Kinetics characteristics of NO₃^- absorption of barley (Hordeum vulgare L.) pretreated with different concentrations of NaCl and NO3-N

To learn nitrogen absorption characteristics of plant under salt stress, the NO₃^--N absorption ability of barley (Hordeum vulgare L.) cultivar ‘Jian 4’ pretreated with NaCl and NO₃^--N were investigated using culture solution. The pretreatment concentrations of NaCl were 1 mmolL^-1 (CK) and 120 mmolL^-1, those of NO₃^--N were 1 mmol (NO₃^--N)L^-1 and 10 mmol (NO₃^--N)L^-1. Barley growth and NO₃^--N absorption were measured and the kinetics of NO₃^--N absorption of high- affinity transport system and low-affinity transport system of barley were investigated. The results showed that the uptake of NO₃^--N of barley pretreated with different concentrations of NaCl and NO₃^--N was in accordance with Michelis-Menten equation. Also the uptake kinetics parameters Vmax and Km were enhanced with increasing pretreatment concentration of NO₃^--N. For high-affinity system, the uptake of NO₃^--N of barley was in accordance with Michaelis-Menten equation for all the pretreatments. Under 1 mmol(NO₃^--N)L^-1 pretreatment, compared with 1 mmolL^-1 NaCl treatment, 120 mmolL1 NaCl pretreatment significantly increased barley uptake rate of NO₃^--N; while under 10 mmol(NO₃^--N)L^-1, no significant difference in the rate of uptake of NO₃^--N was observed between 1 mmolL1 NaCl and 120 mmolL^-1 NaCl treatments. This indicated that in low nitrogen environment, NaCl restrained uptake of NO₃^--N of high-affinity system. For low-affinity systems, the uptake rate of NO₃^--N of barley was in accordance with Michaelis-Menten equation for all pretreatments. Under 1 mmol(NO₃^--N)L^-1 pretreatment, compared with 1 mmolL^-1 NaCl treatment, 120 mmolL^-1 NaCl treatment significantly increased the rate of uptake of NO₃^--N. With 10 mmolL^-1 NO₃^--N pretreatment, the uptake rate of NO₃^--N under 120 mmolL^-1 NaCl was lower than that of under 1 mmolL^-1 NaCl pretreatment. This showed that under low nitrogen environment, salt stress improved root uptake of NO₃^--N in low-affinity system. However, under high nitrogen environment, NaCl stress did not alter obviously root uptake of NO₃^--N in low-affinity systems.