A known Arabidopsis cDNA clone, the CRT/DRE binding factor 1 (CBF1), was isolated and introduced into tomato plants. CBF1 is a member of the CBF gene family related to low temperature and enhanced low temperature tolerance in plants. In the present work, transcripts of CBF1 could be detected in transgenic tomato leaves, and the photochemical efficiency of PSII (F(v) /F(m)) and oxidisable P700 in the transgenic tomato over-expressing CBF1 were higher than in non-transformed plants under low temperature stress at low irradiance. Similarly, higher activity of superoxide dismutase (SOD), higher non-photochemical quenching (NPQ), and lower malondialdehyde (MDA) content were also detected in transgenic tomato leaves. These results suggest that CBF1 protein plays an important role in protection of PSII and PSI during low temperature stress at low irradiance. © 2010 German Botanical Society and The Royal Botanical Society of the Netherlands.