The Ca²⁺ signaling, Glu, and GABA responds to Cd stress in duckweed

Cadmium (Cd) affects plants and animal health seriously. Ca²⁺ signals in plant cells are important for adaptive responses to environmental stresses. Here we showed that 50 μM Cd shock stimulated the Ca²⁺ signal via modifying the instantaneous Ca²⁺ flux from influx of 17 pmol·cm^-2·s^-1 to the efflux of 240 pmol·cm^-2·s^-1 at 100 μm from rhizoid tip. And the Ca²⁺ signal transferred to the vein and mesophyll cell. The Ca addition decreased the accumulation of Cd. The gene expression of glutamate receptor-like (GLR) proteins, which is activated by Glu and triggers Ca²⁺ flux, was increased significantly by 24 h Cd stress. Glu content was increased under Cd stress and exogenous Glu triggered the Ca²⁺ signal in duckweed, while Ca²⁺ addition caused no influence to Glu content. GABA, which is synthesized from Glu and acts as an inhibitory neurotransmitter, has been decreased with 24 h Cd treatment. GABA addition increased the abscission rate and Glu addition decreased the abscission rate during Cd stress, suggesting that the Glu/GABA ratio is important for responding to Cd. This research shows the sight of the Glu, Ca²⁺, GABA signaling networks during Cd stress.