Phytotoxic effects of Cu, Zn, Cd and Pb on in vitro regeneration and concomitant protein changes in Holarrhena antidysenterica

The nodal explants of in vitro shoots of Holarrhena antidysenterica L. were cultured on Murashige and Skoog's (MS) medium augmented with 15 μM N⁶-benzyladenine (BA) alone (control) or supplemented with different concentrations (1, 5, 10 and 20 mg dm⁻³) of CdCl₂, CuSO₄, Pb(NO₃)₂ and ZnSO₄. The maximum morphogenic response in terms of average shoot number (4.95 ± 0.17) was seen in control. ZnSO₄ proved to be less inhibitory in comparison to CuSO₄, Pb(NO₃)₂ and CdCl₂. None of the explants cultured on CdCl₂ containing medium induced multiple shoots. Maximum protein content [3.80 ± 0.04 mg g⁻¹(f.m.)] was observed in control and slightly less [3.50 ± 0.02 mg g⁻¹(f.m.)] in tissues exposed to 1 mg dm⁻³ of CuSO₄ and minimum [1.00 ± 0.02 mg g⁻¹(f.m.)] in Zn treated (20 mg dm⁻³) explants. SDS-PAGE analysis of the treated tissues revealed that two new polypeptides (29 and 20 kDa) in response to Cu and Zn treatment, respectively, have been synthesized.