The present invention provide methods of imparting stress tolerance, characterized in that an expression amount of at least one stress defense gene is increased compared with a non-transformant by transforming the plant with an exogenous spermidine synthase (SPDS) gene, an exogenous S-adenosylmethionine decarboxylase (SAMDC) gene, an exogenous arginine decarboxylase (ADC) gene, an ornithine decarboxylase (ODC) gene and/or a spermine synthase (SPMS) gene under the control of a promoter capable of functioning in the plant.