Effects of arsenate on tobacco hairy root and seedling growth, and its removal

Arsenic (As) is a highly toxic environmental contaminant to which most living organisms are exposed. Plants have evolved several mechanisms to cope with this toxic metalloid; however, these mechanisms are only partially understood. The response of plants to As phytotoxicity is highly complex, with considerable variation among species. In this study, arsenate (As+5) effects on germination and early root development of tobacco (Nicotiana tabacum) seedlings were investigated. Also, As+5 tolerance and removal efficiency of tobacco hairy roots (HRs) and seedlings were assessed and compared. Total seed germination capacity was not affected by 10 to 200 μM As+5, while primary root length and root branching were reduced by As+5 concentrations that were at or above 100 μM. Both systems were able to tolerate As+5 concentrations of 10 μM since no growth inhibition was detected. For higher As+5 concentrations, phytotoxicity increased, but it was mitigated by higher phosphate (Pi) availability. Under the studied conditions, As+5 removal efficiency of HRs greatly exceeded that of seedlings. Further, tobacco HRs were able to accumulate As in their tissues. These results justify further investigations on As tolerance and detoxification mechanisms in tobacco, an easy-to-transform crop species with high biomass, which could allow evaluation of the possible application of wild type or alternatively transgenic tobacco plants for As phytoextraction.