Abstract: The influence of paclobutrazol (PP₃₃₃ ) on perennial ryegrass (Lolium perenne L. ) under heat stress was examined. The results showed that the plant height were significantly decreased after the seeds were treated with PP₃₃₃. The decline of soluble protein content in perennial ryegrass leaves treated with PP₃₃₃ was delayed in relation with the reduction of cellmembrane permeability, while the activity of SOD and the proline accumulation were increased, which indicated that the active oxygen species have been scavenged efficiently.
These results suggested that the damage of high temperature on perennial ryegrass could be alleviated by PP₃₃₃.

Key words: Lolium perenne L., Paclobutrazol, Thermotolerance, Superoxide dismutase, Proline