Mediation of NO on Cd2+ uptake in Populus euphratica cells under cadmium stress

We investigated the effect of nitric oxide (NO)on cadmium (Cd2+) tolerance in Populus euphratica cells.Results showed that 50 μmol/L Cd2+ significantly restricted cell growth; however, the inhibition of Cd2+ on cell growth was evidently alleviated by the addition of sodium nitroprusside (SNP, nitric oxide donor, 25 μmol/L). Moreover, SNP could relieve the decline of Cd2+-induced cell viability and damage to membrane during the period of cadmium stress. The effect of NO on cadmium kinetics was investigated using the non-invasive micro-test technique (NMT). After being subjected to 50 μmol/L CdCl2solution, P. euphratica showed a substantial Cd2+ influx. However, the cadmium-induced Cd2+ influx and the subsequent accumulation were both significantly restricted by 25 μmol/L SNP. Furthermore, pharmacological experiments showed that NO mediated the Cd2+ entry through calcium permeable channels in P.euphratica. The Cd2+ influx caused by Cd2+ stress was strongly inhibited by lanthanum chloride, a specific inhibitor of calcium channels. Noteworthy, NO was found to increase Ca2+ influx, which competitively inhibited the entry of Cd2+ through calcium permeable channels.Consequently, the Cd2+ uptake and buildup were limited, and thus the growth inhibition by cadmium was alleviated in P. euphratica cells.