Causes of Root Growth Retardation Induced by Ultraviolet-B Irradiation of Shoots in Barley Seedlings

摘要

In barley seedlings (Hordeum vulgare L.) during two days after irradiation of shoots with UV-B (0.5 W/m2, 6 h), the rate of elongation of primary roots decreased 2-3 times compared to that in control plants. The modulus of elasticity of roots (e) increased at most twofold in 12 h after the onset of irradiation; the hydraulic conductivity (L_p) diminished by a factor of two in 12 h, and the root osmotic pressure gradually decreased by 0.08 MPa in 24 h. Changes in E and L_p were shown to be related tooxidative stress in growing roots, which was evidenced from the increase in H_2O_2 level up to 15-fold increase in 6 h and in activity of guaiacol peroxidase (3.5-fold in 12 h). After 48 h, the characteristics of oxidative metabolism and root characteristics 8 and L_p became identical in untreated and treated plants. On the third day, the rate of root growth in treated plants reached its initial value. It is concluded that the main causes of retardation of root growth under these conditions were as foll