Little is known about the mechanism of how trehalose responds to various abiotic stresses although trehalose is considered as an important protectant in fungi. We investigated the role of nitric oxide (NO) in regulating trehalose accumulation during heat stress in Pleurotus eryngii var. tuoliensis. The addition of 100 or 200 g trehalose/l significantly inhibited the production of thiobarbituric acid-reactive substance under heat stress in mycelial cells. High temperature induced endogenous trehalose accumulation and sodium nitroprusside, a NO donor, further enhanced trehalose accumulation. Finally, heat-induced trehalose accumulation could be arrested by the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-1-oxyl-3-oxide, at 250 mu M by inhibiting the transcription of trehalose phosphate synthase gene. Thus NO plays an important role in the regulation of trehalose accumulation during abiotic stresses in P. eryngii var. tuoliensis.