盐胁迫对大豆根系木质部压力和Na+吸收的影响

取栽培大豆的水培幼苗为材料,用木质部压力探针和原子吸收分光光度计测定了盐胁迫条件下其根木质部压力和伤流液中Na~+含量的变化,以分析大豆抗盐吸水的机制.结果表明:在25～150 mmol/L NaCl的浓度范围内,随着盐胁迫强度的增加,大豆根木质部负压力的绝对值逐渐增大,但相对负压力和根的径向反射系数则逐渐减小;木质部伤流液中Na~+含量逐渐增加,但Na~+的相对含量则逐渐降低.同时,虽然根系吸水所需的木质部负压力(压力势)及根木质部伤流液的渗透势随着盐胁迫强度的增加都有所下降,但两者共同作用使木质部水势下降的幅度远远小于根外溶液水势(渗透势)下降的幅度,即随着根外溶液盐浓度的升高,根木质部溶液的总水势逐渐高出根外溶液的水势.上述结果说明,在盐胁迫下大豆可以利用相对小的木质部负压力逆水势梯度吸水,且通过避免对Na~+的过量吸收来适应盐胁迫环境.

Xylem pressure and Na+ uptake in roots of soybean under saline stresses

The pressure potentials of xylem vessels of the root system and the Na+ content of the xylem sap in soybean seedlings under salt stresses were measured with a xylem pressure probe and an atomic absorption spectrometer, respectively. The results showed that the negative pressures in xylem vessels increased, but the relative pressures and the radial refliection coefficient of root decreased with the elevation of salinity in the root environment. Although the Na+ content in the xylem sap increased with the elevated salinity levels in the root bathing solution, the relative amount of Na+ declined. Meanwhile, both the pressure and osmotic potentials in the root xylem declined with the increase in salinity, but the changes in the total water potential of the root xylem solution (osmotic potential plus pressure potential) resulted from salt stress were always smaller than the changes in the water (osmotic) potentials of the solutions bathing the root. In other words, the total water potential of the xylem solution was increasing steadily over the water potential of the root bathing solution with the increase in the intensity of salt stress. These results indicated that the soybean plants could use small negative xylem pressures to absorb water from salinized solution, and avoided the uptake of excessive amount of Na+ to combat saline stresses.