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

Dong, M. A.*; Bufford, J. L.*; Ono, Yutaka; Church, K.*; Dau, M. Q.*; Michels, K.*; Haughton, M.*; Tallman, G.*

Cultured guard cell protoplasts (GCP) of Nicotiana glauca, tree tobacco, comprise a novel system for investigating the cell signaling mechanisms that lead to acquired thermotolerance and thermoinhibition. At 32 C in a medium containing an auxin and a cytokinin, GCP expand, regenerate cell walls, dedifferentiate, and divide. At 38 C, GCP acquire thermotolerance, but their expansion is limited and they neither regenerate walls nor re-enter the cell cycle. Protoplasts were transformed with the fusion gene of BA auxin-responsive promoter and green fluorescent protein (GFP) gene. Heat suppressed auxin-mediated activation of BA. Heat-stressed cells accumulate reactive oxygen species, and HO suppresses auxin-responsive promoter activation. HO did not suppress BA activation at 32 C, nor did superoxide and HO scavengers prevent BA suppression at 38 C.