Ammonium-induced shoot ethylene production is associated with the inhibition of lateral root formation in Arabidopsis

Foliar NH4 exposure is linked to inhibition of lateral root (LR) formation. Here, the role of shoot ethylene in NH4-induced inhibition of LR formation in Arabidopsis was investigated using wild-type and mutant lines that show either blocked ethylene signalling (etr1) or enhanced ethylene synthesis (eto1, xbat32). NH4 exposure of wild-type Arabidopsis led to pronounced inhibition of LR production chiefly in the distal root, and triggered ethylene evolution and enhanced activity of the ethylene reporter EBS:GUS in the shoot. It is shown that shoot contact with NH4 is necessary to stimulate shoot ethylene evolution. The ethylene antagonists Ag and aminoethoxyvinylglycine (AVG) mitigated LR inhibition under NH4 treatment. The decrease in LR production was significantly greater for eto1-1 and xbat32 and significantly less for etr1-3. Enhanced shoot ethylene synthesis/signalling blocked recovery of LR production when auxin was applied in the presence of NH4 and negatively impacted shoot AUX1 expression. The findings highlight the important role of shoot ethylene evolution in NH4-mediated inhibition of LR formation.