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A unique aluminum resistance mechanism conferred by aluminum and salicylic-acid-activated root efflux of benzoxazinoids in maize

Zunkang Zhao, Xiaofeng Gao, Ye Ke, Minmin Chang, Lu Xie, Xiaofeng Li, Minghua Gu, Jiping Liu, Xinlian Tang
Plant and soil 2019 v.437 no.1-2 pp. 273-289
aluminum, benzoxazinoids, biosynthesis, chelation, corn, cultivars, exudation, hydroxamic acids, root growth, root tips, salicylic acid
BACKGROUND AND AIMS: Although aluminum (Al) exclusion via root exudation of organic matters is a common resistance mechanism adopted by many plant species, whether root exudation of benzoxazinoids, such as hydroxamic acids (HAs), confers Al resistance remains unclear. METHODS: We performed physiological characterization for an Al-resistant maize cultivar TY and a sensitive maize cultivar ZD. RESULTS: First, Al exposure induced HA exudation from the root tip of TY, but not from ZD. Second, HAs formed non-toxic Al chelation complexes in vitro and exogenous HAs alleviated root damage and improved root growth under Al stresses. Third, both Al and exogenous salicylic acid (SA) treatments induced accumulation of endogenous SAs in the root apices of TY, which in turn enhanced root HA exudation and Al resistance in TY. Furthermore, an SA biosynthesis inhibitor significantly decreased Al resistance in TY and abolished the beneficial effects of exogenous SA on Al resistance, suggesting a key role of the endogenous SAs in induction of Al resistance. Finally, it was the root-tip HA exudation but not the root-tip HA contents that determined Al resistance in maize. CONCLUSION: We have revealed a unique Al exclusion mechanism underlying Al resistance via Al and SA-mediated root HA efflux in maize.