Little information is available about signaling response to magnesium toxicity(MgT)in plants.This study presents the first evidence that abscisic acid(ABA)and DELLA proteins participate in signaling response to long-term MgT in Arabidopsis thaliana(Landsberg erecta).Morphological,physiological,and molecular characteristics of a wild-type and two Arabidopsis mutants,ABA-insensitive mutant abi1-1 and constitutive elevated GA response mutant quadruple-DELLA(DELLA-Q: gai-t6 rgat2 rgl1-1 rgl2-1)were monitored under MgT and normal magnesium conditions.Two weeks of MgT treatment strongly influenced the growth of young plants,but growth inhibition of the DELLA-Q and abi1-1 mutants was less than that of the wild-type plants.Exogenous ABA further inhibited the growth of the DELLAQ mutants,similar to that of the wild-type.Both ABA and MgT also promoted DELLA protein RGA accumulation in the nuclei.Transcriptional analysis supported these results and revealed that a complex signaling network has responded to MgT in Arabidopsis.DELLA enhancement,which depends on ABI1,contributed to the remodeling growth and development of young seedlings.