Differential cadmium resistance of two morphologically distinct types of potato (Solanum tuberosum) callus

Callus culture has been used to study the cellular basis of sensitivity of plants to toxic trace elements including cadmium. Callus friability may be related to plant response to exposure to trace elements as callus friability is related to the plant cell wall which plays a role in resistance of plant cells to trace element toxicity. The aim of this study was to investigate the relationship between two types of potato callus with different friability and their sensitivity to cadmium. A high frequency (about 80%) of leaf or internodal explants of potato (Solanum tuberosum L., cv, Iwa) formed a friable, pale green callus (type-A callus) on half-strength basal Murashige and Skoog medium supplemented with 12.42 μM picloram. On medium supplemented with 4.43 μM 6-benzyladenine (BA) and 5.37 μM 1-naphthalene acetic acid (NAA), a compact, non-friable callus (type-B callus) was induced in about 80% of the explants. Type-B callus was greener than type-A callus. Callus formation in both the leaf and internodal explants were completely inhibited on the medium used for induction of type-A or type-B callus when the respective medium was supplemented with 54 μM cadmium chloride (Cd). The type-B callus was found to be more resistant (less necrosis and higher relative growth rates) to 27, 54, and 109 μM of Cd than the type-A callus. The type-B callus also exhibited a higher level of peroxidase activity (a marker antioxidant enzyme counteracting oxidative stress) than the type-A callus when cultured on these Cd concentrations. This is the first study showing the importance of callus friability in plant cell response to Cd treatment.