Accumulation and distribution of copper in castor bean (Ricinus communis L.) callus cultures: in vitro

Abstract

Copper (Cu) accumulation, subcellular distribution and the chemical forms of Cu, and amino acids metabolism were investigated in castor bean (Ricinus communis L.) callus via in vitro culture. The castor bean callus was obtained from the embryo cultured in Murashige and Skoog (MS) medium and then transferred to MS medium with different Cu doses (0, 20, 40, and 60 mg L−1; Cu0, Cu20, etc.) for 28-days cultivation. The stress from Cu inhibited the growth of the castor bean callus, and the Cu content in the castor bean callus increased with the increasing Cu dose, reaching a maximum value of 293.2 mg kg−1 fresh weight (FW) in the 60 mg L−1 Cu treatment. Concentrations of Cu in the cell wall, organelles, and cytoplasm increased significantly with the elevated Cu dose, with the cell wall containing 50.2 % of the total Cu in the 60 mg L−1 Cu treatment. The major Cu fractions were C (bound to the exchangeable polar compounds) (28.1 %) and E (bound to the structural polar compounds and nucleic acids) (27.5 %) in the control treatment, and the main fraction was C (51.2 %) in the treatment with 60 mg L−1 Cu. The concentration of free amino acids in the cytoplasm was closely related to the Cu content in the castor bean callus. In addition, most of the Cu in the cell wall bound with functional groups of the cell chemical components, hydroxyl (–OH), acylamino (–CONH2), and carboxylate ion (–COO−). The castor bean exhibited a strong tolerance to Cu, which accumulated mainly in the cell wall.