Lead tolerance and accumulation in Arthrocaulon macrostachyum: Growth, physiological and antioxidant responses.

Lead (Pb) is a non-essential and toxic metal for plants. Current study was planned to assess Pb-induced toxicity with and without NaCl in a halophyte Arthrocaulon macrostachyum. Three month old seedlings (after germination) were grown in pots containing quartz sand and sub-irrigated with 300 mM NaCl and different Pb(NO 3) 2 concentrations (0, 0.75, 3, 6 and 12 mM) in plastic trays where 0 mM NaCl and Pb(NO 3) 2 were taken as control for monitoring growth, physiological and biochemical characteristics. Plant growth (height and biomass) was optimized in 300 mM NaCl while progressive increases in fresh weights up to 3 mM Pb(NO 3) 2 may be related to better shoot turgor, succulence and more plant pigments. Growth was substantially reduced in 6 and 12 mM Pb(NO 3) 2 both with and without NaCl. Plant shoots accumulated higher levels of Pb and Na+ of up to 3 mM Pb;while root Pb increased in > 6 mM Pb(NO 3) 2 treatments. Decreased pigments, potential quantum yield (F v /F m) and yield of photosystem II (ɸ PSII) enhanced the accumulation of H 2 O 2 , electrolyte leakage and consequently reactive oxygen species (ROS) in 12 mM Pb(NO 3) 2. The scavenging of ROS was manifested with the increased in vitro activity of superoxide dismutase (SOD) of up to 6 mM Pb(NO 3) 2 ; whereas higher Guaiacol peroxidase (GPx) may be related to cell wall hardening and poor growth. The increases in SOD, marginal changes in catalase (CAT) and unchanged APX of up to 6 mM Pb(NO 3) 2 demonstrated the activation of stress-responsive metabolism in Arthrocaulon machrostachyum ; and Pb accumulation of up to 200 mg kg-1 making this species a useful candidate for Pb phytoremediation. [Display omitted] • Arthrocaulon macrostachyum plants were able to tolerate up to 6 mM while 12 mM Pb (NO 3) 2 concentration was highly inhibitory to growth. • Arthrocaulon macrostachyum plants accumulated up to 200 mg kg−1 Pb under saline conditions. • The dual stress tolerance to Pb and salts in Arthrocaulon macrostachyum was associated with optimised regulation of water balances, ion fluxes and antioxidant feedback. [ABSTRACT FROM AUTHOR]