Rapid Ammonia Gas Transport Accounts for Futile Transmembrane Cycling under NH3/NH4 + Toxicity in Plant Roots

Futile transmembrane NH3/NH4 + cycling in plant root cells, characterized by extremely rapid fluxes and high efflux to influx ratios, has been successfully linked to NH3/NH4 + toxicity. Surprisingly, the fundamental question of which species of the conjugate pair (NH3 or NH4 +) participates in such fluxes is unresolved. Using flux analyses with the short-lived radioisotope 13N and electrophysiological, respiratory, and histochemical...