Cell wall polysaccharides play a vital role in binding with toxic metals such as copper(Cu)ions.However, it is still unclear whether the major binding site of Cu in the cell wall varies with different degrees of Cu stresses.Moreover, the contribution of each cell wall polysaccharide fraction to Cu sequestration with different degrees of Cu stresses also remains to be verified.The distribution of Cu in cell wall polysaccharide fractions of castor(Ricinus communis L.) root was investigated with various Cu concentrations in the hydroponic experiment.The results showed that the hemicellulose1(HC1) fraction fixed 44.9%–67.8% of the total cell wall Cu under Cu stress.In addition, the pectin fraction and hemicelluloses2(HC2) fraction also contributed to the Cu binding in root cell wall,accounting for 11.0%–25.9% and 14.1%–26.6% of the total cell wall Cu under Cu treatments, respectively.When the Cu levels were ≤ 25 μmol/L, pectin and HC2 contributed equally to Cu storage in root cell wall.However, when the Cu level was higher than 25 μmol/L, the ability of the pectin to bind Cu was easy to reach saturation.Much more Cu ions were bound on HC1 and HC2 fractions, and the HC2 played a much more important role in Cu binding than pectin.Combining fourier transform infrared(FT-IR) and twodimensional correlation analysis(2 D-COS) techniques, the hemicellulose components were showed not only to accumulate most of Cu in cell wall, but also respond fastest to Cu stress.
Chao RenYongbo QiGuoyong HuangShiyuan YaoJinwei YouHongqing Hu
Ricinus communis L.is a new copper hyperaccumulator growing on Tonglushan copper mine in Hubei Province,China.This study aimed to establish a suspension cell line of R.communis L.with stable and rapid growth for further screening of heavy metal-resistant R.communis L.cells and breeding of hyperaccumulators.In this study,cell suspension culture conditions were optimized by using orthogonal experimental design with previously induced R.communis L.embyrogenic calluses as experimental materials,to establish the suspension cell line of R.communis L.Under the optimal conditions,growth curves of suspension cells and changes in pH of culture liquid were determined.The results showed that the optimal culture conditions for R.communis L.suspension cell line were:MS+0.5 mg/L 6-BA+0.2 mg/L NAA+50 mg/L sucrose+350 mg/L casein hydrolysate as basic medium,with callus inoculation amount of 2.5 g/50 ml,dark culture at(26±2)℃with shaking at 110 r/min.Under these conditions,increment of fresh weight and dry weight of R.communis L.suspension cells reached the maximum of 4.56 g/(50 ml·14 d)and 0.49 g/(50 ml·16 d),respectively.Growth curves of R.communis L.suspension cells were basically in"S"shape.Each culture cycle lasted 16 d,and the rapid growth stage was from the 6thd to the 14thd.In a culture cycle,pH of the culture liquid declined first and then increased to the maximum and stabilized gradually.
