Comparative study of alleviation effects of DMTU and PCIB on root growth inhibition in two tall fescue varieties under cadmium stress.

In plants, tolerance to cadmium (Cd) stress is closely related to indole-3-acetic acid (IAA) and hydrogen peroxide (HO). However, it is unclear whether Cd-resistant and -sensitive varieties respond differently to Cd stress. In this study, the effects of dimethylthiourea (DMTU, a HO scavenger) and p-chlorophenoxy isobutyric acid (PCIB, an IAA signaling inhibitor) on root growth, endogenous hormones and antioxidant system were investigated to decipher how DMTU and PCIB treatments alleviate the inhibition of root elongation in Cd-resistant (Commander) and -sensitive (Crossfire III) tall fescue varieties under Cd stress. Both varieties subjected to 10 μM Cd treatments for 12 h presented a substantial decrease in root elongation coupled with a reduction in brassinosteroid (BR) and zeatin riboside (ZR) contents, but the changes in IAA and abscisic acid (ABA) contents under Cd stress were opposite in the two varieties. In addition, the HO content and antioxidant enzyme activities significantly increased in both varieties. However, pretreatment with PCIB or DMTU mitigated the inhibition of root elongation caused by Cd, accompanied by the significant changes of aforementioned physiological parameters. PCIB significantly reduced the IAA content in 'Commander', while DMTU significantly increased the IAA content in 'Crossfire III' and effectively relieved the inhibition of root elongation. But both treatments decreased the Cd-induced HO accumulation. These results indicated that DMTU or PCIB can alleviate the Cd-inhibited root elongation in two varieties whose resistance differed under Cd stress, but they presented differences in the response of hormones, especially IAA, which may be due to the different adaptation mechanisms of two varieties in response to Cd stress.