzed. Additionally, a PC synthase gene fragment was cloned and expressed under Cd stress conditions. The Cd content and proportion of Cd bound to root cell walls were higher in ‘Lvbao-701’plants (68%–77%) than in ‘Chixin-4’ plants (35%–54%) following exposure to Cd stress. The proportions of Cd bound to root cell walls measured using cell walls isolated with a non-destructive method were higher than those obtained using a conventional method that required grinding and centrifugation steps. Exposure to Cd stress conditions induced the production of PCs, and resulted in higher PC contents in ‘Lvbao-701’ plants than in ‘Chixin-4’ plants. Cloning and expression analysis of a B. parachinensis PC synthase cDNA fragment indicated that PC synthase gene expression was induced by Cd, and occurred mainly in the roots of both ‘Lvbao-701’ and ‘Chixin-4’ plants. However, the PC synthase gene expression level was higher in the Lvbao-701 roots than in the ‘Chixin-4’ roots. Therefore, a greater abundance of Cd in the root cell walls and up-regulated PC production in the roots are likely the main reasons ‘Lvbao-701’ plants exhibit lower Cd translocation to shoots and greater tolerance to Cd than ‘Chixin-4’ plants.