Abstract
Fructan is a saccharide associated with freezing tolerance in overwintering plants. We have reported an increase in cold tolerance of transgenic rice expressing wheat sucrose:sucrose fructosyltransferase, (Kawakami et al. , JXB, 2008). To clarify the mechanism of this enhancement of cold tolerance by fructan, we examined the changes in sugar content and the expression levels of OsCIN, OsVIN, OsSus genes in the source and sink tissues of booting-stage rice exposed to a temperature of 12oC. Transcript levels of almost all genes, especially OsCIN2 and OsSus2, in source and sink tissues in both fructan-accumulated rice and non-transgenic rice decreased at 12oC and increased at 26oC after cold treatment. Increases in sucrose contents in source leaves and their sheaths were observed in plants at 12oC. Those changes recovered after exposure to a temperature of 26oC. In the transgenic rice, fructan increased under the cold treatment condition. Transcript levels of OsVIN1, which has fructan exohydrolase activity, in the leaves of non-transgenic rice decreased in response to a low temperature, whereas those in fructan-accumulated rice were maintained at almost the same level.
