Aluminum-induced ethylene production is associated with inhibition of root elongation in Lotus japonicus L.

Inhibition of root elongation by toxic aluminum (Al3+) occurs rapidly and is one of the most distinct and earliest symptoms of Al toxicity. To elucidate mechanism underlying Al3+-induced inhibition of root elongation, we investigated the involvement of ethylene in Al3+ -induced inhibition of root elongation using the legume model plants Lotus japonicus and Medicago truncatula. Root elongation of L. japonicus and M. truncatula was rapidly inhibited by exposure to AlCl3. A similar rapid inhibition of root elongation by the ethylene-releasing substance, ethephon, and the ethylene precursor, 1-aminocyclopropane-1-carboxytic acid (ACC), was also observed. The Al3+ -induced inhibition of root elongation was substantially ameliorated in the presence of antagonists of ethylene biosynthesis [Co2+ and aminoethoxyvinylglycine (AVG)I. Al3+ increased the activity of ACC oxidase (ACO), and induced a rapid evolution of ethylene from root apices and expression of genes of ACC synthase (ACS) and ACO. These findings suggest that induction of ethylene evolution resulting from up-regulation of ACS and ACO plays a critical role in Al3+ -induced inhibition of root elongation.