Ethylene Inhibited Plasma Membrane H ⁺ ‐ATPase to Decrease Root Na ⁺ Efflux in Maize to Break Na ⁺ /H ⁺ Homeostasis Under Salt Stress

ABSTRACT Ethylene plays an indispensable role in regulating plant growth and stress responses. However, the mechanisms underlying the regulation of Na + /H + homoeostasis by ethylene and subsequent mediation of maize growth under salt stress remain unclear. ZmACO2 , which encodes ethylene biosynthesis enzyme 1‐aminocyclopropane‐1‐carboxylate oxidase2, is induced by salt stress. Thus, ZmACO2 ‐overexpressing ( ACO2‐OE ) and mutant ( aco2‐cr ) plants were used to investigate how ethylene regulates Na + /H + homoeostasis in maize under salt stress. The aco2‐cr mutants exhibited significantly lower Na⁺ accumulation and Na⁺/K⁺ ratios than the wild‐type and ACO2‐OE plants. This phenotype was attributed to their higher expression of ZmSOS1 and ZmHKT1 , which increased root net Na⁺ efflux by 20.65% and decreased Na⁺ transport from roots to shoots by 42.49% ( p < 0.001), respectively. Compared to the other plants, aco2‐cr mutants showed higher ZmMHA2 expression and plasma membrane H + ‐ATPase activities, which promoted net root H + efflux to provide a greater H + proton gradient for salt‐overly‐sensitive 1 (SOS1). Inhibition efficiencies of Na + efflux and H + influx by sodium orthovanadate were lower in aco2‐cr mutants than in ACO2‐OE and wild‐type plants under salt stress; however, ACO2‐OE plants showed a salt‐sensitive phenotype. Overall, these findings showed that salt‐induced ethylene inhibited plasma membrane H + ‐ATPase and SOS1 from disrupting Na + /H + homoeostasis, thereby decreasing Na + efflux in maize roots and also provided a strategy to improve salt tolerance by optimising ethylene levels in maize.