Water stress-induced chilling tolerance in rice;: putative relationship between chilling tolerance and Ca2+ flux

Chilling-sensitive rice varieties acquire chilling tolerance when their roots are exposed to short term water stress (0.5 M mannitol, 30 min M mannitol, 30 min). Pharmacological experiments using various Ca2+ channel blockers suggested that the water stress signal gives rise to Ca2+ flux, resulting in induction of chilling tolerance. Ca2+ flux in rice root cells was directly determined by microscopic fluorometry using the fluorescent Ca2+ indicator, fluo-3. In a chilling-tolerant rice variety, Ca2+ flux in root cells was induced by both chilling and water stress, whereas in a chilling-sensitive rice variety, Ca2+ flux in root cells was not induced by chilling, but was induced by water stress. The Ca2+ flux in root cells was found to be generated by different mechanisms for chilling and water stress signals; amiodarone-sensitive Ca2+ flux was related to the response for water stress signals, but not for chilling signals, and caffeine-sensitive Ca flux was related to the responses for both chilling and water stress signals. Caffeine-sensitive Ca2+ flux appears to be closely related to the induction of chilling tolerance in rice because ii is generated in chilling-tolerant rice varieties at low temperature. but not in chilling-sensitive rice varieties. Chilling-sensitive rice varieties generate caffeine-sensitive Ca2+ flux in root cells upon treatment with mannitol, resulting in induction of chilling tolerance. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.