Osmoprimed seeds increased the abundance of pGlcT proteins. Osmopriming together with heat shock increased the abundance of RBR proteins. NAD-ME increased when osmoprimed and heat-shocked seeds were imbibed at low temperature. The purpose of seed priming is to accelerate and synchronize germination and to increase stress tolerance through the activation of genes that function when seeds are exposed to unfavorable conditions. The objectives of this study were: (1) to evaluate the effects of osmopriming and heat-shock treatment on the germination of Eucalyptus urophylla seeds at different temperatures and (2) to analyze the seed proteome to elucidate the mechanisms of tolerance to thermal stress in primed and unprimed seeds. Untreated (control) seeds, osmoprimed (polyethylene glycol for 3 days) and redried seeds, and osmoprimed/heat-shocked (45 A degrees C for 1 h) and redried seeds were germinated for 14 days under constant light (2 x 40 W fluorescent daylight tubes) at 9, 16, 22, 24, or 31 A degrees C. Osmopriming, with or without heat-shock, led to a significant increase in the germination percentage at 9 A degrees C and induced the highest germination speed index at 31 A degrees C. According to proteomic analysis, osmoprimed seeds exhibited an increased abundance of several proteins, including sugar transport proteins, and this may have influenced the metabolic rate during germination. Osmopriming together with heat-shock treatment increased the abundance of proteins associated with regulation of the cell cycle suggesting that such proteins may be involved in protection against thermal stress. The Krebs cycle enzyme was increased when osmoprimed and heat-shocked seeds were imbibed at low temperature, possibly signifying increased synthesis of adenosine triphosphate. The results reported herein serve to explain some of the benefits of osmopriming/heat-shock treatment.