Calcium channel blockers protect against aluminium-induced DNA damage and block adaptive response to genotoxic stress in plant cells

Abstract

Calcium is an important second messenger in signal transduction pathways. The role of Ca2+ signalling in Al-induced DNA damage, cell death, and adaptive response to genotoxic stress caused by ethyl methanesulfonate (EMS) or methylmercuric chloride (MMCl) in the root cells of Allium cepa was investigated in the current study. Root cells in planta were treated with Al3+ (800μM of AlCl3) for 3h without or with 2h pre-treatment with the Ca2+ chelator (EGTA) or Ca2+ channel blockers (lanthanum chloride, verapamil) or CaM/CDPK antagonist (W7). In addition, root cells in planta were conditioned by treatment with Al3+ (5 or 10μM of AlCl3) for 2h followed by the genotoxic challenge with MMCl (1.25μM) or EMS (2.5 or 5mM) for 3h without or with the pre-treatment of the chosen Ca2+ chelator/channel blockers/antagonist. Following the treatments, cell death and DNA damage were investigated in the root cells by comet assay. Furthermore, genotoxicity in the root meristems was determined after 18–30h of recovery. These results revealed that Al3+ (800μM) significantly induced DNA damage and cell death in the root cells of A. cepa. On the other hand, conditioning of the root cells with Al3+ at low concentrations (5 or 10μM) offered adaptive response leading to the protection against genotoxic stress induced by MMCl and EMS. Pre-treatment of root cells with the Ca2+ chelator/channel blockers/antagonist not only alleviated Al3+-induced DNA damage and cell death induced but also blocked the Al3+-mediated adaptive response to genotoxic stress induced by MMCl and EMS. For the first time, the results of the present study highlighted the role of Ca2+ signalling underlying the biphasic mode of action of Al3+ that induced DNA damage and cell death at high doses and offered adaptation to genotoxic response in plants at low doses.