Heat suppresses activation of an auxin-responsive promoter in cultured guard cell protoplasts of tree tobacco.

Cultured guard cell protoplasts (GCP) of tree tobacco (Nicotiana glauca) comprise a novel system for investigating the cell signaling mechanisms that lead to acquired thermotolerance and thermoinhibition. At 32 degrees C in a medium containing an auxin (1-naphthaleneacetic acid [NAA]) and a cytokinin (6-benzylaminopurine), GCP expand, regenerate cell walls, dedifferentiate, and divide. At 38 degrees C, GCP acquire thermotolerance within 24 h, but their expansion is limited and they neither regenerate walls nor reenter the cell cycle.