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Heavy metal stress in culture media is always rhizotoxic. Our study aims to investigate the role of negative potential ( ψ ) at root cell membrane surface (CMs) on modeling Zn toxicity to wheat seedling roots and to examine the effects of different nitrogen forms (NH and NO ) on ψ and Zn rhizotoxicity. Solution culture experiments were conducted to measure the root elongation and Zn accumulation under Zn exposure. The role of two nitrogen forms in affecting Zn toxicity was compared, giving particular consideration to ψ and Zn activities at CMs ({Zn}). Results showed that NH alleviates Zn rhizotoxicity and NO increases Zn rhizotoxicity. In modeling the rhizotoxicity, root length correlated better with {Zn} than {Zn}, and the predictive accuracy ( r ) of NH treatment increased from 0.748 to 0.917 when incorporation of {Zn} and {Ca} into analysis. Oppositely, ψ played a limited role in modeling Zn rhizotoxicity and bioavailability in NO treated medium ( r = 0.609). Moreover, higher concentration of Zn in roots was found in NO treatment, compared with the NH treatment. ψ rather than the rhizotoxicity data correlated better with Zn accumulation especially in the NO treatment ( r > 0.7), which meant the electrical driving force at CMs playing a dominant role in modeling the metal accumulation. In conclusion, the alleviatory role of NH on Zn toxicity and uptake was well explained and modeled by electrostatic effects at CMs. Though our data do not explore mechanisms for the NO -Zn interactions, we propose that ψ worked better in affecting the driving force for root Zn uptake, than influencing metal bioavailability at CMs. [ABSTRACT FROM AUTHOR]