The phytotoxicity of mercury vapor

Seed germination and early growth were unexpectedly resistant to Hg-vapor at air saturation levels (14 μg L^?1). Among 15 species and cultivars tested, inhibition of shoot or root growth in excess of 50% was not seen, but occasional stimulation was noted. During extended (70 to 75 days) cultivation at Hg-vapor saturation, inhibitory effects on growth increased with time, and later effects on abscission and necrosis were more severe. Seven days exposures confirmed juvenile resistance at air saturation levels and mature plant sensitivity, expressed by massive abscission at 0.05 μg L^?1. It is suggested that Hg-vapor accelerates senescence-related processes via elevated ethylene production. Evidence suggests that elemental Hg, not ionic Hg, is the active toxicant. An ecophysiological role for Hg-vapor in volcanically active regions is suggested.